Effects of contact stress on patellarfemoral joint and quadriceps force in fixed and mobile-bearing medial unicompartmental knee arthroplasty

A finite element analysis of patellofemoral joint biomechanics: Exploring potential causes of postoperative anterior knee pain following unicompartmental knee arthroplasty

Purpose

Anterior knee pain is a common complication following unicompartmental knee arthroplasty (UKA). This study aimed to elucidate the mechanism of anterior knee pain after UKA by examining the biomechanical characteristics of the patellofemoral joint.

Methods

This study employs the finite element analysis method. A healthy model of the right lower limb was created using CT scans of an intact right lower limb from a healthy woman. Based on this model, a preoperative pathological model was generated by removing the meniscus and part of the articular cartilage. The UKA prosthesis was then applied to this model with five different bearing thicknesses: 5 mm, 7 mm, 10 mm, 11 mm, and 13 mm. To simulate various degrees of knee joint flexion, the femur was rotated relative to the knee joint's rotational axis, producing lower limb models at flexion angles of 0°, 30°, 60°, 90°, and 120°. We applied a constant force from the center of the femoral head to the center of the ankle joint to simulate lower limb loading during squatting. The simulations were conducted using Ansys 17.0.

Results

Both overstuffing and understuffing increased the peak stress on the patellar cartilage, with overstuffing having a more pronounced effect. Compared to healthy and balanced models, overstuffed and understuffed models exhibited abnormal stress distribution and stress concentration in the patellar cartilage during knee flexion.

Conclusion

Overstuffing and understuffing lead to residual varus or valgus deformities after UKA, causing mechanical abnormalities in the patellofemoral joint. These abnormalities, characterized by irregular stress distribution and excessive stress, result in cartilage damage, exacerbate wear in the patellofemoral joint and consequently lead to the occurrence of anterior knee pain.

Is Patella Facet Arthritis a Contraindication to Unicompartmental Knee Arthroplasty: Current Concepts

Medial knee unicompartmental arthroplasty (UKA) has increased in popularity for treatment of end-stage anteromedial osteoarthritis in part secondary to its quicker recovery, improved function, and decreased risk of medical complications over total knee arthroplasty (TKA). However, despite the success of medial UKA, dilemma still exists over certain patient characteristics as to suitability for undergoing the procedure. In addition to patient age, body mass index (BMI), and the presence, or lack thereof, of an anterior cruciate ligament (ACL), one of the most contentious issues surrounding suitability for medial UKA is the preoperative status of the patellofemoral joint (PFJ). This review aims to look at the historical factors leading to the current dilemma as well as recent evidence surrounding anterior knee pain and preoperative PFJ arthritis on the survivability and outcomes of medial UKA. This article will also evaluate other PFJ factors possibly affecting the outcome of medial UKA such as lateral patellar subluxation and lateral facet grooving, future perspectives that may influence the utilization of medial UKA such as cementless implants, and the choice of mobile versus fixed bearing articulations.

[Research progress on unicompartmental knee arthroplasty for elderly patients with knee osteoarthritis]

Objective

To conclude the research progress of unicompartmental knee arthroplasty (UKA) in the treatment of elderly patients with knee osteoarthritis (KOA).

Methods

The literature on UKA at home and abroad in recent years was reviewed to summarize the clinical characteristics of elderly patients with KOA, perioperative management (including evaluating indications preoperatively, intraoperative prosthesis selection, postoperative complication management, etc).

Results

Through reasonable preoperative evaluation, prosthesis selection, and advanced perioperative management, for elderly patients with KOA who meet the indications, UKA can be considered. Compared with total knee arthroplasty, the incidence of postoperative complications in elderly patients undergoing UKA is lower, joint awareness is reduced, functional improvement and satisfaction are higher. Meanwhile, choosing appropriate prostheses and fixation methods can lead to a good survival rate.

Conclusion

UKA can provide a safe and effective treatment option for elderly patients with KOA within a certain range of indications.

Finite Element Analysis of the Effect of Femoral Prosthesis Varus and Valgus Angle Installation on the Lateral Compartment in Unicompartmental Knee Arthroplasty

BACKGROUND

This study used finite element analysis (FEA) to investigate the effect of varus and valgus angle on the lateral compartment in unicompartmental knee arthroplasty (UKA).

METHODS

One patient who underwent UKA was enrolled as the subject. Thirteen working conditions of the femoral prosthesis were simulated at varus and valgus angles of 0°, 2°, 4°, 6°, 8°, 10°, and 12°. A load of 1,000 N was applied downward along the mechanical axis of the femur, and the highest stress values on the surface of the polyethylene liner, cancellous bone under the tibial prosthesis, cartilage of femur lateral condyle, lateral meniscus, and tibial lateral plateau cartilage in each model were recorded. The six highest points were used to calculate the mean value.

RESULTS

The highest stress values on the surface of the polyethylene liner, cancellous bone under the tibial prosthesis, cartilage of femur lateral condyle, lateral meniscus, and tibial lateral plateau cartilage increased with an increase in the femoral prosthesis varus/valgus angle. As compared with the standard position of the femoral prosthesis, there was no significant difference in the surface stress values of the polyethylene liner, cancellous bone under the tibial prosthesis, cartilage of femur lateral condyle, lateral meniscus and tibial lateral plateau cartilage when the femoral prosthesis varus/valgus angle was less than 4° (p > 0.05). In addition, the stress magnitude on the polyethylene liner, cancellous bone under the tibial prosthesis, cartilage of femur lateral condyle, lateral meniscus, and tibial lateral plateau cartilage significantly increased when the femoral prosthesis varus/valgus angle was greater than 4° (p < 0.001).

CONCLUSIONS

The optimal femoral prosthesis varus/valgus angle in UKA was less than 4°.

Severe patellofemoral arthritis does not compromise 6-month post-operative range of motion or function following unicondylar knee arthroplasty

BACKGROUND

The presence of significant patellofemoral arthritis (PFA) is still considered a contraindication for unicondylar knee arthroplasty (UKA) by many surgeons. The purpose of this study was to determine if the presence of severe PFA at the time of UKA compromised early (< 6 months) post-operative knee range of motion or functional outcomes.

METHODS

This retrospective review evaluated unilateral and bilateral UKA (323 patients; 418 knees) between 2015 and 2019. Procedures were grouped by degree of PFA present at the time of surgery, including mild PFA (Group 1; N = 266), moderate to severe PFA (Group 2; N = 101), and severe PFA with lateral compartment bone-on-bone contact (Group 3; N = 51). Knee range of motion and Knee Society Knee (KSS-K) and Function (KSS-F) scores were collected both before and at 6 months following surgery. Group differences were evaluated with Kruskal-Wallis and Chi-square tests for continuous and categorical variables, respectively. Univariate and multivariable logistic regressions were performed to determine influential variables associated with post-operative knee flexion being ≤ 120° and presented as odds ratios (OR) and 95% confidence intervals (CI).

RESULTS

Pre-operative flexion was lowest in Group 3 (p = 0.010) with 17.6% of knees having flexion ≤ 120°. Post-operative flexion was lowest in Group 3 (119.1° ± 8.4°, p = 0.003) with 19.6% knees having flexion ≤ 120° compared to 9.8% and 8.9% in Groups 1 and 2, respectively. No significant difference in KSS-F following surgery was found; all three groups demonstrated similar clinical improvement. Increased age (OR 1.089, CI 1.036-1.144; p = 0.001) and body mass index (OR 1.082, CI 1.006-1.163; p = 0.034) were found to be associated with post-operative knee flexion ≤ 120°, while high pre-operative flexion (OR 0.949, CI 0.921-0.978; p = 0.001) was found to be inversely associated with poor knee flexion following surgery.

CONCLUSION

Patients with severe PFA demonstrate similar clinical improvement following UKA at 6 months as patients with less severe PFA.

Comparison of Functional Recovery Between Unicompartmental and Total Knee Arthroplasty: A Randomized Controlled Trial

BACKGROUND

Comparisons of functional recovery between unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) using performance-based tests are lacking. Therefore, this study aimed to compare 2-minute walk test (2MWT) and Timed Up-and-Go test (TUG) results between UKA and TKA for isolated medial knee osteoarthritis (OA). We hypothesized that UKA yields faster functional recovery than TKA as measured with the 2MWT and TUG.

METHODS

We conducted a randomized controlled trial comparing medial UKA and TKA in patients with isolated medial knee OA. A total of 110 patients were enrolled; after 11 exclusions, 99 patients (50 UKA, 49 TKA) were included in the final analysis. The patients were tested using the 2MWT and TUG preoperatively and at 6 weeks, 3 and 6 months, and 1 and 2 years postoperatively. Patient-reported outcome measures (PROMs) were also evaluated. The mean 2MWT, TUG, and PROM results were compared between groups at each time point.

RESULTS

The mean 2MWT distance after UKA was significantly longer than that after TKA at 6 weeks (96.5 ± 22.6 m for UKA compared with 81.1 ± 19.1 m for TKA; difference, 18 m [95% confidence interval (CI),10.4 to 25.6 m]; p < 0.001), 3 months (102.1± 24.4 compared with 87.5 ± 22.3 m; difference, 14.7 m [95% CI, 5.4 to 24.0 m]; p = 0.002), and 6 months (102.8 ± 16.2 compared with 89.6 ± 15.3 m; difference, 13.2 m [95% CI, 6.9 to 19.5 m]; p < 0.001). The values at 1 and 2 years were similar after UKA and TKA. The mean TUG after UKA was also significantly shorter than that after TKA at 6 weeks and 3 months. The mean PROMs were similar after both treatments, with the exception of the Oxford Knee Score and subscales of the Knee injury and Osteoarthritis Outcome Score at 6 weeks and 3 months postoperatively.

CONCLUSIONS

The 2MWT indicated that UKA for isolated medial knee OA enabled faster recovery than TKA did at 6 weeks to 6 months, and earlier recovery was also seen with the TUG at 6 weeks to 3 months. The 2MWT and TUG results after UKA and TKA were similar to one another at 1 and 2 years.

LEVEL OF EVIDENCE

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

Patellofemoral osteoarthritis does not influence clinical outcomes of fixed-bearing unicompartmental knee arthroplasty

Unicompartmental knee arthroplasty (UKA) is an ideal surgical approach in treatment of end-stage knee osteoarthritis (KOA), however, indications of UKA have been controversial, and the radiographic and symptomatic patellofemoral osteoarthritis (PFOA) are often considered as a contraindication of medial UKA. 337 fixed bearing UKAs were retrospectively recruited in our joint center between January 1, 2011 and June 30, 2020. There were 105 patients accompanied by PFOA and 232 patients have normal PF joint. International Cartilage Repair Society (ICRS) system was introduced to quantify the degeneration degree of PF joint. Oxford Knee Score (OKS), Forgotten Joint Score (FJS), Kellgren-Lawrence (K-L) classifying system and visual analogue scale (VAS) were adopted to evaluate outcomes between with and without PFOA. There was no significant difference of age, BMI, gender, OKS, FJS and other variables between PFOA and Non-PFOA group. After more than 5 years follow-up, UKA patients with or without PFOA could all achieve a satisfactory improvement of OKS, VAS and FJS score. ROM of the replaced knee increased from preoperative 110° to 130°. 74.3% (78/105) and 75.0% (174/232) patients have no change of K-L grade in PFOA and Non-PFOA group, OKS, FJS, VAS score and ROM were also comparable in all patients and no significant outcomes difference were found between two group. The presence of patellofemoral joint osteoarthritis and anterior knee pain should not be considered to be contraindications to medial fixed-bearing UKA.

Implantation of the Femoral Component Relative to the Tibial Component in Medial Unicompartmental Knee Arthroplasty: A Clinical, Radiological, and Biomechanical Study

BACKGROUND

Unicompartmental knee arthroplasty (UKA) is a procedure with low morbidity and fast recovery. Anatomic implants or robotic-assisted UKA has been proposed to improve outcomes with precise positioning. Femoral component position (FCP) relative to the tibial insert could be a factor influencing the contact stresses. We aimed to evaluate the effect of the FCP relative to the tibial insert on clinical outcomes and stress distribution after medial UKA.

METHODS

Sixty-two medial fixed-bearing UKAs were evaluated at a minimum two-year follow-up using the Knee Society Score. Postoperative radiological evaluation performed on frontal X-rays classified the FCP relative to the tibial insert into the following: group M (medial), group C (central), and group L (lateral). A finite element model was developed to evaluate the biomechanical effects of the FCP relative to the tibial component.

RESULTS

The postoperative radiological evaluation showed 9 cases in group M, 46 cases in group C, and 7 cases in group L. The maximum knee flexion angle and the 2-year postoperative "symptom" and "patient satisfaction" scores of the Knee Society Score were significantly higher in group C. Compared with central positioning, a shift along the mediolateral axis leads to a displacement of the contact pressure center.

CONCLUSION

The FCP relative to the tibial insert may increase patient outcomes at a minimum follow-up of two years after fixed-bearing medial UKA. Accordance between FCP and contact stresses on the polyethylene insert could be a contributing factor of long-term survival of UKA.