Arjan H de Zwart, Joost Dekker, Willem Lems, Leo D. Roorda, Martin van der Esch, Marike van der Leeden
Amsterdam Rehabilitation Research Center, Reade, Amsterdam, The Netherlands. E-mail: a.d.zwart@reade.nl
DOI: 10.2340/16501977-2284

Objective: Muscle weakness is common and strongly related to clinical outcome in patients with knee or hip osteoarthritis. To date, there is no clear overview of the information on factors associated with muscle strength in knee and hip osteoarthritis. The aim of this paper is to provide an overview of current knowledge on factors associated with upper leg muscle strength in this population.
Design: The framework of a scoping review was chosen. MEDLINE database was searched systematically up to 22 April 2017. Studies that described a relationship between a factor and muscle strength in knee or hip osteoarthritis were included.
Results: A total of 65 studies met the inclusion criteria. In studies of knee osteoarthritis, 4 factors were consistently found to be associated with lower muscle strength. Due to the low number of studies on hip osteoarthritis no conclusions could be drawn on associations.
Conclusion: Lower muscle quality, physical inactivity, more severe joint degeneration, and higher pain are reported to be associated with lower strength in the upper leg muscles in knee osteoarthritis. Future research into knee osteoarthritis should focus on other potential determinants of muscle strength, such as muscle quantity, muscle activation, nutrition and vitamins, and inflammation. In hip osteoarthritis, more research is needed into all potential determinants.

Muscle weakness is common in patients with knee or hip osteoarthritis (OA). Those patients with weaker upper leg muscles have more pain and are limited to greater extend in their daily activities. In order to better understand which factors contribute to muscle weakness in knee and hip OA, an important first step is to get insight in which factors are associated with muscle strength. Based on the findings in the scientific literature, we created an overview of factors related to muscle strength. We found consistent evidence that lower muscle quality (i.e. more intramuscular fat ), physical inactivity, more severe degeneration of the joint, and more pain were associated with lower muscle strength in the upper leg in patients with knee OA. To date, it is unclear whether factors such as muscle quantity (i.e. lower muscle mass), muscle activation, nutrition and vitamin intake, and inflammation are associated with muscle strength in knee OA. More research is required to clarify the relations between these factors and muscle strength. Since only a limited number of studies have been found in hip OA, more research is needed on all factors in hip OA.