Vibromyographic analysis of knee muscle imbalances in knee osteoarthritis

Abstract

Muscle imbalances are a well accepted cause of musculo-skeletal pain, yet clinicians lack a simple, non-invasive, and reproducible means to assess muscle effort during activities of daily living. To address this issue, we have been developing vibromyography (VMG) as a means to quantitatively assess muscle mechanical effort such that accurate muscle effort ratios can be determined in the clinic. In this study, VMG was used to characterize muscle imbalances in older adults with low-level knee pain while they performed step-up and step-down activities. In addition to determining whether VMG can identify the imbalances previously reported in individuals with knee pain, we address the question of whether these knee muscle imbalances were a likely cause of knee pain, or whether the imbalances represented a coping response for pre-existing knee pain. A population (N = 30) of 35 - 85 year old men and women with a total of 42 painful knees were assessed. Robust multiple step-wise regression analysis identified weak hip abductor muscle effort relative to hamstring muscle effort as the best predictor of knee pain (p = 0.00006), with weak vastus lateralis effort in eccentric contraction, relative to concentric contraction, being the second best predictor (p = 0.0003). Muscle imbalances were able to account for 40% of the variation in reported pain, and the observed pattern of increasing knee pain with increasing quadriceps strength during concentric contraction leads us to infer that the observed muscle imbalances are not the result of a protective action by the individual, but rather are a principle cause of the knee pain.