Better quadriceps and hamstring strength is achieved after Total knee Arthroplasty with single radius femoral prostheses: a retrospective study based on isokinetic and isometric data

BACKGROUND: Strength deficits, muscle imbalances, and quadriceps inhibition are common after the total knee arthroplasty (TKA). It was suggested that theoretically single radius (SR) femoral protheses could provide longer extensor moment arm compared to the multiple radius (MR) design. However, quantitative evidence has not yet been reported. Thus, the aim of the study was to investigate the differences in isokinetic data and to compare the patient-reported outcome scores between TKA SR and MR design. METHOD: The present retrospective study included 36 TKA involving 16 knees (9 patients) using SR design implant and 20 knees (11 patients) using MR design implant. The mean follow-up time was longer than 1 year. Isokinetic knee flexion and extension torques of the operated leg were evaluated at 60°/s and 180°/s. Quadriceps and hamstring torques and ratios, work and power were recorded. Angle-specific torques were also collected at different extension or flexion angles. RESULTS: Both groups showed improvement in knee society scores (KSS) and knee injury, and osteoarthritis outcome score (KOOS) after operation. Patients in SR group had significantly higher scores in KSS-knee, symptoms and activities of daily living KOOS sub-score than those in the MR group at the end of the follow-up. The peak knee flexion torque, peak knee extension torque and maximum knee flexion work were greater in SR group at 180°/s and 60°/s. At 60°/s, and SR group had higher average knee flexion power and average knee extension power than MR group. In the isometric contraction test, the knee extension torque was higher in SR group than in MR group. At 180°/s, SR group showed higher flexion torques at 30°, 40°, 50°, 60° compared with MR group. At 60°/s, SR group showed higher flexion torques at 30°, 40°, 50°, 60°, 80° when compared with MR group. Additionally, SR group also provided higher extension torques at 40°, 50°, 60° than the MR group. There were no differences in other isokinetic and isometric parameters between the two groups. CONCLUSION: Femoral design exerted an influence on quadriceps and hamstring strength after TKA, and SR design shows advantages, in terms of higher extension and flexion strength, over MR design.