Relationship Between Pedometer-Based Physical Activity and Physical Function in Patients With Osteoarthritis of the Knee: A Cross-Sectional Study

Objective: To examine the association between pedometer-based ambulatory physical activity (PA) and physical function in patients with knee osteoarthritis (OA).

Design: Cross-sectional observational study.

Setting: Institutional practice.

Participants: Participants in orthopedic clinics (N=207; age, 56-90y; 71.5% women) with diagnosed radiographic knee OA (Kellgren/Lawrence [K/L] grade ≥1).

Interventions: Not applicable.

Main outcome measures: Ambulatory PA was objectively measured as steps per day. Physical function was assessed using the Japanese Knee Osteoarthritis Measure (JKOM) functional subcategory, 10-m walk, Timed Up and Go (TUG), and 5-repetition chair stand (5CS) tests.

Results: Patients walking <2500 steps/d had a low level of physical function with a slower gait speed, longer TUG time, and worse JKOM functional score compared with those who walk 2500 to 4999, 5000 to 7499, and ≥7500 steps/d adjusted for age, sex, body mass index [BMI], and K/L grade. Ordinal logistic regression analysis revealed that steps per day (continuous) was associated with better physical function adjusted for age, sex, BMI, and K/L grade. These relationships were still robust in sensitivity analyses that included patients with K/L grades ≥2 (n=140).

Conclusions: Although increased ambulatory PA had a positive relationship with better physical function, walking <2500 steps/d may be a simple indicator for a decrease in physical function in patients with knee OA among standard PA categories. Our findings might be a basis for counseling patients with knee OA about their ambulatory PA and for developing better strategies for improving physical function in sedentary patients with knee OA.