What is the optimal alignment of the tibial and femoral components in knee arthroplasty?

Oxidation and Damage Mechanisms of Second-Generation Highly Cross-Linked Polyethylene Tibial Inserts

BACKGROUND

After clinical introduction in 2005, sequentially annealed, highly cross-linked polyethylene (SA HXLPE) was studied for retrievals with short implantation times; however, long-term follow-ups are lacking. The objective of this study was to examine and compare the revision reasons, damage mechanisms, and oxidation indices of SA HXLPE and conventional gamma inert-sterilized (Gamma Inert) ultra-high-molecular-weight polyethylene tibial inserts implanted for >5 years.

METHODS

There were 74 total knee arthroplasty tibial inserts (46 SA HXLPEs, 28 Gamma Inerts) implanted for >5 years (mean 7 ± 2 years) retrieved as part of a multicenter retrieval program. Cruciate-retaining implants comprised 44% of the SA HXLPEs and 14% of the Gamma Inerts. Patient factors and revision reasons were collected from revision operating notes. A semiquantitative scoring method was used to assess surface damage mechanisms. Oxidation was measured using Fourier transform infrared microscopy according to American Society for Testing and Materials 2102. Differences between cohorts were assessed with Mann-Whitney U-tests.

RESULTS

Loosening (Gamma Inert: 17 of 28, SA HXLPE: 15 of 46) and instability (Gamma Inert: 6 of 28, SA HXLPE: 15 of 46) were the most common revision reasons for both cohorts. The most prevalent surface damage mechanisms were burnishing, pitting, and scratching, with burnishing of the condyles being higher in Gamma Inert components (P = .022). Mean oxidation was higher in the SA HXLPE inserts at the articulating surface (P = .002) and anterior-posterior faces (P = .023). No difference was observed at the backside surface (P = .060).

CONCLUSIONS

Revision reasons and surface damage mechanisms were comparable in the Gamma Inert and SA cohorts. Further studies are needed to continue to assess the in vivo damage and clinical relevance, if any, of oxidation in SA HXLPE over longer implantation times, particularly for implants implanted for more than 10 years.

Does inverse kinematic alignment coupled with robot-assisted TKA optimize patellofemoral clinical and radiological results?

INTRODUCTION

With a satisfaction rate of 80%, total knee arthroplasty (TKA) surgery has seen significant improvements in recent decades. The 20% of poor results may be explained by the alignment technique used for implant placement, which can influence patellofemoral kinematics. The objective of this study was to demonstrate that the use of inverse kinematic alignment makes it possible to obtain satisfactory clinical and radiological patellar scores in robotic TKA.

HYPOTHESIS

The inverse kinematic alignment technique coupled with robotic surgery makes it possible to restore the native kinematics of the patella.

MATERIALS AND METHODS

This prospective study including 100 TKAs with a primary TKA performed using the Stryker Mako™ robotic surgery system, and the inverse kinematic alignment technique. Patients who underwent patella resurfacing were excluded. Clinical and radiological scores were recorded preoperatively and 1 year postoperatively.

RESULTS

At one year, the specific patellar clinical scores were excellent with an average Kujala score of 85.69 and an average HSS Patellar score 88.15. The average patellar lateralization index was 0.15 and the average patellar tilt was 5.1°, showing no significant difference compared to preoperation (p=0.45 and p=0.18). The average external rotation of the femoral implant was 0.47±0.6° [-1.9; 2.1].

DISCUSSION

The patellofemoral clinical results were excellent. The use of the robotic arm coupled with this alignment technique makes it possible to obtain a controlled external rotation of the femoral implant as well as an optimized orientation of the tibial component, favoring good restitution of the alignment of the extensor apparatus. This study did not demonstrate any radiological correction of patellar tilt and lateralization.

CONCLUSION

The combined use of robotic surgery with the inverse kinematic alignment technique seems effective on specific clinical results of the patellofemoral joint.

LEVEL OF EVIDENCE

II; prospective cohort.

Efficiency assessment of intelligent patient-specific instrumentation in total knee arthroplasty: a prospective randomized controlled trial

BACKGROUND

In total knee arthroplasty (TKA), the practical use of patient-specific instrumentation (PSI) has been reported previously with both advantage and disadvantage. The application of artificial intelligent (AI) forces overwhelmingly development of medical industries, while the impact of AI on PSI efficiency remains unknown. Thus, this study aimed to assess the efficiency of Intelligent-PSI (i-PSI) in TKA, compared with the conventional instrumentation-TKA (CI).

METHODS

102 late-stage OA patients who met inclusive criteria were recruited in this prospective randomized controlled trial and separated into two groups (i-PSI vs. CI). In both groups, an AI preoperative planning engine was applied for surgery decision making. In CI group, conventional instrumentation was applied for bony resection, while resection of i-PSI group was completed with i-PSI. A convolutional neural network was applied to automatically process computer tomography images and thus produced i-PSI. With the help of three-dimension printing, the workflow of production was largely simplified. AI-driven preoperative planning guided resection and alignment decisions. Resection measurement, perioperative radiography and perioperative clinical outcomes were analyzed to verify efficiency of i-PSI.

RESULTS

In resection outcomes, smaller deviation of lateral and medial distal femoral resection were found in i-PSI group than CI group (P = 0.032 and 0.035), while no difference was found in other resection planes. In radiography outcomes, postoperative coronal alignments of i-PSI group, including postoperative Hip-knee-ankle axis (HKA) (P = 0.025), postoperative HKA outliners (P = 0.042), Femoral coronal alignment (FCA) (P = 0.019) and Joint line convergence angle (JLCA) (P = 0.043) showed closer to neutral position than CI group. Moreover, Femoral sagittal alignment (FSA) of i-PSI group showed closer to neutral position than CI group(P = 0.005). No difference was found in other alignments. In clinical outcomes, i-PSI group seemed to cost more surgical time than CI group (P = 0.027), while others showed no differences between the two groups.

CONCLUSION

Intelligent Patient-specific Instrumentation in TKA achieved simplified production flow than conventional PSI, while also showed more accurate resection, improved synthesis position and limb alignment than conventional instrumentation. Above all, this study proved that i-PSI being an applicable and promising tool in TKA.

Midterm results for revision total knee arthroplasty for component malrotation

INTRODUCTION

Accurate positioning of components in total knee arthroplasty (TKA) is essential to a satisfactory outcome. Significant malrotation may lead to chronic pain, stiffness, and dysfunction. This study aims to quantify improvements in functional outcomes following revision surgery for malrotation of either one or both components in TKA versus revision for aseptic loosening.

METHODS

This was a retrospective review of TKAs that matched and compared the two-year functional outcomes of the malrotation group to a functionally similar aseptic loosening group. Functional outcomes were compared between groups using Short Form (SF-12), Western Ontario and McMaster University Osteoarthritis Index (WOMAC), and Knee Society Functional Score (KSFS). Student t-tests and chi-squared or Fisher's tests were used for statistical analysis.

RESULTS

Of the patients revised, 24 had malrotation and 57 had aseptic loosening. A total of 16 femoral and 17 tibial components were revised for malrotation. All 16 femoral components were internally malrotated (mean -4.8 ± 4.1 degrees; range, -0.5 to -16.6). Of the tibial components, 15 were internally malrotated, (mean -9.5 ± 6.6 degrees; range, -2.2 to -23.5) and 2 were externally malrotated (mean 4.6 ± 2.1 degrees; range, 3.1 to 6.0). All functional outcome measures significantly improved comparably within both groups preoperatively to 24 months postoperatively. At 24 months, functional outcome measures were comparable between the groups and WOMAC function scores were significantly higher in the malrotation group.

CONCLUSION

Revision TKA for malrotation can yield clinically and statistically significant functional improvements, similar in magnitude to those seen following revision TKA for aseptic loosening.

LEVEL OF EVIDENCE

Level III.

Comparison of short-term clinical results between modified kinematically-aligned and guided motion bicruciate stabilized total knee arthroplasty

BACKGROUND

Both kinematically-aligned (KA) total knee arthroplasty (TKA) and bicruciate stabilized (BCS) TKA aim to reproduce the physiological knee kinematics. In this study, we compared the femoro-tibial component rotational mismatch between patients who underwent modified KA-TKA and those who received guided-motion BCS-TKA, and its influence on the clinical outcomes.

METHODS

In this retrospective study, 77 consecutive patients were included and divided into two groups: subjects who underwent modified KA-TKA with Persona (KA Group; n = 42) and those who received BCS-TKA with JOURNEY II (BCS group; n = 35). Range of motion, the 2011 Knee Society Score (KSS), the rotational alignment of the femoral and tibial components, and the correlations between the rotational mismatch and the 2011 KSS subscales were examined.

RESULTS

The postoperative objective knee indicators (P = 0.0157), patient satisfaction (P = 0.0039) and functional activity scores (P = 0.0013) in the KA group were significantly superior to those in the BCS group 1 year postoperatively. There was no significant difference between the two groups observed in the rotational mismatch. In the BCS group, significant negative correlations were identified between the rotational mismatch and objective indicators, patient satisfaction, and functional activity scores but not in the KA group.

CONCLUSIONS

The short-term clinical results following KA-TKA showed superior objective knee indicators, patient satisfaction and functional activity scores. A negative correlation was observed between component rotational mismatch and the 2011 KSS subscales in the BCS group, compared to no relationship found between the two in the KA group. These findings suggested that KA-TKA has a relatively higher tolerance for rotational mismatch than BCS-TKA.

Risk Factors Associated With Quadriceps Tendon Extensor Mechanism Disruption Following Total Knee Arthroplasty

BACKGROUND

Quadriceps tendon extensor mechanism disruption is an infrequent but devastating complication after total knee arthroplasty (TKA). Our knowledge of specific risk factors for this complication is limited by the current literature. Thus, this study aimed to identify potential risk factors for quadriceps tendon extensor mechanism disruption following TKA.

METHODS

A retrospective cohort analysis was performed using the PearlDiver Administrative Claims Database. Patients undergoing TKA without a prior history of quadriceps tendon extensor mechanism disruption were identified. Quadriceps tendon extensor mechanism disruption included rupture of the quadriceps tendon, patellar tendon, or fracture of the patella. Patients who had a minimum of 5 years of follow-up after TKA were included. A total of 126,819 patients were included. Among them, 517 cases of quadriceps tendon extensor mechanism disruption occurred (incidence 0.41%). Hypothesized risk factors were compared between those who had postoperative quadriceps tendon extensor mechanism disruption and those who did not.

RESULTS

On multivariate analysis, increased Charlson Comorbidity Index (odds ratio (OR): 1.10, 95% confidence interval (CI) [1.07 to 1.13]; P < .001), obesity (OR: 1.49, 95% CI [1.24 to 1.79]; P < .001), and fluoroquinolone use any time after TKA (OR: 1.24, 95% CI [1.01 to 1.52]; P = .036) were significantly associated with quadriceps tendon extensor mechanism disruption.

CONCLUSIONS

Our study identified the incidence of quadriceps tendon extensor mechanism disruption following TKA as 0.41%. Identified risk factors for quadriceps tendon extensor mechanism disruption after TKA include an increased Charlson Comorbidity Index, obesity, and use of fluoroquinolones postoperatively.

Comparison of Clinical and Radiological Outcomes of Total Knee Arthroplasty in Osteoarthritic Patients

Background The knee is the joint most commonly affected by osteoarthritis, more than any other. Osteoarthritis is a progressive, long-term condition that leads to the deterioration of joint tissue and cartilage, resulting in pain and impairment. Total knee arthroplasty (TKA) is a successful intervention that improves functional capability, decreases pain, and enhances quality of life. We conducted this study to evaluate whether radiological parameters following TKA influence the clinical outcomes of patients with knee osteoarthritis. Methods The study was conducted on patients treated for knee osteoarthritis at the Department of Orthopedics, Rajindra Hospital and Government Medical College, Patiala, Punjab, in collaboration with the Department of Radiology over a period of 1.5 years. A total of 152 patients diagnosed with knee osteoarthritis were included in the study; all underwent TKA. Patients underwent clinical evaluation and were graded using the Knee Society Score (KSS) during follow-up examinations. Pain was evaluated using the Visual Analog Scale (VAS). Postoperative X-rays were obtained, and various angles, including the distal femoral angle (DFA), the proximal tibial angle (PTA), and the posterior slope angle (PSA), were measured. Patient follow-up was conducted at three days, three months, and six months. Subsequently, a comparison of the clinical and radiological outcomes of TKA was performed. Results In this study, a total of 152 patients participated, with the majority falling into the 61-70 age group. Of these patients, 40.13% were female and 59.87% were male. The average medial DFA was 94.05°, the average medial PTA was 89.31°, and the PSA was 6.6°. Patients with a medial DFA of 94.05° (±3), a medial PTA of 89.31° (±3), and a PSA of 6.6° (±3) were categorized into the normal group. Conclusion Patients with DFA, PTA, and PSA in the normal range demonstrate improved KSS and clinical outcomes.

Functional knee phenotypes appear to be more suitable for the Chinese OA population compared with CPAK classification: A study based on 3D CT reconstruction models

PURPOSE

The aim of this study was to investigate the distribution of coronal plane alignment of the knee (CPAK) classification and functional knee phenotypes in a Chinese osteoarthritis (OA) population and to compare different lower limb alignment targets according to the distribution characteristics to find suitable total knee arthroplasty (TKA) bone cut strategies for the Chinese OA patients.

METHODS

The computed tomography (CT) images were retrospectively collected and the three-dimensional (3D) models were reconstructed from 434 Chinese OA patients, including 93 males and 341 females, with a mean age of 66.4 ± 9.3 years. Femoral mechanical angle (FMA), tibial mechanical angle (TMA) and mechanical hip-knee-ankle angle (mHKA) were measured on the 3D models. Arithmetic hip-knee-ankle angle (aHKA) was calculated using FMA plus TMA, and joint line obliquity was calculated as 180 + TMA-FMA. The CPAK according to MacDessi and the functional knee phenotypes according to Hirschmann were performed. In addition, the suitable TKA bone cut strategies were explored according to the phenotypes and based on the characteristics of different alignment targets, such as mechanical alignment, anatomic alignment (AA), kinematic alignment, restricted KA (rKA) and adjusted MA (aMA). Statistical differences were determined using the independent-samples t-test or the two independent-samples Wilcoxon test, with p < 0.05 considered statistically significant.

RESULTS

The Chinese OA population showed a varus alignment tendency (mHKA = 172.1° ± 7.2°), to which the TMA was a major contributor (TMA = 84.7° ± 4.4° vs. FMA = 91.3° ± 3.2°). The mHKA was on average 3.9° more varus than the aHKA. A total of 140 functional knee phenotypes were found and 45.6% were concentrated in VARFMA3°-NEUFMA0° to VARTMA3°-NEUTMA0°. More than 70% of patients had different FMA and TMA phenotypes. There were 92.9% of CPAK distributed in types I to IV, with type I accounting for 53.9%. The FMA phenotypes were less changed if the aMA and rKA were chosen, and the TMA phenotypes were less changed if the AA and rKA were chosen.

CONCLUSION

Compared with the CPAK, the functional knee phenotypes were more suitable for the Chinese OA population with a wide distribution and a varus tendency, and it seemed more appropriate to choose aMA and rKA as TKA alignment targets for resection.

LEVEL OF EVIDENCE

Level Ⅲ.

Off-the-Shelf Tibial Cone Sizes May Not Accommodate All Patients' Bone Morphology and May Lead to Cortical Breaches in Revision Total Knee Arthroplasty: A 3D Modeling Study

Background

In revision total knee arthroplasty, tibial cones have demonstrated improved longevity and reduced incidence of aseptic loosening. Several currently available "off-the-shelf" (OTS) cone systems may not have sizes to accommodate all patient bone morphologies.

Methods

Computed tomographies from one hundred primary total knee arthroplasty patients and dimensions of 4 OTS cones were obtained. Press-fit stems were positioned in 3D tibia models to fit the diaphyseal trajectory. Cones were positioned around the stem at 1, 6, and 13 mm resections measured from the trough of the medial tibial plateau, simulating proximal tibial cuts and bone loss. Tibias were examined for cortical breaching following modeled cone preparation.

Results

Increased rate of breaching was observed as size and depth of the cone increased. In 2/49 (4.1%) male and 19/46 (41.3%) female tibias, cones could not be positioned without breaching. No breaches were found in 22/49 (45.0%) male and 5/46 (10.9%) female tibias. For every 1 centimeter increase in patient height, odds of breaching decreased by 12% (odds ratio: 0.88, confidence interval: 0.84, 0.92). For every size increase in cone width, odds of breaching increased by 34% (odds ratio: 1.34, confidence interval: 1.28, 1.47). Placing cones deeper also increased breaching compared to the 1 mm cut.

Conclusions

In revision total knee arthroplasty, smaller OTS or custom tibial cones may be needed to fit a patient's proximal tibial geometry. This is especially true in patients not accommodated by the OTS cone sizes we tested, which impacted shorter patients and/or those with substantial bone loss requiring more tibial resection and deeper cone placement. Use of smaller or custom tibial cones should be considered where indicated.

Towards a better understanding of knee angular deformities: discrepancies between clinical examination and 2D/3D assessments

INTRODUCTION

Discrepancy between the clinical examination and the 2D/3D radiographs is a common concern in patients with angular or rotational deformities of the lower limbs, as it may alter clinical judgment and subsequent treatment. The aim was to identify such discrepancies and assess determinants that may contribute to their existence.

MATERIALS AND METHODS

A retrospective chart review was conducted on 329 consecutive patients (658 lower limbs) who underwent physical examination and long-leg biplanar radiographs in our institution between 2013 and 2018 for limb length discrepancy or angular deformity of the knees (varus/valgus). Eleven parameters were measured on 2D and 3D images. 3D measurements were based on standing biplanar X-rays and their 3D reconstructions and were considered the gold standard. Contingency tables and multiple linear regression were used to assess discrepancies between the three modalities and their determinants respectively.

RESULTS

Significant mismatches were found between physical examination and 2D images (1% in varus and 1% in valgus), between physical examination and 3D assessment (1% in varus and 4.6% in valgus) as well as between 2 and 3D assessments (1.9% in varus and 7.6% in valgus). The significant determinants of the mismatch between 2 and 3D modalities were frontal pelvic obliquity, neck shaft angle, knee flexion, femoral torsion, and tibial mechanical angle.

CONCLUSION

In the presence of positional and/or morphological deformities, physical examination and 2D assessment of knee alignment could be biased due to axes projection errors. A better understanding of 3D alignment of the knee as part of the entire lower limb from pelvis to toes, may lead to a better diagnosis and subsequently a better treatment of knee angular deformities.

The main cause of tibial prosthesis malalignment after total knee arthroplasty in Southern Chinese population

Objectives

This study aimed to determine the occurrence rate of malalignment of tibial prosthesis and explore the influencing factors.

Methods

296 patients from Southern China who underwent total knee arthroplasty (TKA) were selected as the research objects. Their general demographic data were recorded. The tibial bowing angle (TBA), tibial length, medial proximal tibial angle (MPTA), tibial plateau shift angle (TPSA), tibial bone loss, lateral distal tibial angle, and overall width of tibial plateau and widths of medial and lateral tibial plateau were measured before TKA. The tibial component coronal alignment angle (TCCA) was measured after the operation. Malalignment of the tibial prosthesis was defined as TCCA <87° or TCCA >93°. Tibial bowing was indicated by TBA >2°, and lateral bowing was recorded as +. The correlations of TCCA with demographic data and pre-operation imaging measurement parameters were statistically analyzed.

Results

Bivariate correlation analysis revealed negative correlations between TCCA and TBA (r = -0.602, P < 0.001) and TPSA (r = -0.304, P < 0.001), and a positive correlation with MPTA (r = -0.318, P < 0.001). Multivariate linear regression analysis demonstrated a significant negative correlation between TCCA and TBA (P < 0.001). The occurrence rate of malalignment of tibial prosthesis was 12.37 %. The occurrence rates of malalignment were 22.54 % in the tibial bowing group and 6.87 % in the non-tibial bowing group, showing statistical differences (P < 0.001).

Conclusion

The malalignment rate of tibial prosthesis among Southern Chinese patients is relatively high, possibly attributed to the tibial anatomy anomalies, particularly the tibial bowing. The entry point should be determined based on tibial morphology.

[Patellar tracking in knee arthroplasty]

Knee arthroplasty is a demanding procedure that, when carried out appropriately, results in significant pain relief and patient satisfaction. The success of the operation is influenced by many factors. The most important ones describe the implant design, the orientation of the components and the ligament tension. The patellofemoral joint is often neglected as an important part of the operation. Initially, complications in the area of the patellofemoral joint do not appear to be devastating, but in many cases, they lead to significant consequences for the patient, along with severe pain and limited mobility. The most common complications arise from patellar maltracking. This often occurs due to misplacement of the tibial and femoral components and the altered shape of the patella. If the placement of the components with regard to patellar tracking is considered, bony and/or soft tissue addressing measures remain to further optimize the movement of the patella. The following manuscript is dedicated to discussing causes to avoid patellar maltracking and improve clinical outcomes.

Restoring Tibial Slope and Sagittal Alignment of the Femoral Component in Unrestricted Kinematically Aligned Total Knee Arthroplasty Using Conventional versus Patient-Specific Instrumentation

Restoring sagittal alignment in kinematically aligned (KA) total knee arthroplasty (TKA) is crucial to avoid patellofemoral joint instability or overstuffing and to restore an adequate range of motion. This prospective study compared the accuracy of conventional instrumentation (CI) versus patient-specific instrumentation (PSI) in restoring sagittal alignment of KA TKA measured by the tibial slope and degree of flexion of the femoral component to the sagittal femoral axis. One hundred patients were randomized to receive either CI (n = 50) or PSI (n = 50) for KA TKA. Two observers measured pre- and postoperative X-rays to assess restoration of the tibial slope and sagittal flexion. Inter- and intraclass correlations were calculated, and postoperative tibial and femoral components were compared with preoperative anatomy. In 50 CI patients, 86% (n = 43) had the tibial slope restored exactly, and no deviation more than 1 degree was found. Deviations of 0 to 1 degree were detected in 14% (n = 7). In 50 patients of the PSI group, 56% (n = 28) achieved an exact anatomic tibial slope restoration and 20% (n = 10) showed a deviation more than 2 degrees compared with the preoperative measurement. Deviations ranging between 0 to 1 and 1 to 2 degrees were found in 22% (n = 11) and 2% (n = 1) of cases, respectively. Sagittal alignment of the femoral component showed in both groups no deviation exceeding 1 degree. The restoration of sagittal alignment in KA TKA was statistically significantly differently distributed between CI and PSI (p = < 0.001) without clinical relevance. We found that PSI increased the odds for deviations >2 degrees in tibial slope reconstructions from 0 to 0.20 ([95% confidence interval: 0.09-0.31]; p = 0.001). Both CI and PSI revealed adequate results with respect to restoring sagittal alignment of the tibial and femoral components in KA TKA. The conventional technique requires adequate adjustment of the intramedullary rod to avoid hyperflexion of the femoral component and attention must be paid when restoring the tibial slope using PSI. This is a prospective Level II study.

Increased accuracy in component positioning using an image-less robotic arm system in primary total knee arthroplasty: a retrospective study

BACKGROUND

Robotic-assisted total knee arthroplasty (RTKA) and navigated total knee arthroplasty (NTKA) have shown improved knee alignment and reduced radiographic outliers. Recent studies have proven that conventional mechanical alignment may not be the optimal goal for every patient. The aim of this study was to compare the accuracy of the planned implant positioning of a novel image-less robotic technique with an established navigated technique (NTKA).

METHOD

The study is a retrospective analysis of prospectively collected data that compared the implant positioning and lower-limb alignment of 86 image-less RTKA with 86 image-less NTKA. Radiographic analysis was performed to evaluate the lower-limb overall alignment, femoral and tibial components positioning in the coronal and sagittal planes. Outliers were evaluated with a cutoff of ± 3°.

RESULTS

No difference was noted between the two groups for radiographic outliers within ± 3° from neutral (p = 0.098). The mean hip-knee-ankle angle deviation from target was 1.3° in the RTKA group compared to 1.9° in the NTKA (p < 0.001). Femoral sagittal deviation (femoral component flexion) was smaller in the RTKA group (0.9° vs 1.9°; p < 0.001). Similarly, tibial coronal deviation (0.8° vs 1.5°; p < 0.001) and tibial sagittal deviation (tibial slope) were smaller in the RTKA group compared to the NTKA group (0.9° vs 1.7°; p < 0.001).

CONCLUSIONS

The RTKA group reported a substantial and significant reduced error from the planned target angles for both tibial and femoral components. No difference in terms of radiographic outliers was noted between navigation and robotic assistance.

Computed tomography-based patient-specific cutting guides used for positioning of the femoral component of implants during unicompartmental knee arthroplasty: a cadaver study

BACKGROUND

To investigate whether patient-specific instrumentation (PSI) improves the femoral component positioning of implants during unicompartmental knee arthroplasty (UKA) using cadaver bone models.

METHODS

Fifty adult cadaveric femoral bone specimens collected from February 2016-2018, were randomized to receive medial UKA with a PSI guide (n = 25) or conventional instrumentation (CI) (n = 25). Standard anteroposterior and lateral view radiographs were obtained postoperatively to assess the coronal and sagittal positioning of the femoral prostheses, respectively. The osteotomy time was recorded to assess the convenience of PSI in guiding osteotomy.

RESULTS

Osteotomy time significantly shortened in the PSI group (3.12 ± 0.65 versus 4.33 ± 0.73 min, p < 0.001). There was a significant difference in the postoperative coronal alignment of the femoral component between the PSI and CI groups (varus/valgus angle: 1.43 ± 0.93° vs. 2.65 ± 1.50°, p = 0.001). The prevalence of outliers in coronal alignment was lower in the PSI than the CI group (2/25, 8% vs. 9/25, 36%). Sagittal posterior slope angle of the femoral component was significantly different between the two groups (8.80 ± 0.65° and 6.29 ± 1.88° in the CI and PSI groups, respectively, p < 0.001). The malalignment rate of the femoral component in the sagittal plane was 60% in the CI group, whereas no positioning deviation was observed in the PSI group.

CONCLUSION

This study used a cadaver model to support the fact that CT-based PSI shows an advantage over CI in optimizing implant positioning for UKAs.

Knee kinematics are primarily determined by implant alignment but knee kinetics are mainly influenced by muscle coordination strategy

Implant malalignment has been reported to be a primary reason for revision total knee arthroplasty (TKA). In addition, altered muscle coordination patterns are commonly observed in TKA patients, which is thought to alter knee contact loads. A comprehensive understanding of the influence of surgical implantation and muscle recruitment strategies on joint contact mechanics is crucial to improve surgical techniques, increase implant longevity, and inform rehabilitation protocols. In this study, a detailed musculoskeletal model with a 12 degrees of freedom knee was developed to represent a TKA subject from the CAMS-Knee datasets. Using motion capture and ground reaction force data, a level walking cycle was simulated and the joint movement and loading patterns were estimated using a novel technique for concurrent optimization of muscle activations and joint kinematics. In addition, over 12'000 Monte Carlo simulations were performed to predict knee contact mechanics during walking, considering numerous combinations of implant alignment and muscle activation scenarios. Validation of our baseline simulation showed good agreement between the model kinematics and loading patterns against the in vivo data. Our analyses reveal a considerable impact of implant alignment on the joint kinematics, while variation in muscle activation strategies mainly affects knee contact loading. Moreover, our results indicate that high knee compressive forces do not necessarily originate from extreme kinematics and vice versa. This study provides an improved understanding of the complex inter-relationships between loading and movement patterns resulting from different surgical implantation and muscle coordination strategies and presents a validated framework towards population-based modelling in TKA.

Aseptic survival of the 1.5-stage exchange arthroplasty for periprosthetic joint infection was acceptable when using an autoclaved femoral component and a new polyethylene insert

PURPOSE

To investigate the aseptic survival of 1.5-stage exchange arthroplasty for periprosthetic joint infection (PJI) after total knee arthroplasty (TKA).

METHODS

Eighty-eight cases of 1.5-stage exchange arthroplasty for PJI without reinfection were retrospectively analysed. The autoclaved femoral component and new polyethylene insert (PE) were implanted using antibiotic mixed cement. The explanted tibial component was not reinserted. The Western Ontario and McMaster Universities Osteoarthritis Index and range of motion were clinically evaluated preoperatively and at the last follow-up (the last time for the implant in situ). Radiographically, hip-knee-ankle angle (HKA) and component positions were measured preoperatively, postoperatively (1 month after the 1.5-stage exchange arthroplasty), and at the last follow-up. The survival rate was analysed using the Kaplan-Meier method, in which failure was defined as reoperation due to aseptic failure. Mean period to failure and failure site were analysed. Factors affecting survival were investigated in terms of demographics and inappropriateness of the postoperative HKA (HKA > 0 ± 3°) and component positions (α angle > 95 ± 3°, β angle > 90 ± 3°, γ angle > 3 ± 3°, and δ angle > 87 ± 3°).

RESULTS

The spacer in-situ time was 3.7 years (0.2-6.4). The clinical results improved hip-knee-ankle significantly at the last follow-up. Radiographically, the average HKA was valgus 0.1° postoperatively. The average α, β, γ, and δ angles of the postoperative component positions were 95.9°, 90.4°, 3.8°, and 86.7°, respectively. The 1-, 2-, and 5-year postoperative survival rates were 90.9%, 86.4%, and 80.6%, respectively. The mean period to failure was 2.0 years (0.2-5.3). There were 18 cases of aseptic loosening (20.8%), occurring on both the femur and tibial sides in 1 knee, and only on the tibial side in 17 knees. Inappropriate coronal position of the PE (β angle > 90 ± 3°) was a significant factor affecting survival (odds ratio = 5.491; p = 0.011).

CONCLUSION

The aseptic survival of the 1.5-stage exchange arthroplasty was acceptable when using an autoclaved femoral component and new PE. The appropriate coronal position of the PE helps ensure favourable survival of 1.5-stage exchange arthroplasty.

LEVEL OF EVIDENCE

IV.

Linear correlation between patellar positioning and rotation of the lower limb in radiographic imaging: a 3D simulation study

PURPOSE

The purpose of this study was to quantify changes in rotation of the lower limb between image pairs based on patellar position. Additionally, we investigated the differences in alignment between centralized patellar and orthograde-positioned condyles.

METHODS

Three-dimensional models of 30 paired legs were aligned in neutral position with condyles orthogonal to the sagittal axis and then rotated internally and externally in 1° increments up to 15°. For each rotation, the deviation of the patella and the subsequent changes in alignment parameters were calculated and plotted using a linear regression model. Differences between neutral position and patellar centralization were analysed qualitatively.

RESULTS

A linear relationship between lower limb rotation and patellar position can be postulated. The regression model (R2 = 0.99) calculated a change of the patellar position of - 0.9 mm per degree rotation and alignment parameters showed small changes due to rotation. The physiological lateralization of the patella at neutral position was on average - 8.3 mm (SD: ± 5.4 mm). From neutral position, internal rotation that led to a centralized patella was on average - 9.8° (SD: ± 5.2°).

CONCLUSION

The approximately linear dependence of the patellar position on rotation allows an inverse estimation of the rotation during image acquisition and its influence on the alignment parameters. As there is still no absolute consensus about lower limb positioning during image acquisition, data about the impact of a centralized patella compared to an orthograde condyle positioning on alignment parameters was provided.

LEVEL OF EVIDENCE

IV.

Short-term clinical outcomes of primary total knee arthroplasty with a new-type kinematic retaining implant: A comparison with preexisting cruciate retaining prosthesis

Despite the success of total knee arthroplasty (TKA), current implant designs could not consistently restore the physiological knee kinematics, especially in cruciate-retaining (CR) implants. This study aimed to investigate the short-term clinical outcomes, particularly patient satisfaction, of primary TKA employing a new-type kinematic retaining (KR) implant. We analyzed 149 cases applied the KR implant at our institutions during June 2017 to May 2019. The effectiveness of this implant design was compared with another CR one (171 cases). Both groups underwent primary TKA in the same period and all patients completed 2 years of follow-up. Perioperative changes in range of motion (ROM), Knee Score, function score, and patient satisfaction by Forgotten Joint Score-12 (FJS-12) method were evaluated. Postoperative ROM, Knee Score, and function score were significantly improved at 1 year after surgeries and maintained for another year in both KR and CR groups. The improvement rate of ROM in KR group (108.1%) was substantially higher than that in CR (104.5%), even 4% increase could have affected patients' satisfaction in a real-world setting. Regarding the patient satisfaction, such 4 items as climbing stairs, walking on a bumpy road, doing housework or gardening, and taking a walk or hiking were significantly enhanced in KR cases compared to CR. There were no loosening or revision cases and the short-term survivorships of both implants were 100%. In addition, there has been no case of obvious complications in both groups during and after surgeries. The results of the present study suggest that this novel KR prosthesis can reproduce physiological knee kinematics, recover its functions, and contribute to pain relief after TKA. TKA procedure using the KR implant should be a good surgical option to improve postoperative outcomes.

Combined femoral and tibial component total knee arthroplasty device rotation measurement is reliable and predicts clinical outcome

BACKGROUND

The optimal total knee arthroplasty (TKA) rotational alignment and how best to obtain and measure it are debatable. The aim was to analyse the reliability of the Berger femoral, three different tibial and four different combined two-dimensional computer tomography (2D-CT) TKA component rotation measurements, and to ascertain which rotational values best predict a successful clinical outcome.

METHODS

The 2D-CT scans were obtained post-operatively on 60 patients who had TKA. We determined one femoral [Berger's femoral angle (BFA)], three tibial [Berger's tibial angle (BTA), anatomical tibial angle (ATA) and bimalleolar posterior tibial component angle (BM_PTCA)] and four combined [transepicondylar posterior tibial component angle (TE_PTCA), bicondylar posterior tibial component angle (BC_PTCA, transepicondylar bimalleolar angle (TE_BM) and bicondylar bimalleolar angle (BC_BM)] TKA rotation angles. We made all measures in 23 patients twice by three observers and determined inter- and intra-observer agreement using the Bland-Altman plot method. We analysed measures of 55 patients using the area under the ROC curve (AUC) analysis to ascertain the discriminative capacity of BFA, ATA, TE_PTCA and BC_PTCA for predicting a successful clinical outcome according to the Knee Society Score (KSS) threshold.

RESULTS

ATA showed the smaller inter- and intra-observer average of differences (-0.1° and 1.6°, respectively) of the studied methods followed by BFA (-0.9° and 1.4°), TE_PTCA (-2.1° and 2.7°) and BC_PTCA (-0.5° and 1.8°). BFA (-4° to 2.1° and -6.1° to 8.8°) and BC_PTCA (-4.4° to 3.4° and -7.9° to 4.4°) showed the narrower inter- and intra-observer limits of agreement. A TKA device rotation (BC_PTCA) < 0.8° of external rotation (ER) predicted a KSS and KSS knee successful outcome, and < 3.8° ER for KSS functional (AUC = 0.889; 0.907 and 0.764, respectively). BFA and ATA < 0.9° ER and < 3.9° internal rotation (IR) predicted a successful KSS knee outcome (AUC = 0.796 and 0.889, respectively).

CONCLUSION

The ATA tibial component rotation measurement was the most reliable of those studied. BFA, TE_PTCA and BC_PTCA were reliable measures for TKA femoral and combined rotation. The presence of a minimal rotation between the TKA components (BC_PTCA) and a small femoral ER or tibial IR predicted a successful KSS outcome.

LEVEL OF EVIDENCE II

Patients undergoing revisions for total knee replacement malposition are younger and more often female: An analysis of data from the Dutch Arthroplasty register

Background

The proportion of patients who are dissatisfied with the outcome following total knee replacement (TKR) is high. Malalignment is considered a probable cause for persistent pain, but whether this reason for revision could be the result of specific patient characteristics remains unclear. Therefore, we aim to assess whether specific patient characteristics are associated with revision for symptomatic TKR malalignment.

Methods

Data was obtained from the Dutch Arthroplasty Register (LROI), which contains data from all Dutch hospitals. All patients who underwent TKR revision surgery between 2008 and 2019 were included in this study. The (primary) reason for revision as well as patient characteristics (age, gender, ASA classification, and pre-operative patient-reported outcome measures) were abstracted. The Chi-square test for categorical variables, and ANOVA or Kruskal-Wallis for continuous variables were used to determine differences in patient characteristics between the subgroups based on reason for revision.

Results

A total of 11,044 TKR revisions were registered in The Netherlands between 2008 and 2019. Malalignment was registered as the primary reason for revision in 13% of the patients. Subgroup analyses showed that patients who underwent TKR revisions for malalignment where younger (63.8 year, SD ± 9.3) and more often female (70%) compared to other major reasons for TKR revisions.

Conclusion

Patients who had a TKR revision for malalignment were younger and more often female. This suggests that patient characteristics may play a role when reasons to perform revision surgery are considered. Surgeons should invest in the expectation management in (young) patients and inform patients of these potential risk factors as part of shared decision-making.

Sexual dimorphism of the posterior condylar offset of the femur and the medial posterior slope of the tibia in non-arthritic knees of Egyptian adults: an MRI study

BACKGROUND

The aim of this magnetic resonance imaging (MRI) study was to investigate controversial sexual dimorphism of the posterior condylar offset of the femur (the offset) and the posterior slope of the tibia (the slope) in non-arthritic knees of Egyptian adults.

METHODS

On 100 male and 100 female MRIs of non-arthritic knees, linear measurements of the distal part of the femur (the offset) and the angular measurements of the proximal part of the tibia (the slope) were performed and compared regarding sex and ethnicity. The intraclass correlation coefficient (ICC) was used to test the interrater agreement.

RESULTS

Both offsets and the lateral offset ratio were larger in males (p < 0.001), the medial offset ratio, and the medial slope in females (p from < 0.001 to 0.007), whereas the lateral slope was sex-free (p = 0.41). Irrespective of sex, however, the medial offset with its ratio, and the medial slope were larger than their counterparts (p < 0.001). Our means of the offsets, their ratios, and the slopes mostly differed from those of other ethnicities (p from ≤ 0.001 to 0.004). ICCs > 0.8 proved MRI's precision was high.

CONCLUSION

There was a sexual dimorphism of both the offset and the medial slope in non-arthritic knees of Egyptian adults. We believe future designs of knee implants should consider these differences in order to improve postoperative range of motion and patients' satisfaction after total knee arthroplasty. Level of evidence Level III Retrospective Cohort Study. Trial registration ClinicalTrials.gov identifier: NCT03622034, registered on July 28, 2018.

Coronal and Sagittal Component Position in Contemporary TKA: Targeting Native Alignment Optimizes Clinical Outcomes

BACKGROUND

Advanced technologies, like robotics, provide enhanced precision for implanting total knee arthroplasty (TKA) components; however, optimal component position and limb alignment remain unknown. This study sought to identify sagittal and coronal alignment targets that correlate with minimal clinically important differences (MCID) in patient-reported outcome measures (PROMs).

METHODS

A total of 1,311 consecutive TKAs were retrospectively reviewed. Posterior tibial slope (PTS), femoral flexion (FF), and tibio-femoral alignment (TFA) were measured radiographically. Patients were grouped based on whether they achieved multiple MCIDs for PROM scores. Classification and regression tree machine learning models were utilized to identify optimal alignment zones. Mean follow-up was 2.4 years (range, 1 to 11).

RESULTS

The change in PTS and postoperative TFA were most predictive for achieving MCIDs in 90% of the models. Approximating native PTS within 4° correlated with MCID achievement and superior PROMs. Preoperative varus and neutral aligned knees were more likely to meet MCIDs and superior PROM scores when not overcorrected into valgus postoperatively (≥ 7°). Preoperative valgus aligned knees correlated with MCID achievement when postoperative TFA was not overcorrected into substantial varus (<0°). Albeit less impactful, FF ≤ 7° correlated with MCID achievement and superior PROMs regardless of preoperative alignment. Sagittal and coronal alignment measurements had moderate to strong interactions in 13 of 20 models.

CONCLUSION

Optimized PROM MCIDs correlated with approximating native PTS while maintaining similar preoperative TFA and incorporating moderate FF. Study findings demonstrate interactions between sagittal and coronal alignment which may optimize PROMs, highlighting the importance of three-dimensional implant alignment targets.

Virtual Joint Motion Simulator Accurately Predicts Effects of Femoral Component Malalignment during TKA

Component alignment accuracy during total knee arthroplasty (TKA) has been improving through the adoption of image-based navigation and robotic surgical systems. The biomechanical implications of resulting component alignment error, however, should be better characterized to better understand how sensitive surgical outcomes are to alignment error. Thus, means for analyzing the relationships between alignment, joint kinematics, and ligament mechanics for candidate prosthesis component design are necessary. We used a digital twin of a commercially available joint motion simulator to evaluate the effects of femoral component rotational alignment. As anticipated, the model showed that an externally rotated femoral component results in a knee which is more varus in flexion, with lower medial collateral ligament tension compared to a TKA knee with a neutrally aligned femoral implant. With the simulation yielding logical results for this relatively simple test scenario, we can have more confidence in the accuracy of its predictions for more complicated scenarios.

Excessive flexed position of the femoral component causes abnormal kinematics and joint contact/ ligament forces in total knee arthroplasty

Poor clinical outcomes are reported in excessive flexion of the femoral component in total knee arthroplasty (TKA), but their mechanisms have not yet been elucidated. This study aimed to investigate the biomechanical effect of flexion of the femoral component. Cruciate-substituting (CS) and posterior-stabilised (PS) TKA were reproduced in a computer simulation. The femoral component was then flexed from 0° to 10° with anterior reference, keeping the implant size and the extension gap. Knee kinematics, joint contact, and ligament forces were evaluated in deep-knee-bend activity. When the femoral component was flexed 10° in CS TKA, paradoxical anterior translation of the medial compartment was observed at mid-flexion. The PS implant was best stabilised with a 4° flexion model in mid-flexion range. The medial compartment contact force and the medial collateral ligament (MCL) force increased with the flexion of the implant. There were no remarkable changes in the patellofemoral contact force or quadriceps in either implant. In conclusions, excessive flexion of the femoral component yielded abnormal kinematics and contact/ligament forces. Avoiding excessive flexion and maintaining mild flexion of the femoral component would provide better kinematics and biomechanical effects in CS and PS TKA.

Decrease of tibial tuberosity trochlear groove distance following mechanically aligned total knee arthroplasty

PURPOSE

Anterior knee pain (AKP) is common following total knee arthroplasty. The tibial tuberosity trochlear groove distance (TTTG) influences patellofemoral joint loading in the native knee. Increased TTTG may lead to maltracking of the patella and anterior knee pain. The purpose of this study was to investigate potential changes in TTTG following total knee arthroplasty (TKA).

METHODS

TTTG was measured on preoperative CT data on a consecutive series of patients scheduled to receive TKA with patient-specific instrumentation, and compared to a computer simulation of the postoperative TTTG. Preoperative TTTG was measured with a 3D planning software in 250 knees. The postoperative result was simulated and TTTG measured within the software. Three different groups were analysed: neutral (180° ± 3) (n = 50), valgus (> 190°) (n = 100), and varus (< 170°) (n = 100).

RESULTS

Median preoperative to simulated postoperative TTTG decreased from 15.0 [interquartile range (IQR) 6.0] mm to 6.5 (IQR 5.0) mm for all axes combined. A significant postoperative reduction of TTTG was found in each group (p < 0.001). The mean change in TTTG did not differ significantly between the groups [- 8.8 (IQR 5.5) mm neutral, - 8.3 (IQR 7.0) mm valgus, - 7.5 (IQR 5.8) mm varus, p = 0.223].

CONCLUSION

This computer-based study suggests that mechanically aligned TKA significantly decreases TTTG distance in neutral, valgus and varus knees, assuming that the postoperative result coincides with the preoperative planning. Further study is warranted to evaluate the clinical relevance of this finding.

Navigated, gap-balanced, adjusted mechanical alignment achieves alignment and balancing goals in a very high percentage but with partially non-anatomical resections

PURPOSE

Navigated, gap-balanced adjusted mechanical alignment (AMA) including a 0° varus tibial cut and modification of angles and resections of the femoral cuts to obtain optimal balance accepting minor axis deviations. Objectives of this study were (1) to analyse to what extent AMA achieves the goals for leg alignment and gap balance, and (2) in what percentage non-anatomical cuts are needed to achieve these goals.

METHODS

Out of 1000 total knee arthroplasties (TKA) all varus knees (hip-knee-ankle (HKA) angle < 178°; n = 680) were included. All surgeries were performed as computer assisted surgery (CAS) in AMA technique. CAS data at the end of surgery were analysed with respect to HKA and gap-sizes. All bone cuts were quantified. Depending on the amount of deformity, a subgroup analysis was performed. It was analysed whether the amount of deformity influences the non-anatomical cuts by correlation analysis.

RESULTS

AMA reached the goals for postoperative HKA (3° corridor) in 636 cases (93.5%). While extension and flexion gap balance were achieved in more than 653 cases (96%), flexion and extension gap size were equalled in 615 knees (90.4%). The resections of the lateral tibia plateau and distal and posterior medial femoral condyle were anatomical (Tibia: 7.0 ± 1.7 mm; medial condyle distal: 7.8 ± 1.4 mm; medial posterior: 8.2 ± 1.8 mm). The number of non-anatomical resections for those cuts were low; 67 (9.9%); 24 (3.5%); 32 (4.7%). For the medial tibia plateau and the lateral posterior condyle, the cuts were non-anatomical in a high percentage of cases; Tibia: 606 (89.1%), lateral posterior condyle: 398 (58.5%). Moderate but significant correlations were found between resection differences and amount of deformity (medio-lateral: tibia: 0.399; distal femur: 0.310; posterior femur: 0.167). No correlations were found between resection differences and gap values.

CONCLUSION

AMA reaches the intended target for HKA and gap balance in over 612 (90%) of cases and maintains the medial femoral condyle anatomically. Non-anatomical tibial resection causes increased external rotation of the femoral component and by that non-anatomical cut of the posterior lateral condyle. Nonanatomical resections of AMA might be one reason for the persisting high rate of unsatisfied patients after TKA. Anatomical and individual alignment philosophies might help to reduce this rate of dissatisfaction.

Is the femoral intramedullary alignment already actual in total knee arthroplasty?

Clinical outcomes and overall alignment after total knee arthroplasty (TKA) depend on femoral component positioning in the sagittal and the coronal plane, making choice of the distal femoral cutting guide crucial. Currently, there is no consensus on the potential advantage of an extramedullary (EM) guide compared to an intramedullary (IM) guide in TKA. The IM guide is the most widely used system for making the distal femoral cut although evidence for its superiority over the EM guide is lacking. However, inaccuracies arising with the IM guide include location of the rod entry point in the coronal plane, femoral canal diameter, femoral bowing, and structural features of the rod. Furthermore, the invasive procedure is associated with increased risk of postoperative blood loss, thromboembolic complications, and intraoperative fractures. While the EM guide has no such difficulties, its accuracy depends on the instruments used. Studies have reported results not inferior to the IM guide and a lower number of postoperative complications. Patient-specific instrumentation (PSI) and robotic and computer-assisted TKA have achieved excellent clinical and radiographic results and can overcome the problems inherent to the IM and the EM guide. Authors performed a systematic review of the literature and proposed a narrative review to summarize the characteristics of the IM and the EM guide and compare the advantages and disadvantages of each, as well as their limitations in comparison with new technologies. Authors also expressed their expert opinion.

The impact of surgical trainee involvement in total knee arthroplasty: a systematic review of surgical efficacy, patient safety, and outcomes

PURPOSE

Trainee involvement in patient care has raised concerns about the potential risk of adverse outcomes and harming patients. We sought to analyze the impact and potential consequence of surgical trainee involvement in total knee arthroplasty (TKA) procedures in terms of surgical efficacy, patient safety, and functional outcomes.

METHODS

We systematically reviewed Medline/PubMed, EMBASE, the Cochrane library, and Scopus databases in April 2021. Eligible studies reported on the impact of trainee participation in TKA procedures performed with and without such involvement.

RESULTS

Twenty-three publications met our eligibility criteria and were included in our study. These studies reported on 132,624 surgeries completed on 132,416 patients. Specifically, 23,988 and 108,636 TKAs were performed with and without trainee involvement, respectively. The mean operative times for procedures with (n = 19,573) and without (n = 94,581) trainee involvement were 99.77 and 85.05 min, respectively. Both studies that reported data on cost of TKAs indicated a significant increase (p < 0.001) associated with procedures completed by teaching hospitals compared to private practices. Mean overall complication rates were 7.20% and 7.36% for TKAs performed with (n = 9,386) and without (n = 31,406) trainees. Lastly, the mean Knee Society Scale (KSS) knee scores for TKAs with (n = 478) and without (n = 806) trainee involvement were similar; 82.81 and 82.71, respectively.

CONCLUSION

Our systematic review concurred with previous studies that reported trainee involvement during TKAs increases the mean operative time. However, the overall complication rates and functional outcomes were similar. Larger studies with a better methodology and higher level of evidence are still needed for a resolute conclusion.

Clinical applications of augmented reality in orthopaedic surgery: a comprehensive narrative review

PURPOSE

The development of augmented reality (AR) technology allows orthopaedic surgeons to incorporate and visualize surgical data, assisting the execution of both routine and complex surgical operations. Uniquely, AR technology allows a surgeon to view the surgical field and superimpose peri-operative imaging, anatomical landmarks, navigation guidance, and more, all in one view without the need for conjugate gaze between multiple screens. The aim of this literature review was to introduce the fundamental requirements for an augmented reality system and to assess the current applications, outcomes, and potential limitations to this technology.

METHODS

A literature search was performed using MEDLINE and Embase databases, by two independent reviewers, who then collaboratively synthesized and collated the results of the literature search into a narrative review focused on the applications of augmented reality in major orthopaedic sub-specialties.

RESULTS

Current technology requires that pre-operative patient data be acquired, and AR-compatible models constructed. Intra-operatively, to produce manipulatable virtual images into the user's view in real time, four major components are required including a camera, computer image processing technology, tracking tools, and an output screen. The user is provided with a heads-up display, which is a transparent display, enabling the user to look at both their natural view and the computer-generated images. Currently, high-quality evidence for clinical implementation of AR technology in the orthopaedic surgery operating room is lacking; however, growing in vitro literature highlights a multitude of potential applications, including increasing operative accuracy, improved biomechanical angular and alignment parameters, and potentially reduced operative time.

CONCLUSION

While the application of AR systems in surgery is currently in its infancy, we anticipate rapid and widespread implementation of this technology in various orthopaedic sub-specialties.

Clinical three-dimensional anatomy of the femur considering navigation-aided surgery of total knee arthroplasty in Japanese patients

PURPOSE

Few studies exist regarding sagittal alignment describing femur morphology in navigation-aided surgery. This study investigated the three-dimensional (3D) sagittal femoral alignment of the whole femur.

METHODS

Seventy-three consecutive patients (59 females, 14 males, mean age: 76.1 years), yielding 140 femurs, were included in this study. A computed-tomography-based patient-specific 3D femur model was used to define a mechanical axis-based reference plane. Proximal and distal femoral axis angles (PFA, DFA) to the reference plane were measured in 3D using custom software. PFA and DFA represent the proximal and distal inclination of the femoral anatomical axis in sagittal plane, respectively.

RESULTS

PFA (10.6 ± 1.5°) was greater than DFA (2.6 ± 1.6°; P < 0.0001). DFA in females (2.3 ± 1.4°) was smaller than in males (3.9 ± 1.7°; P < 0.0001).

CONCLUSION

This is the first report of measurement of femoral sagittal alignment related to both 3D anatomy and decision making of femoral flexion angle using navigation surgery for total knee arthroplasty. This report shows a robust DFA measurement that could be used as a template for femoral implants flexion angle when performing both conventional and navigated total knee arthroplasty.

3D-printed patient-specific instrumentation decreases the variability of patellar height in total knee arthroplasty

Objective

Three-dimensionally (3D) printed patient-specific instrumentation (PSI) might help in this regard with individual design and more accurate osteotomy, but whether the utility of such instrumentations minimizes the variability of patellar height in total knee arthroplasty (TKA) and the reasons for this effect are unknown. Our aim is to compare and analyze the variability of patellar height with PSI and conventional instrumentation (CI) in TKA.

Methods

Between March 2018 and November 2021, 215 patients with severe knee osteoarthritis who were treated with primary unilateral TKA were identified for this observational study. The patients were divided into the CI-TKA group and PSI-TKA group according to the osteotomy tools used in TKA. Preoperative and postoperative radiographic parameters including hip-knee-ankle angle (HKA), posterior tibial slope (PTS), Insall-Salvati ratio, modified Caton-Deschamps (mCD) ratio, anterior condylar offset (ACO), and posterior condylar offset (PCO) were evaluated.

Results

The groups were similar in patients' demographic data, clinical scores, and radiographic parameters preoperatively. Overall, according to the results of the Insall-Salvati ratio, postoperative patellar height reduction was noted in 140 patients (65.1%). Interestingly, the variability of patellar height was smaller in the PSI-TKA group. Radiographic evaluation revealed that the Insall-Salvati ratio after TKA had a minor change in the PSI-TKA group (p = 0.005). Similarly, the mCD ratio after TKA also had a minor change in the PSI-TKA group (p < 0.001). Compared to those in the CI-TKA group, the ACO (p < 0.001) and PCO (p = 0.011) after TKA had a minor change in the PSI-TKA group, but no minor PTS change (p = 0.951) was achieved in the PSI-TKA group after TKA. However, even with 3D-printed patient-specific instrumentation, there were still significant reductions in patellar height, ACO, PCO, and PTS after TKA (p < 0.001).

Conclusion

The variability of patellar height was sufficiently minimized with more accurate anterior and posterior femoral condyle osteotomy when 3D printed PSI was used. Furthermore, there was a trend in over-resection of the femoral anterior and posterior condyle and a marked reduction in PTS during TKA, which could lead to a change in patellar height and might result in more patellofemoral complications following TKA.

Level of evidence

Level II.

Reference Axes for Tibial Component Rotation in Total Knee Arthroplasty: Computed Tomography-Based Study of 1,351 Tibiae

BACKGROUND

Many anatomic landmarks have been described for setting tibial component rotation intraoperatively. There is no consensus as to which axis is best for reducing outliers and preventing malrotation.

METHODS

The SOMA (Stryker Orthopaedic Modeling and Analytics) database (Stryker) was used to identify 1,351 computed tomography (CT) scans of the entire tibia. Several reference axes for the tibia (including the Mayo axis, Akagi line, Insall line, anterior condylar axis [ACA], posterior condylar axis [PCA], lateral tibial cortex [LTC], Cobb axis, tibial crest line [TCL], and transmalleolar axis [TMA]) were constructed according to published guidelines. The Berger method served as the reference standard.

RESULTS

The Mayo method (involving a line connecting the medial and middle one-thirds of the tibial tubercle and the geometric center of the tibia) and the Insall line (involving a line connecting the posterior cruciate ligament [PCL] insertion and the intersection of the middle and medial one-thirds of the tibial tubercle) both had low variability relative to the Berger method (7.8° ± 1.0° and 5.1° ± 2.2°, respectively) and a low likelihood of internal rotation errors (0.7% and 1.8%, respectively). No clinically significant gender-based differences were found (<0.7° for all). The same was true for ethnicity, with the exception of consistently greater tibial intorsion in Asian versus Caucasian individuals (mean difference in TCL position, +4.5° intorsion for Asian individuals; p < 0.001).

CONCLUSIONS

This CT-based study of 1,351 tibiae (which we believe to be the largest study of its kind) showed that the Mayo and Insall methods (both of which reference the medial and middle one-thirds of the tibial tubercle) offer an ideal balance of accuracy, low variability, and a reduced likelihood of internal rotation errors. Setting rotation on the basis of distal landmarks (tibial shaft and beyond) may predispose surgeons to substantial malrotation errors, especially given the differences in tibial torsion found between ethnic groups in this study.

LEVEL OF EVIDENCE

Therapeutic Level IV . See Instructions for Authors for a complete description of levels of evidence.

Accelerometer-Based Navigation versus Conventional Total Knee Arthroplasty for Posttraumatic Knee Osteoarthritis

BACKGROUND

Posttraumatic osteoarthritis (PTOA) frequently comprises femoral or tibial deformity, which makes it difficult to perform total knee arthroplasty (TKA). Accelerometer-based navigation (ABN) could be effective in restoring a neutral mechanical axis (MA) in TKA, but a limited number of studies have been reported in association with PTOA. Therefore, we aimed to compare the lower limb MA between ABN-assisted TKA (ABN-TKA) and conventional TKA in patients with PTOA.

METHODS

We conducted a retrospective analysis of 28 PTOA patients who underwent TKA using a conventional system (cTKA group, n = 16) and the ABN system (iTKA group, n = 12). Standing long-leg radiographs were assessed for MA and prosthesis alignment as primary outcomes. A postoperative MA deviating beyond ± 3° was defined as an outlier. Perioperative outcomes, Oxford Knee Score (OKS) at 2-year follow-up, and complications were also assessed.

RESULTS

The cTKA group and the iTKA group had a mean age of 63.07 years and 65.25 years, respectively. The iTKA group had significantly better MA accuracy when compared to the cTKA group (1.60° ± 2.09° vs. 3.59° ± 1.34°, p = 0.01). The iTKA group showed significantly less MA outlier than the cTKA group (78.6% vs. 25.0%, p = 0.02). The prosthesis alignment and OKS were comparable between the groups. There were 2 periprosthetic joint infections in the cTKA group and 1 periprosthetic fracture of the distal femur in the iTKA group.

CONCLUSIONS

For PTOA of the knee, both conventional TKA and ABN-TKA significantly improved the postoperative mechanical alignment and functional outcomes. The ABN-TKA seemed to offer higher accuracy and less MA outlier when compared to conventional TKA, and thus ABN could be a good alternative option.

Comparison of the Imaging and Clinical Outcomes among the Measured Resection, Gap Balancing, and Hybrid Techniques in Primary Total Knee Arthroplasty

OBJECTIVE

Although many studies have compared the measured resection (MR) technique to the gap balancing (GB) technique, few studies have investigated the hybrid technique. In this study, we compared imaging and clinical outcomes of the MR, GB, and hybrid techniques in primary total knee arthroplasty (TKA).

METHODS

From January 2016 to January 2019, we conducted a retrospective study on 90 patients who underwent unilateral primary TKA; 30 received the MR technique, 30 received the GB technique, and 30 received the hybrid technique. Radiological outcomes, including joint line level, mechanical alignment of the lower limb, positions of the femoral and tibial components, and rotation of the femoral component, and clinical outcomes, including the visual analog scale score for pain, the Knee Society Score, and the range of motion, were assessed among the three groups. One-way analysis of variance and Dunnett's test were performed for normally distributed data. Kruskal-Wallis H test and Dunn-Bonferroni test were conducted for non-normally distributed data.

RESULTS

No significant difference in the mechanical alignment (p = 0.151) and the positions of the tibial and femoral components (p = 0.230 for α angle, p = 0.517 for β angle, p = 0.686 for femoral flexion angle, and p = 0.918 for tibial slope angle) was found among the three groups. No significant difference in the elevation of the joint line between the MR and the hybrid groups was found (2.1 ± 0.3 mm vs 2.1 ± 0.1 mm, p = 0.627), but the GB group (2.8 ± 0.2 mm) differed significantly from the other two groups (p < 0.001). Although rotation of the femoral component in the GB group was larger than that of the MR and hybrid groups, the difference was not significant (1.8° ± 0.2° vs 1.7° ± 0.3° vs. 1.7° ± 0.2°, p = 0.101). The clinical outcomes were not significantly different (p > 0.05), although the results in the hybrid group were slightly higher.

CONCLUSION

The hybrid technique helped to restore the mechanical alignment of the lower limb and realize optimal positions of the femoral and tibial components without significant differences relative to the MR and GB techniques. The hybrid technique was more helpful for maintaining the original height of the joint line, which was similar to the MR technique. Additionally, although the improvement in the clinical outcomes in the hybrid group was slightly higher, it was not significantly different among the three groups.

Correlation between component alignment and short-term clinical outcomes after total knee arthroplasty

OBJECTIVE

This study aimed to investigate the correlation between component alignment and short-term clinical outcomes after total knee arthroplasty (TKA).

METHODS

50 TKA patients from a regional hospital were enrolled in the study. The following component alignments were measured from radiological data acquired within 1 week after surgery: hip-knee-ankle angle (HKA), medial distal femoral angle (MDFA), medial proximal tibial angle (MPTA), femoral flexion-extension angle (FEA), tibial slope angle (TSA), femoral rotational angle (FRA) and tibial rotational angle (TRA). The Hospital for Special Surgery (HSS) knee scoring system was used to assess clinical outcomes after 1 year, with patients being divided into three groups (excellent, good and not good) according to the HSS scores. Difference analysis and linear correlation analysis were used for the statistical analysis.

RESULTS

The results showed significant differences in MDFA (p = 0.050) and FEA (p = 0.001) among the three patient groups. It was also found that the total HSS had only a moderate correlation with FEA (r = 0.572, p < 0.001), but FEA had a positive linear correlation with pain scores (r = 0.347, p = 0.013), function scores (r = 0.535, p = 0.000), ROM scores (r = 0.368, p = 0.009), muscle scores (r = 0.354, p = 0.012) and stability scores (r = 0.312, p = 0.028). A larger MDFA was associated with lower FE deformity scores (r = -0.289, p = 0.042) and the TSA had a positive influence on the ROM (r = 0.436, p = 0.002). Also, changes in FRA produced a consequent change in the FE deformity score (r = 0.312, p = 0.027), and the muscle strength scores increased as TRA increased (r = 0.402, p = 0.004).

CONCLUSION

The results show that the FEA plays a significant role in clinical outcomes after TKA. Surgical techniques and tools may need to be improved to accurately adjust the FEA to improve joint functionality and patient satisfaction.

Inaccuracy of the intramedullary femoral guide: traditional instrumentation lacks precision and accuracy

PURPOSE

The purpose of the study was to utilize a large-scale biomorphometric computer tomography (CT) database to determine the desirable starting point and angle for placement of the femoral intramedullary rod in the sagittal plane.

METHODS

A CT-based modeling and analytics system (SOMA, Stryker, Mahwah, NJ) was used to evaluate 1029 entire-femur CT scans. From this, 19,464 simulations were run to test whether a 20 cm intramedullary rod, with a radius of 4 mm, would successfully pass through the femoral canal before contacting cortical bone. First, modelling included varying angles from 0-6 degrees in the sagittal plane, at 1-degree intervals. Next, the start point was adjusted with an assumed 3 degrees of induced flexion in comparison to the mechanical axis.

RESULTS

A total of 5012 simulations were able to place the femoral intramedullary rod 20 cm into the canal. The angle of the rod that created the highest proportion of successful jig placement was at a 3-degree angle of induced flexion to the orthogonal plane of the transepicondylar axis (TEA), with 33.7% successful jig placements. The starting point for the greatest proportion of successful guide placements was 48.5% along the distance between the sTEA, slightly closer to the lateral side. In the AP plane, the average distance to the ideal start point was 12.1 mm anterior to the PCL.

CONCLUSION

By examining over a thousand femoral CT scans, an angle of 3 degrees of induced flexion was identified in the sagittal plane with the highest proportion of successful placement of an intramedullary rod before cortical contact. It is important to note the high rate of failure in completely inserting the 20 mm rod.

LEVEL OF EVIDENCE

This is a prospective computer based model.

Correlations of typical pain patterns with SPECT/CT findings in unhappy patients after total knee arthroplasty

PURPOSE

The diagnostic process in patients after painful total knee arthroplasty (TKA) is challenging. The more clinical and radiological information about a patient with pain after TKA is included in the assessment, the more reliable and sustainable the advice regarding TKA revision can be. The primary aim was to investigate the position of TKA components and evaluate bone tracer uptake (BTU) using pre-revision SPECT/CT and correlate these findings with previously published pain patterns in painful patients after TKA.

METHODS

A prospectively collected cohort of 83 painful primary TKA patients was retrospectively evaluated. All patients followed a standardized diagnostic algorithm including 99m-Tc-HDP-SPECT/CT, which led to a diagnosis indicating revision surgery. Pain character, location, dynamics and radiation were systematically assessed as well as TKA component position in 3D-CT. BTU was anatomically localized and quantified using a validated localization scheme. Component positioning and BTU were correlated with pain characteristics using non-parametric Spearman correlations (p < 0.05).

RESULTS

Based on Spearman's rho, significant correlations were found between pain and patients characteristics and SPECT/CT findings resulting in nine specific patterns. The most outstanding ones include: Pattern 1: More flexion in the femoral component correlated with tender/splitting pain and patella-related pathologies. Pattern 3: More varus in the femoral component correlated with dull/heavy and tingling/stinging pain during descending stairs, unloading and long sitting in patients with high BMI and unresurfaced patella. Pattern 6: More posterior slope in the tibial component correlated with constant pain.

CONCLUSION

The results of this study help to place component positioning in the overall context of the "painful knee arthroplasty" including specific pain patterns. The findings further differentiate the clinical picture of a painful TKA. Knowing these patterns enables a prediction of the cause of the pain to be made as early as possible in the diagnostic process before the state of pain becomes chronic.

LEVEL OF EVIDENCE

Level III.

Different squatting positions after total knee arthroplasty: A retrospective study

BACKGROUND

Total knee arthroplasty (TKA) has been shown to improve quality of life and reduce pain. High-flexion activities such as squatting, kneeling, and floor transfers are mainly listed as demanding tasks. Among them, squatting is an important position.

AIM

To provide a new squat position classification and evaluate the different squatting positions of a series of patients after primary TKA.

METHODS

From May 2018 to October 2019, we retrospectively reviewed 154 video recordings of the squatting-related motions of patients after TKA. Among the included patients, 119 were women and 35 were men. Their mean age at the index surgery was 61.4 years (range, 30 to 77).

RESULTS

The median follow-up was 12 mo (range, 6 to 156 mo). We classified those squatting-related motions into three major variations according to squatting depth: Half squat, parallel squat, and deep squat. The angles of hip flexion, knee flexion, and ankle dorsiflexion were measured in the screenshots captured from the videos at the moment of squatting nadir. A total of 26 patients were classified as half squats, 75 as parallel squats, and 53 as deep squats. The angles of hip flexion, knee flexion, and ankle dorsiflexion all differed significantly among the three squatting positions (P < 0.001). In the parallel squat group, the mean knee flexion angle (°) was 116.5 (SD, 8.1; range, 97 to 137). In the deep squat group, the mean knee flexion angle (°) was 132.5 (SD, 9.3; range, 116 to 158).

CONCLUSION

Among the three squatting positions, deep squat showed the highest hip, knee, and ankle flexion angles, followed by the parallel squat. With the improvement of squatting ability, the patient's postoperative satisfaction rate was also significantly enhanced. However, the different squatting abilities of the patients cannot be effectively distinguished from the scoring results (P > 0.05). Our squatting position classification offers a pragmatic approach to evaluating patients’ squatting ability after TKA.

Failure modes in malrotated total knee replacement

PURPOSE

Achieving normal rotational alignment of both components in total knee arthroplasty (TKA) is essential for improved knee survivorship and function. However, malrotation is a known complication resulting in higher revision rates. Understanding malrotation of the components and its concomitant clinical and functional outcomes are important for early diagnosis and management. The purpose of this study was to evaluate the effect of malrotation on clinical outcomes and failure modes in both single and combined rotational malalignment.

METHODS

From our hospital database of 364 revisions, a cohort of 76 knees with patellar maltracking, stiffness, reduced range of motion and early aseptic failure were reviewed and investigated for component malrotation using computed tomography following Berger protocol. CT findings confirmed component malrotation in 70 of these patients. Investigations included (1) measurement of femoral component malrotation using surgical transepicondylar axis, (2) measurement of tibial component malrotation using anteroposterior axis and (3) measurement of combined component rotational errors.

RESULTS

The correlation of CT analysis and clinical outcomes after primary TKA revealed association of patellar maltracking with femoral internal rotation, pain and instability with tibial internal rotation and knee stiffness in patients with combined component malrotation as the commonest mode of presentation. Our study showed that patients with isolated femoral, tibial and combined malrotation presented at a mean period of 3.4 ± 1.34, 1.7 ± 0.8 and 2.3 ± 0.69 years, respectively, after the index surgery. Post-revision, the mean Knee Society Score and Oxford Knee Score improved from 29.1 to 78.7, and 10.5 to 32.8, respectively, and the mean range of motion improved from 74.9 ± 24.8 to 97.1 ± 12.7 degrees at a mean follow-up of 42 months.

CONCLUSION

Early detection of malrotation in TKA and its management with revision of both components can lead to better clinical and functional outcomes.

LEVEL OF EVIDENCE

III.

Minimum 5-Year Outcomes of a Multicenter, Prospective, Randomized Control Trial Assessing Clinical and Radiological Outcomes of Patient-Specific Instrumentation in Total Knee Arthroplasty

BACKGROUND

Patient-specific instrumentation (PSI) was developed to produce more accurate alignment of components and consequently improve clinical outcomes when used in total knee arthroplasty. We compare radiological accuracy and clinical outcomes at a minimum of 5-year follow-up between patients randomized to undergo total knee arthroplasty performed using PSI or traditional cutting block techniques.

METHODS

This multicenter, randomized control trial included patients blinded to the technique 1used. Outcome measures were coronal alignment measured radiologically, Euroqol-5D, Oxford knee score, and International Knee Society Score measured at 1- and 5-year follow-up.

RESULTS

At a minimum 5-year follow-up, there were 38 knees in the PSI group and 39 in the conventional instrumentation group for analysis. Baseline demographics and clinical outcome scores were matched between groups. Overall, there was no significant difference in the coronal femoral angle (P = .59), coronal tibial angle (P = .37), tibiofemoral angle (P = .99), sagittal femoral angle (P = .34), or the posterior tibia slope (P = .12) between knees implanted using PSI and those implanted with traditional cutting blocks. On the measurement of coronal alignment, intraobserver reliability tests demonstrated substantial agreement (k = 0.64). Clinical outcomes at both 1-year and 5-year follow-up demonstrated statistically significant and clinically relevant improvement in scores from baseline in both groups, but no difference could be detected between the Euroqol-5D (P = .78), Oxford knee score (P = .24), or International Knee Society Score (P = .86) between the 2 groups.

CONCLUSION

This study has shown no additional benefit to PSI in terms of improved alignment or functional outcomes at minimum 5-year follow-up over traditional techniques.

Revision for coronal malalignment will improve functional outcome up to 5 years postoperatively

PURPOSE

Revision of a total knee arthroplasty (TKA) for the diagnosis of malalignment is widely performed. However, very little is known about the functional outcome in revision TKA surgery for malalignment. The aim of this study was to assess the functional outcome and to identify factors influencing the functional outcome of patients who have had a revision of a TKA for the diagnosis of malalignment at 5 years follow-up.

METHODS

All patients with a revision of a TKA for malalignment as the primary reason were selected from a prospective database. The diagnosis of symptomatic malalignment was made by the surgeon and quantified by radiologic examination. Functional outcome was scored by the functional score of the Knee Society Clinical Rating System (fKSS) at 0, 12, 24 and 60 months. Multiple imputation for missing data and multivariable analysis were performed to identify factors influencing functional outcome.

RESULTS

After selection, 105 patients (age: 65.1 ± 9.1 years, gender M:F 30:75) were eligible for outcome analysis. Functional outcome significantly improved from the preoperative (fKSS: 44.1 ± 22.0) to 5 years postoperative (64.7 ± 24.0, p < 0.001) time frames. Higher degree of coronal deviation, younger age and lower preoperative KSS were found to be strongest positive influencing factors for the change in fKSS.

CONCLUSION

Revision of TKA for malalignment appears to be an effective treatment to improve functional outcome up to 5 years postoperatively. Higher degree of coronal deviation, younger age and lower preoperative KSS are the strongest contributing factors for functional improvement.

LEVEL OF EVIDENCE

Level III; Therapeutic prospective cohort study.

Functional outcomes of residual varus alignment versus mechanical alignment in total knee arthroplasty for varus osteoarthritis: A preferred reporting items for systematic reviews and meta-analyses-compliant meta-analysis

BACKGROUND

One in five patients with mechanical alignment (MA) after total knee arthroplasty (TKA) was reportedly dissatisfied. As constitutional varus knees are common, restoring the patients' natural residual varus (RV) alignment is as an appealing alternative to neutral MA. This meta-analysis aimed to evaluate the effects of RV alignment on the functional outcomes compared with those of MA in TKA for the knees with varus osteoarthritis.

METHODS

The MEDLINE/PubMed, Cochrane Library, and EMBASE databases were comprehensively searched for papers comparing the effects of RV alignment and MA on the functional outcomes from the time of inception of the databases to July 2020. Studies comparing the functional outcomes in the knees subjected to TKA with RV alignment (case group) and MA (control group) were included. The Knee Society knee and functional scores (KSKS and KSFS, respectively), Western Ontario and McMaster University Osteoarthritis Index (WOMAC), Oxford knee score (OKS), and forgotten joint score (FJS) were compared.

RESULTS

Seven studies were finally included; all studies showed a low risk of selection bias and provided detailed demographic data. The pooled mean difference in the KSKS (0.06, 95% confidence interval [CI]: -0.14 to 0.27; p = 0.55) and KSFS (0.08, 95% CI: -0.08 to 0.35; p = 0.56) between RV alignment and MA did not significantly differ. The pooled mean differences in the WOMAC (-0.25, 95% CI: -0.57 to 0.07; p = 0.12), OKS (0.06, 95% CI: -0.15 to 0.27; p = 0.56), and FJS (0.41, 95% CI: -0.18 to 1.00; p = 0.18) between the groups were not significant.

CONCLUSION

The beneficial effects of RV alignment on the functional outcomes are limited compared to those of MA in TKA for varus osteoarthritis to date. Currently, TKA with neutral MA should be considered as the gold standard.

Using short knee radiographs to predict the coronal alignment after TKA: Is it an accurate proxy for HKA on full-length images?

Background

The postoperative clinical outcomes has been extensively demonstrated to correlate with the coronal alignment after total knee arthroplasty (TKA). However, in different studies, either the hip-knee-ankle angle (HKA) on a full-length radiograph or the femorotibial angle (FTA) on a short knee film was used to categorize the postoperative coronal alignment. Meanwhile, several different FTA ranges were regarded as neutral alignment in different studies. As a result, it is still unknown that how FTA on short knee films and HKA related to each other. The FTA may be able to become an accurate proxy of HKA to predict the coronal alignment. The purpose of this study was to explore the correlation between the FTA and the HKA after TKA and to find the most accurate FTA range.

Methods

About 223 patients were included in this study and standard weight-bearing short knee films as well as full-length radiographs were acquired. The pre- and postoperative FTA, as well as the postoperative anatomical lateral distal femoral angle (aLDFA) and anatomical medial proximal tibial angle (aMPTA) were measured on short knee films by two orthopedic surgeons independently. On full-length films, the pre- and postoperative FTA, the pre- and postoperative HKA, as well as the postoperative mechanical lateral distal femoral angle (mLDFA) and mechanical medial proximal tibial angle (mMPTA) were also recorded by two other surgeons independently. Pearson correlation analysis was performed to compare FTA and HKA, aMTPA and mMTPA, aLDFA and mLDFA, respectively.

Results

The postoperative FTA and HKA had a good correlation (r = 0.86). The agreements were reached 82.7%, 71.0%, and 68.2% of all patients using three previously reported FTA ranges. When analyzing the independent alignment of the tibial tray and the femoral component, 84.1% and 57.9% of all patients was reached an agreement on the classification.

Conclusions

On most occasions, the consistence between the FTA and HKA in assessing the coronal limb alignment of the lower extremity and the tibial component is satisfactory. However, the postoperative full-length film is still needed to evaluate accurately the coronal alignment of the femoral component.

Comminuted periprosthetic distal femoral fractures have greater postoperative extension malalignment

INTRODUCTION

Comminution is a significant aspect of periprosthetic distal femoral fracture characterization and may influence post-surgical outcomes. Existing classification systems that guide treatment decisions do not take into account comminution and current literature is unclear on which surgical approach is optimal. We hypothesize that fractures with comminution will have poorer quality post-reduction alignment, especially with a lateral approach.

MATERIALS AND METHODS

37 study patients were identified with billing codes designating a distal femoral periprosthetic fracture. A retrospective chart review was performed to categorize fractures by absence or presence of comminution and medial parapatellar versus lateral surgical approach. These patients underwent an imaging evaluation for the primary outcome of reduction quality including the anatomic lateral distal femoral angle (LDFA) and the posterior distal femoral angle (PDFA). Differences in radiographic outcomes were analyzed with Wilcoxon/Kruskal-Wallis tests, and analysis by approach was through Fisher's exact test.

RESULTS

Patients with comminuted fractures had significantly greater extension of the fragment (PDFA = 95.4° vs 90.0°, p = 0.018) and similar coronal alignment (LDFA = 85.3° vs 86.3°, p = 0.83) of the knee compared to non-comminuted fractures after surgical reduction. This difference was more prominent amongst those treated with a lateral approach (PDFA = 96.1° vs 89.4°, p = 0.032) than with a medial approach (PDFA = 93.7° vs 91.5°, p = 0.41) (Table 1).

DISCUSSION

Current classification systems and treatment guidelines for periprosthetic distal femoral fractures do not adequately address several issues that may influence treatment outcomes, especially comminution. Comminuted fractures had greater post-reduction extension malalignment, falling outside the recommended PDFA range of 87-90°, especially with a lateral approach. Consideration should be given to surgical approach and techniques to reduce excessive extension when treating comminuted periprosthetic distal femoral fractures.

Implant Malalignment may be a Risk Factor for Poor Patient-Reported Outcomes Measures (PROMs) Following Total Knee Arthroplasty (TKA)

BACKGROUND

Implant malalignment may be a risk factor for poor patient-reported outcomes measures (PROMs) following total knee arthroplasty (TKA).

METHODS

Postoperative surveys were administered to assess PROMs regarding satisfaction, pain, and function in 262 patients who underwent surgery at 4 centers in the U.S. and U.K (average age, 67.2) at a mean 5.5 years after primary TKA. Postoperative distal femoral angle (DFA), proximal tibial angle (PTA), and posterior tibial slope angle (PSA) were radiographically measured, and outliers were recorded. PROMs were compared between patients with aligned versus malaligned knees using univariate analysis.

RESULTS

Patients with DFA, PTA, and PSA outliers were more likely to experience similar or decreased activity levels postoperatively than patients with no alignment outliers, as were patients with 1 or 2 outliers of any kind (P < .05). Patients with DFA, PTA, and PSA outliers were significantly more likely to be dissatisfied with their ability to perform activities of daily living (ADLs), as were patients with 1 or 2 outliers of any kind (P < .05). Patients with DFA and PSA outliers were more likely to be dissatisfied with their degree of pain relief, as were patients with 2 outliers of any kind (P < .05). Finally, patients with DFA and PSA outliers, as well as those with 1 outlier of any kind, were more likely to be dissatisfied with their overall knee function (P < .05).

CONCLUSION

DFA, PTA, and PSA outliers represent a significant risk factor for decreased satisfaction with activities of daily living(ADLs), pain relief, and knee function, as well as decreased activity levels.

LEVEL OF EVIDENCE

Level III.

Osseous Morphological Differences in Knee Osteoarthritis

BACKGROUND

Improved understanding of the morphological characteristics of knees with osteoarthritis (OA) and various deformities can enable personalized implant positioning and balancing in total knee arthroplasty in an effort to continue improving clinical outcomes and optimizing procedural value. Therefore, the purpose of this study was to outline morphological differences in the medial and lateral distal femur and proximal tibia associated with varus and valgus deformities in knee OA.

METHODS

A large computed tomography (CT) database was used to identify 1,158 knees, which were divided into normal and osteoarthritic groups; the latter was further divided on the basis of deformity into neutral, varus, and valgus subgroups. Morphological measurements included the non-weight-bearing hip-knee-ankle angle (nwHKA), mechanical lateral distal femoral angle (mLDFA), medial proximal tibial angle (MPTA), rotation of the posterior condylar axis (PCA) relative to the surgical transepicondylar axis (sTEA), ratio of medial to lateral posterior condylar offset, ratio of medial to lateral condylar radius, medial posterior slope (MPS), lateral posterior slope (LPS), medial coronal slope (MCS), and lateral coronal slope (LCS).

RESULTS

Compared with the normal group, the OA group was in overall varus (nwHKA, -2.2° ± 5.0° compared with -0.2° ± 2.4°) and had a significantly smaller MPS (8.4° ± 4.0° compared with 9.2° ± 4.0°), larger LPS (9.2° ± 3.6° compared with 7.2° ± 3.3°), and smaller MCS (82.1° ± 4.3° compared with 83.9° ± 3.3°). Differences among the OA subgroups were also observed for the MCS and LCS. Compared with the normal group, the sTEA of the OA group was less externally rotated relative to the PCA (0.3° ± 1.5° compared with 1.2° ± 1.9°), and both the condylar offset ratio (1.01 ± 0.06 compared with 1.04 ± 0.07) and the condylar radius ratio (0.98 ± 0.07 compared with 1.03 ± 0.07) were smaller. Only the condylar radius ratio showed differences among the OA subgroups, with valgus deformity associated with a larger ratio.

CONCLUSIONS

An analysis of CT scans of 965 healthy and 193 osteoarthritic knees revealed significant differences in PCA, condylar offset, and condylar radius as well as tibial slope in both the sagittal and coronal planes.

CLINICAL RELEVANCE

There is a strong need to evolve toward a more personalized treatment for osteoarthritic knees that utilizes implants and technology to help tailor total knee arthroplasty on the basis of the patient's morphologic characteristics.

Medial and Lateral Posterior Tibial Slope in the Skeletally Immature: A Cadaveric Study

Background:

An increased posterior tibial slope (PTS) results in greater force on the anterior cruciate ligament (ACL) and is a risk factor for ACL injuries. Biomechanical studies have suggested that a reduction in the PTS angle may lower the risk of ACL injuries. However, the majority of these investigations have been in the adult population.

Purpose:

To assess the mean medial and lateral PTS on pediatric cadaveric specimens without known knee injuries.

Study Design:

Cross-sectional study; Level of evidence, 3.

Methods:

A total of 39 pediatric knee specimens with computed tomography scans were analyzed. Specimens analyzed were between the ages of 2 and 12 years. The PTS of each specimen was measured on sagittal computed tomography slices at 2 locations for the medial and lateral angles. The measurements were plotted graphically by age to account for the variability in development within age groups. The anterior medial and lateral tibial plateau widths were measured. The distance between the top of the tibial plateau and the physis was measured. The independent-samples t test and analysis of variance were used to analyze the measurements.

Results:

The mean PTS angle for the medial and lateral tibial plateaus was 5.53° ± 4.17° and 5.95° ± 3.96°, respectively. The difference between the PTS angles of the medial and lateral tibial plateaus was not statistically significant (P > .05). When plotted graphically by age, no trend between age and PTS was identified.

Conclusion:

This data set offers values for the PTS in skeletally immature specimens without a history of ACL injury and suggests that age may not be an accurate predictive factor for PTS.

Effect of varus alignment on the bone-implant interaction of a cementless tibial baseplate during gait

Component alignment in total knee arthroplasty is a determining factor for implant longevity. Mechanical alignment, which provides balanced load transfer, is the most common alignment strategy. However, a retrospective review found that varus alignment, which could lead to unbalanced loading, can happen in up to 18% of tibial baseplates. This may be particularly burdensome for cementless tibial baseplates, which require low bone-implant micromotion and avoidance of bone overload to obtain bone ingrowth. Our aim was to assess the effect of varus alignment on the bone-implant interaction of cementless baseplates. We virtually implanted 11 patients with knee OA with a modern cementless tibial baseplate in mechanical alignment and in 2° of tibial varus alignment. We performed finite element simulations throughout gait, with loading conditions derived from literature. Throughout the stance phase, varus alignment had greater micromotion and percentage of bone volume at risk of failure than mechanical alignment. At mid-stance, when the most critical conditions occurred, the average increase in peak micromotion and amount of bone at risk of failure due to varus alignment were 79% and 59%, respectively. Varus alignment also resulted in the decrease of the surface area with micromotion compatible with bone ingrowth. However, for both alignments, this surface area was larger than the average area of ingrowth reported for well-fixed implants retrieved post-mortem. Our findings suggest that small varus deviations from mechanical alignment can adversely impact the biomechanics of the bone-implant interaction for cementless tibial baseplates during gait; however, the clinical implications of such changes remain unclear.