Abstract
Introduction
Mid-flexion stability after total knee arthroplasty (TKA) is dependent, in large part, on implant design. Design variables include retention or sacrifice of the posterior cruciate ligament, conformity of the polyethylene tibial surface, and radius of curvature of the femoral component. In this study, we attempted to isolate the impact of femoral component design by comparing a single-radius design (SR) to a J-Curve design (JC). We selected cruciate-retaining implants to eliminate the effect of a cam-and-post mechanism. Mid-flexion performance these two designs were compared using the Lower-Quarter Y-Balance Test (YBT-LQ), as well as patient reported outcomes and measures of physical performance. The YBT-LQ is a simple functional test of unilateral lower extremity strength and balance. Reach of the contralateral limb is measured in three different directions (Figures 1–3). Our hypothesis was that the SR design would provide superior mid-flexion stability, and therefore, a greater reach distance in the YBT-LQ when compared to the JC group.
Methods
Patients undergoing primary, unilateral TKA were prospectively enrolled and block randomized to receive either the SR (n=30) or JC (n=30) implant. All surgeries were performed by one surgeon using a gap-balancing technique with a cruciate-retaining implant design. Patients completed outcome measures (KOOS, KSS, UCLA Activity), performed the YBT-LQ, and completed physical performance measures (walking speed, timed up-and-go, sit-to-stand) before surgery and 1 year postoperatively. A series of 2×2 repeated measures ANOVAS (Implant group x Time) were completed.
Results
One year post-operatively, 40 patients (20 SR, 20 JC) were available for analysis. The groups were closely matched for age, gender, BMI, and ASA score. No significant differences existed between implant groups for the YBT-LQ or any other variable of interest. Significant improvements in both implant groups were observed for all variables of interest when comparing pre-operative to one year post-operative.
Conclusions
Both groups improved significantly across time in all measures, but no differences were seen between SR and JC designs. Based on reach distances achieved, it is probable that many patients were not able to achieve mid-flexion during the YBT-LQ test. With regards to mid-flexion function after TKA, the significant limitations in strength and balance in this cohort of patients likely outweigh any subtle differences in implant design.
For any figures or tables, please contact authors directly (see Info & Metrics tab above).
