Skeletal Muscle Composition, Power, and Mitochondrial Energetics in Older Men and Women With Knee Osteoarthritis

Abstract

Objective: Our objective was to investigate the overall and sex-specific relationships between the presence and severity of knee osteoarthritis (KOA) and muscle composition, power, and energetics in older adults.

Methods: Male and female patients (n = 655, mean ± SD age 76.1 ± 4.9 years; 57% female) enrolled in the Study of Muscle, Mobility, and Aging completed standing knee radiographs and knee pain assessments. Participants were divided into three groups using Kellgren-Lawrence grade (KLG) of KOA severity (0-1, 2, or 3-4). Outcome measures included whole-body muscle mass, thigh fat-free muscle (FFM) volume and muscle fat infiltration (MFI), leg power, specific power (power normalized to muscle volume), and muscle mitochondrial energetics.

Results: Overall, the presence and severity of KOA is associated with greater MFI, lower leg power and specific power, and reduced oxidative phosphorylation (P trend < 0.036). Sex-specific analysis revealed reduced energetics only in female patients with KOA (P trend < 0.007) compared to female patients without KOA. In models adjusted for age, sex, race, nonsteroidal anti-inflammatory drug administration, site or technician, physical activity, height, and participants with abdominal adiposity with KLG 3 to 4 had greater MFI (mean 0.008%, 95% confidence interval [CI] 0.004%-0.011%) and lower leg power (mean -51.56 W, 95% CI -74.03 to -29.10 W) and specific power (mean -5.38 W/L, 95% CI -7.31 to -3.45 W/L) than those with KLG 0 to 1. No interactions were found between pain and KLG status. Among those with KOA, MFI and oxidative phosphorylation were associated with thigh FFM volume, leg power, and specific power.

Conclusion: Muscle health is associated with the presence and severity of KOA and differs by sex. Although muscle composition and power are lower in both male and female patients with KOA, regardless of pain status, mitochondrial energetics is reduced only in female patients.

Figure 1

Study flowchart. KLG, Kellgren Lawrence Grade system for classification of osteoarthritis; ‐Pain, No knee pain; +Pain, Presence of knee pain. Reasons for exclusion from this study include refusal or unable to have a knee x‐ray obtained (n=116), bilateral knee replacement (n=39), other (n=33), and did not complete knee pain questionnaire (n=3).

Figure 2

Associations between muscle intrinsic characteristics (anterior thigh muscle fat infiltration and mitochondrial respiration) and muscle volume, peak power, and specific power in study participants with knee osteoarthritis. (A–C) Association between anterior thigh muscle fat infiltration assessed by magnetic resonance imaging with (A) anterior thigh fat free muscle volume, (B) knee extensor peak power, and (C) anterior thigh specific power (knee extensor peak power/thigh fat free muscle volume, specific power). (D–F) Association between OXPHOS assessed on muscle biopsy samples and (D) anterior thigh fat free muscle volume, (E) knee extensor peak power, and (F) anterior thigh specific power (knee extensor peak power or thigh fat free muscle volume and specific power). Results represent simple linear regressions for male (blue dots and line) and female (red dots and line) patients. P < 0.05. OXPHOS, maximal complex I‐ and II‐supported oxidative phosphorylation. Color figure can be viewed in the online issue, which is available at http://onlinelibrary.wiley.com/doi/10.1002/art.42953/abstract.