VMO-VL reflex latency difference in osteoarthritic knees and controls

It was hypothesized that onset of reflex electromyographic (EMG) activity of vastus medialis oblique (VMO) was delayed relative to that of vastus lateralis (VL) in patients with osteoarthritis (OA) of the knee compared to controls. Three subject groups were tested: young asymptomatics (n = 20), mean (±SD) 31.1±7.9 years; older asymptomatics (n = 17), 56.7±8.6 years; and symptomatic OA knee patients, diagnosed by an orthopaedic surgeon (n = 16), 65.9±7.8 years. The patellar tendon reflex latencies of VMO and VL were measured using surface EMG, and the reflex latency difference (RLD) between the two muscles was calculated for each subject. Mean RLD values were 0.75±1.17, 1.05±1.06 and 1.27±0.81 ms for young asymptomatics, older asymptomatics and OA knee patients respectively, indicating that on average VMO was activated after VL in all groups. However, analysis of variance showed that these RLD values were not significantly different between the groups, F(2,50) = 1.140, p = 0.33. The results demonstrate that the onset of reflex VMO EMG activity relative to VL is not delayed in OA knee patients compared to controls. This has important implications for rehabilitation programmes aimed at developing preferential activation of VMO compared to VL in OA knee.