The effects of total knee arthroplasty on postural control

Total knee arthroplasty (TKA) is a common and effective treatment for severe knee osteoarthritis (OA), a chronic disease that affects millions of adults. While several investigators have reported balance deficits in persons with knee OA, the few studies that have assessed the effects of TKA on postural control have reported mixed results. The purpose of this study was to compare postural control in 10 subjects pre- and post-TKA with 10 healthy control subjects. Subjects in both groups were free of other comorbidities that could affect their balance. Subjects were tested on three postural control tasks: (1) a standing reaching task that required anticipatory postural control; (2) a platform perturbation task that required reactive postural control; and (3) the Berg Balance Scale, a clinical test of balance. For the standing reaching and platform perturbation tasks, electromyography (EMG) onset latencies of lower extremity muscles, EMG amplitudes, and excursion of the center of pressure (COP) were measured. EMG amplitude data were normalized to EMG data collected as subjects walked at their normal pace. Data were also collected for isometric knee extension and flexion torque. TKA had a negligible effect on postural control for subjects with knee OA who were tested before and after surgery. Subjects with TKA demonstrated less EMG amplitude of lower extremity muscles that crossed the knee joint during the standing reaching and platform perturbation tasks when comparing groups. Subjects with TKA also demonstrated less excursion of their COP during platform perturbations, earlier onsets of the calf muscle during the reaching task, and less knee extension strength than the control group. Group differences may be related to differences in muscle strength, the degree of neural activation, or a subconscious desire to protect the involved knee joint. The clinical significance of these group differences is unclear. Persons with knee OA and TKA may have simply developed a different strategy to maintain postural control. Determining if these group differences predispose individuals with knee OA and TKA to instability and falls in real-world situations would require prospective follow-up.