Maximal voluntary isokinetic knee flexion torque is associated with femoral shaft bone strength indices in knee replacement patients

It is currently unknown whether knee replacement-associated bone loss is modified by rehabilitation programs. Thus, a sample of 45 (18 men and 25 women) persons with unilateral knee replacement were recruited; age 66 years (sd 6), height 169 cm (sd 8), body mass 83 kg (sd 15), time since operation 10 months (sd 4) to explore the associations between maximal torque/power in knee extension/flexion and femoral mid-shaft bone traits (Cortical cross-sectional area (CoA, mm ²), cortical volumetric bone mineral density (CoD, mg/mm ³) and bone bending strength index (SSI, mm ³)). Bone traits were calculated from a single computed tomography slice from the femoral mid-shaft. Pain in the operated knee was assessed with the WOMAC questionnaire. Stepwise regression models were built for the operated leg bone traits, with knee extension and flexion torque and power, age, height, body mass, pain score and time since operation as independent variables. CoA was 2.3% (P = 0.015), CoD 1.2% (P < 0.001) and SSI 1.6% (P = 0.235) lower in the operated compared to non-operated leg. The overall proportions of the variation explained by the regression models were 50%, 29% and 55% for CoA, CoD and SSI, respectively. Body mass explained 12% of Coa, 11% of CoD and 11% of SSI (P ≤ 0.003). Maximal knee flexion torque explained 38% of Coa, 7% of CoD and 44% of SSI (p ≤ 0.047). For CoD time since operation also became a significant predictor (11%, P = 0.045). Knee flexion torque of the operated leg was positively associated with bone strength in the operated leg. Thus, successful rehabilitation may diminish bone loss in the operated leg.