Background/Purpose: Knee osteoarthritis (OA) is a leading cause of functional limitation and disability in older adults. But why some knee OA patients develop functional limitation but not others, is unclear. Systemic inflammation is a strong risk factor for aging-related muscle impairment which can contribute to functional limitation. Modest elevations in measures of systemic inflammation are present in persons with knee OA.. We hypothesized that this inflammation might play a role in contributing to OA-related function limitation.  We examined the relation of serum TNF-α level (marker of systemic inflammation) with 20 meter walk time and timed chair stands (measures of physical function) in community-dwelling older adults, with and without knee OA.

Methods: We included a subset of participants from the Multicenter Osteoarthritis (MOST) study, a NIH-funded longitudinal cohort of persons with or at risk of knee OA who had assessments of serum TNF-α, knee radiographs, 20m walk time (time to walk 20 meters) and timed chair stands (time to perform chair stands X 5) assessed at baseline visit. Persons with whole knee radiographic OA (ROA, yes/no) were defined by the presence of tibiofemoral (KL grade ≥2) or patellofemoral (osteophytes ≥ 2 or joint space narrowing score (JSN) ≥1 or JSN plus any osteophyte) OA in either or both knees.  Persons with symptomatic knee OA (SOA, yes/no) were defined by presence of pain plus ROA in the same knee. To examine the association of serum TNF-α with 20 m walk time and timed chair stands (separate analyses), we performed linear regression, adjusting for age, sex, BMI, physical activity score (PASE) and site, stratified by ROA and SOA status.

Results: Among 953 subjects (55% women, mean± SD age 62 ± 7.7, mean± SD BMI 30 ± 5.4), 494 subjects had ROA (52%) and 276 (30%) had SOA at baseline. We found higher serum TNF-α levels were significantly associated with slower 20 m walk time (Std. β 0.15 ± 0.04) and slower chair stands (Std. β 0.08 ± 0.04), among those with ROA but not in persons without ROA (walk time Std. β 0.02 ± 0.05; chair stands Std. β 0.01 ± 0.05) (Table). Similar significant association between higher serum TNF- α level and slower walk time was found in those with SOA but not those without SOA (Table). Serum TNF-α was not associated with timed chair stands, irrespective of SOA status (Table).

Conclusion: In this large cross-sectional study of community-dwelling older adults, a systemic inflammatory marker was significantly associated with measures of physical function in those with knee OA but not in those without knee OA. Future longitudinal studies are warranted to evaluate whether presence of systemic inflammation leads to development of functional limitation in knee OA.