Purpose: Previous studies including systematic reviews have suggested that knee extensor muscle weakness is a risk factor for the development of knee osteoarthritis (OA). However, systematic reviews have not aggregated the reported data into a meta-analysis. The aim of this study was to estimate the impact of knee extensor muscle weakness on the risk of knee OA. Methods: A systematic review and meta-analysis was performed with literature searches in Medline, SportsDiscus, EMBASE, CINAHL, and AMED, all up to September 2013. Furthermore reference lists and systematic reviews on the topic were scrutinized for additional relevant studies. No restriction on language or publication year was made. Eligible studies had to include participants with no radiographic or symptomatic knee OA at baseline, and have a follow-up time of minimum 2 years. Studies had to include a measure of knee extensor muscle strength. Participants were classified as having knee extensor muscle weakness if they belonged to the lowest tertile or less in muscle strength or defined from a leg symmetry index (LSI). If more than one muscle strength outcome or knee OA definition were reported, a predefined hierarchy for extracting data was used. The hierarchy was: 1) Symptomatic radiographic knee OA for the whole knee, 2) Radiographic knee OA, and 3) Self-reported OA. Peak knee extensor muscle strength per kg body weight was preferred as measure of muscle strength; secondly average knee peak torque was extracted. Odds ratio (OR) for knee OA at follow-upwas estimated in the included trials and combined using a random effects model. Stratified analysis for men and women were performed. Results: A total of 1000 studies were identified thorough the literature searches. After review, four cohort studies with a follow-up time between 2.5 and 14 years were included. A total of 5102 participants (3325 men and 1777 women) were included in the final analysis. The studies included different groups of participants; middle-aged individuals with and without previous knee injury, elderly individuals without previous knee injury, as well as younger anterior cruciate ligament reconstructed (ACLR) individuals.Weak muscle strengthwas in 2 trials defined as being in the lowest tertile, when assessing the isokinetic knee extensor muscle strength. In one trial low muscle strength was defined as having a leg symmetry index of less than 80% (muscle strength in the affected leg was less than 80% of the muscle strength in the non-affected leg). Finally in one trial only data on the differences in muscle strength between patients with and without OA was available. Overall the meta-analysis showed an increased risk of knee OA in participants with knee extensor muscle weakness (OR 1.54 95%CI 1.28, 1.88; I2 = 14.5%). Three trials reported separate data for men and women and subgroup analysis showed increased risk in men (OR 1.43 95%CI 1.14, 1.78; I2 = 0%) and women (OR 1.79 95%CI 1.37, 2.31; I2 = 3.3%), but differences in risk between men and women did not reach statistical significance (P=0.200). Conclusions: Knee extensor weakness increased the risk of having knee OA at follow-up. Even though not statistically significant, the analysis indicated that weak knee extensor strength seems to be a stronger risk factor for OA in women than in men.
Øiestad, B. E., Juhl, C. B., Eizen, I., & Thorlund, J. B. (2014). Knee extensor muscle weakness increases the risk of knee osteoarthritis. a systematic review and meta-analysis. Osteoarthritis and Cartilage, 22, S336. https://doi.org/10.1016/j.joca.2014.02.621