Roles of low muscle strength and sarcopenic obesity on incident symptomatic knee osteoarthritis

1. Low muscle strength, obesity, and sarcopenic obesity were associated with a greater risk of incident symptomatic knee osteoarthritis (OA) 7 years later in middle-aged and older Chinese adults. 

2. Muscle strength mediated the association between obesity and knee OA.

Evidence Rating Level: 1 (Excellent)

Study Rundown: Age-related obesity has been linked with lower muscle mass and greater fat infiltration in muscles that could result in mechanical imbalances in knee joints, suggesting that lower muscle strength may mediate the impact of obesity on onset of knee osteoarthritis (OA). Sarcopenic obesity involves muscle loss combined with fat accumulation. Previous research found that obesity and sarcopenic obesity but not sarcopenia alone was associated with increased risk of knee OA, highlighting the importance of considering both conditions when assessing knee OA risk. However, research on sarcopenic obesity and knee OA is still limited. This study thus investigated the impact of muscle strength and sarcopenic obesity on knee OA onset and whether lower muscle strength mediates the link between obesity and knee OA in a middle- and old-age Chinese population. Of the 12,043 included in this prospective cohort study, 2,008 progressed to symptomatic knee OA during the 7-year follow-up. Results found that lower muscle strength (normalized grip strength and chair-rising time), obesity (general and abdominal), sarcopenic obesity was associated with an increased risk of symptomatic knee OA. Additionally, participants with sarcopenia obesity were about 2 times more at risk of incident knee OA than those with sarcopenia alone. Muscle strength mediated the relationship between obesity and knee OA incidence. Overall study findings suggest that improving muscle strength may mitigate knee OA risk in Chinese middle- to old-age adults with obesity. Future research is needed to validate study findings. 

Click to read the study in BMC Medicine 

Relevant reading: Risk of Knee Osteoarthritis With Obesity, Sarcopenic Obesity, and Sarcopenia

In-Depth [Longitudinal cohort study]: This study investigated the impact of muscle strength and sarcopenic obesity on knee OA onset and whether lower muscle strength mediates the link between obesity and knee OA in a middle- and old-age Chinese population. This study analyzed baseline and 7-year follow-up data from the China Health and Retirement Longitudinal Study (CHARLS), a prospective cohort study including adults > 45 years old. Muscle strength and function were assessed by normalized grip strength and 5-time chair stand test, respectively. The study outcome was incidence of symptomatic knee OA, defined as both physician-diagnosed arthritis and the presence of concurrent pain in either knee joint. Out of the 12,043 included in this study (mean age = 58.66 ± 9.85 years, female = 6230 (51.7%), mean BMI = 23.48 ± 3.64 kg/m2), 2,008 progressed to knee OA during the 7-year follow-up (mean age = 58.94 ± 9.27 years, female 1227 (61%), mean BMI = 23.71 ± 3.74 kg/m2). General obesity (relative risk (RR): 1.23, 95% CI: 1.08 to 1.39) and abdominal obesity (RR:1.23, 95% CI: 1.11 to 1.35) both increased knee OA onset by 23% compared to participants with normal BMI and waist circumference, respectively. Participants with the highest level of normalized grip strength (> 0.65) at baseline had a 33% decreased risk of incident knee OA (RR:0.67, 95% CI: 0.60 to 0.75) compared to the group with lowest level of normalized grip strength (< 0.45). Participants with the greatest chair-rising time (>12.30) at baseline had a 65% increased risk of incident knee OA (RR:1.65, 95% CI: 1.17 to 2.33) compared to those with the lowest chair-rising times (< 7.80s). Associations remained significant even after adjusting for covariates. Based on BMI definitions of obesity, those with sarcopenia obesity (RR: 2.41, 95% CI: 1.78 to 3.26) were about 2 times more at risk of incident knee OA than those with sarcopenia alone (RR: 1.45, 95% CI: 1.22 to 1.74). The relationship between general obesity and incidence of knee OA was fully mediated by normalized grip strength (β = 0.064, 95% CI: 0.004 to 0.126) and chair-rising time (β = 0.013, 95% CI: 0.004 to 0.024). Additionally, the relationship between abdominal obesity and incidence of knee OA was 22% mediated by normalized grip strength (β = 0.013, 95% CI: 0.004 to 0.024) and 6.2% mediated by chair-rising time (β = 0.013, 95% CI: 0.004 to 0.024). Overall, study results found that low muscle strength and sarcopenic obesity are associated with increased risk of incidence of symptomatic knee OA and that muscle strength is a mediator between obesity and symptomatic knee OA incidence. These findings suggest that improving muscle strength may be effective in mitigating knee OA risk in Chinese middle- to old-age adults with general and/or abdominal obesity. To validate study findings, future research could assess how other measures of muscle quality and quantity relate to knee OA onset.

Image: PD

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