Muscle weakness in hip osteoarthritis: A systematic review

Abstract

Hip osteoarthritis (OA) is responsible for hip pain, stiffness, and dysfunction during activities of daily living and is the most common reason for a total hip replacement (1). It has been estimated that 3% of the adult population (2) and 8% of people ages 60 years (3,4) are affected by hip OA. There is no known cure for OA and therefore, clinical management of hip OA largely focuses on alleviating pain and maximizing function (5–10). A thorough understanding of the musculoskeletal factors underlying dysfunction in hip OA is required to effectively achieve these goals. There is consistent evidence for quadriceps muscle weakness in knee OA (11), with quadriceps strengthening exercise considered a core component of programs for the management of knee OA (12–16). A commonly held view among clinicians appears to be that lower extremity muscle weakness is also apparent in hip OA. However, compared to the knee, there is less literature on muscle strength in hip OA, and guidelines for therapeutic exercise prescription in hip OA tend to be based on expert opinion rather than supporting evidence (17,18). It therefore remains unclear whether muscle weakness as observed in knee OA is evident in hip OA, and if so, which muscles are most affected. The force generated by a muscle is largely a function of the muscle’s physiologic cross-sectional area and the level of motor unit pool activation (19,20), and weakness can result from one or both of these mechanisms. Another factor with the potential to influence muscle strength is muscle quality, which manifests as a reduction in muscle force per unit of muscle physiologic cross-sectional area, and can arise due to an increase in noncontractile material such as fat in the muscle, as reported for older compared to younger adults (21). If individuals with hip OA do exhibit muscle weakness, characterization of the mechanisms underlying this weakness is required to inform the development of best practice intervention programs to treat the weakness. The purpose of this systematic review and critical evaluation of the literature was to determine whether muscles of the affected legs of individuals with unilateral hip OA are weaker, smaller, and more inhibited than those of their contralateral leg and/or the legs of healthy controls.