Statistical shape analysis and computational modeling reveal novel relationships between tibiofemoral bony geometry and knee mechanics in young, female athletes

Young female athletes participating in sports requiring rapid changes of direction are at heightened risk of suffering traumatic knee injury, especially noncontact rupture of the anterior cruciate ligament (ACL). Clinical studies have revealed that geometric features of the tibiofemoral joint are associated with increased risk of suffering noncontact ACL injury. However, the relationship between three-dimensional (3D) tibiofemoral geometry and knee mechanics in young female athletes is not well understood. We developed a statistically augmented computational modeling workflow to determine relationships between 3D geometry of the knee and tibiofemoral kinematics and ACL force in response to an applied loading sequence of compression, valgus, and anterior force, which is known to load the ACL. This workflow included 3D characterization of tibiofemoral bony geometry via principal component analysis and multibody dynamics models incorporating subject-specific knee geometries. A combination of geometric features of both the tibia and the femur that spanned all three anatomical planes was related to increased ACL force and to increased kinematic coupling (i.e., anterior, medial, and distal tibial translations and internal tibial rotation) in response to the applied loads. In contrast, a uniplanar measure of tibiofemoral geometry that is associated with ACL injury risk, sagittal plane slope of the lateral tibial plateau subchondral bone, was not related to ACL force. Thus, our workflow may aid in developing mechanics-based ACL injury screening tools for young, active females based on a unique combination of bony geometric features that are related to increased ACL loading.

A practical guide to the development and deployment of deep learning models for the orthopaedic surgeon: Part III, focus on registry creation, diagnosis, and data privacy

Deep learning is a subset of artificial intelligence (AI) with enormous potential to transform orthopaedic surgery. As has already become evident with the deployment of Large Language Models (LLMs) like ChatGPT (OpenAI Inc.), deep learning can rapidly enter clinical and surgical practices. As such, it is imperative that orthopaedic surgeons acquire a deeper understanding of the technical terminology, capabilities and limitations associated with deep learning models. The focus of this series thus far has been providing surgeons with an overview of the steps needed to implement a deep learning-based pipeline, emphasizing some of the important technical details for surgeons to understand as they encounter, evaluate or lead deep learning projects. However, this series would be remiss without providing practical examples of how deep learning models have begun to be deployed and highlighting the areas where the authors feel deep learning may have the most profound potential. While computer vision applications of deep learning were the focus of Parts I and II, due to the enormous impact that natural language processing (NLP) has had in recent months, NLP-based deep learning models are also discussed in this final part of the series. In this review, three applications that the authors believe can be impacted the most by deep learning but with which many surgeons may not be familiar are discussed: (1) registry construction, (2) diagnostic AI and (3) data privacy. Deep learning-based registry construction will be essential for the development of more impactful clinical applications, with diagnostic AI being one of those applications likely to augment clinical decision-making in the near future. As the applications of deep learning continue to grow, the protection of patient information will become increasingly essential; as such, applications of deep learning to enhance data privacy are likely to become more important than ever before. Level of Evidence: Level IV.

Independent data collectors decrease bias in the measurement of adherence to anterior cruciate ligament injury prevention programs

OBJECTIVES

Studies on adherence to neuromuscular training (NMT) for anterior cruciate ligament (ACL) injury prevention are frequently biased due to the use of self-reporting by coaches or the athletes themselves. Few NMT studies use data collectors (aside from the athletes or the individuals administering the NMT program) to decrease bias when assessing the adherence of coaches and sports teams. We hypothesized that the use of a data collector who is independent of the team to evaluate adherence to NMT programs would be reliable.

METHODS

In a prior a cluster-randomized controlled trial evaluating adherence to NMT training trial, twelve boys' and nine girls' high school athletic teams in a variety of sports were enrolled. Eight data collectors (unaffiliated with the NMT program) were hired specifically to record adherence of the athletes to the NMT exercises at each team's warm-ups 2-3 times a week, prior to practices and games. In addition to the data collectors, a control group of independent observers made visits throughout the season to also record adherence (solely for the purpose of this study, alongside the data collectors and in the same fashion) in order to evaluate the data collectors' performance and determine inter-observer reliability. The inter-observer reliability between data collectors and independent observers was measured using the Kappa statistic.

RESULTS

A total of 399 warm-ups for practices or games were observed by data collectors to obtain adherence data. Independent observers also measured adherence at 58 practices or games for inter-observer reliability. Exercise instruction and alignment cues for 29 different exercises were analysed. The Kappa values ranged from 0.63 to 1.0, indicating substantial to perfect agreement. The overall Kappa values of 0.89 and 0.90 for exercise instruction and alignment cues, respectively, indicated almost perfect agreement.

CONCLUSION

The use of a data collector who is independent of the team to evaluate adherence to NMT programs (rather than athlete or coach self-reporting), was shown to be a reliable method for measurement of adherence in studies of NMT for injury prevention. Avoiding self-reporting in adherence research to NMT training may decrease bias.

LEVEL OF EVIDENCE

I.

Medical Imaging Applications Developed Using Artificial Intelligence Demonstrate High Internal Validity Yet Are Limited in Scope and Lack External Validation

PURPOSE

To (1) review definitions and concepts necessary to interpret applications of deep learning (DL; a domain of artificial intelligence that leverages neural networks to make predictions on media inputs such as images) and (2) identify knowledge and translational gaps in the literature to provide insight into specific areas for improvement as adoption of this technology continues.

METHODS

A comprehensive search of the literature was performed in December 2023 for articles regarding the use of DL in sports medicine. For each study, information regarding the joint of focus, specific anatomic structure/pathology to which DL was applied, imaging modality utilized, source of images used for model training and testing, data set size, model performance, and whether the DL model was externally validated was recorded. A numerical scale was used to rate each DL model's clinical impact, with 1 corresponding to proof-of-concept studies with little to no direct clinical impact and 5 corresponding to practice-changing clinical impact and ready for clinical deployment.

RESULTS

Fifty-five studies were identified, all of which were published within the past 5 years, while 82% were published within the past 3 years. Of the DL models identified, 84% were developed for classification tasks, 9% for automated measurements, and 7% for segmentation. A total of 62% of studies utilized magnetic resonance imaging as the imaging modality, 25% radiographs, and 7% ultrasound, while 1 study each used computed tomography, arthroscopic images, or arthroscopic video. Sixty-five percent of studies focused on the detection of tears (anterior cruciate ligament [ACL], rotator cuff [RC], and meniscus). The diagnostic performance of ACL tears, as determined by the area under the receiver operator curve (AUROC), ranged from 0.81 to 0.99 for ACL tears (excellent to near perfect), 0.83 to 0.94 for RC tears (excellent), and from 0.75 to 0.96 for meniscus tears (acceptable to excellent). In addition, 3 studies focused on detection of cartilage lesions had AUROC ranging from 0.90 to 0.92 (excellent performance). However, only 4 (7%) studies externally validated their models, suggesting that they may not be generalizable or may not perform well when applied to populations other than that used to develop the model. Finally, the mean clinical impact score was 2 (range, 1-3) on scale of 1 to 5, corresponding to limited clinical applicability.

CONCLUSIONS

DL models in orthopaedic sports medicine show generally excellent performance (high internal validity) but require external validation to facilitate clinical deployment. In addition, current models have low clinical applicability and fail to advance the field due to a focus on routine tasks and a narrow conceptual framework.

LEVEL OF EVIDENCE

Level IV, scoping review of Level I to IV studies.

The phenotypic diversity of anteromedial osteoarthritis before and after treatment with medial unicompartmental knee arthroplasty: A radiographic analysis of 1000 knees

PURPOSE

This study aimed to assess phenotypic variation in the coronal plane of knees with anteromedial osteoarthritis using the functional knee phenotype classification, before and after treatment with medial unicompartmental knee arthroplasty (UKA).

METHODS

The study comprised 1000 knees of 835 patients (45% females, 55% males, 90% Caucasian) who underwent medial UKA for anteromedial osteoarthritis. Pre and postoperative alignment was evaluated through the hip-knee-ankle angle (HKA), femoral mechanical angle (FMA), and tibial mechanical angle (TMA). Knees were classified according to the functional knee phenotype system which combines limb phenotype (HKA), and femoral and tibial knee phenotypes (FMA and TMA, respectively). Restoration of prearthritic coronal alignment following medial UKA was evaluated by phenotype.

RESULTS

Preoperatively, 76 distinct and 25 relevant (prevalence ≥1%) functional knee phenotypes were identified, of which VARHKA 6°VARFMA 3°NEUTMA 0° was the most common (9.4% of knees). The most prevalent limb phenotype, VARHKA 6°, comprised 15 distinct knee phenotypes (FMA and TMA combinations). Postoperatively, 58 distinct and 17 relevant functional knee phenotypes were observed, of which VARHKA 3°NEUFMA 0°NEUTMA 0° had the highest prevalence at 18.3%. Knees with combined tibial and femoral deformities were associated with a lower probability of restoration of prearthritic coronal alignment following medial UKA, compared to knees without extra-articular deformity, or knees with an isolated tibial or femoral deformity.

CONCLUSION

Phenotype analysis using the functional knee phenotype system demonstrated a wide diversity of coronal alignment phenotypes among knees with anteromedial osteoarthritis in a predominantly Caucasian population. Following medial UKA, a reduction from 25 preoperative to 17 postoperative relevant phenotypes was observed. Consideration of phenotypic variation can be of importance when aiming to restore prearthritic coronal alignment during medial UKA.

LEVEL OF EVIDENCE

Level III, retrospective cohort study.

Magnitude of Change in Leg Length and Clinical Impact Following Medial Unicompartmental Knee Arthroplasty

BACKGROUND

Change in leg length and leg-length discrepancy (LLD) are common concerns among patients undergoing medial unicompartmental knee arthroplasty (UKA). This study aimed to quantify the magnitude of leg-length change, prevalence of postoperative LLD, and their clinical implications following medial UKA.

METHODS

Leg length and mechanical hip-knee-ankle angle (mHKA) were retrospectively measured in 332 patients following unilateral robotic-arm assisted medial UKA for medial compartment osteoarthritis, using calibrated long-leg radiographs. The Knee Injury and Osteoarthritis Otcome Score for Joint Replacement and patient satisfaction were analyzed to assess impact of leg-length change and LLD on outcomes.

RESULTS

Following medial UKA, median leg-length change was 2.0 mm (interquartile range, -1.0 to 5.0 mm; P < .001) with a mean correction in mHKA of 4.4° ± 2.7 (P < .001). A total of 158 patients (48%) had a leg-length increase by 0 to 5 mm, 64 (19%) by 6 to 10 mm, and 11 (3%) by >10 mm. Leg-length change was positively correlated with mHKA correction (R = 0.44, P < .001). Postoperatively, moderate (5 to 10 mm) and substantial LLD (≥10 mm) were present in 49% and 17% of patients, respectively. Four-year Knee Injury and Osteoarthritis Outcome Score for Joint Replacement were comparable between patients with and without substantial postoperative LLD (P = .976). Proportions of satisfied patients were similar between groups (P = .687).

CONCLUSION

Following medial UKA, the majority of patients had a moderate increase in leg length, the magnitude of which was positively correlated to the correction in mechanical alignment. Postoperative substantial LLD was not uncommon (17% prevalence); however, it had no significant impact on patient-reported outcomes or satisfaction at 4 years follow-up.

Role of Lateral Extra-articular Tenodesis in Restraining Internal Tibial Rotation: In Vitro Biomechanical Assessment of Lateral Tissue Engagement

BACKGROUND

The way in which force increases in the anterolateral tissues and the lateral extra-articular tenodesis (LET) tissue to resist internal rotation (IR) of the tibia after anterior cruciate ligament (ACL) reconstruction in isolation and after LET augmentation, respectively, is not well understood.

PURPOSE

(1) To compare in a cadaveric model how force increases (ie, engages) in the anterolateral tissues with IR of the tibia after isolated ACL reconstruction and in the LET tissue after augmentation of the ACL reconstruction with LET and (2) to determine whether IR of the tibia is related to engagement of the LET tissue.

STUDY DESIGN

Controlled laboratory study.

METHODS

IR moments were applied to 9 human cadaveric knees at 0°, 30°, 60°, and 90° of flexion using a robotic manipulator. Each knee was tested in 2 states: (1) after isolated ACL reconstruction with intact anterolateral tissues and (2) after LET was performed using a modified Lemaire technique with the LET tissue fixed at 60° of flexion under 44 N of tension. Resultant forces carried by the anterolateral tissues and the LET tissue were determined via superposition. The way force increased in these tissues was characterized via parameters of tissue engagement, namely in situ slack, in situ stiffness, and tissue force at peak applied IR moment, and then compared (α < .05). IR was related to parameters of engagement of the LET tissue via simple linear regression (α < .05).

RESULTS

The LET tissue exhibited less in situ slack than the anterolateral tissues at 30°, 60°, and 90° of flexion (P≤ .04) and greater in situ stiffness at 30° and 90° of flexion (P≤ .043). The LET tissue carried greater force at the peak applied IR moment at 0° and 30° of flexion (P≤ .01). IR was related to the in situ slack of the LET tissue (R2≥ 0.88; P≤ .0003).

CONCLUSION

LET increased restraint to IR of the tibia compared with the anterolateral tissue, particularly at 30°, 60°, and 90° of flexion. IR of the tibia was positively associated with in situ slack of the LET tissue.

CLINICAL RELEVANCE

Fixing the LET at 60° of flexion still provided IR restraint in the more functionally relevant flexion angle of 30°. Surgeons should pay close attention to the angle of internal and/or external tibial rotation when fixing the LET tissue intraoperatively because this surgical parameter is related to in situ slack of the LET tissue and, therefore, the amount of IR of the tibia.

Knees with anteromedial osteoarthritis show a substantial phenotypic variation prior and following medial unicompartmental knee arthroplasty

PURPOSE

The primary aim of this study was to evaluate the phenotypic variation using the Coronal Plane Alignment of the Knee (CPAK) classification among 1000 knees with anteromedial osteoarthritis (OA) both prior to and following medial unicompartmental knee arthroplasty (UKA). The secondary aim of this study was to investigate whether knees maintained their preoperative CPAK phenotype and to evaluate the phenotypic alterations following medial UKA.

METHODS

The CPAK classification was used to analyze 1000 knees that underwent medial UKA as treatment for anteromedial OA. Knees were categorized into nine distinct CPAK phenotypes based on their arithmetic hip-knee-ankle angle (aHKA), which estimates the pre-arthritic alignment, and joint line obliquity (JLO), both pre- and postoperatively. Phenotypic variation was analyzed by sex and age, and the phenotypic alterations following medial UKA were evaluated by phenotype.

RESULTS

Preoperatively, CPAK phenotype I had the highest prevalence (45.0%). Among males, the preoperative prevalence of CPAK phenotype I was significantly higher compared to females (53.2% vs. 35.0%, respectively; p ≤ .001), whereas females exhibited a significantly higher occurrence of CPAK phenotype V compared to males (9.8% vs. 4.4%, respectively; p ≤ .015). Following medial UKA, CPAK phenotype II had the highest prevalence (53.3%). Overall, 45.1% of knees maintained their preoperative CPAK phenotype following medial UKA, which was most frequently observed among CPAK phenotype II (67.7%) and III (65.8%).

CONCLUSION

There is a substantial variation in CPAK phenotypes among knees with anteromedial OA, as well as following treatment with medial UKA. This variability challenges the assumption of uniform characteristics among knees with an identical wear pattern associated with anteromedial OA and emphasizes the complexity and variability of this specific form of OA.

LEVEL OF EVIDENCE

III, Retrospective cohort study.

Higher incidence of patellar incongruence after under correction of pre-arthritic coronal alignment following medial unicompartmental knee arthroplasty

PURPOSE

This study aimed to compare patellofemoral joint alignment of knees with restored pre-arthritic coronal alignment versus knees with under- or overcorrection from their pre-arthritic coronal alignment following medial unicompartmental knee arthroplasty (UKA) and evaluate the effect of patellofemoral joint alignment on patient-reported outcomes.

METHODS

A retrospective analysis of 517 knees following robotic-arm assisted medial UKA was conducted. Postoperative mechanical hip-knee-ankle angle (mHKA) was compared to estimated pre-arthritic coronal alignment, using the arithmetic hip-knee-ankle angle (aHKA). Knees were considered restored to the pre-arthritic coronal alignment if mHKA was within 2.0° of aHKA (Group 1). Non-restored knees were subdivided into > 2.0° over correction (Group 2), or > 2.0° under correction (Group 3) from the pre-arthritic coronal alignment. Patellar congruence and patellar tilt angles were compared between groups. The Kujala score and Knee Injury and Osteoarthritic Outcome Score for Joint Replacement (KOOS, JR) were analyzed by group. Continuous data was compared using analysis of variance or Kruskal-Wallis tests. Chi-squared tests were used to compare discrete variables. Logistic regressions were conducted to estimate the probability of postoperative patellofemoral malalignment.

RESULTS

Group 1 included 357 knees (69.1%), Group 2 included 57 knees (11.0%), and Group 3 included 57 knees (11.0%). The prevalence of postoperative abnormal patellar congruence (i.e. ≥ 17°) was higher in Group 3 at 40.4% (p = 0.009), with a higher odds ratio of having an abnormal patellar congruence angle (2.3, p = 0.01) compared to Group 1. The prevalence of postoperative abnormal patellar tilt (i.e. ≥ 14°) was comparable between groups (n.s.). At mean follow up of 4.4 ± 1.6 years, Kujala was worse in Group 3 (76.6 ± 17.4 compared to 84.0 ± 14.9 and 85.0 ± 14.4 in Groups 1 and 2, respectively; p = 0.006). Mean KOOS, JR outcomes were comparable among groups. No significantly inferior Kujala or KOOS, JR outcomes were observed in patients across all groups with abnormal patellar congruence or tilt angles.

CONCLUSION

Knees with under correction from their pre-arthritic coronal alignment following medial UKA were associated with a two-fold higher probability of having postoperative patellofemoral incongruence, as well as inferior mid-term Kujala scores compared to knees with restored pre-arthritic coronal alignment and knees with overcorrection from their pre-arthritic coronal alignment. Patellofemoral incongruence alone did not negatively impact functional outcome scores.

LEVEL OF EVIDENCE

IV, case series.

Artificial Intelligence for Automated Implant Identification in Knee Arthroplasty: A Multicenter External Validation Study Exceeding 3.5 Million Plain Radiographs

BACKGROUND

Surgical management of complications following knee arthroplasty demands accurate and timely identification of implant manufacturer and model. Automated image processing using deep machine learning has been previously developed and internally validated; however, external validation is essential prior to scaling clinical implementation for generalizability.

METHODS

We trained, validated, and externally tested a deep learning system to classify knee arthroplasty systems as one of the 9 models from 4 manufacturers derived from 4,724 original, retrospectively collected anteroposterior plain knee radiographs across 3 academic referral centers. From these radiographs, 3,568 were used for training, 412 for validation, and 744 for external testing. Augmentation was applied to the training set (n = 3,568,000) to increase model robustness. Performance was determined by the area under the receiver operating characteristic curve, sensitivity, specificity, and accuracy. Implant identification processing speed was calculated. The training and testing sets were drawn from statistically different populations of implants (P < .001).

RESULTS

After 1,000 training epochs by the deep learning system, the system discriminated 9 implant models with a mean area under the receiver operating characteristic curve of 0.989, accuracy of 97.4%, sensitivity of 89.2%, and specificity of 99.0% in the external testing dataset of 744 anteroposterior radiographs. The software classified implants at a mean speed of 0.02 seconds per image.

CONCLUSION

An artificial intelligence-based software for identifying knee arthroplasty implants demonstrated excellent internal and external validation. Although continued surveillance is necessary with implant library expansion, this software represents a responsible and meaningful clinical application of artificial intelligence with immediate potential to globally scale and assist in preoperative planning prior to revision knee arthroplasty.

Restoration or relative overcorrection of pre-arthritic coronal alignment leads to improved results following medial unicompartmental knee arthroplasty

PURPOSE

A pre-arthritic alignment strategy for medial unicompartmental knee arthroplasty (UKA) aims to restore a patient's native lower limb alignment which may translate into improved outcomes. This study aimed to assess whether patients with pre-arthritically aligned knees versus patients with non-pre-arthritically aligned knees demonstrated improved mid-term outcomes and survivorship following medial UKA. The hypothesis was that pre-arthritic alignment in medial UKA would lead to better postoperative outcomes.

METHODS

A retrospective study of 537 robotic-assisted fixed-bearing medial UKA was conducted. During this procedure, the surgical goal was to restore pre-arthritic alignment guided by re-tensioning of the medial collateral ligament (MCL). For study purposes, coronal alignment was retrospectively evaluated using the mechanical hip-knee-ankle angle (mHKA). Pre-arthritic alignment was estimated through the arithmetic hip-knee-ankle (aHKA) algorithm. Knees were grouped according to the difference between postoperative mHKA and estimated pre-arthritic alignment (i.e., mHKA - aHKA) as Group 1 (pre-arthritically aligned: mHKA restored within 2.0° of the aHKA), Group 2 (mHKA > 2.0° overcorrected relative to the aHKA), or Group 3 (mHKA > 2.0° undercorrected relative to the aHKA). Outcomes included the Knee Injury and Osteoarthritic Outcome Score for Joint Replacement (KOOS, JR), Kujala, proportions of knees achieving the patient acceptable symptom state (PASS) for these scores, and survivorship. PASS thresholds for KOOS, JR and Kujala were determined using a receiver operating characteristic curve method.

RESULTS

A total of 369 knees were categorized as Group 1, 107 as Group 2, and 61 as Group 3. At 4.4 ± 1.6 years follow-up, mean KOOS, JR was comparable among groups, while Kujala was significantly worse in Group 3. The proportion of knees achieving the PASS for Kujala (76.5 points) was lower in Group 3 (n = 32; 59%) compared to Group 1 (n = 260; 74%) (p = 0.02). 5-year survivorship was higher in Group 1 and Group 2 (99% and 100%, respectively) compared to Group 3 (91%) (p = 0.04).

CONCLUSION

Pre-arthritically aligned knees and knees with relative overcorrection from their pre-arthritic alignment following medial UKA demonstrated improved mid-term outcomes and survivorship compared to knees with relative under correction from their pre-arthritic alignment. These results encourage restoring or relatively overcorrecting pre-arthritic alignment to optimize outcomes following medial UKA, and caution against under correction from the pre-arthritic alignment.

LEVEL OF EVIDENCE

IV, case series.

Bayesian Calibration of Computational Knee Models to Estimate Subject-Specific Ligament Properties, Tibiofemoral Kinematics, and Anterior Cruciate Ligament Force With Uncertainty Quantification

High-grade knee laxity is associated with early anterior cruciate ligament (ACL) graft failure, poor function, and compromised clinical outcome. Yet, the specific ligaments and ligament properties driving knee laxity remain poorly understood. We described a Bayesian calibration methodology for predicting unknown ligament properties in a computational knee model. Then, we applied the method to estimate unknown ligament properties with uncertainty bounds using tibiofemoral kinematics and ACL force measurements from two cadaver knees that spanned a range of laxities; these knees were tested using a robotic manipulator. The unknown ligament properties were from the Bayesian set of plausible ligament properties, as specified by their posterior distribution. Finally, we developed a calibrated predictor of tibiofemoral kinematics and ACL force with their own uncertainty bounds. The calibrated predictor was developed by first collecting the posterior draws of the kinematics and ACL force that are induced by the posterior draws of the ligament properties and model parameters. Bayesian calibration identified unique ligament slack lengths for the two knee models and produced ACL force and kinematic predictions that were closer to the corresponding in vitro measurement than those from a standard optimization technique. This Bayesian framework quantifies uncertainty in both ligament properties and model outputs; an important step towards developing subject-specific computational models to improve treatment for ACL injury.

De Novo Synovial Chondromatosis following Primary Total Knee Arthroplasty: A Case Report

In this case report, we present a rare case of a female patient who developed pain and swelling after a total knee arthroplasty. An extensive diagnostic workup including serum and synovial testing to rule out infection was performed in addition to advanced imaging including an MRI of the knee, but it was only after an arthroscopic synovectomy that the diagnosis of secondary synovial chondromatosis was confirmed. The purpose of this case report is to highlight the occurrence of secondary synovial chondromatosis as a rare cause of pain and swelling after total knee arthroplasty, thereby assisting clinicians in providing prompt diagnosis, surgical treatment, and efficient recovery in the setting of secondary synovial chondromatosis after total knee arthroplasty.

Ten-Year Survivorship and Patient Satisfaction Following Robotic-Arm-Assisted Medial Unicompartmental Knee Arthroplasty: A Prospective Multicenter Study

BACKGROUND

Robotic-arm-assisted unicompartmental knee arthroplasty (UKA) has been shown to result in high short- and mid-term survivorship. However, it is not known whether these outcomes are maintained at long-term follow-up. This study aimed to evaluate long-term implant survivorship, modes of failure, and patient satisfaction following robotic-arm-assisted medial UKA.

METHODS

A prospective multicenter study of 474 consecutive patients (531 knees) undergoing robotic-arm-assisted medial UKA was conducted. A cemented, fixed-bearing system with a metal-backed onlay tibial implant was used in all cases. Patients were contacted at 10-year follow-up to determine implant survivorship and satisfaction. Survival was analyzed using Kaplan-Meier models.

RESULTS

Data were analyzed for 366 patients (411 knees) with a mean follow-up of 10.2 ± 0.4 years. A total of 29 revisions were reported, corresponding to a 10-year survivorship of 91.7% (95% confidence interval, 88.8% to 94.6%). Of all revisions, 26 UKAs were revised to total knee arthroplasty. Unexplained pain and aseptic loosening were the most commonly reported modes of failure, accounting for 38% and 35% of revisions, respectively. Of patients without revision, 91% were either satisfied or very satisfied with their overall knee function.

CONCLUSIONS

This prospective multicenter study found high 10-year survivorship and patient satisfaction following robotic-arm-assisted medial UKA. Pain and fixation failure remained common causes for revision following cemented fixed-bearing medial UKA, despite the use of a robotic-arm-assisted technique. Prospective comparative studies are needed to assess the clinical value of robotic assistance over conventional techniques in UKA.

LEVEL OF EVIDENCE

Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.

Key Thresholds and Relative Contributions of Knee Geometry, Anteroposterior Laxity, and Body Weight as Risk Factors for Noncontact ACL Injury

Background

Limited data exist regarding the association of tibiofemoral bony and soft tissue geometry and knee laxity with risk of first-time noncontact anterior cruciate ligament (ACL) rupture.

Purpose

To determine associations of tibiofemoral geometry and anteroposterior (AP) knee laxity with risk of first-time noncontact ACL injury in high school and collegiate athletes.

Study Design

Cohort study; Level of evidence, 2.

Methods

Over a 4-year period, noncontact ACL injury events were identified as they occurred in 86 high school and collegiate athletes (59 female, 27 male). Sex- and age-matched control participants were selected from the same team. AP laxity of the uninjured knee was measured using a KT-2000 arthrometer. Magnetic resonance imaging was taken on ipsilateral and contralateral knees, and articular geometries were measured. Sex-specific general additive models were implemented to investigate associations between injury risk and 6 features: ACL volume, meniscus-bone wedge angle in the lateral compartment of the tibia, articular cartilage slope at the middle region of the lateral compartment of the tibia, femoral notch width at the anterior outlet, body weight, and AP displacement of the tibia relative to the femur. Importance scores (in percentages) were calculated to rank the relative contribution of each variable.

Results

In the female cohort, the 2 features with the highest importance scores were tibial cartilage slope (8.6%) and notch width (8.1%). In the male cohort, the 2 top-ranked features were AP laxity (5.6%) and tibial cartilage slope (4.8%). In female patients, injury risk increased by 25.5% with lateral middle cartilage slope becoming more posteroinferior from -6.2° to -2.0° and by 17.5% with lateral meniscus-bone wedge angle increasing from 27.3° to 28.2°. In males, an increase in AP displacement from 12.5 to 14.4 mm in response to a 133-N anterior-directed load was associated with a 16.7% increase in risk.

Conclusion

Of the 6 variables studied, there was no single dominant geometric or laxity risk factor for ACL injury in either the female or male cohort. In males, AP laxity >13 to 14 mm was associated with sharply increased risk of noncontact ACL injury. In females, lateral meniscus-bone wedge angle >28° was associated with a sharply decreased risk of noncontact ACL injury.

Robotic-Arm-Assisted Lateral Unicompartmental Knee Arthroplasty with a Fixed-Bearing Implant

Background

Approximately 5% to 10% of patients with knee arthritis have isolated lateral compartment arthritis; however, lateral unicompartmental knee arthroplasty (UKA) comprises just 1% of all knee arthroplasties1. This low proportion is partly because of the perceived complexity of lateral UKA and concerns over implant longevity and survivorship compared with total knee arthroplasty (TKA)2,3. With an improved understanding of knee kinematics alongside advances in implant design and tools to aid in appropriate restoration of limb alignment, lateral UKA can be an appealing surgical alternative to TKA for certain patients with lateral knee arthritis4,5. In appropriately selected patients, lateral UKA has been associated with reduced osseous and soft-tissue resection, more natural knee kinematics, less pain, shorter hospitalization, decreased blood loss and infection rates, and excellent survivorship and patient-reported outcomes6-9.

Description

This surgical approach and technique described for lateral UKA utilizes robotic-arm assistance and modern fixed-bearing implants10. The specific steps involve appropriate patient evaluation and selection, extensive radiographic and computed-tomography-based preoperative templating, a lateral parapatellar approach, intraoperative confirmation of component position and alignment, and robotic-arm assistance to perform osseous resections to achieve limb alignment and kinematic targets10. Final implants are cemented in place, and patients typically are discharged home on the day of surgery10.

Alternatives

Nonoperative treatment for end-stage knee arthritis includes weight loss, activity modification, assistive devices, bracing, nonsteroidal anti-inflammatory medications, and various injections11. Alternative surgical treatments include TKA4 and, in certain patients, an offloading periarticular osteotomy12.

Rationale

Lateral UKA is an appealing surgical option for nonobese patients who have disabling knee pain isolated to the lateral compartment, good preoperative range of motion, and a passively correctable valgus limb deformity10,13.

Expected Outcomes

Patients are typically discharged home on the day of surgery, or occasionally on postoperative day 1 if medical comorbidities dictate hospital monitoring overnight10. Patients return to light activities, including walking, immediately postoperatively. By 3 months postoperatively, patients will generally have returned to all desired activities9. The mid-term outcomes of this procedure, as performed by the corresponding author, have been published recently14,15. The 5-year survivorship of 171 lateral UKAs was 97.7%, with 72.8% of patients reporting that they were very satisfied with their procedure and 19.8%, that they were satisfied14. Only 3.8% of patients reported dissatisfaction with their lateral UKA14. The mean Knee Injury and Osteoarthritis Outcome Score (KOOS) and standard deviation were 85.6 ± 14.314. These outcomes did not differ from those observed in 802 medial UKAs, which showed a survivorship of 97.8% and KOOS of 84.3 ± 15.914. These findings are generally in line with previously published studies, which have demonstrated excellent survivorship and patient-reported outcomes with fixed-bearing lateral UKA16-19.

Important Tips

Component position and alignment are critical to achieve target knee kinematics.Target postoperative alignment is 1° to 4° of valgus.A meticulous cementation technique is required for optimal fixation and avoidance of excess residual cement in the posterior knee.

Acronyms and Abbreviations

ACL = anterior cruciate ligamentAP = anteroposteriorBMI = body mass indexCT = computed tomographyCAT = computed axial tomographyIT = iliotibialKOOS JR = Knee Injury and Osteoarthritis Outcome Score for Joint ReplacementMCL = medial collateral ligamentMRI = magnetic resonance imagingOR = operating roomPFJ = patellofemoral jointpoly = polyethyleneROM = range of motionTKA = total knee arthroplastyUKA = unicompartmental knee arthroplasty.

Survival analyses and their applications in orthopaedics

Survival analyses are a powerful statistical tool used to analyse data when the outcome of interest involves the time until an event. There is an array of models fit for this goal; however, there are subtle differences in assumptions, as well as a number of pitfalls, that can lead to biased results if researchers are unaware of the subtleties. As larger amounts of data become available, and more survival analyses are published every year, it is important that healthcare professionals understand how to evaluate these models and apply them into their practice. Therefore, the purpose of this study was to present an overview of survival analyses, including required assumptions and important pitfalls, as well as examples of their use within orthopaedic surgery.

Does a Uni "Feel Better" than a Total Knee? Not Necessarily, When Using Modern Implant Designs

Background: When comparing functional outcomes of patients with unicompartmental knee arthroplasty (UKA) versus total knee arthroplasty (TKA), studies often report the UKA as the preferred procedure; however, recent improvements in the design of modern TKA implants have aimed at narrowing this gap. Purpose: We sought to compare the "feel" of modern TKA implants to that of UKA, using the Forgotten Joint Score (FJS), a validated patient-reported outcome measure. Methods: We performed a retrospective review of patients who underwent TKA and UKA at 2 institutions between 2014 and 2017. All UKA procedures were robotic arm-assisted with a single implant, "traditional TKAs" were performed using traditional posterior-stabilized implants, and "modern TKAs" were performed using posterior-stabilized implants with a modern design. Differences in FJS were assessed using 1-way analysis of variance and independent 2-sample t tests. Results: A total of 600 patients were included in our study, with 200 patients in each surgical subcategory. Mean age was 62.8 ± 10.2 years and mean body mass index was 29.9 ± 4.9. Modern TKA and UKA had similar FJS at 1 year. While modern TKA had a significantly higher FJS than traditional TKA, UKA did not have a significantly higher FJS than traditional TKA. Conclusion: Our retrospective analysis found no significant differences in the FJS of patients who underwent UKA and TKA with a modern design; however, both had superior scores than traditional TKA designs. This finding suggests that modern TKA designs may have the potential to achieve the natural feeling that is typically associated with joint-conserving surgeries such as UKA, although longer follow-up is necessary.

A practical guide to the development and deployment of deep learning models for the Orthopedic surgeon: part I

Deep learning has a profound impact on daily life. As Orthopedics makes use of this rapid escalation in technology, Orthopedic surgeons will need to take leadership roles on deep learning projects. Moreover, surgeons must possess an understanding of what is necessary to design and implement deep learning-based project pipelines. This review provides a practical guide for the Orthopedic surgeon to understand the steps needed to design, develop, and deploy a deep learning pipeline for clinical applications. A detailed description of the processes involved in defining the problem, building the team, acquiring and curating the data, labeling the data, establishing the ground truth, pre-processing and augmenting the data, and selecting the required hardware is provided. In addition, an overview of unique considerations involved in the training and evaluation of deep learning models is provided. This review strives to provide surgeons with the groundwork needed to identify gaps in the clinical landscape that deep learning models may be able to fill and equips them with the knowledge needed to lead an interdisciplinary team through the process of creating novel deep-learning-based solutions to fill those gaps.

Robotic-assisted medial unicompartmental knee arthroplasty restores estimated pre-arthritic coronal limb alignment: A retrospective cohort study

BACKGROUND

Robotic-assisted medial unicompartmental knee arthroplasty (UKA) aims to restore pre-arthritic (constitutional) limb alignment, by re-tensioning of the medial collateral ligament (MCL). This study aimed to determine whether pre-arthritic coronal alignment was restored following robotic-assisted medial UKA in patients with medial compartment osteoarthritis.

METHOD

A retrospective study was undertaken, including 102 patients with a unilateral robotic-assisted medial UKA and a contralateral unaffected knee. Both the validated arithmetic hip-knee-ankle angle (aHKA) and alignment of the contralateral unaffected knee were used to estimate pre-arthritic alignment. The aHKA is a radiographic method to estimate the pre-arthritic mechanical hip-knee-ankle angle (mHKA). To verify restoration of pre-arthritic alignment, postoperative mHKA was compared to the aHKA. Additionally, postoperative mHKA, joint line congruence (JLCA), and knee joint line obliquity (KJLO) angles were compared between the operative and contralateral unaffected knee. Equivalence between postoperative and pre-arthritic alignment was assessed through the two-one-sided t-test (TOST), using equivalence margins of ±2.0°.

RESULTS

Postoperative mHKA was equivalent to the aHKA (mean difference -0.38°, 90% CI -0.69 to -0.07;p < .001), with 93 knees (91%) restored within 3.0° their aHKA. Postoperative mHKA, JLCA and KJLO were equivalent between the operative and contralateral unaffected knees, with mean differences of -0.65°, -0.65°, and -0.40°, respectively; all p < .001.

CONCLUSIONS

Postoperative and pre-arthritic coronal alignment were equivalent following robotic-assisted medial UKA, with 91% of knees restored within 3.0° of their pre-arthritic mechanical axis. These results demonstrate that both mechanical alignment and joint line congruence are restored by MCL re-tensioning in patients undergoing robotic-assisted medial UKA for medial compartment osteoarthritis.

Higher Adherence to Anterior Cruciate Ligament Injury Prevention Programs Is Associated With Lower Injury Rates: A Meta-Analysis and Meta-Regression

Background: Athletes who participate in sports that involve cutting and pivoting movements are particularly susceptible to anterior cruciate ligament (ACL) injury. Preventing this injury is the best way to combat its health consequences and costs. There may be a dose-response relationship between adherence and injury reduction. Purpose: We sought to examine whether athletes’ adherence to injury prevention programs (IPPs) is associated with reductions in ACL and lower extremity (LE) injuries. Methods: We conducted a systematic review of the PubMed, EMBASE, and Cochrane Library databases, searching for studies published between 2011 and 2021. Studies were included if they reported on the use of an ACL IPP compared with a control group and recorded the rate of injuries to calculate a rate ratio, as well as adherence to the program as a percentage of sessions performed. For the meta-analysis, the rate ratios were pooled using the DerSimonian-Laird random-effects model. Results: For the 15 studies included (11 randomized controlled trials and 4 cohort studies), the random-effects model grouped athletes’ adherence to an IPP as high (76% or more of the sessions), moderate (51%–75% of the sessions), and low (50% or fewer of the sessions). We found that athletes with the highest level of IPP adherence had a significantly lower incidence of ACL injury. The rate ratios for moderate and low adherence did not demonstrate a reduced incidence of ACL injury. Injury prevention program participation was also associated with a decrease in LE injury rates. Conclusion: This systematic review and meta-analysis found that athletes with high adherence to IPPs had reduced rates of ACL and LE injuries. Our findings suggest that educating coaches and athletes on the dose-dependent benefits of IPPs may promote the routine incorporation of these programs into warm-up sessions to decrease the risk of ACL and LE injuries.

Natural language processing: using artificial intelligence to understand human language in orthopedics

Natural language processing (NLP) describes the broad field of artificial intelligence by which computers are trained to understand and generate human language. Within healthcare research, NLP is commonly used for variable extraction and classification/cohort identification tasks. While these tools are becoming increasingly popular and available as both open-source and commercial products, there is a paucity of the literature within the orthopedic space describing the key tasks within these powerful pipelines. Curation and navigation of the electronic medical record are becoming increasingly onerous, and it is important for physicians and other healthcare professionals to understand potential methods of harnessing this large data resource. The purpose of this study is to provide an overview of the tasks required to develop an NLP pipeline for orthopedic research and present recent examples of successful implementations.

Arthroplasty Surgeons Differ in Their Intraoperative Soft Tissue Assessments: A Study in Human Cadavers to Quantify Surgical Decision-making in TKA

BACKGROUND

In TKA, soft tissue balancing is assessed through manual intraoperative trialing. This assessment is a physical examination via manually applied forces at the ankle, generating varus and valgus moments at the knee while the surgeon visualizes the lateral and medial gaps at the joint line. Based on this examination, important surgical decisions are made that influence knee stability, such as choosing the polyethylene insert thickness. Yet, the applied forces and the assessed gaps in this examination represent a qualitative art that relies on each surgeon's intuition, experience, and training. Therefore, the extent of variation among surgeons in conducting this exam, in terms of applied loads and assessed gaps, is unknown. Moreover, whether variability in the applied loads yields different surgical decisions, such as choice of insert thickness, is also unclear. Thus, surgeons and developers have no basis for deciding to what extent the applied loads need to be standardized and controlled during a knee balance exam in TKA.

QUESTIONS/PURPOSES

(1) Do the applied moments in soft tissue assessment differ among surgeons? (2) Do the assessed gaps in soft tissue assessment differ among surgeons? (3) Is the choice of insert thickness associated with the applied moments?

METHODS

Seven independent human cadaveric nonarthritic lower extremities from pelvis to toe were acquired (including five females and two males with a mean age of 73 ± 7 years and a mean BMI of 25.8 ± 3.8 kg/m 2 ). Posterior cruciate ligament substituting (posterior stabilized) TKA was performed only on the right knees. Five fellowship-trained knee surgeons (with 24, 15, 15, 7, and 6 years of clinical experience) and one chief orthopaedic resident independently examined soft tissue balance in each knee in extension (0° of flexion), midflexion (30° of flexion), and flexion (90° of flexion) and selected a polyethylene insert based on their assessment. Pliable force sensors were wrapped around the leg to measure the loads applied by each surgeon. A three-dimensional (3D) motion capture system was used to measure knee kinematics and a dynamic analysis software was used to estimate the medial and lateral gaps. We assessed (1) whether surgeons applied different moments by comparing the mean applied moment by surgeons in extension, midflexion, and flexion using repeated measures (RM)-ANOVA (p < 0.05 was assumed significantly different); (2) whether surgeons assessed different gaps by comparing the mean medial and lateral gaps in extension, midflexion, and flexion using RM-ANOVA (p < 0.05 was assumed significantly different); and (3) whether the applied moments in extension, midflexion, and flexion were associated with the insert thickness choice using a generalized estimating equation (p < 0.05 was assumed a significant association).

RESULTS

The applied moments differed among surgeons, with the largest mean differences occurring in varus in midflexion (16.5 Nm; p = 0.02) and flexion (7.9 Nm; p < 0.001). The measured gaps differed among surgeons at all flexion angles, with the largest mean difference occurring in flexion (1.1 ± 0.4 mm; p < 0.001). In all knees except one, the choice of insert thickness varied by l mm among surgeons. The choice of insert thickness was weakly associated with the applied moments in varus (β = -0.06 ± 0.02 [95% confidence interval -0.11 to -0.01]; p = 0.03) and valgus (β = -0.09 ± 0.03 [95% CI -0.18 to -0.01]; p= 0.03) in extension and in varus in flexion (β = -0.11 ± 0.04 [95% CI -0.22 to 0.00]; p = 0.04). To put our findings in context, the greatest regression coefficient (β = -0.11) indicates that for every 9-Nm increase in the applied varus moment (that is, 22 N of force applied to the foot assuming a shank length of 0.4 m), the choice of insert thickness decreased by 1 mm.

CONCLUSION

In TKA soft tissue assessment in a human cadaver model, five surgeons and one chief resident applied different moments in midflexion and flexion and targeted different gaps in extension, midflexion, and flexion. A weak association between the applied moments in extension and flexion and the insert choice was observed. Our results indicate that in the manual assessment of soft tissue, changes in the applied moments of 9 and 11 Nm (22 to 27 N on the surgeons' hands) in flexion and extension, respectively, yielded at least a 1-mm change in choice of insert thickness. The choice of insert thickness may be more sensitive to the applied moments in in vivo surgery because the surgeon is allowed a greater array of choices beyond insert thickness.

CLINICAL RELEVANCE

Among five arthroplasty surgeons with different levels of experience and a chief resident, subjective soft tissue assessment yielded 1 to 2 mm of variation in their choice of insert thickness. Therefore, developers of tools to standardize soft tissue assessment in TKA should consider controlling the force applied by the surgeon to better control for variations in insert selection.

Patient and Surgeon Risk-Taking Regarding Total Joint Arthroplasty

BACKGROUND

Decisions regarding care for osteoarthritis involve physicians helping patients understand likely benefits and harms of treatment. Little work has directly compared patient and surgeon risk-taking attitudes, which may help inform strategies for shared decision-making and improve patient satisfaction.

METHODS

We surveyed patients contemplating total joint arthroplasty visiting a high-volume specialty hospital regarding general questions about risk-taking, as well as willingness to undergo surgery under hypothetical likelihoods of moderate improvement and complications. We compared responses from surgeons answering similar questions about willingness to recommend surgery.

RESULTS

Altogether 82% (162/197) of patients responded, as did 65% (30/46) of joint replacement surgeons. Mean age among patients was 66.4 years; 58% were female. Surgeons averaged 399 surgeries in 2019. Responses were similar between groups for general, health, career, financial, and sports/leisure risk-taking (P > .20); surgeons were marginally more risk-taking in driving (P = .05). For willingness to have or recommend surgery, as the chance of benefit decreased, or the chance of harm increased, the percentage willing to have or recommend surgery decreased. Between a 70% and 95% chance of moderate improvement (for a 2% complication risk), as well as between a 90% and 95% chance of moderate improvement (for 4% and 6% complication risks), the percentage willing to have or recommend surgery was indistinguishable between patients and surgeons. However, for lower likelihoods of improvement, a higher percentage of patients were willing to undergo surgery than surgeons recommended. Patients were also more often indifferent between complication risks.

CONCLUSION

Although patients and surgeons were often willing to have or recommend joint replacement surgery at similar rates, they diverged for lower-benefit higher-harm scenarios.

Patient-Reported Outcome, Return to Sport, and Revision Rates 7-9 Years After Anterior Cruciate Ligament Reconstruction: Results From a Cohort of 2042 Patients

BACKGROUND

Long-term patient-reported outcome measures (PROMs), rates of return to sport, and revision risk after anterior cruciate ligament (ACL) reconstruction (ACLR) are not well understood.

PURPOSE

To provide long-term follow-up of PROMs, return-to-sport rates, and revision rates after ACLR and to identify predictors for poor outcome.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

A total of 2042 patients were included in an institutional ACL registry (2009-2013) and longitudinally followed. PROMs were completed preoperatively and at all follow-up time points. Questions regarding return to sport and knee stability were completed at final follow-up. Predictors for poor outcome on the International Knee Documentation Committee (IKDC) score were estimated in a regression model incorporating risk factors such as patient characteristics, graft choice, and concomitant injuries. Revision rates and risk of subsequent non-ACL surgeries were calculated.

RESULTS

Autografts were used in 76% of the patients (patellar tendon, 62%; hamstring grafts, 38%). Allografts were used in 24% of patients. The questionnaires were returned by 1045 (51.2%) patients at a mean of 7.2 years (range, 5.0-9.8 years) after surgery. Improvements in IKDC score of >30 points were sustained for all patient categories. The strongest predictor for lesser improvement in IKDC score was a cartilage lesion >2 cm2 identified during surgery. Male sex and college education completion were associated with improved IKDC scores. Meniscal lesions did not predict change) in the IKDC score. A total of 69% of patients had returned to sport after 8.1 years (range, 6.7-9.8 years). The main reason for not returning to sport was fear of reinjury. The revision rate was 7.2% after 9 years (range, 8-11 years), 13% of patients needed subsequent ipsilateral non-ACL surgery, and 6% underwent contralateral ACLR. The absence of a meniscal tear, younger age, and male sex were predictors for revision. Graft choice did not predict PROM results or revision risk.

CONCLUSION

Improvements in IKDC scores were sustained 7 years after ACLR. The strongest predictor for poor outcome was a cartilage lesion >2 cm2. Patients can expect a 70% return-to-sport rate and an 87% chance of their knee feeling stable during daily and athletic activities after 8 years. Young male patients have better PROM scores but a higher risk of revision. There is a 26% chance of subsequent knee surgery within 9 years, including a revision rate of 7%, subsequent non-ACL surgery to the operated knee in 13%, and a 6% chance of contralateral ACLR.

Comparable incidence of periprosthetic tibial fractures in cementless and cemented unicompartmental knee arthroplasty: a systematic review and meta-analysis

PURPOSE

(I) To determine the incidence of periprosthetic tibial fractures in cemented and cementless unicompartmental knee arthroplasty (UKA) and (II) to summarize the existing evidence on characteristics and risk factors of periprosthetic fractures in UKA.

METHODS

Pubmed, Cochrane and Embase databases were comprehensively searched. Any clinical, laboratory or case report study describing information on proportion, characteristics or risk factors of periprosthetic tibial fractures in UKA was included. Proportion meta-analysis was performed to estimate the incidence of fractures only using data from clinical studies. Information on characteristics and risk factors was evaluated and summarized.

RESULTS

A total of 81 studies were considered to be eligible for inclusion. Based on 41 clinical studies, incidences of fractures were 1.24% (95%CI 0.64-2.41) for cementless and 1.58% (95%CI 1.06-2.36) for cemented UKAs (9451 UKAs). The majority of fractures in the current literature occurred during surgery or presented within 3 months postoperatively (91 of 127; 72%) and were non-traumatic (95 of 113; 84%). Six different fracture types were observed in 21 available radiographs. Laboratory studies revealed that an excessive interference fit (press fit), excessive tibial bone resection, a sagittal cut too deep posteriorly and low bone mineral density (BMD) reduce the force required for a periprosthetic tibial fracture to occur. Clinical studies showed that periprosthetic tibial fractures were associated with increased body mass index and postoperative alignment angles, advanced age, decreased BMD, female gender, and a very overhanging medial tibial condyle.

CONCLUSION

Comparable low incidences of periprosthetic tibial fractures in cementless and cemented UKA can be achieved. However, surgeons should be aware that an excessive interference fit in cementless UKAs in combination with an impaction technique may introduce an additional risk, and could therefore be less forgiving to surgical errors and patients who are at higher risk of periprosthetic tibial fractures.

LEVEL OF EVIDENCE

V.

Anterior cruciate ligament graft forces are sensitive to fixation angle and tunnel position within the native femoral footprint during passive flexion

BACKGROUND

Anterior cruciate ligament (ACL) graft position within the anatomic femoral footprint of the native ACL and the flexion angle at which the graft is fixed (i.e., fixation angle) are important considerations in ACL reconstruction surgery. However, their combined effect on ACL graft force remains less well understood.

HYPOTHESIS

During passive flexion, grafts placed high within the femoral footprint carry lower forces than grafts placed low within the femoral footprint (i.e., high and low grafts, respectively). Forces carried by high grafts are independent of fixation angle. All reconstructions impart higher forces on the graft than those carried by the native ACL.

STUDY DESIGN

Controlled laboratory study.

METHODS

Five fresh-frozen cadaveric knees were mounted to a robotic manipulator and flexed from full extension to 90° of flexion. The ACL was sectioned and ACL force was calculated via superposition. ACL reconstructions were then performed using a patellar tendon autograft. For each knee, four different reconstruction permutations were tested: high and low femoral graft positions fixed at 15° and at 30° of flexion. Graft forces were calculated from full extension to 90° of flexion for each combination of femoral graft position and fixation angle again via superposition. Native ACL and ACL graft forces were compared through early flexion (by averaging tissue force from 0 to 30° of flexion) and in 5° increments from full extension to 90° of flexion.

RESULTS

When fixed at 30° of flexion, high grafts carried less force than low grafts through early flexion bearing a respective 64 ± 19 N and 88 ± 11 N (p = 0.02). Increasing fixation angle from 15° to 30° caused graft forces through early flexion to increase 40 ± 13 N in low grafts and 23 ± 6 N in high grafts (p < 0.001). Low grafts fixed at 30° of flexion differed most from the native ACL, carrying 67 ± 9 N more force through early flexion (p < 0.001).

CONCLUSION

ACL grafts placed high within the femoral footprint and fixed at a lower flexion angle carried less force through passive flexion compared to grafts placed lower within the femoral footprint and fixed at a higher flexion angle. At the prescribed pretensions, all grafts carried higher forces than the native ACL through passive flexion.

CLINICAL RELEVANCE

Both fixation angle and femoral graft location within the anatomic ACL footprint influence graft forces and, therefore, should be considered when performing ACL reconstruction.

The Accuracy and Clinical Success of Robotic-Assisted Total Knee Arthroplasty

Background: Robotic-assisted total knee arthroplasty (rTKA) has emerged as a patient-specific customizable tool that enables 3-dimensional preoperative planning, intraoperative adjustment, robotic-assisted bone preparation, and soft-tissue protection. Haptic rTKA may enhance component positioning, but only a few small studies have examined patient satisfaction and clinical outcomes after haptic rTKA. Purpose: In patients who underwent haptic rTKA, we sought to evaluate (1) the discrepancy in alignment between the executed surgical plan and implanted alignment in the coronal and sagittal planes 1 year postoperatively and (2) patient-reported outcomes 2 years postoperatively. Methods: From a prospectively collected database, we reviewed 105 patients who underwent haptic rTKA from August 2016 to May 2017. Two fellowship-trained arthroplasty surgeons independently reviewed hip-to-ankle standing biplanar radiographs to measure overall limb alignment and individual tibial and femoral component alignment relative to the mechanical axis and compared this to the executed surgical plan. Patient-reported outcomes were collected preoperatively and at 2 years postoperatively using the Lower Activity Extremity Score (LEAS), Knee Injury and Osteoarthritis Outcome Score Junior (KOOS Jr.), and Numeric Pain Rating Scale (NPRS). Results: Mean patient age was 62.4 years, and mean body mass index was 30.6 kg/m². Interobserver reliability was significant with a κ of 0.89. Absolute mean deviations in postoperative coronal alignment compared to intraoperative alignment were 0.625° ± 0.70° and 0.45° ± 0.50° for the tibia and femur, respectively. Absolute mean deviations in postoperative tibial sagittal alignment were 0.47° ± 0.76°. Overall mechanical alignment was 0.97° ± 1.79°. Outcomes in LEAS, KOOS Jr., and NPRS changed from 8 to 10, 78 to 88.3, and 8 to 1, respectively. Conclusions: Haptic rTKA demonstrated high reliability and accuracy (less than 1°) of tibial coronal, femoral coronal, and tibial sagittal component alignment postoperatively compared to the surgical plan. Patient-reported outcomes improved, as well. A more rigorous study on long-term outcomes is warranted.

Lateral Extra-articular Tenodesis Alters Lateral Compartment Contact Mechanics under Simulated Pivoting Maneuvers: An In Vitro Study

BACKGROUND

There is concern that utilization of lateral extra-articular tenodesis (LET) in conjunction with anterior cruciate ligament (ACL) reconstruction (ACLR) may disturb lateral compartment contact mechanics and contribute to joint degeneration.

HYPOTHESIS

ACLR augmented with LET will alter lateral compartment contact mechanics in response to simulated pivoting maneuvers.

STUDY DESIGN

Controlled laboratory study.

METHODS

Loads simulating a pivot shift were applied to 7 cadaveric knees (4 male; mean age, 39 ± 12 years; range, 28-54 years) using a robotic manipulator. Each knee was tested with the ACL intact, sectioned, reconstructed (via patellar tendon autograft), and, finally, after augmenting ACLR with LET (using a modified Lemaire technique) in the presence of a sectioned anterolateral ligament and Kaplan fibers. Lateral compartment contact mechanics were measured using a contact stress transducer. Outcome measures were anteroposterior location of the center of contact stress (CCS), contact force from anterior to posterior, and peak and mean contact stress.

RESULTS

On average, augmenting ACLR with LET shifted the lateral compartment CCS anteriorly compared with the intact knee and compared with ACLR in isolation by a maximum of 5.4 ± 2.3 mm (P < .001) and 6.0 ± 2.6 mm (P < .001), respectively. ACLR augmented with LET also increased contact force anteriorly on the lateral tibial plateau compared with the intact knee and compared with isolated ACLR by a maximum of 12 ± 6 N (P = .001) and 17 ± 10 N (P = .002), respectively. Compared with ACLR in isolation, ACLR augmented with LET increased peak and mean lateral compartment contact stress by 0.7 ± 0.5 MPa (P = .005) and by 0.17 ± 0.12 (P = .006), respectively, at 15° of flexion.

CONCLUSION

Under simulated pivoting loads, adding LET to ACLR anteriorized the CCS on the lateral tibial plateau, thereby increasing contact force anteriorly. Compared with ACLR in isolation, ACLR augmented with LET increased peak and mean lateral compartment contact stress at 15° of flexion.

CLINICAL RELEVANCE

The clinical and biological effect of increased anterior loading of the lateral compartment after LET merits further investigation. The ability of LET to anteriorize contact stress on the lateral compartment may be useful in knees with passive anterior subluxation of the lateral tibia.

Complications Following Biologic Therapeutic Injections: A Multicenter Case Series

PURPOSE

To describe the complications that occur following biologic therapeutic injections.

METHODS

We queried physician members of the Biologic Association, a multidisciplinary organization dedicated to providing a unified voice for all matters related to musculoskeletal biologics and regenerative medicine. Patients included in this study must have (1) received a biologic injection, (2) sustained an adverse reaction, and (3) had a minimum of 1-year follow-up after the injection. Patient demographic information, medical comorbidities, diagnoses, and previous treatments were recorded. The type of injection, injection setting, injection manufacturers, and specific details about the complication and outcome were collected.

RESULTS

In total, 14 patients were identified across 6 institutions in the United States (mean age 63 years, range: 36-83 years). The most common injections in this series were intra-articular knee injections (50%), followed intra-articular shoulder injections (21.4%). The most common underlying diagnosis was osteoarthritis (78.5%). Types of injections included umbilical cord blood, platelet-rich plasma, bone marrow aspirate concentrate, placental tissue, and unspecified "stem cell" injections. Complications included infection (50%), suspected sterile inflammatory response (42.9%), and a combination of both (7.1%). The most common pathogen identified from infection cases was Escherichia coli (n = 4). All patients who had isolated infections underwent treatment with at least one subsequent surgical intervention (mean: 3.6, range: 1-12) and intravenous antibiotic therapy.

CONCLUSIONS

This study demonstrates that serious complications can occur following treatment with biologic injections, including infections requiring multiple surgical procedures and inflammatory reactions.

LEVEL OF EVIDENCE

Level IV, case series.

Risk of revision for medial unicompartmental knee arthroplasty according to fixation and bearing type : short- to mid-term results from the Dutch Arthroplasty Register

AIMS

Uncemented mobile bearing designs in medial unicompartmental knee arthroplasty (UKA) have seen an increase over the last decade. However, there are a lack of large-scale studies comparing survivorship of these specific designs to commonly used cemented mobile and fixed bearing designs. The aim of this study was to evaluate the survivorship of these designs.

METHODS

A total of 21,610 medial UKAs from 2007 to 2018 were selected from the Dutch Arthroplasty Register. Multivariate Cox regression analyses were used to compare uncemented mobile bearings with cemented mobile and fixed bearings. Adjustments were made for patient and surgical factors, with their interactions being considered. Reasons and type of revision in the first two years after surgery were assessed.

RESULTS

In hospitals performing less than 100 cases per year, cemented mobile bearings reported comparable adjusted risks of revision as uncemented mobile bearings. However, in hospitals performing more than 100 cases per year, the adjusted risk of revision was higher for cemented mobile bearings compared to uncemented mobile bearings (hazard ratio 1.78 (95% confidence interval 1.34 to 2.35)). The adjusted risk of revision between cemented fixed bearing and uncemented mobile bearing was comparable, independent of annual hospital volume. In addition, 12.3% of uncemented mobile bearing, 20.3% of cemented mobile bearing, and 41.5% of uncemented fixed bearing revisions were for tibial component loosening. The figures for instability were 23.6%, 14.5% and 11.7%, respectively, and for periprosthetic fractures were 10.0%, 2.8%, and 3.5%. Bearing exchange was the type of revision in 40% of uncemented mobile bearing, 24.3% of cemented mobile bearing, and 5.3% cemented fixed bearing revisions.

CONCLUSION

The findings of this study demonstrated improved survival with use of uncemented compared to cemented mobile bearings in medial UKA, only in those hospitals performing more than 100 cases per year. Cemented fixed bearings reported comparable survival results as uncemented mobile bearings, regardless of the annual hospital volume. The high rates of instability, periprosthetic fractures, and bearing exchange in uncemented mobile bearings emphasize the need for further research. Cite this article: Bone Joint J 2021;103-B(7):1261-1269.

Postoperative Disposal of Unused Opioids: A Systematic Review

Introduction: Opioid misuse and overprescription have contributed to a national public health crisis in the United States. Postoperatively, patients are often left with unused opioids, which pose a risk for diversion if not appropriately disposed of. Patients are infrequently provided instructions on safe disposal methods of surplus opioids. Purpose: We sought to determine the current rates of disposal of unused opioids and the reported disposal mechanisms for unused opioids that were prescribed for acute postoperative pain control. Methods: A systematic review was performed of the PubMed, Cochrane, and Embase databases for relevant articles from their earliest entries through October 2, 2019. We used the search terms "opioid" or "narcotic" and "disposal" and "surgery." Studies were considered for inclusion if they reported the rate of disposal of unused opioids following surgery. A screening strategy was used to identify relevant articles using Covidence. For studies meeting inclusion criteria, relevant information was extracted. Results: Sixteen studies met inclusion criteria. We found that surplus opioid disposal rates varied widely, from 4.9% to 87.0%. Among studies with no intervention (opioid disposal education or drug disposal kit/bag), rates of opioid disposal ranged from 4.9% to 46.5%. While 7 studies used opioid disposal education as an intervention, only 3 showed a significant increase in surplus opioid disposal compared with standard care. All 3 studies that used an opioid disposal kit or bag as an intervention demonstrated significant increases in opioid disposal. Conclusions: Baseline rates of surplus opioid disposal are relatively low in the postoperative setting. Our findings suggest that opioid disposal kits significantly increase rates of surplus opioid disposal postoperatively. Further research, including a large-scale cost-benefit analysis, will be necessary prior to recommending widespread implementation of drug disposal kits or bags.

Comparing clinical and radiographic outcomes of robotic-assisted, computer-navigated and conventional unicompartmental knee arthroplasty: A network meta-analysis of randomized controlled trials

Introduction

The purpose was to compare robotic assisted (RA), computer navigated (CN), and conventional UKA techniques.

Methods

Databases were queried for data on study characteristics, UKA systems, complications, and tibiofemoral alignment.

Results

Four RA and six CN RCTs were identified. No significant differences were found in operative time, tibiofemoral alignment, and reoperation rates when comparing RA or CN to conventional UKA. RA UKA resulted in a significantly lower risk of complications compared to conventional UKA.

Conclusions

RA UKA results in fewer complications than conventional UKA with a clinically significant increase in operative time. All groups were similar in remaining evaluated parameters.

Editorial Commentary: The Pivot Shift and Lachman Examinations: Teammates With Distinct Roles

The pivot shift and Lachman examinations are "teammates" with complementary but distinct roles in the successful diagnosis and treatment of anterior cruciate ligament rupture and injury to the surrounding soft-tissue envelope of the knee. The Lachman test measures anterior tibial translation in response to an applied anterior tibial load. This test assesses the integrity of the native or reconstructed anterior cruciate ligament and the secondary medial restraints including the medial meniscus and medial collateral ligament. In contrast, the pivot shift exam creates coupled tibiofemoral motions in response to a complex combination of multiplanar loads. This test assesses the stabilizing role of the native or reconstructed anterior cruciate ligament and the secondary lateral restraints including the lateral meniscus and anterolateral complex. The pivot shift grade depends not only on the soft the tissue stabilizers of the knee but also on the shape of the proximal tibia and the distal femur including lateral tibial slope and femoral condylar offset. Both examinations have unique strengths and weaknesses, but when combined as diagnostic tools, they achieve far more collectively than what each can achieve alone.

Pre-operative Static Anterior Tibial Translation Assessed on MRI Does Not Influence Return to Sport or Satisfaction After Anterior Cruciate Ligament Reconstruction

BACKGROUND

It has been suggested that the degree of anterior tibial translation (ATT) as measured passively on imaging studies (static ATT) after an anterior cruciate ligament (ACL) injury may influence outcomes after ACL reconstruction. However, there is a lack of evidence supporting these suggestions.

QUESTIONS/PURPOSES

The purpose of this retrospective prognostic study was to assess the predictive value of pre-operative static ATT in knees with ACL injury on return to sport and in satisfaction after ACL reconstruction. Our hypothesis was that greater static ATT would be associated with lower rates of return to sport and lower levels of satisfaction.

METHODS

Patients treated with ACL reconstruction were identified from an institutional registry and assigned to one of three groups according to their ACL injury type: acute ACL injury, chronic ACL injury, and failed ACL reconstruction. ATT in each knee compartment was measured using magnetic resonance imaging, and a retrospective telephone questionnaire was used to investigate post-ACL reconstruction return to sport and subjects' satisfaction.

RESULTS

One hundred thirty patients (52 acute with ACL injury, 29 with chronic ACL injury, and 49 with failed ACL reconstruction) completed the questionnaire, with a mean follow-up of 5.67 years. Ninety-seven patients (74.6%) returned to their primary sport, of whom 63 (65%) returned to the same level of sport. The mean time to return to sport was 10.1 months (range, 2 to 24 months). Overall, 113 patients (87%) were either very satisfied or satisfied with their outcomes. No difference in medial or lateral ATT was found between patients who returned to sport and those who did not. The failed-ACL reconstruction group had significantly lower rates of return to sport than did acutely and chronically injured patients (60.4% versus 88.5% and 75.9%, respectively).

CONCLUSION

The degree of pre-operative ATT in an ACL-deficient knee was not correlated with return to sport or satisfaction after ACL reconstruction. In this study cohort, only failed-ACL reconstruction patients undergoing revision ACL reconstruction were significantly less likely to return to their main sport. They were also less likely to return to sport at their pre-operative level, if they did return to sport.

Lateral Extra-articular Tenodesis Reduces Anterior Cruciate Ligament Graft Force and Anterior Tibial Translation in Response to Applied Pivoting and Anterior Drawer Loads

BACKGROUND

The biomechanical effect of lateral extra-articular tenodesis (LET) performed in conjunction with anterior cruciate ligament (ACL) reconstruction (ACLR) on load sharing between the ACL graft and the LET and on knee kinematics is not clear.

PURPOSE/HYPOTHESIS

The purpose was to quantify the effect of LET on (1) forces carried by both the ACL graft and the LET and (2) tibiofemoral kinematics in response to simulated pivot shift and anterior laxity tests. We hypothesized that LET would decrease forces carried by the ACL graft and anterior tibial translation (ATT) in response to simulated pivoting maneuvers and during simulated tests of anterior laxity.

STUDY DESIGN

Controlled laboratory study.

METHODS

Seven cadaveric knees (mean age, 39 ± 12 years [range, 28-54 years]; 4 male) were mounted to a robotic manipulator. The robot simulated clinical pivoting maneuvers and tests of anterior laxity: namely, the Lachman and anterior drawer tests. Each knee was assessed in the following states: ACL intact, ACL sectioned, ACL reconstructed (using a bone-patellar tendon-bone autograft), and after performing LET (the modified Lemaire technique after sectioning of the anterolateral ligament and Kaplan fibers). Resultant forces carried by the ACL graft and LET at the peak applied loads were determined via superposition. ATT was determined in response to the applied loads.

RESULTS

With the applied pivoting loads, performing LET decreased ACL graft force up to 80% (44 ± 12 N; P < .001) and decreased ATT of the lateral compartment compared with that of the intact knee up to 7.6 ± 2.9 mm (P < .001). The LET carried up to 91% of the force generated in the ACL graft during isolated ACLR (without LET). For simulated tests of anterior laxity, performing LET decreased ACL graft force by 70% (40 ± 20 N; P = .001) for the anterior drawer test with no significant difference detected for the Lachman test. No differences in ATT were deteced between ACLR with LET and the intact knee on both the Lachman and the anterior drawer tests (P = .409). LET reduced ATT compared with isolated ACLR on the simulated anterior drawer test by 2.4 ± 1.8 mm (P = .032) but not on the simulated Lachman test.

CONCLUSION

In a cadaveric model, LET in combination with ACLR transferred loads from the ACL graft to the LET and reduced ATT with applied pivoting loads and during the simulated anterior drawer test. The effect of LET on ACL graft force and ATT was less pronounced on the simulated Lachman test.

CLINICAL RELEVANCE

LET in addition to ACLR may be a suitable option to offload the ACL graft and to reduce ATT in the lateral compartment to magnitudes less than that of the intact knee with clinical pivoting maneuvers. In contrast, LET did not offload the ACL graft or add to the anterior restraint provided by the ACL graft during the Lachman test.

The Incidence of Kaplan Fiber Injury Associated With Acute Anterior Cruciate Ligament Tear Based on Magnetic Resonance Imaging

BACKGROUND

Kaplan fibers are distinct deep layers of the distal iliotibial band (ITB) that anchor the ITB to the distal femur and have a role in rotational stability of the knee. However, the incidence of Kaplan fiber injury in the setting of acute anterior cruciate ligament (ACL) tear is unknown.

PURPOSE

To determine the reliability of identifying and evaluating Kaplan fibers on magnetic resonance imaging (MRI) examinations based on previously reported characteristics and to report on the incidence of combined ACL and Kaplan fiber injuries based on MRI examinations.

STUDY DESIGN

Cohort study (diagnosis); Level of evidence, 3.

METHODS

Patients with an acute primary ACL tear who obtained a postinjury MRI scan at our institution and were treated with ACL reconstruction between January 1, 2007, and May 31, 2012, were identified from an institutional registry. Each patient's postinjury MRI scan was reviewed by 2 musculoskeletal radiologists, who identified Kaplan fibers and graded them as intact, injured, or not visualized. Intrarater reliability was measured using the intraclass correlation coefficient (ICC), and interrater reliability was measured using the kappa statistic.

RESULTS

A total of 72 patients were identified. For the proximal Kaplan fibers, 50% versus 58% were identified as injured, 32% versus 29% were identified as intact, and 18% versus 13% were not visualized by radiologist 1 and 2, respectively. For the distal Kaplan fibers, 46% versus 60% were identified as injured, 43% versus 28% were identified as intact, and 11% versus 12% were not visualized by radiologist 1 and 2, respectively. The ICC intrarater reliability measurements were 0.89 (95% CI, 0.83-0.93) for proximal Kaplan fibers and 0.66 (95% CI, 0.51-0.78) for distal Kaplan fibers. The interrater reliability measurements for both radiologists showed substantial agreement (kappa = 0.7) for proximal Kaplan fibers and moderate agreement (kappa = 0.51) for distal Kaplan fibers.

CONCLUSION

Kaplan fibers were visualized on MRI studies in the majority of cases, with substantial reliability for the proximal fibers and moderate reliability for the distal fibers. There was an associated injury to either the proximal or distal or both Kaplan fibers in the majority of acute primary ACL tears.

A geometric ratio to predict the flexion gap in total knee arthroplasty

Measured resection is a common technique for obtaining symmetric flexion and extension gaps in posterior-stabilized (PS) total knee arthroplasty (TKA). A known limitation of measured resection, however, is its reliance on osseous landmarks to guide bone resection and component alignment while ignoring the geometry of the surrounding soft tissues such as the medial collateral ligament (MCL), a possible reason for knee instability. To address this clinical concern, we introduce a new geometric proportion, the MCL ratio, which incorporates features of condylar geometry and MCL anterior fibers. The goal of this study was to determine whether the MCL ratio can predict the flexion gaps and to determine whether a range of MCL ratio corresponds to balanced gaps. Six computational knee models each implanted with PS TKA were utilized. Medial and lateral gaps were measured in response to varus and valgus loads at extension and flexion. The MCL ratio was related to the measured gaps for each knee. We found that the MCL ratio was associated with the flexion gaps and had a stronger association with the medial gap (β = -7.2 ± 3.05, P < .001) than with the lateral gap (β = 3.9 ± 7.26, P = .04). In addition, an MCL ratio ranging between 1.1 and 1.25 corresponded to balanced flexion gaps in the six knee models. Future studies will focus on defining MCL ratio targets after accounting for variations in ligament properties in TKA patients. Our results suggest that the MCL ratio could help guide femoral bone resections in measured resection TKA, but further clinical validation is required.

What is the impact of patellofemoral joint degeneration and malalignment on patient-reported outcomes after lateral unicompartmental knee arthroplasty?

Aims

It remains controversial whether patellofemoral joint pathology is a contraindication to lateral unicompartmental knee arthroplasty (UKA). This study aimed to evaluate the effect of preoperative radiological degenerative changes and alignment on patient-reported outcome scores (PROMs) after lateral UKA. Secondarily, the influence of lateral UKA on the alignment of the patellofemoral joint was studied.

Methods

A consecutive series of patients who underwent robotic arm-assisted fixed-bearing lateral UKA with at least two-year follow-up were retrospectively reviewed. Radiological evaluation was conducted to obtain a Kellgren Lawrence (KL) grade, an Altman score, and alignment measurements for each knee. Postoperative PROMs were assessed using the Kujala (Anterior Knee Pain Scale) score, Knee Injury and Osteoarthritis Outcome Score Joint Replacement (KOOS JR), and satisfaction levels.

Results

A total of 140 knees (130 patients) were identified for analysis. At mean 4.1 years (2.0 to 8.5) follow-up, good to excellent Kujala scores were reported. The presence of mild to moderate preoperative patellofemoral joint osteoarthritis had no impact on these scores (KL grade 0 vs 1 to 3, p = 0.203; grade 0 to 1 vs 2 to 3, p = 0.674). Comparable scores were reported by patients with osteoarthritis (Altman score of ≥ 2) evident on either the medial or lateral patellofemoral joint facet (medial, p = 0.600 and lateral, p = 0.950). Patients with abnormal patellar congruence and tilt angles (≥ 17° and ≥ 14°, respectively) reported good to excellent Kujala scores. Furthermore, lateral UKA resulted in improvements to patellofemoral alignment.

Conclusion

This is the first study demonstrating that mild to moderate preoperative radiological degenerative changes and malalignment of the patellofemoral joint are not associated with poor patient-reported outcomes at mid-term follow-up after lateral fixed-bearing UKA. Our data suggest that this may be explained by realignment of the patella and thereby redistribution of loads across the patellofemoral joint. Cite this article: Bone Joint J 2020;102-B(6):727–735.

Satisfaction with return to sports after unicompartmental knee arthroplasty and what type of sports are patients doing

PURPOSE

The present study provides insight into patient satisfaction with return to sports after unicompartmental knee arthroplasty (UKA) and to what type of activities patients return. This is important because indications for UKA have expanded and younger and more active patients undergo surgery currently.

METHODS

Patients who received a UKA were contacted between 12 and 24 months' post-surgery, receiving a questionnaire to evaluate postoperative satisfaction with return to sports, level of return, type of activities performed pre- and postoperatively, and (activity) outcome scores (NRS, UCLA, HAAS). Descriptive statistical analysis focused on the influence of patients' sex and age, and a regression model was fitted to assess the predictors for high satisfaction postoperatively.

RESULTS

One hundred and sixty-four patients (179 UKAs) with a mean age of 62.3 years responded at an average follow-up of 20.2 months. Preoperatively, 132 patients (81%) participated in sports, which increased to 147 patients (90%) after UKA. Analyzing outcomes for each knee individually, satisfaction with return to sports was recorded in 83% (149/179). Return to a higher or similar level was reported in 85.4% of the cases (117/137). Most common sports after UKA were cycling (45%), swimming (38%), and stationary cycling (27%). Overall, 93.9% of patients were able to return to low impact sports, 63.9% to intermediate and 32.7% to high impact sports. Regarding activity scores, preoperative NRS score improved from 6.40 ± 2.10 to 1.33 ± 1.73 postoperatively (p < .001). The mean preoperative UCLA score improved from 5.93 ± 2.19 to 6.78 ± 1.92 (p < .001) and HAAS score from 9.13 ± 3.55 to 11.08 ± 2.83 postoperatively (p < .001). Regression analyses showed that male sex, preoperative UCLA score and sports participation predicted high activity scores postoperatively.

CONCLUSION

The vast majority of patients undergoing medial UKA returned to sports postoperatively, of which over 80% was satisfied with their restoration of sports ability. Male patients, patients aged ≥70, and patients who participated in low-impact sports preoperatively achieved the highest satisfaction rates. Regarding type of sports, male patients and patients aged ≤55 were most likely to return to high and intermediate impact sports. This study may offer valuable information to help manage patients' expectations regarding their ability to return to sports based on demographics and type of preoperative sporting activities.

LEVEL OF EVIDENCE

Case series; Level of evidence IV.

Postoperative outcomes of total knee arthroplasty compared to unicompartmental knee arthroplasty: A matched comparison

BACKGROUND

The purpose of this study was to evaluate early postoperative outcomes in patients following UKA (unicompartmental knee arthroplasty) compared to a matched cohort of TKA (total knee arthroplasty) patients.

METHODS

Patients who met radiographic criteria for a medial UKA who underwent either a TKA or UKA at a single institution were matched based on age, gender, and BMI.

RESULTS

One hundredy and fifty UKA in 138 patients and 150 TKA in 148 patients were included in this retrospective analysis. Mean age was 62.6 ± 9 years and 65.2 ± 9 years in the UKA and TKA groups respectively (p = .01). Patients who underwent UKA had significantly less pain at two and six weeks postoperatively compared to TKA patients with mean Numeric Pain Rating Scale (NPRS) scores of 3.7 ± 1.1 vs. 7.8 ± 1.2, p < .001 and 2.6 ± 1.3 vs. 4.6 ± 1.6, p < .001 respectively. Knee Society Scores (KSS) were higher in the UKA group at six weeks and two years postoperative (86.5 ± 2.8 vs. 81.4 ± 3.6, p < .001 and 89.5 ± 2.4 vs. 84.5 ± 3.3, p < .001 respectively). Return to work was faster in the UKA group (mean 20.6 ± 7.89 vs. 38.6 ± 6.23 days, p < .001). The UKA group also had higher mean Forgotten Joint Scores of 90.5 ± 3.6 vs. 79.5 ± 9.5 (p < .001).

CONCLUSIONS

Patients with primarily medial compartment OA who underwent UKA had less postoperative pain, earlier return to work, and higher KSS compared to a matched group who underwent TKA.

Engagement of the Secondary Ligamentous and Meniscal Restraints Relative to the Anterior Cruciate Ligament Predicts Anterior Knee Laxity

BACKGROUND

Patients with high-grade preoperative side-to-side differences in anterior laxity as assessed via the Lachman test after unilateral anterior cruciate ligament (ACL) rupture are at heightened risk of early ACL graft failure. Biomechanical factors that predict preoperative side-to-side differences in anterior laxity are poorly understood.

PURPOSE

To assess, in a cadaveric model, whether the increase in anterior laxity caused by sectioning the ACL (a surrogate for preoperative side-to-side differences in anterior laxity) during a simulated Lachman test is associated with two biomechanical factors: (1) the tibial translation at which the secondary anterior stabilizers, including the remaining ligaments and the menisci, begin to carry force, or engage, relative to that of the ACL or (2) the forces carried by the ACL and secondary stabilizers at the peak applied anterior load.

STUDY DESIGN

Controlled laboratory study.

METHODS

Seventeen fresh-frozen human cadaveric knees underwent Lachman tests simulated through a robotic manipulator with the ACL intact and sectioned. The net forces carried by the ACL and secondary soft tissue stabilizers (the medial meniscus and all remaining ligaments, measured as a whole) were characterized as a function of anterior tibial translation. The engagement points of the ACL (with the ACL intact) and each secondary stabilizer (with the ACL sectioned) were defined as the anterior translation at which they began to carry force, or engaged, during a simulated Lachman test. Then, the relative engagement point of each secondary stabilizer was defined as the difference between the engagement point of each secondary stabilizer and that of the ACL. Linear regressions were performed to test each association (P < .05).

RESULTS

The increase in anterior laxity caused by ACL sectioning was associated with increased relative engagement points of both the secondary ligaments (β = 0.87; P < .001; R² = 0.75) and the medial meniscus (β = 0.66; P < .001; R² = 0.58). Smaller changes in anterior laxity were also associated with increased in situ medial meniscal force at the peak applied load when the ACL was intact (β = -0.06; P < .001; R² = 0.53).

CONCLUSION

The secondary ligaments and the medial meniscus require greater anterior tibial translation to engage (ie, begin to carry force) relative to the ACL in knees with greater changes in anterior laxity after ACL sectioning. Moreover, with the ACL intact, the medial meniscus carries more force in knees with smaller changes in anterior laxity after ACL sectioning.

CLINICAL RELEVANCE

Relative tissue engagement is a new biomechanical measure to characterize in situ function of the ligaments and menisci. This measure may aid in developing more personalized surgical approaches to reduce high rates of ACL graft revision in patients with high-grade laxity.

Mid-term survivorship and patient-reported outcomes of robotic-arm assisted partial knee arthroplasty

Aims

Limited evidence is available on mid-term outcomes of robotic-arm assisted (RA) partial knee arthroplasty (PKA). Therefore, the purpose of this study was to evaluate mid-term survivorship, modes of failure, and patient-reported outcomes of RA PKA.

Methods

A retrospective review of patients who underwent RA PKA between June 2007 and August 2016 was performed. Patients received a fixed-bearing medial or lateral unicompartmental knee arthroplasty (UKA), patellofemoral arthroplasty (PFA), or bicompartmental knee arthroplasty (BiKA; PFA plus medial UKA). All patients completed a questionnaire regarding revision surgery, reoperations, and level of satisfaction. Knee Injury and Osteoarthritis Outcome Scores (KOOS) were assessed using the KOOS for Joint Replacement Junior survey.

Results

Mean follow-up was 4.7 years (2.0 to 10.8). Five-year survivorship of medial UKA (n = 802), lateral UKA (n = 171), and PFA/BiKA (n = 35/10) was 97.8%, 97.7%, and 93.3%, respectively. Component loosening and progression of osteoarthritis (OA) were the most common reasons for revision. Mean KOOS scores after medial UKA, lateral UKA, and PFA/BiKA were 84.3 (SD 15.9), 85.6 (SD 14.3), and 78.2 (SD 14.2), respectively. The vast majority of the patients reported high satisfaction levels after RA PKA. Subgroup analyses suggested tibial component design, body mass index (BMI), and age affects RA PKA outcomes. Five-year survivorship was 98.4% (95% confidence interval (CI) 97.2 to 99.5) for onlay medial UKA (n = 742) and 99.1% (95% CI 97.9 to 100) for onlay medial UKA in patients with a BMI < 30 kg/m2 (n = 479).

Conclusion

This large single-surgeon study showed high mid-term survivorship, satisfaction levels, and functional outcomes in RA UKA using metal-backed tibial onlay components. In addition, favourable results were reported in RA PFA and BiKA. Cite this article: Bone Joint J 2020;102-B(1):108–116

The Influence of Preoperative Radiographic Patellofemoral Degenerative Changes and Malalignment on Patellofemoral-Specific Outcome Scores Following Fixed-Bearing Medial Unicompartmental Knee Arthroplasty

BACKGROUND

There is controversy as to whether the presence of degenerative changes and malalignment of the patellofemoral joint is a contraindication to medial unicompartmental knee arthroplasty. Therefore, the aim of the present study was to examine the influence of preoperative radiographic patellofemoral joint osteoarthritis and alignment on intermediate-term knee and patellofemoral joint-specific patient-reported outcomes following fixed-bearing medial unicompartmental knee arthroplasty.

METHODS

We performed a retrospective review of the records on a consecutive series of patients who had undergone robotic arm-assisted fixed-bearing onlay medial unicompartmental knee arthroplasty and had a minimum duration of follow-up of 2 years. All records were collected from a single surgeon's arthroplasty registry. Patients with severe bone loss or grooving of the lateral patellar facet were excluded. Radiographic assessment was performed with use of the Kellgren-Lawrence and Altman classification systems as well as with patellofemoral joint alignment measurements. The latest follow-up consisted of a patient-reported questionnaire, including the Kujala (Anterior Knee Pain Scale) score, the Knee Injury and Osteoarthritis Outcome Score (KOOS), Junior (JR), and satisfaction levels.

RESULTS

A total of 536 patients (639 knees) were included. After a mean duration of follow-up (and standard deviation) of 4.3 ± 1.6 years (range, 2.0 to 9.2 years), good-to-excellent Kujala scores were reported independent of the presence of patellofemoral joint osteoarthritis preoperatively (Kellgren-Lawrence grade 0 compared with ≥1, p = 0.82; grade ≤1 compared with ≥2, p = 0.84). Similar findings were found when osteoarthritis was present in either the medial or lateral side of the patellofemoral joint as defined by an Altman score of ≥2 (medial, p = 0.81; lateral, p = 0.90). KOOS scores and satisfaction also were not affected by degenerative patellofemoral joint changes. Furthermore, neither the patellar tilt angle nor the congruence angle influenced patient-reported outcomes.

CONCLUSIONS

Preoperative radiographic mild to moderate patellofemoral joint degeneration (Kellgren-Lawrence grades 1 through 3) and/or malalignment did not compromise intermediate-term knee and patellofemoral joint-specific patient-reported outcomes in patients managed with fixed-bearing medial unicompartmental knee arthroplasty. On the basis of the results of the present study, we believe that neither mild to moderate patellofemoral degeneration nor abnormal patellar tilt or congruence should be considered a contraindication to fixed-bearing medial unicompartmental knee arthroplasty.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Tibiofemoral Kinematics During Compressive Loading of the ACL-Intact and ACL-Sectioned Knee: Roles of Tibial Slope, Medial Eminence Volume, and Anterior Laxity

BACKGROUND

Tibial geometry and knee laxity have been identified as risk factors for both noncontact anterior cruciate ligament (ACL) rupture and instability in the setting of ACL insufficiency via clinical studies; yet, their biomechanical relationships with tibiofemoral kinematics during compressive loading are less well understood. The purpose of this study was to identify the relative contributions of sagittal tibial slope, medial tibial eminence volume, and anterior knee laxity to tibiofemoral kinematics with axial compression in both ACL-intact and ACL-sectioned cadaveric knees.

METHODS

Computed tomography (CT) data were collected from 13 human cadaveric knees (mean donor age, 45 ± 11 years; 8 male). Validated algorithms were used to calculate the sagittal slope of the medial and of the lateral tibial plateau as well as volume of the medial tibial eminence. Specimens were then mounted to a robotic manipulator. For both intact and ACL-sectioned conditions, the robot compressed the knee from 10 to 300 N at 15° of flexion; the net anterior tibial translation of the medial and lateral compartments and internal tibial rotation were recorded. Simple and multiple linear regressions were performed to identify correlations between kinematic outcomes and (1) osseous geometric parameters and (2) anterior laxity during a simulated Lachman test.

RESULTS

In ACL-intact knees, anterior tibial translation of each compartment was positively correlated with the corresponding sagittal slope, and internal tibial rotation was positively correlated with the lateral sagittal slope and the sagittal slope differential (p ≤ 0.044). In ACL-sectioned knees, anterior tibial translation of the medial compartment was positively associated with medial sagittal slope as well as a combination of medial tibial eminence volume and anterior laxity; internal tibial rotation was inversely correlated with anterior knee laxity (p < 0.05).

CONCLUSIONS

Under compressive loading, sagittal slope of the medial and of the lateral tibial plateau was predictive of kinematics with the ACL intact, while medial tibial eminence volume and anterior laxity were predictive of kinematics with the ACL sectioned.

CLINICAL RELEVANCE

The relationships between tibial osseous morphology, anterior laxity, and knee kinematics under compression may help explain heightened risk of ACL injury and might predict knee instability after ACL rupture.

Neither Anterior nor Posterior Referencing Consistently Balances the Flexion Gap in Measured Resection Total Knee Arthroplasty: A Computational Analysis

BACKGROUND

Whether anterior referencing (AR) or posterior referencing (PR) produces a more balanced flexion gap in total knee arthroplasty (TKA) using measured resection remains controversial. Our goal was to compare AR and PR in terms of (1) medial and lateral gaps at full extension and 90° of flexion, and (2) maximum medial and lateral collateral ligament (MCL and LCL) forces in flexion.

METHODS

Computational models of 6 knees implanted with posterior-stabilized TKA were virtually positioned with both AR and PR techniques. The ligament properties were standardized to achieve a balanced knee at full extension. Medial-lateral gaps were measured in response to varus and valgus loading at full extension and 90° of flexion; MCL and LCL forces were estimated during passive flexion.

RESULTS

At full extension, the maximum difference in the medial-lateral gap for both AR and PR was <1 mm in all 6 knee models. However, in flexion, only 3 AR and 3 PR models produced a difference in medial-lateral gap <2 mm. During passive flexion, the maximum MCL force ranged from 2 N to 87 N in AR and from 17 N to 127 N in PR models. The LCL was unloaded at >25° of flexion in all models.

CONCLUSION

In measured resection TKA, neither AR nor PR better balance the ligaments and produce symmetrical gaps in flexion. Alternative bone resection techniques and rotation alignment targets are needed to achieve more predictable knee balance.

Distal Femoral Rotation is not Associated With Preoperative Proximal Tibial Varus Angle in Patients With Isolated Medial Compartment Osteoarthritis

BACKGROUND

Prior studies have found that greater proximal tibial varus was associated with increased external femoral rotation at time of total knee arthroplasty. These works suggest that measuring the tibial plateau-tibial shaft (TPTS) angle on preoperative weight-bearing long leg radiographs could predict significant variations in the posterior condylar angle.

METHODS

A minimum of 68 patients were needed to reach 80% power. Patients were included if they had primary medial compartment osteoarthritis and excluded if they had a valgus mechanical axis. The clinical posterior condylar angle (cPCA) was defined as the angle between the anatomic transepicondylar axis and posterior condylar line. Correlation analyses were performed to test for any relationship between the TPTS and cPCA. Two patient groups were created based on TPTS angle: TPTS ≤4° (mild varus) and TPTS >4° (moderate varus). Mechanical axis and rotational measurements were compared between the groups using independent t-tests.

RESULTS

The mean mechanical axis and TPTS angle were 6.9° and 4.8° of varus, respectively. The mean cPCA was 5.0° (standard deviation [SD], 1.4°; range, 2.4°-7.9°). No correlation was found between the TPTS angle and cPCA (P = .15). The mean cPCA in the mild varus group (n = 28 patients) was 5.2° (SD, 1.5°; range, 2.7°-7.9°), and the mean cPCA in the moderate varus group (n = 45 patients) was 4.4° (SD, 1.7°; range, 0.6°-7.5°). These groups were not statistically significantly different from each other (P = .62).

CONCLUSION

The present study does not support the conclusions of previous works and suggests that the amount of distal femoral rotation cannot be predicted by tibial varus alignment measured on preoperative long leg radiographs. Consequently, we believe that proximal tibial varus should not be used to preoperatively predict external rotation of the femoral component in patients with isolated medial compartment osteoarthritis.