Introduction: The ability to reach functional capacity following knee arthroplasty depends on the strength of the quadriceps and hamstring muscles. Following total knee arthroplasty, weakness of these muscles can persist for up to one year postoperatively; however, this phenomenon is not well-studied in unicompartmental knee arthroplasty (UKA) patients. Therefore, we assessed: 1) quadriceps muscle strength; 2) hamstring muscle strength; and 3) correlation to functional outcomes.
Materials and methods: A review of all patients with medial compartment osteoarthritis treated with UKA at a minimum of one-year follow-up was performed. This yielded 26 patients (32 knees), comprising of eight females and 18 males who had a mean age of 67 years (range, 47 to 83 years). Muscle strength was assessed pre-and postoperatively via dynamometer. Functional outcomes were assessed using Knee Society Scores (KSS). Comparisons of groups were performed by paired t-tests.
Results: At a minimum one-year postoperatively, quadriceps muscle strength was 27 Nm (range, 13 to 71Nm) and hamstring muscle strength was 19.5Nm (range, 7 to 81Nm). Quadriceps muscle strength increased by 40% (p=0.002) and hamstring muscle strength by 26% (p=0.057). The mean KSS pain was 97 points (range, 85 to 100 points) and mean KSS function was 90 points (range, 45 to 100 points) at the final follow-up. Range of motion was 125° (range, 110° to 135° ) at the final follow-up. The Pearson Correlation Coefficient for postoperative extension strength and postoperative flexion strength to postoperative KSS functional scores were 0.268 and 0.220 respectively.
Conclusion: Within one-year following UKA, patients can expect restoration of quadriceps and hamstring muscle strength with a corresponding functional improvement. Although long-term follow-up is warranted to determine sustainability, the short-term results demonstrate excellent restoration of function.