A multicenter analysis of axial femorotibial rotation after total knee arthroplasty

Mobile bearing shows larger rollback motion than fixed bearing in total knee arthroplasty using a medial stabilising technique with a navigation system

Purpose

This study aimed to investigate the intraoperative knee kinematics of cruciate-retaining total knee arthroplasty with a medial stabilising technique (MST-TKA) and compare the kinematics between mobile- and fixed-bearing MST-TKAs. We hypothesised that mobile-bearing MST-TKA would result in greater physiological kinematic motion than fixed-bearing MST-TKA.

Methods

Twenty-one and 20 knees underwent mobile- and fixed-bearing MST-TKAs using a navigation system (Orthopilot® ver. 6.0; B. Braun Aesculap), respectively. In the preoperative and postoperative kinematic analysis, the knee was moved manually from 0° to 120°, and femoral anteroposterior translations of the medial femoral condyle (MFC) and lateral femoral condyle (LFC) were recorded every 0.1 s from 0° to 120°. Data were subsequently extracted from the software every 10° of flexion and compared between the two groups, and the correlation coefficients between preoperative and postoperative kinematics were calculated.

Results

In the postoperative analysis, the MFC in the mobile-bearing group showed significant posterior translation at 100°, 110° and 120° compared to the fixed-bearing group (p < 0.01). Similarly, the LFC in the mobile-bearing group showed significant posterior translation at 100°, 110° and 120° compared to the fixed-bearing group (p < 0.05, p < 0.01 and p < 0.05, respectively). In the mobile-bearing group, the preoperative and postoperative anteroposterior translations of the MFC and LFC were correlated (p < 0.01), while in the fixed-bearing group, there was no correlation.

Conclusion

The femoral rollback motion in the mobile-bearing MST-TKA correlated with the preoperative kinematics and was larger than that in the fixed-bearing group.

Level of Evidence

Level II, therapeutic prospective cohort study.

Tibiofemoral articulation and axial tibial rotation of the knee after a cruciate retaining total knee arthroplasty

PURPOSE

Numerous research has reported that total knee arthroplasty (TKA) cannot reproduce axial tibial rotations of normal knees. The objective of this study was to measure the tibiofemoral articular contact motions and axial tibial rotations of TKA knees to investigate the mechanism causing the knee kinematics change of after TKAs.

METHODS

Eleven patients with unilateral cruciate retaining (CR) TKA were tested for measurements of knee motion during a weight-bearing flexion from 0° to 105° using an imaging technique. The tibiofemoral contact kinematics were determined using the contact points on medial and lateral surfaces of the tibia and femoral condyles. Axial tibial rotations were calculated using the differences between the medial and lateral articulation distances on the femoral condyles and tibial surfaces at each flexion interval of 15°.

RESULTS

On femoral condyles, articular contact distances are consistently longer on the medial than on the lateral sides (p < 0.05) up to 60° of flexion, corresponding to internal tibial rotations (e.g., 1.3° ± 1.0° at 15-30° interval). On tibial surfaces, the articular contact point on the medial side moved more posteriorly than on the lateral side at low flexion angles, corresponding to external tibial rotations (e.g., -1.4° ± 1.8° at 15-30° interval); and more anteriorly than on the lateral sides at mid-range flexion, corresponding to internal tibial rotations (e.g., 0.8° ± 1.7° at 45-60° interval). At higher flexion, articular motions on both femoral condyles and tibial surfaces caused minimal changes in tibial rotations.

CONCLUSIONS

These results indicate that the axial tibial rotations of these TKA knees were mainly attributed to asymmetric articulations on the medial and lateral femoral condyles and tibial surfaces. The data can help understand the mechanisms causing axial tibial rotations of TKA knees and help improve implant designs for restoration of normal knee kinematics.

Knee kinematics are not different between asymmetrical and symmetrical tibial baseplates in total knee arthroplasty: A fluoroscopic analysis of step-up and lunge motions

PURPOSE

This clinical fluoroscopy study investigated knee kinematics of two different cemented fixed-bearing, posterior-stabilised (PS) total knee arthroplasty (TKA) designs: an asymmetric tibial component including an asymmetric insert designed to optimise personalised balance and fit and its precursor symmetrical design with symmetric insert.

METHODS

A consecutive series of patients (16 TKAs from each treatment group) participating in a randomised controlled trial comparing TKA migration was included. The exclusion criterion was the use of walking aids. Flat-panel fluoroscopic recordings of step-up and lunge motions were acquired 1-year postoperatively. Medial and lateral contact points (CPs) were determined to calculate CP displacement, femoral axial rotation and pivot position. Using linear mixed-effects modelling techniques, kinematics between TKA designs were compared.

RESULTS

During knee extension between 20° flexion and full extension, the CPs moved anteriorly combined with a small internal femoral rotation (a screw-home mechanism). Whereas CP movement was reversed: femoral rollback, external femoral rotation while flexing the knee between full extension and 20° knee flexion, At larger flexion angles, femoral axial rotation (FAR) occurred around a lateral pivot point both during step-up and lunge. The symmetric design had a 2.3° larger range of FAR compared to the asymmetric design during lunge (p = 0.02). All other kinematics were comparable.

CONCLUSION

Despite the differences in design, this study showed that the asymmetric and symmetric PS TKA designs had mostly comparable knee kinematics during step-up and lunge motions. It is therefore expected that the functionality of the successor TKA design is similar to that of its precursor design.

LEVEL OF EVIDENCE

Level II, prospective comparative study.

Mid-term outcomes of a kinematically designed cruciate retaining total knee arthroplasty

BACKGROUND

Advances in implant material and design have allowed for improvements in total knee arthroplasty (TKA) outcomes. A cruciate retaining (CR) TKA provides the least constraint of TKA designs by preserving the native posterior cruciate ligament. Limited research exists that has examined clinical outcomes or patient reported outcome measures (PROMs) of a large cohort of patients undergoing a CR TKA utilizing a kinematically designed implant. It was hypothesized that the studied CR Knee System would demonstrate favorable outcomes and a clinically significant improvement in pain and functional scores.

AIM

To assess both short-term and mid-term clinical outcomes and PROMs of a novel CR TKA design.

METHODS

A retrospective, multi-surgeon study identified 255 knees undergoing a TKA utilizing a kinematically designed CR Knee System (JOURNEY™ II CR; Smith and Nephew, Inc., Memphis, TN) at an urban, academic medical institution between March 2015 and July 2021 with a minimum of two-years of clinical follow-up with an orthopedic surgeon. Patient demographics, surgical information, clinical outcomes, and PROMs data were collected via query of electronic medical records. The PROMs collected in the present study included the Knee Injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS JR) and Patient-Reported Outcomes Measurement Information System (PROMIS®) scores. The significance of improvements in mean PROM scores from preoperative scores to scores collected at six months and two-years postoperatively was analyzed using Independent Samples t-tests.

RESULTS

Of the 255 patients, 65.5% were female, 43.8% were White, and patients had an average age of 60.6 years. Primary osteoarthritis (96.9%) was the most common primary diagnosis. The mean surgical time was 105.3 minutes and mean length of stay was 2.1 d with most patients discharged home (92.5%). There were 18 emergency department (ED) visits within 90 d of surgery resulting in a 90 d ED visit rate of 7.1%, including a 2.4% orthopedic-related ED visit rate and a 4.7% non-orthopedic-related ED visit rate. There were three (1.2%) hospital readmissions within 90 d postoperatively. With a mean time to latest follow-up of 3.3 years, four patients (1.6%) required revision, two for arthrofibrosis, one for aseptic femoral loosening, and one for peri-prosthetic joint infection. There were significant improvements in KOOS JR, PROMIS Pain Intensity, PROMIS Pain Interference, PROMIS Mobility, and PROMIS Physical Health from preoperative scores to six month and two-year postoperative scores.

CONCLUSION

The evaluated implant is an effective, novel design offering excellent outcomes and low complication rates. At a mean follow up of 3.3 years, four patients required revisions, three aseptic and one septic, resulting in an overall implant survival rate of 98.4% and an aseptic survival rate of 98.8%. The results of our study demonstrate the utility of this kinematically designed implant in the setting of primary TKA.

Measurement of Condylar Offset and Posterior Condylar Cartilage Thickness in Normal Knees: An MRI Study From Saudi Arabia

Background The maximum amount of knee flexion after total knee replacement is largely determined by the knee's posterior condylar offset (PCO). Using magnetic resonance imaging (MRI), this study examined the relationship between PCO and the thickness of the femoral posterior condylar cartilage (PCC) in healthy people. Methodology We reviewed the medical records of 300 skeletally mature patients who did not exhibit symptoms of knee arthritis and had undergone MRI for traumatic soft tissue knee injuries that did not affect the femoral PCC. Results The study cohort consisted of 300 participants, of whom 68.3% (205) were male, and 31.7% (95) were female aged between 18 and 59 years, with a mean age of 31.13 ± 8.83 years. Most participants were under 30 years of age (45.7%), and the mean body mass index was 27.52 ± 5.64 kg/m2. The total medial distance was 28.50 ± 3.11 mm, ranging from 21.20 to 39.80 mm. The medial PCC was 1.71 ± 0.63 mm, ranging from 0.60 to 4.00 mm. The medial bony PCO was 38.40 mm, ranging from 18.80 to 38.40 mm. The total lateral distance was 25.24 ± 3.16 mm, ranging from 13.50 to 34.90 mm. The lateral PCC was 1.48 ± 0.75 mm, ranging from 0.30 to 10.70 mm. Finally, the lateral bony PCO was 23.76 ± 3.19 mm, ranging from 11.99 to 32.8 mm. There was a statistically significant weak positive relationship between the bony lateral PCO and the patients' age in females only (p = 0.016; r = 0.00-0.39). There was a statistically significant mean difference in the total medial distance, medial PCC, and lateral PCC between the two knees (p < 0.05). Conclusions These findings shed light on the factors influencing these parameters, offer insightful information about the associations between particular patient characteristics and knee measurements, and may help guide clinical evaluations and treatment decisions.

The morphology of the femoral posterior condyle affects the external rotation of the femur

PURPOSE

The purpose of this study was to identify factors related to the external rotation of the femur during knee flexion.

METHODS

Three-dimensional (3D) digital models of the femur and tibia were reconstructed from computed tomography images of 41 healthy Japanese subjects. Thirteen parameters related to femoral and tibial morphology and alignment of the lower extremities were evaluated, including the inclination angle of the posterior lateral and medial femoral condyles, the ratio of the medial and lateral posterior condyle radii approximated as spheres, the spherical condylar angle, the posterior condylar angle, the medial and lateral posterior tibial slope, the difference of medial and lateral posterior tibial slope, the tibiofemoral rotation angle, the 3D femorotibial angle, the 3D hip-knee-ankle angle, and the passing point of the weight-bearing line (medial-lateral and anterior-posterior). The rotation angle of the femur relative to the tibia during squatting was investigated using a 3D to 2D image matching technique and the relationships with the13 parameters were determined.

RESULTS

The femur externally rotated substantially up to 20° of knee flexion (9.2° ± 3.7°) and gently rotated after 20° of knee flexion (12.8° ± 6.2°). The external rotation angle at 20°-120° of knee flexion correlated with the spherical condylar angle, the tibiofemoral rotation angle and the inclination angle of the posterior medial condyles (correlation coefficient; 0.506, 0.364, 0.337, respectively).

CONCLUSION

The parameter that was most related to the external rotation of the femur during knee flexion was the spherical condylar angle.

LEVEL OF EVIDENCE

IV.

Wider translations and rotations in posterior-stabilised mobile-bearing total knee arthroplasty compared to fixed-bearing both implanted with mechanical alignment: a dynamic RSA study

PURPOSE

The purpose of this study was to investigate the in vivo kinematics of the same femoral design mechanically aligned posterior-stabilised (PS) total knee arthroplasty (TKA) with either fixed-bearing (FB) or mobile-bearing (MB) inlay, implanted by the same surgeon, using model-based dynamic radiostereometric analysis (RSA). The hypothesis of the present study was that the MB design would show wider axial rotation than the FB design, without affecting the clinical outcomes.

MATERIALS AND METHODS

A cohort of 21 non-randomised patients (21 DePuy Attune PS-FB) was evaluated by dynamic RSA analysis at a minimum 9-month follow-up, while performing differently demanding daily living activities such as sit to stand (STS) and deep knee lunge (DKL). Kinematic data were compared with those of a cohort of 22 patients implanted with the same prosthetic design but with MB inlay. Anterior-posterior (AP) translations, varus-valgus (VV) and internal-external (IE) rotations of the femoral component with respect to the tibial baseplate were investigated. Translation of medial and lateral compartment was analysed using the low point method according to Freeman et al. Questionnaires to calculate objective and subjective clinical scores were administered preoperatively and during follow-up visit by the same investigator.

RESULTS

The FB TKA design showed lower AP translation during STS (6.8 ± 3.3 mm in FB vs 9.9 ± 3.7 mm in MB, p = 0.006*), lower VV rotation (1.9 ± 0.8° in FB vs 5.3 ± 3.3° in MB, p = 0.005) and lower IE rotation (2.8 ± 1.1° in FB vs 9.5 ± 4.3° in MB, p = 0.001) during DKL than the mobile-bearing TKA design. Posterior-stabilised FB group showed significant lower translation of the low point of the medial compartment than the MB group (p = 0.008). The percentage of patients performing medial pivot in the FB group was higher compared to MB group in the examined motor tasks. No significant differences in post-operative range of motion (117° ± 16° for FB group and 124° ± 13° for MB group) and in clinical outcomes emerged between the two cohort.

CONCLUSIONS

The FB and MB designs differed in AP translations, VV rotations and IE rotations of the femoral component with respect to the tibial component in STS and DKL. Furthermore, FB cohort reported a significant higher percentage of medial pivot with respect to MB cohort. Despite this, no differences in clinical outcomes were detected between groups. Both designs showed stable kinematics and represent a viable option in primary TKA.

LEVEL OF EVIDENCE

Prospective cohort study, II.

Postoperative Medial Tilting of the Joint Line and Preoperative Kinematics Influence Postoperative Medial Pivot Pattern Reproduction in Total Knee Arthroplasty

Background

Reproducing the medial pivot pattern after total knee arthroplasty (TKA) is known to improve patient satisfaction. However, the factors affecting the postoperative medial pivot pattern in TKA are controversial. The purpose of this study was to examine the factors affecting the postoperative medial pivot pattern in posterior-stabilized TKA.

Methods

This study involved 30 cases with knee osteoarthritis who underwent primary posterior-stabilized TKA. The preoperative and postoperative kinematics were measured using a computed tomography-free navigation system, and the patients were divided into the following 2 groups: the medial pivot pattern (MP) group and non-medial pivot pattern (non-MP) group. In addition, we measured each of the following angles on X-ray films (preoperative and postoperative femorotibial angle, hip-knee-ankle angle, mechanical lateral distal femoral angle, medial proximal tibial angle). We examine the factors affecting the postoperative medial pivot pattern.

Results

There were 14 cases in the MP group and 16 cases in the non-MP group at the preoperative knee kinematic assessment and 17 cases in the MP group and 13 cases in the non-MP group at the postoperative knee kinematic assessment. The preoperative kinematic pattern was conserved after the surgery at a rate of 76.7%. The postoperative MP-group showed a significantly smaller preoperative femorotibial angle and hip-knee-ankle and a significantly smaller postoperative mechanical lateral distal femoral angle and medial proximal tibial angle in comparison to the postoperative non-MP group.

Conclusions

Preoperative kinematics and postoperative mechanical lateral distal femoral angle and medial proximal tibial angle may be important factors that affect the postoperative medial pivot pattern.

Larger Medial Contact Area and More Anterior Contact Position in Medial-Pivot than Posterior-Stabilized Total Knee Arthroplasty during In-Vivo Lunge Activity

This study aimed to compare the in-vivo kinematics and articular contact status between medial-pivot total knee arthroplasty (MP-TKA) and posterior stabilized (PS) TKA during weight-bearing single-leg lunge. 16 MP-TKA and 12 PS-TKA patients performed bilateral single-leg lunges under dual fluoroscopy surveillance to determine the in-vivo six degrees-of-freedom knee kinematics. The closest point between the surface models of the femoral condyle and the polyethylene insert was used to determine the contact position and area. The nonparametric statistics analysis was performed to test the symmetry of the kinematics between MP-TKA and PS-TKA. PS-TKA demonstrated a significantly greater range of AP translation than MP-TKA during high flexion (p = 0.0002). Both groups showed a significantly greater range of lateral compartment posterior translation with medial pivot rotation. The contact points of PS-TKA were located significantly more posterior than MP-TKA in both medial (10°–100°) and lateral (5°–40°, 55°–100°) compartments (p < 0.0500). MP-TKA had a significantly larger contact area in the medial compartment than in the lateral compartment. In contrast, no significant differences were observed in PS-TKA. The present study revealed no significant differences in clinical outcomes between the MP and PS groups. The PS-TKA demonstrated significantly more posterior translations than MP-TKA at high flexion. The contact points are located more posteriorly in PS-TKA compared with MP-TKA. A larger contact area and medial pivot pattern during high flexion in MP-TKA indicated that MP-TKA provides enhanced medial pivot rotation.

The James A. Rand Young Investigator's Award: Increased Revision Risk With Mobile Bearings in Total Knee Arthroplasty: An Analysis of the American Joint Replacement Registry

BACKGROUND

Mobile-bearing (MB) total knee arthroplasty (TKA) may reduce wear and improve patellar tracking but may increase revision risk due to tibial component design, balance complexity, and bearing dislocation. We utilized the American Joint Replacement Registry to examine risk of revision with MB compared to fixed-bearing (FB) designs.

METHODS

An analysis of primary TKA in patients over 65 years was performed with American Joint Replacement Registry data linked to Centers for Medicare and Medicaid Services data from 2012 to 2019. Analyses compared MB to FB designs with a subanalysis of implants from a single company. We identified 485,024 TKAs, with 452,199 (93.2%) FB-TKAs and 32,825 (6.8%) MB-TKAs. Cox proportional hazards regression modeling was used for all-cause revision and revision for infection, adjusting for sex, age, and competing risk of mortality. Event-free survival curves evaluated time to all-cause revision and revision for infection.

RESULTS

MB-TKAs were at an increased risk for all-cause revision: hazard ratio (HR) 1.36 ([95% confidence interval (CI) 1.24-1.49], P < .0001) but not revision for infection: HR 1.06 ([95% CI 0.90-1.25], P = .52). When comparing implants within a single company, MB-TKAs were at an increased risk of all-cause revision: HR 1.55 ([95% CI 1.38-1.73], P < .0001). Event-free survival curves demonstrated increased risk for all-cause revision for MB-TKA across all time points, with a greater magnitude of risk up to 8 years.

CONCLUSION

Although survivorship of both designs was outstanding, MB-TKA designs demonstrated increased risk for all-cause revision. Additional investigation is needed to determine if this is related to patient selection factors, surgical technique, bearing, or implant design.

Kinematic function of knee implant designs across a range of daily activities

The aim of this randomized controlled trial was to measure and compare six-degree-of-freedom (6-DOF) knee joint motion of three total knee arthroplasty (TKA) implant designs across a range of daily activities. Seventy-five TKA patients were recruited to this study and randomly assigned a posterior-stabilized (PS), cruciate-retaining (CR), or medial-stabilized (MS) implant. Six months after surgery, patients performed five activities of daily living: level walking, step-up, step-down, sit-to-stand, and stand-to-sit. Mobile biplane X-ray imaging was used to measure 6-DOF knee kinematics and the center of rotation of the knee in the transverse plane for each activity. Mean 6-DOF knee kinematics were consistently similar for PS and CR, whereas MS was more externally rotated and abducted, and lateral shift was lower across all activities. Peak-to-peak anterior drawer for MS was also significantly lower during walking, step-up, and step-down (p < 0.017). The center of rotation of the knee in the transverse plane was located on the medial side for MS, whereas PS and CR rotated about the lateral compartment or close to the tibial origin. The kinematic function of MS was more similar to that of the healthy knee than PS and CR based on reduced paradoxical anterior translation at low flexion angles and a transverse center of rotation located in the medial compartment. Overall, 6-DOF knee joint motion for PS and CR were similar across all daily activities, whereas that measured for MS was appreciably different. The kinematic patterns observed for MS reflects a highly conforming medial articulation in the MS design.

Posterior-Stabilized Versus Cruciate-Retaining Prostheses for Total Knee Arthroplasty: An Overview of Systematic Reviews and Risk of Bias Considerations

Background

Numerous systematic reviews have been published comparing the outcomes of patients undergoing posterior stabilized (PS) versus cruciate-retaining (CR) procedures in total knee arthroplasty (TKA), but with some overlaps and contradictions. The objectives of this study were (1) to perform an overview of current systematic reviews comparing PS versus CR in TKA, by evaluating their methodological quality and risk of bias, and (2) to provide recommendations through the best evidence.

Methods

A systematic search of systematic reviews comparing PS and CR in TKA, published until June 2021 was conducted using the MEDLINE, EMBASE, and Cochrane Library databases. Included systematic reviews were assessed for methodological quality and risk of bias by the AMSTAR2 instrument and ROBIS tool, respectively. The choice of best evidence was conducted according to the Jadad decision algorithm.

Results

A total of eight systematic reviews were eligible for inclusion in this study. The Jadad decision algorithm suggested that reviews with the highest AMSTAR2 scores should be selected. According to the ROBIS tool, there were three reviews with a low risk of bias and five with a high risk of bias. Consequently, one systematic review conducted by Verra et al. with the highest AMSTAR2 score and low risk of bias was selected as the best evidence.

Conclusions

Although current systematic reviews demonstrated some statistical differences in clinical presentation and functional outcomes between PS and CR, the current outcome indicators cannot be taken to provide recommendations for undergoing PS or CR. The decision for prosthesis selection could be made mostly based on the surgeon's preference, indications and other indicators.

In vivo knee kinematics of an innovative prosthesis design

Up to 20% of patients after total knee arthroplasty (TKA) are not satisfied with the result. Several designs of new implants try to rebuild natural knee kinematics. We hypothesized that an innovative implant design leads to better results concerning femoral rollback compared to an established implant design. For this pilot study, 21 patients were examined during TKA, receiving either an innovative (ATTUNE^TM Knee System (DePuy Inc.), n = 10) or an established (PFC^TM (DePuy Inc.), n = 11) knee system. All patients underwent computer navigation. Knee kinematics was assessed after implantation. Outcome measure was anterior–posterior translation between femur and tibia. We were able to demonstrate a significantly higher femoral rollback in the innovative implant group (p < 0.001). The mean rollback of the innovative system was 11.00 mm (95%-confidence interval [CI], 10.77–11.24), of the established system 8.12 mm (95%-CI, 7.84–8.42). This study revealed a significantly increased lateral as well as medial femoral rollback of knees with the innovative prosthesis design. Our intraoperative finding needs to be confirmed using fluoroscopic or radiographic three-dimensional matching under full-weight-bearing conditions after complete recovery from surgery.

Gait and Knee Flexion In Vivo Kinematics of Asymmetric Tibial Polyethylene Geometry Cruciate Retaining Total Knee Arthroplasty

The preservation of the posterior cruciate ligament in cruciate retaining (CR) total knee arthroplasty (TKA) designs has the potential to restore healthy knee biomechanics; however, concerns related to kinematic asymmetries during functional activities still exist in unilateral TKA patients. As there is a limited data available regarding the ability of the contemporary CR TKA design with concave medial and convex lateral tibial polyethylene bearing components to restore healthy knee biomechanics, this study aimed to investigate in vivo three-dimensional knee kinematics in CR TKA patients during strenuous knee flexion activities and gait. Using a combined computer tomography and dual fluoroscopic imaging system approach, in vivo kinematics of 15 unilateral CR TKA patients (comparison of replaced and contralateral nonreplaced knee) were evaluated during sit-to-stand, step-ups, single-leg deep lunge, and level walking. The patient cohort was followed-up at an average of 24.5 months ( ± 12.6, range 13-42) from surgical procedure. Significantly smaller internal knee rotation angles were observed for the contemporary CR TKA design during step-ups (2.6 ± 5.8 vs. 6.3 ± 6.6 degrees, p < 0.05) and gait (0.6 ± 4.6 vs. 6.3 ± 6.8 degrees, p < 0.05). Significantly larger proximal and anterior femoral translations were measured during sit-to-stand (34.7 ± 4.5 vs. 29.9 ± 3.1 mm, p < 0.05; -2.5 ± 2.9 vs. -8.1 ± 4.4 mm, p < 0.05) and step-ups (34.1 ± 4.5 vs. 30.8 ± 2.9 mm, p < 0.05; 2.2 ± 3.2 vs. -3.5 ± 4.5 mm, p < 0.05). Significantly smaller ranges of varus/valgus and internal/external rotation range of motion were observed for CR TKA, when compared with the nonoperated nee, during strenuous activities and gait. The preservation of the posterior cruciate ligament in the contemporary asymmetric bearing geometry CR TKA design with concave medial and convex lateral tibial polyethylene bearing components has the potential to restore healthy knee biomechanics; however, the study findings demonstrate that native knee kinematics were not fully restored in patients with unilateral asymmetric tibial polyethylene bearing geometry CR TKA during functional activities.

Impact of femoro-tibial size combinations and TKA design on kinematics

INTRODUCTION

The variability in patients' femoral and tibial anatomy requires to use different tibia component sizes with the same femoral component size. These size combinations are allowed by manufacturers, but the clinical impact remains unclear. Therefore, the goals of our study were to investigate whether combining different sizes has an impact on the kinematics for two well-established knee systems and to compare these systems' kinematics to the native kinematics.

MATERIALS AND METHODS

Six fresh frozen knee specimens were tested in a force controlled knee rig before and after implantation of a cruciate retaining (CR) and a posterior-stabilized (PS) implant. Femoro-tibial kinematics were recorded using a ultrasonic-based motion analysis system while performing a loaded squat from 30° to 130°. In each knee, the original best fit inlay was then replaced by different inlays simulating a smaller or bigger tibia component. The kinematics obtained with the simulated sizes were compared to the original inlay kinematics using descriptive statistics.

RESULTS

For all size combinations, the difference to the original kinematics reached an average of 1.3 ± 3.3 mm in translation and - 0.1 ± 1.2° in rotation with the CR implant. With the PS implant, the average differences reached 0.4 ± 2.7 mm and  - 0.2 ± 0.8°. Among all knees, no size combination consistently resulted in significantly different kinematics. Each knee showed a singular kinematic pattern. For both knee systems, the rotation was smaller than in the native knee, but the direction of the rotation was preserved. The PS showed more rollback and the CR less rollback than the native knee.

CONCLUSION

TKA systems designed with a constant tibio-femoral congruency among size combinations should enable to combine different sizes without having substantial impact on the kinematics. The rotational pattern was preserved by both TKA systems, while the rollback could only be maintained by the PS design.

Biomechanics and Outcomes of Modern Tibial Polyethylene Inserts

PURPOSE OF REVIEW

There have been many attempts to use variations in tibial polyethylene design to better recreate normal knee kinematics in the total knee arthroplasty. The goal of this review is to provide an overview of the various types of tibial inserts that exist and review the theoretical mechanics versus what was demonstrated in vivo.

RECENT FINDINGS

Many polyethylene inserts have been attempted to re-create normal knee kinematics, but none have been able to successfully do so. Previously the only two types of inserts were posterior stabilized (PS) and cruciate retaining (CR) polyethylene inserts. Both of these have shown excellent long-term survival but neither has demonstrated native kinematics. Initially, it was thought that retention of the posterior cruciate ligament (PCL) would allow for more native kinematics, but fluoroscopic evidence has shown that the PCL alone cannot accomplish this. Newer inserts try to restore femoral roll back and the screw home mechanism. The bicruciate retaining total knee inserts are having the most "normal" kinematics, suggesting the importance of both the ACL and PCL in knee biomechanics. Modern polyethylene inserts show favorable short-term data with bicruciate retaining inserts having the best kinematics; however, long-term studies are still needed to determine if survivorship and patient outcomes remain favorable.

Postoperative Valgus Laxity and Medial Pivot Kinematics Are Significantly Associated With Better Clinical Outcomes

BACKGROUND

The relative impact of soft tissue balance and knee laxity on clinical outcomes after total knee arthroplasty (TKA) is not fully understood. We analyzed associations among knee laxity, kinematics, and patient-reported outcomes.

METHODS

Knee Society Scores were recorded in 67 patients before and after primary TKA for osteoarthritis with varus deformity (N = 78). Varus and valgus laxity was measured in 78 knees using stress radiographs. Knee kinematics were measured fluoroscopically during stair ascent in 16 knees.

RESULTS

On average, varus laxity decreased significantly, and valgus laxity increased significantly after TKA, although the net combined varus-valgus laxity did not change significantly. Postoperatively, the magnitude of valgus laxity correlated significantly with greater patient symptoms and satisfaction scores. Patients with medial pivot kinematics scored higher on patient satisfaction and standard activities.

CONCLUSION

We found that postoperative valgus laxity and medial pivot kinematics were significantly associated with better clinical outcomes. These results emphasize the importance of careful preoperative planning and attention to intraoperative alignment and ligament balancing.

Selective Iliotibial Band Release for Iliotibial Band Traction Syndrome After Second-Generation Motion-Guided Bicruciate Stabilizing Total Knee Arthroplasty and Its Rationale: A Case Report With Review of Literature

Iliotibial band traction syndrome (ITBTS) after total knee arthroplasty (TKA) has been well documented following first-generation guided motion bicruciate substituting (BCS) TKA. The incidence of ITBTS following second-generation BCS has been found to be rare, and surgical release of the IT band has not been reported. A 64-year old male was diagnosed with ITBTS following second-generation guided motion BCS TKA. After a three-month trial of non-surgical treatment, he underwent selective open release of the iliotibial band (ITB), which successfully relieved his symptoms. Orthopedic surgeons should keep ITBTS as a possible differential diagnosis when evaluating the lateral-sided knee pain following guided motion BCS TKA.

Bicompartmental, medial and patellofemoral knee replacement might be able to maintain unloaded knee kinematics

INTRODUCTION

Unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) are standard procedures for treating knee joint arthritis. Neither UKA nor TKA seems to be optimally suited for patients with bicompartmental osteoarthritis that affects only the medial and patellofemoral compartments. A bicompartmental knee arthroplasty (BKA) was designed for this patient group. This study aimed to compare the effectiveness of a BKA and TKA in restoring the kinematics of the knee joint.

MATERIALS AND METHODS

In this in vitro study, three types of knee arthroplasties (BKA, posterior cruciate ligament-retaining, and posterior cruciate ligament-resecting TKA) were biomechanically tested in six freshly frozen human cadaveric specimens. Complete three-dimensional kinematics was analyzed for each knee arthroplasty during both passive and loaded conditions in a validated knee kinematics rig. Infrared motion capture cameras and retroreflective markers were used for recording data.

RESULTS

No significant differences could be found between the three types of arthroplasties. However, similar kinematic changes between BKA and a native knee joint were documented under passive conditions. However, in a weight-bearing mode, a significant decrease in femoral rotation during the range of motion was found in arthroplasties compared to the native knee, probably caused by contraction of the quadriceps femoris muscle, which leads to a decrease in the anterior translation of the tibia.

CONCLUSIONS

Kinematics similar to that of the natural knee can be achieved by BKA under passive conditions. However, no functional advantage of BKA over TKA was detected, which suggests that natural knee kinematics cannot be fully imitated by an arthroplasty yet. Further prospective studies are required to determine the anatomic and design factors that might affect the physiologic kinematics.

Obtaining anatomic motion and laxity characteristics in a total knee design

BACKGROUND

Since the introduction of the first total knee designs, a frequent design goal has been to reproduce normal knee motion. However, studies of many currently used total knee designs, have shown that this goal has not been achieved. We proposed that Guided Motion total knee designs, could achieve more anatomic motion than present standard designs.

METHODS

Several Guided Motion knees for application without cruciate ligaments were designed using a computer method where the bearing surfaces were generated by the motion required. A knee testing machine was constructed where physiological forces including compressive, shear and torque were applied during knee flexion. The neutral path of motion and the laxity about the neutral path were measured. This evaluation method was a modification of the ASTM standard Constraint Test.

RESULTS

The motions of the Guided Motion knees and a standard PS knee were compared with the anatomic motion of knee specimens determined in an earlier study The Guided Motion knees showed motion patterns which were closer to anatomic than the PS knee.

CONCLUSIONS

The results provided justification for carrying out further evaluations of functional conditions, using either knee simulators or computer modelling. If anatomic motions could be reproduced in vivo, it is possible that clinical outcomes could be improved.

Kinematics and kinetics comparison of ultra-congruent versus medial-pivot designs for total knee arthroplasty by multibody analysis

Nowadays, several configurations of total knee arthroplasty (TKA) implants are commercially available whose designs resulted from clinical and biomechanical considerations. Previous research activities led to the development of the so-called medial-pivot (MP) design. However, the actual benefits of the MP, with respect to other prosthesis designs, are still not well understood. The present work compares the impact of two insert geometries, namely the ultra-congruent (UC) and medial-pivot (MP), on the biomechanical behaviour of a bicondylar total knee endoprosthesis. For this purpose, a multibody model of a lower limb was created alternatively integrating the two implants having the insert geometry discretized. Joint dynamics and contact pressure distributions were evaluated by simulating a squat motion. Results showed a similar tibial internal rotation range of about 3.5°, but an early rotation occurs for the MP design. Furthermore, the discretization of the insert geometry allowed to efficiently derive the contact pressure distributions, directly within the multibody simulation framework, reporting peak pressure values of 33 MPa and 20 MPa for the UC and MP, respectively. Clinically, the presented findings confirm the possibility, through a MP design, to achieve a more natural joint kinematics, consequently improving the post-operative patient satisfaction and potentially reducing the occurrence of phenomena leading to the insert loosening.

Effect of weight-bearing in bicruciate-retaining total knee arthroplasty during high-flexion activities

BACKGROUND

To evaluate the effect of weight-bearing on the kinematics of the bicruciate-retaining total knee arthroplasty design during high knee flexion activities.

METHODS

The kinematics of 21 bicruciate-retaining total knee arthroplasties were evaluated under fluoroscopy, with two- and three-dimensional image registrations, during squatting (weight-bearing) and active-assisted knee flexion (non-weight-bearing). The following variables were measured: knee range of motion, axis of femoral rotation and varus-valgus angle relative to the tibial component, anteroposterior translation of the medial and lateral contact points, and the kinematic pathway of the joint surfaces.

FINDINGS

From 20° to 100° of flexion, the femoral external rotation during weight-bearing was larger than that during non-weight-bearing. There were no differences in the varus-valgus angles between the two conditions. From 10° to 50° of flexion, the medial contact point during weight-bearing was located posterior to the point of contact during non-weight-bearing; this difference between the two weight-bearing conditions was significant. From 0° to 90° of flexion, the lateral contact point in weight-bearing was located posterior to the contact point in non-weight-bearing; this difference between the two weight-bearing conditions was also significant.

INTERPRETATION

The anteroposterior position of the medial and lateral contact points of the bicruciate-retaining total knee arthroplasty design was significantly more posterior in the mid-range of knee flexion in weight-bearing than in non-weight-bearing. However, no anterior translation of the bicruciate-retaining total knee arthroplasty design was observed. Therefore, bicruciate-retaining total knee arthroplasty appears to have good anteroposterior stability throughout the range of knee flexion, regardless of the weight-bearing condition.

Anatomic vs Dome Patella: Is There a Difference Between Fixed- vs Mobile-Bearing Posterior-Stabilized Total Knee Arthroplasties?

BACKGROUND

It has been hypothesized that the patella, working in conjunction with both medial and lateral femoral condyles, can influence kinematic parameters such as posterior femoral rollback and axial rotation. The objective of this study is to determine the in vivo kinematics of subjects implanted with a fixed-bearing (FB) or mobile-bearing (MB) posterior-stabilized (PS) total knee arthroplasty (TKA), with a specific focus on evaluating the impact that Anatomic and Medialized Dome patellar components have on tibiofemoral kinematic patterns.

METHODS

Tibiofemoral kinematics were assessed for 40 subjects; 20 with an anatomic patella and 20 with a dome patella. Within these groups, 10 subjects received an FB PS TKA and 10 subjects received an MB PS TKA. All subjects were analyzed using fluoroscopy while performing a deep knee bend activity. Kinematics were collected during specific intervals to determine similarities and differences in regard to patella and bearing type.

RESULTS

The greatest variation in kinematics was detected between the 2 Anatomic patellar groups. Specifically, the MB-Anatomic subjects experienced greater translation of the lateral condyle, the highest magnitude of axial rotation, and the highest range of motion compared to the FB-Anatomic subjects. Subjects with a Dome Patella displayed much variability among the average kinematics, with all parameters between FB and MB cohorts being similar.

CONCLUSION

The findings in this study suggest that subjects with an Anatomic patellar component could have more normal kinematic patterns with an MB PS TKA as opposed to an FB PS TKA, while subjects with a Dome patella could achieve similar kinematics regardless of TKA type.

Optimal designs and surgical technique for hip and knee joint replacement: The best is yet to come!

Over the last three decades, there have been significant advancements in knee and hip replacement technology. The implants and the surgical technology we now have to aid in their implantation are advancing and improving functional outcomes and survivorship. Despite these advancements, there are still issues with patient satisfaction, functional limitations, and early revisions due to instability and aseptic loosening. This article reviews the state of current technology in hip and knee replacement implant design and surgical technique, and reviews some of the current implant designs and surgical technologies that may be able to solve some of the most common issues in the knee and hip replacement surgery.

Kinematics of bicruciate and posterior stabilized total knee arthroplasty during deep knee flexion and stair climbing

Second-generation bicruciate stabilized (BCS) total knee arthroplasty (TKA) was developed to substitute both anterior and posterior cruciate ligaments and replicate physiological kinematics. This study aimed to evaluate if the postcam mechanism and the surface geometry function effectively. Seventeen and twelve knees implanted with BCS TKA and posterior stabilized (PS) TKA, respectively, were analyzed. In vivo kinematics during deep knee flexion were estimated from single-plane fluoroscopic images using a 2-dimensional to 3-dimensional image registration technique. Flexion angle, anteroposterior translation, femoral external rotation (ER), and postcam engagement were compared between the groups. Postoperative 2011 Knee Society Score (KSS) was obtained at the last follow-up. The medial femoral condyle in BCS was positioned more anteriorly than that in PS from minimum flexion to maximum flexion. Posterior motion of the lateral femoral condyle was observed in both groups. ER of BCS was significantly larger compared to PS from minimum flexion to 100°. However, the amount of ER from minimum flexion to maximum flexion was similar: 6.2° ± 4.5° and 7.7° ± 4.1° in BCS and PS, respectively (P = .364). Anterior postcam engagement was observed in 76.5% and 25.0% in BCS and PS, respectively (P = .006). Posterior postcam engagement was observed in all cases in BCS and PS. There were no significant differences in KSS between the groups. The kinematic differences were likely a result of variations in articular surface geometry.

In Vivo Knee Kinematics: How Important Are the Roles of Femoral Geometry and the Cruciate Ligaments?

BACKGROUND

While posterior cruciate-retaining (PCR) implants are a more common total knee arthroplasty (TKA) design, newer bicruciate-retaining (BCR) TKAs are now being considered as an option for many patients, especially those that are younger. While PCR TKAs remove the ACL, the BCR TKA designs keep both cruciate ligaments intact, as it is believed that the resection of the ACL greatly affects the overall kinematic patterns of TKA designs. The objectives of this study are to assess the in vivo kinematics for subjects implanted with either a PCR or BCR TKA and to compare the in vivo kinematic patterns to the normal knee during flexion. These objectives were achieved with an emphasis on understanding the roles of the cruciate ligaments, as well as the role of changes in femoral geometry of nonimplanted anatomical femurs vs implanted subjects having a metal femoral component.

METHODS

Tibiofemoral kinematics of 50 subjects having a PCR (40 subjects) or BCR (10 subjects) TKA were analyzed using fluoroscopy while performing a deep knee bend activity. The kinematics were compared to previously published normal knee data (10 subjects). Kinematics were determined during specific intervals of flexion where the ACL or PCL was most dominant.

RESULTS

In early flexion, subjects having a BCR TKA experienced more normal-like kinematic patterns, possibly attributed to the ACL. In mid-flexion, both TKA groups exhibited variable kinematic patterns, which could be due to the transitional cruciate ligament function period. In deeper flexion, both TKA functioned more similar to the normal knee, leading to the assumption that the PCL was properly balanced and functioning in the TKA groups. Interestingly, during late flexion (after 90°), the kinematic patterns for all three groups appeared to be statistically similar.

CONCLUSION

Subjects having a PCR TKA experienced greater weight-bearing flexion than the BCR TKA group. Subjects having a BCR TKA exhibited a more normal-like kinematic pattern in early and late flexion. The normal knee subjects achieved greater lateral condyle rollback and axial rotation compared to the TKA groups.

Weight-bearing status affects in vivo kinematics following mobile-bearing unicompartmental knee arthroplasty

PURPOSE

The effects of weight bearing (WB) on knee kinematics following mobile-bearing unicompartmental knee arthroplasty (UKA) remain unknown. The purpose of this study was to clarify the effects of WB on in vivo kinematics of mobile-bearing UKA during high knee flexion activities.

METHODS

The kinematics of UKA were evaluated under fluoroscopy during squatting (WB) and active-assisted knee flexion (non-weight bearing, NWB). Range of motion, femoral axis rotation relative to the tibia, anteroposterior (AP) translation of the medial and lateral sides, and kinematic pathway were measured.

RESULTS

There were no differences in knee flexion range and external rotation of the femur in each flexion angle between the WB conditions. The amount of femoral external rotation between minimum flexion and 60° of flexion during WB was significantly larger than that during NWB, and that between 60° and 130° of flexion during NWB was significantly larger than that during WB. There were no differences in medial AP translation of the femur in each flexion angle between the WB conditions. However, on the lateral side, posterior translation of 52.9 ± 12.7% was observed between minimum flexion and 130° of flexion during WB. During NWB, there was no significant translation between minimum flexion and 60° of flexion; beyond 60° of flexion, posterior translation was 41.6 ± 8.7%. Between 20° and 80° of flexion, the lateral side in WB was located more posteriorly than in NWB (p < 0.05).

CONCLUSION

Mobile-bearing UKA has good anterior stability throughout the range of knee flexion. WB status affects the in vivo kinematics following mobile-bearing UKA.

LEVEL OF EVIDENCE

III.

In Vivo Kinematics of Bicruciate-Retaining Total Knee Arthroplasty with Anatomical Articular Surface under High-Flexion Conditions

Bicruciate-retaining total knee arthroplasty (BCR-TKA) recreates normal knee movement by preserving the anterior cruciate and posterior cruciate ligaments. However, in vivo kinematics of BCR-TKA with the anatomical articular surface remains unknown. The objective of this study was to evaluate in vivo kinematics of BCR-TKA with the anatomical articular surface during high-flexion activities. For this purpose, 17 knees after BCR-TKA with an anatomical articular surface were examined. Under fluoroscopy, each patient performed squatting and cross-legged sitting motions. To estimate the spatial position and orientation of the knee, a two-dimensional or three-dimensional registration technique was used. Rotation, varus-valgus angle, and anteroposterior translation of medial and lateral contact points of the femoral component relative to the tibial component were evaluated in each flexion angle. The results showed that from 80 to 110° of flexion, the femoral external rotation during squatting was significantly larger than that during cross-legged sitting. At maximum flexion, the knees during sitting indicated significantly more varus alignment than during squatting. During squatting, a medial pivot pattern was observed from minimum flexion to 10° flexion, with no significant movement beyond 10° of flexion. Conversely, during cross-legged sitting, no significant movement was detected from minimum flexion to 60° of flexion, with a medial pivot beyond 60° of flexion. Therefore, the knees showed relatively normal kinematics after BCR-TKA with an anatomical articular surface; however, it varied during high-flexion activities depending on the activity.

Mid-term survivorship and clinical outcomes of the medial stabilized systems in primary total knee arthroplasty: A systematic review

Introduction

Medial Pivot Total Knee Arthroplasty was introduced in clinical practice in 1990s to reproduce the in vivo-natural knee kinematics. This design is characterized by an asymmetric constraint profile, with aa highly congruent medial compartment, and a less congruent lateral compartment. Short-term outcomes of the medial pivot systems in primary knee arthroplasty have been widely reported in the current literature, however, only few studies have described results beyond 5-year follow-up.

Objectives

The primary objectives of this systematic review of the literature is to analyze the mid-term studies on medial pivot total knee arthroplasty focusing on the reoperation rate, survivorship and clinical outcome scores.

Methods

The US National Library of Medicine (PubMed/MEDLINE), EMBASE, and the Cochrane Database of Systematic Reviews were queried for publications from January 1980 to December 2019 utilizing the following keywords: "medial pivot", "medial stabilized", "medial rotating", "medial congruent", medial ball and socket", "arthroplasty", "TKA", "TKR", and "knee surgery".

Results

18 articles met the inclusion criteria for the present study. The average quality was 11.4 for non-comparative studies and 21.7 for comparative studies based on MINORS criteria. A total 2832 knee arthroplasties were included for the final analysis with an average age of 69 years, and an average follow-up of 8.1 years (minimum 5 years). The overall reoperation rate was 2.4%, with periprosthetic joint infection as the leading cause of revision in 0.9% of cases, followed by aseptic loosening in 0.4% of cases. The average Knee Society Score improved to a mean preoperative score of 40.1 to a mean postoperative score of 89.2. The functional knee society score improved from a mean preoperative score of 44.8 to an average postoperative score of 82.9. The global range of motion improved from 104.8° preoperatively to 115.6° postoperatively.

Conclusion

We found that medial pivot system in primary total knee arthroplasty provide overall mid-term survivorship comparable to other standard implasnts. In addition, medial pivot system is associated with better high-end function compared to standard implants.

Posterior stability in posterior-stabilized vs medially congruent total knee replacement: A radiological comparison of two polyethylene designs in a single model

Objective:

The purpose of this radiological study was to assess the posterior laxity of a single model of a total knee arthroplasty design (TKA) having a medially constrained (MC) or a Posterior-Stabilized (PS) polyethylene insert using a well-documented stress x-ray. To the authors knowledge, this is the first report evaluating MC TKA outcomes according to the “kneeling view.”

Materials and Methods:

Sixty patients with non-traumatic primary knee osteoarthritis undergoing TKA were first matched by age, sex, BMI and diagnosis and then divided in two groups: group A (37 knees) received a MC TKA and group B (23 knees) a PS implant made by the same manufacturer. In all cases the posterior cruciate ligament (PCL) was resected. All patients underwent the same postoperative “kneeling view” and were also clinically evaluated according to the Knee Society Score (KSS) and Oxford Knee Score (OKS). Radiographic measurements were taken by tracing a line along the posterior cortex of the tibia and then measuring the perpendicular distance to a point marked at the posterior corner of Blumensaat’s line.

Results:

At 12 months minimum FU, no statistically significant differences were found between the two groups in all the clinical scores. There was a statistically significant difference on kneeling view values between the two groups (P = 0.0002): the mean value in the MC group was −1.97 ± 3.8 mm while was −5.6 ± 3.1 mm in the PS group. In both groups, the average position of the posterior cortex of the tibia was anterior to the posterior corner of Blumensaat’s line, showing absence of instability in flexion.

Conclusion:

This study highlighted that the PCL removal, accompanied by a precise surgical technique, did not increase the instability in flexion in two groups of patients having the same TKA design but polyethylene inserts characterized by different levels of constraint.

No clinical differences at the 2-year follow-up between single radius and J-curve medial pivot total knee arthroplasty in the treatment of neutral or varus knees

PURPOSE

Modern total knee arthroplasty (TKA) systems are designed to reproduce the normal knee kinematics and improve patient outcome. The authors compared two different third-generation medial pivot TKA implants, having a single-radius or a J-curve design in their sagittal plane, hypothesizing no clinical differences.

METHODS

Two cohorts of 50 patients who underwent primary TKA were first preoperatively matched by sex, deformity, body mass index (BMI), Oxford Knee Score (OKS), Knee society score (KSS) and range of motion (ROM) and then statistically analyzed at a minimum follow-up (FU) of 2 years. An identical surgical technique, which aimed to reproduce a slightly tighter medial than lateral compartment, was used in all knees.

RESULTS

At a minimum follow-up of 2 years (range 24-34 months) there were no statistically significant differences in OKS and KSS between the two implant groups. The final ROM differed statistically between the two groups: the average maximum active flexion was 123° in the J-curve femoral design group with an adapted "medially-congruent" polyethylene insert, and 116° in the single radius femoral design with a medial "ball-in-socket" articulation.

CONCLUSION

No clinical and radiological differences were found when the two cohorts of patients were compared. This study showed that the implant design played a minor role in the final outcome as opposed to a precise surgical technique.

LEVEL OF EVIDENCE

Retrospective case-control study, Level III.

Development of a hip joint mathematical model to assess implanted and non-implanted hips under various conditions

While total hip arthroplasty does generally improve patient quality of life, current systems can still yield atypical forces, premature component wear, and abnormal kinematics compared to native joints. Specifically, common complications include instability, separation, sliding, and edge loading within the hip joint. Unfortunately, evaluating potential solutions to these issues can be costly and time-consuming. Fortunately, mathematical modeling is an accurate and efficient tool that can be used to evaluate potential solutions. A forward dynamics mathematical model of the hip allows users to virtually insert a hip implant into a theoretical patient and observe the predicted postoperative mechanics. The objective of this study is therefore to develop, validate, and use a fully functional forward solution mathematical model that allows for a comparison between various hip implant designs and a determination of factors leading to in vivo hip separation, instability, and edge loading. The model presented herein has been validated kinetically against telemetric data and kinematically against fluoroscopic data. It was determined through this research that shifting of the joint rotation center during total hip arthroplasty has the potential to yield postoperative instability, and surgical errors can exacerbate these outcomes. However, the relationships between subject-specific joint shifting and hip instability are extremely complex, and therefore it becomes essential for surgeons to focus on implanting components as accurately as possible to minimize these risks.

Association of knee flexion angle after posterior-stabilized total knee arthroplasty with postoperative tibial external position relative to the femur and the extent of tibial internal rotation from knee extension to flexion

BACKGROUND

This study evaluated the relationship between preoperative and postoperative knee kinematics, moreover, investigated tibial rotational position and the extent of tibial internal rotation from knee extension to flexion as factors to obtain significant knee flexion after total knee arthroplasty (TKA).

METHODS

Fifty-four patients (60 knees total; 15 males, 16 knees; 39 females, 44 knees) who underwent posterior-stabilized TKA using a navigation system were included. Intraoperative knee kinematics involving tibial rotational position relative to the femur and the extent of tibial internal rotation were examined at two time points: 1) after landmarks registration (pre-TKA) and 2) after skin closure (post-TKA). The relationship between the knee flexion angle at one year postoperatively and intraoperative tibial rotational position, or the extent of tibial rotation among several knee flexion angles calculated with a navigation system were investigated.

RESULTS

The postoperative knee flexion angle was positively associated with the preoperative flexion angle and intraoperative knee kinematics at post-TKA involving tibial external position relative to the femur at knee extension and the extent of tibial internal rotation from extension to 90° of flexion or to maximum flexion. There was a positive relationship between the extent of tibial internal rotation at pre-TKA and that at post-TKA.

CONCLUSIONS

The intraoperative kinematics of the extent of tibial internal rotation at post-TKA was influenced by that at pre-TKA. The greater external position of the tibia relative to the femur at knee extension and the greater extent of tibial internal rotation at post-TKA might lead to good knee flexion angle.

Contact kinematics of patient-specific instrumentation versus conventional instrumentation for total knee arthroplasty

BACKGROUND

The goal was to evaluate the joint contact kinematics of total knee arthroplasties implanted using patient-specific instrumentation (PSI) compared to conventional instrumentation (CI). We hypothesized that use of PSI would not significantly alter contact kinematics.

METHODS

The study was a prospective randomized controlled trial, with equal allocation of fifty patients to PSI and CI groups. At two years post-operation, patients underwent weight-bearing stereo X-ray examinations at 0°, 20°, 40°, 60°, 80°, and 100° of flexion. The shortest tibiofemoral distance on each condyle determined the contact location. Magnitude of the shortest distance was measured and condylar separation was analyzed using thresholds of 0.5 and 0.75 mm. Kinematic measurements derived from the shortest distance included anteroposterior (AP) translation, excursion, axial rotation, and paradoxical anterior motion. Pivot position and cam/post contact were also investigated.

RESULTS

There were no differences (p > 0.05) in medial and lateral AP contact locations, excursions, and magnitude of anterior motion, or in axial rotation, pivot patterns, frequency of cam/post engagement, frequency of medial anterior motion, and condylar separation at a 0.75 mm threshold. Significant differences were found in frequency of lateral anterior motion (p = 0.048) and condylar separation at a 0.5 mm threshold (p = 0.010). Both groups displayed typical kinematics for a fixed-bearing posterior-stabilized implant.

CONCLUSIONS

We found no major differences in knee kinematics between PSI and CI groups, which suggest that PSI does not provide a significant kinematic advantage over conventional instruments.

Bicruciate-retaining total knee arthroplasty reproduces in vivo kinematics of normal knees to a lower extent than unicompartmental knee arthroplasty

PURPOSE

This study aimed to clarify the natural knee kinematics provided by bicruciate-retaining total knee arthroplasty (BCR-TKA) compared with those of unicompartmental knee arthroplasty (UKA) and normal knees.

METHODS

Volunteers and patients who had undergone UKA and BCR-TKA with anatomical articular surface performed squatting motion under fluoroscopy. To estimate the knee's spatial position and orientation, a two-dimensional/three-dimensional registration technique was used. The rotation angle and anteroposterior translation of the medial and lateral sides of the femur relative to the tibia in each flexion angle were directly evaluated using the same local coordinate system and their differences amongst the three groups were analysed using two-way analysis of variance and Bonferroni post hoc pairwise comparison.

RESULTS

From 0° to 10° of flexion, the femoral external rotation angle of BCR-TKA knees was significantly greater than that of normal and UKA knees and the medial side of BCR-TKA knees was significantly more anteriorly located than that of normal and UKA knees. From 40° to 50° of flexion, the medial side of UKA knees was significantly more posteriorly located than that of normal and BCR-TKA knees. From 30° to 120° of flexion, the lateral side of BCR-TKA knees was significantly more anteriorly located than that of normal and UKA knees.

CONCLUSION

The in vivo kinematics of BCR-TKA knees reproduces those of normal knees to a lower extent than those of UKA knees. Thus, BCR-TKA with anatomical articular surface reproduces in vivo kinematics of normal knees to a lower extent than UKA.

LEVEL OF EVIDENCE

III.

The biomechanical effect of different posterior tibial slopes on the tibiofemoral joint after posterior-stabilized total knee arthroplasty

Background

Different posterior tibial slopes (PTS) after posterior-stabilized total knee arthroplasty (PS-TKA) may lead to different biomechanical characteristics of knee joint. This cadaveric study was designed to investigate the tibiofemoral kinematics and contact pressures after PS-TKA with different PTS.

Methods

Nine human cadaveric knee specimens were used for PS-TKA with the PTS of 3°, 6°, and 9°. The tibiofemoral kinematics and contact pressures were measured during knee flexion angle changing from 0 to 120° (with an increment of 10°) with an axial load of 1000 N at each angle.

Results

The root mean square (RMS) of the tibiofemoral contact area and the mean and peak contact pressures during knee flexion were 586.2 mm², 1.85 MPa, and 5.39 MPa before TKA and changed to 130.2 mm², 7.56 MPa, and 17.98 MPa after TKA, respectively. Larger contact area and smaller mean and peak contact pressures were found in the joints with the larger PTS after TKA. The RMS differences of femoral rotation before and after TKA were more than 9.9°. The posterior translation of the lateral condyle with larger PTS was more than that with smaller PTS, while overall, the RMS differences before and after TKA were more than 11.4 mm.

Conclusion

After TKA, the tibiofemoral contact area is reduced, and the contact pressure is increased greatly. Approximately 80% of the femoral rotation is lost, and only about 60% of the femoral translation of lateral condyle is recovered. TKA with larger PTS results in more posterior femoral translation, larger contact area, and smaller contact pressure, indicating that with caution, it may be beneficial to properly increase PTS for PS-TKA.

Comparison of posterior-stabilized, cruciate-retaining, and medial-stabilized knee implant motion during gait

Accurate knowledge of knee joint motion is needed to evaluate the effects of implant design on functional performance and component wear. We conducted a randomized controlled trial to measure and compare 6-degree-of-freedom (6-DOF) kinematics and femoral condylar motion of posterior-stabilized (PS), cruciate-retaining (CR), and medial-stabilized (MS) knee implant designs for one cycle of walking. A mobile biplane X-ray imaging system was used to accurately measure 6-DOF tibiofemoral motion as patients implanted with PS (n = 23), CR (n = 25), or MS (n = 26) knees walked over ground at their self-selected speeds. Knee flexion angle did not differ significantly between the three designs. Relative movements of the femoral and tibial components were generally similar for PS and CR with significant differences observed only for anterior tibial drawer. Knee kinematic profiles measured for MS were appreciably different: external rotation and abduction of the tibia were increased while peak-to-peak anterior drawer was significantly reduced for MS compared with PS and CR. Anterior-posterior drawer and medial-lateral shift of the tibia were strongly coupled to internal-external rotation for MS, as was anterior-posterior translation of the contact center in the lateral compartment. MS exhibited the least amount of paradoxical anterior translation of the femur relative to the tibia during knee flexion. The joint center of rotation in the transverse plane was located in the lateral compartment for PS and CR and in the medial compartment for MS. Substantial differences were evident in 6-DOF knee kinematics between the healthy knee and all three prosthetic designs. Overall, knee kinematic profiles observed for MS resemble those of the healthy joint more closely than PS and CR.

Varus alignment after total knee arthroplasty results in greater axial rotation during deep knee bend activity

BACKGROUNDS

The correlation between in vivo knee kinematics and alignment has not been fully elucidated. Recently, similar or better clinical outcomes have been reported by restoration of mild varus alignment after total knee arthroplasty for preoperative varus knees. The aim of this study was to evaluate the effect of postoperative alignment on knee kinematics during a deep knee bend activity.

METHODS

In vivo knee kinematics of 36 knees (25 patients) implanted with tri-condylar total knee arthroplasty were analyzed with a three dimensional model fitting approach using fluoroscopy. Under fluoroscopic surveillance, individual video frames were digitized at 30° increments from full extension to maximum flexion. Postoperative coronal and sagittal alignments were assessed using radiographs, and rotational alignment was assessed with computed tomography. Pearson correlation coefficients were calculated to determine the correlations between the alignment data and kinematic factors.

FINDINGS

Correlation analysis showed that coronal alignment was significantly correlated with knee kinematics. The varus alignment of the limb and tibial component led to a greater axial rotation from full extension to maximum flexion and more rotated position in the mid to deep flexion range. Neither the rotational alignment of the femoral nor tibial components showed significant correlation with axial rotation from full extension to maximum flexion.

INTERPRETATION

Varus alignment resulted in greater axial rotation, which could represent near-normal knee kinematics. The current study can be a kinematic rationale reporting similar or better clinical and functional outcomes for the total knee arthroplasty with residual varus alignment.

New materials for hip and knee joint replacement: What's hip and what's in kneed?

Over the last three decades there have been significant advancements in the knee and hip replacement technology that has been driven by an issue in the past concerning adverse local tissue reactions, aseptic and septic loosening. The implants and the materials we utilize have improved over the last two decades and in knee and hip replacement there has been a decrease in the failures attributed to wear and osteolysis. Despite these advancements there are still issues with patient satisfaction and early revisions due to septic and aseptic loosening in knee replacement patients. This article reviews the state of current implant material technology in hip and knee replacement surgery, discusses some of the unmet needs we have in biomaterials, and reviews some of the current biomaterials and technology that may be able to solve the most common issues in the knee and hip replacement surgery.

Mobile-bearing insert reduced patellar contact force at knee flexion during posterior stabilized total knee arthroplasty

BACKGROUND

This study aimed to compare tibial rotation and patellar contact force between mobile- and fixed-bearing total knee arthroplasty from extension to flexion by using a navigation system and patellar contact force sensor on the same patients' knees.

METHODS

Thirty-one consecutive patients who had undergone a primary posterior stabilized total knee arthroplasty were included. Patellar contact forces on the medial and lateral sides were measured at each flexion angle, and tibial rotation was assessed during 30-90°, and 90-120° knee flexion. The patellar contact force and tibial rotation were measured twice with the mobile- and fixed-platform trial components and compared between the two groups.

FINDINGS

The patellar contact force was significantly lower with mobile than with fixed-bearing total knee arthroplasty on the medial side at 120° flexion (P = .0138) and lateral side at 60°, 90°, and 120° flexion (P = .0346, P = .0127, and P = .0376). There were no significant differences in tibial rotation between the mobile- and fixed-bearing inserts during both 30-90° and 90-120° knee flexion.

INTERPRETATION

Patellar contact force was significantly lower, especially on the lateral side in mobile than in fixed-bearing total knee arthroplasty, whereas no significant difference in tibial internal rotation was found between the two inserts. Mobile-bearing inserts might reduce the patellar contact force by the bearing rotation, rather than natural tibial rotation during posterior stabilized total knee arthroplasty.

In Vivo Knee Kinematics for a Cruciate Sacrificing Total Knee Arthroplasty Having Both a Symmetrical Femoral and Tibial Component

BACKGROUND

Early total knee arthroplasty (TKA) designs were symmetrical, but lead to complications due to over-constraint leading to loosening and poor flexion. Next-generation TKAs have been designed to include asymmetry, pertaining to the trochlear groove, femoral condylar shapes, and/or the tibial component. More recently, an advanced posterior cruciate sacrificing (PCS) TKA was designed to include both a symmetrical femoral component with a patented V-shaped trochlear groove and a symmetrical tibial component with an ultracongruent insert, in an attempt to reduce inventory costs. Because previous PCS TKA designs produced variable results, the objective of this study is to determine and evaluate the in vivo kinematics for subjects implanted with this symmetrical TKA.

METHODS

Twenty-one subjects, implanted with symmetrical PCS fixed-bearing TKA, were asked to perform a weight-bearing deep knee bend (DKB) while under fluoroscopic surveillance. A 3-dimensional to 2-dimensional registration technique was used to determine each subject's anteroposterior translation of lateral and medial femoral condyles as well as tibiofemoral axial rotation and their weight-bearing knee flexion.

RESULTS

During the DKB, the average active maximum weight-bearing flexion was 111.7° ± 13.3°. On average, from full extension to maximum knee flexion, subjects experienced -2.5 ± 2.0 mm of posterior femoral rollback of the lateral condyle and 2.5 ± 2.2 mm of medial condyle motion in the anterior direction. This medial condyle motion was consistent for the majority of the subjects, with the lateral condyle exhibiting rollback from 0° to 60° of flexion and then experienced an average anterior motion of 0.3 mm from 60° to 90° of knee flexion. On average, the subjects in this study experienced 6.6°± 3.3° of axial rotation, with most of the rotation occurring in early flexion, averaging 4.9°.

CONCLUSION

Although subjects in this study were implanted with a symmetrical PCS TKA, they did experience femoral rollback of the lateral condyle and a normal-like pattern of axial rotation, although less in magnitude than the normal knee. The normal axial rotation pattern occurred because the lateral condyle rolled in the posterior direction, while the medial condyle moved in the anterior direction. Interestingly, the magnitude of posterior femoral rollback and axial rotation for subjects in this study was similar in magnitude reported in previous studies pertaining to asymmetrical TKA designs. It is proposed that more patients be analyzed having this TKA implanted by other surgeons.

Knee kinematics after cruciate retaining highly congruent mobile bearing total knee arthroplasty: An in vivo dynamic RSA study

PURPOSE

This work presents a kinematic evaluation of a cruciate retaining highly congruent mobile bearing total knee arthroplasty design using dynamic Roentgen sterephotogrammetric analysis. The aim was to understand the effect of this implant design on the kinematics of prosthetic knees during dynamic activities.

METHODS

A cohort of 15 patients was evaluated at nine month follow-up after surgery. The mean age was 74.8 (range 66-85) years. The kinematics was evaluated using the Grood and Suntay decomposition and the Low-Point (LP) methods.

RESULTS

?tlsb=-0.15pt?>From sitting to standing up position, the femoral component internally rotated (from -11.3 ± 0.2° to -7.0 ± 0.2°). Varus-valgus rotations were very close to 0° during the whole motor task. LP of medial condyle moved from an anterior position of 12.0 ± 0.2 mm to a posterior position of -12.4 ± 0.2 mm; LP of the lateral condyle moved from an anterior position of 8.1 ± 0.2 mm to a posterior position of -12.4 ± 0.2 mm, showing a bi-condylar rollback where both condyles moved parallel backward. Moreover, the femoral component showed anterior translation with respect to the tibia from 80° to 20° (from -4.9 ± 0.2 mm to 3.3 ± 0.2 mm), then a posterior translation from 20° to full extension was identified (from 3.3 ± 0.2 mm to 0.5 ± 0.2 mm).

CONCLUSIONS

Paradoxical anterior femoral translation and absence of medial-pivoting motion were recorded, highlighting the role of the symmetric deep dishes insert as main driver of the kinematic of this TKA design.

Total Knee Arthroplasty Kinematics

Knee kinematics is an analysis of motion pattern that is utilized to assess a comparative, biomechanical performance of healthy nonimplanted knees, injured nonimplanted knees, and various prosthetic knee designs. Unfortunately, a consensus between implanted knee kinematics and outcomes has not been reached. One might hypothesize that the kinematic variances between the nonimplanted and implanted knee might play a role in patient dissatisfaction following TKA. There is a wide range of TKA designs available today. With such variety, it is important for surgeons and engineers to understand the various geometries and kinematic profiles of available prostheses. The purpose of this review is to provide readers with the pertinent information related to TKA kinematics.

Does mobile-bearing have better flexion and axial rotation than fixed-bearing in total knee arthroplasty? A randomised controlled study based on gait

Objective

To analyse the 6 degrees of freedom of the knee and gait data of patients with medial knee osteoarthritis before and after fixed-bearing (FB) and mobile-bearing (MB) total knee arthroplasty (TKA) ​and examine the influence of TKA on gait characteristics and the difference between FB and MB prosthesis. We also sought to explore the prosthesis options available for TKA in these patients.

Methods

Thirty patients who underwent TKA at the Department of Orthopedics at our hospital from June to October 2017 were included. All patients had a lower limb mechanical axis (hip-knee-ankle angle) of less than 180° which were regarded as genu varum knees and had medial knee osteoarthritis. Patients were randomised divided into the FB group ​and the MB group according to the knee prosthesis implanted. An infrared navigation three-dimensional portable knee motion analysis system (Opti-Knee®, Shanghai Innomotion, Inc.) was used to acquire data on the 6 degrees of freedom of both knees when walking on flat ground before and after surgery (angle of tibia relative to femur parameters: flexion-extension, internal rotation–external rotation, abduction–adduction; displacement parameters: anterior–posterior, proximal–distal, medial–lateral). Postoperative follow-up efficacy was assessed using the Oxford Knee Score system.

Results

There were significant differences in the maximum values of the internal/external rotation and flexion/extension angle between patients post-TKA and the healthy population, p values were 0.007 and <0.001,respectively. The postoperative maximum values of genu varum and internal rotation in both FB [(−9.49 ​± ​5.99°), (−5.77 ​± ​3.42°), respectively] and MB [(−9.64 ​± ​4.83°), (−7.54 ​± ​4.51°), respectively] groups were lower than the preoperative ones [FB (−15.13 ​± ​6.78°), (−8.28 ​± ​4.83°); MB (−13.28 ​± ​3.98°), (−9.46 ​± ​4.99°), respectively] (p ​≤ ​0.001), while the postoperative maximum values of flexion angle and anterior displacement in both FB [(46.11 ​± ​4.14°), (0.71 ​± ​0.35 ​cm), respectively] and MB [(49.33 ​± ​3.98°), (0.75 ​± ​0.89 ​cm), respectively] groups were larger than the preoperative ones [FB (43.15 ​± ​3.77°), (0.26 ​± ​0.74 ​cm); MB (44.62 ​± ​5.92°), (0.33 ​± ​0.79°), respectively] (p ​≤ ​0.001). The postoperative range of flexion/extension angle in both FB (40.13 ​± ​4.14°) and MB (45.82 ​± ​3.76°) groups was significantly larger than the preoperative one [FB (36.17 ​± ​6.07°), MB (37.09 ​± ​3.93°), respectively] (p ​≤ ​0.001). There were also significant increases in range of anterior–posterior displacement in the FB group (0.85 ​± ​0.32 ​cm) postoperatively compared with the preoperative one (0.71 ​± ​0.92 ​cm) (p ​= ​0.016) ​and significant increases in range of medial-lateral displacement (0.64 ​± ​0.73 ​cm) in the MB group postoperatively compared with the preoperative one (0.52 ​± ​0.91 ​cm) (p ​= ​0.025). The mean flexion/extension angle of the MB group was significantly greater than the FB group after surgery in both the stance phase and the swing phase (p ​< ​0.001). There were significant differences in postoperative knee axial rotation during the gait cycle between the MB and FB groups (p ​= ​0.028) ​and that postoperative internal rotation of the tibia relative to the femur increased in the MB group. The Oxford Knee Score at the last follow-up visit about 7.5 months after surgery was 15.6 ​± ​1.3 and 15.1 ​± ​1.1 points for FB and MB groups, respectively. This difference was not significant (p ​= ​0.428).

Conclusions

TKA can make the parameters of knee gait characteristics closer to the normal population. Medial knee osteoarthritis patients who received a MB prosthesis in TKA had better joint flexion function and axial rotation than the FB one. However, there is insufficient evidence to suggest that the MB prosthesis is a better option for patients with medial knee osteoarthritis.

The translational potential of this article

To date, no consensus for prosthesis selection in TKA has been established. This study found significant differences in joint flexion/extension angle and internal/external rotation during gait post-TKA surgery in medial knee osteoarthritis patients who received different prostheses. This will provide some references for prosthesis selection for a large number of genu varum patients in clinical practice.

Bicruciate-stabilised total knee arthroplasty provides good functional stability during high-flexion weight-bearing activities

PURPOSE

Bicruciate-stabilised total knee arthroplasty (BCS-TKA) uses a dual-post-cam mechanism as a substitute for the anterior cruciate ligament and posterior cruciate ligament (PCL), with the surface geometry providing additional guidance for axial rotation and posterior translation. However, the effect of weight-bearing on the kinematics of BCS-TKA has not been investigated. Therefore, the aim of this study was to clarify the effect of weight-bearing on the kinematics of BCS-TKA during high-flexion activities.

METHODS

The kinematics of 11 BCS-TKAs were evaluated under fluoroscopy, with two- and three-dimensional image registration, during squatting weight-bearing and active-assisted knee flexion non-weight-bearing. The following variables were measured: knee range of motion, axis of femoral rotation relative to the tibial component, anteroposterior (AP) translation of the medial contact point, kinematic path of the joint surfaces, lateral femorotibial contact point, and anterior and post-cam engagement.

RESULTS

The weight-bearing condition did not influence the range of knee flexion, axis of femoral rotation, medial pivot pattern during early flexion, or bicondylar rollback beyond mid-flexion. With regard to AP translation, both the medial and lateral contact points had more posterior locations in weight-bearing than in non-weight-bearing at the mid-flexion angle. Anterior engagement was identified in 6/11 knees (54.5%) in weight-bearing and 4/11 knees (36.3%) in non-weight-bearing. Post-cam engagement was observed in all knees, with the angle of flexion at engagement being larger in weight-bearing than in non-weight-bearing.

CONCLUSION

Although weight-bearing resulted in a posterior location of the medial and lateral contact points of the BCS-TKA design compared with non-weight-bearing in the mid-range of knee flexion, the amount of anterior translation was small overall. Therefore, BCS-TKA provides good stability during high-flexion weight-bearing activities. However, BCS-TKA is associated with high rate of the anterior engagement during early flexion. Therefore, understanding a patient's activities is an important factor when selecting the most appropriate TKA method.

Does hamstrings co-contraction constrain knee internal rotation in patients with knee endoprosthesis during decline slope walking?

BACKGROUND

Medial and lateral hamstrings are known for their capacity to promote internal or external rotation of the knee. Apart from implant geometry, increased co-contraction to a larger share of either the medial or lateral hamstrings has the potential to contribute to the restricted knee internal rotation especially under consideration of cruciate ligament substituting compared to cruciate ligament retaining knee endoprosthesis designs. Hence, the purpose of the study was to evaluate, whether increased co-contraction of the hamstrings contribute to the impaired knee internal rotation in total and unicondylar knee arthroplasty patients during level and decline walking.

METHODS

Knee joint angles were calculated using an inverse kinematics model in Anybody. Muscle activity was examined of the semitendinosus and biceps femoris.

FINDINGS

Knee internal rotation was constraint in the operated compared to the non-operated limb only in the total knee arthroplasty group during decline slope walking. Co-contraction values revealed no statistically significant differences between the operated and non-operated limb during the limited knee internal rotation period of time (59-94% of stance). Biceps femoris activity was significantly reduced (69-71% of stance) in the operated limb in the total knee arthroplasty group during decline slope walking.

INTERPRETATION

Contrary to the proposed mechanism, aspects other than co-contraction between semitendinosus and biceps femoris are involved in the impaired transverse plane knee motion. These include implant congruency and probably friction. Unexpectedly, the biceps femoris did not compensate the absence of the anterior cruciate ligament with increased muscular activity in the operated limb of the total knee arthroplasty group.

Improved Range of Motion and Patient-Reported Outcome Scores With Fixed-Bearing Revision Total Knee Arthroplasty for Suboptimal Axial Implant Rotation

BACKGROUND

Suboptimal implant rotation has consequences with respect to knee kinematics and clinical outcomes. We evaluated the functional outcomes of revision total knee arthroplasty (TKA) for poor axial implant rotation.

METHODS

We retrospectively reviewed 42 TKAs undergoing aseptic revision for poor axial implant rotation. We assessed improvements in Knee Society Score (KSS) and final range of motion (ROM). Subgroup analyses were performed for preoperative instability and stiffness, as well as the number of components revised and level of implant constraint used.

RESULTS

Revision for poor axial rotation in isolation improved KSS from 52 ± 22 to 84 ± 25 (P < .001), and flexion increased from 105 ± 21° to 115 ± 13° (P = .001). Revision in the setting of instability significantly improved the KSS (P < .001) but did not affect ROM (P = .172). Revision in the setting of stiffness significantly improved both KSS (P < .001) and ROM (P = .002). There was no statistically significant difference between the postoperative KSS (P = .889) and final knee flexion (P = .629) with single- or both-component revision TKA for isolated poor axial rotation or between the postoperative KSS (P = .956) and final knee flexion (P = .541) with or without the use of higher constraint during revision TKA for isolated poor axial rotation.

CONCLUSION

Revision TKA for poor axial alignment improves clinical outcomes scores and functional ROM.

The medial constrained insert restores native knee rotational kinematics after bicruciate-retaining total knee arthroplasty

PURPOSE

The aim of this study was to test the hypothesis that the medial constrained insert would reproduce the native knee kinematics after bicruciate-retaining (BCR) total knee arthroplasty (TKA).

METHODS

Using an image-free navigation system in six fresh-frozen whole-body cadavers, the rotation angle of the tibia at minimum flexion, at 10° intervals from 0° to 130° flexion, and at maximum flexion during manual passive knee flexion was assessed. The data was collected in native knees, in BCR TKA using a normal flat insert (BCR-XP), and in BCR TKA using a more constrained insert in the medial side (BCR-AS). The differences in the rotation angle of the tibia were statistically evaluated.

RESULTS

The rotation angles of the tibia in BCR-XP were significantly different from those of the native knees both in the early flexion phase (p = 0.002 at minimum knee flexion, p = 0.002 at 0°, p = 0.041 at 10°, p = 0.009 at 20°, p = 0.026 at 30°) and in the late flexion phase (p = 0.015 at 130°, p = 0.015 at maximum knee flexion), whereas the rotational angles of the tibia in BCR-AS were similar to those of the native knee.

CONCLUSION

This study shows that the rotational kinematics of the native knee is reproduced after BCR TKA with the medial constrained insert. Surgeons and implant designers should be aware that constraint of the medial side in BCR TKA is a crucial factor for restoration of native kinematics which may lead to better clinical outcome.

Tibio-Femoral Contact Force Distribution is Not the Only Factor Governing Pivot Location after Total Knee Arthroplasty

Total knee arthroplasty aims to mimic the natural knee kinematics by optimizing implant geometry, but it is not clear how loading relates to tibio-femoral anterior-posterior translation or internal-external pivoting. We hypothesised that the point of pivot in the transverse plane is governed by the location of the highest axial force. Tibio-femoral loading was measured using an instrumented tibial component in six total knee arthroplasty patients (aged 65–80y, 5–7y post-op) during 5–6 squat repetitions, while knee kinematics were captured using a mobile video-fluoroscope. In the range of congruent tibio-femoral contact the medial femoral condyle remained approximately static while the lateral condyle translated posteriorly by 4.1 mm (median). Beyond the congruent range, the medial and lateral condyle motions both abruptly changed to anterior sliding by 4.6 mm, and 2.6 mm respectively. On average, both the axial loading and pivot position were more medial near extension, and transferred to the lateral side in flexion. However, no consistent relationship between pivoting and load distribution was found across all patients throughout flexion, with R² values ranging from 0.00 to 0.65. Tibio-femoral kinematics is not related to the load distribution alone: medial loading of the knee does not necessarily imply a medial pivot location.

How prosthetic design influences knee kinematics: a narrative review of tibiofemoral kinematics of healthy and joint-replaced knees

INTRODUCTION

To improve the total knee arthroplasty (TKA) prosthesis design, it is essential to study the kinematics of the tibiofemoral joint. Many studies have been conducted in this area; however, conflicting results and incomparable testing methods make it difficult to draw definitive conclusions or compare research from studies. The goal of this article is to introduce what is known about both healthy and prosthetic tibiofemoral joint kinematics.

AREAS COVERED

Healthy tibiofemoral joint kinematics are reviewed in vivo by different activities, and the kinematics of existing knee prosthetic design features are considered separately. These features include but are not limited to cruciate retaining, posterior cruciate substituting, mobile-bearing, and high flexion.

EXPERT COMMENTARY

The type of activity that is being performed has a great influence on the kinematics of healthy knees, and the influences of different TKA prosthetic design features on the kinematics are complex and varied. Moreover, the TKA postoperative functional performance is influenced by many factors, and prosthetic design is among them, but not the only one that defines the performance.