Minimum performance on clinical tests of physical function to predict walking 6000 steps/day in knee osteoarthritis: An observational study.

Objective: Evidence of physical function difficulties, such as difficulty rising from a chair, may limit daily walking for people with knee osteoarthritis (OA). The purpose of this study was to identify minimum performance thresholds on clinical tests of physical function predictive to walk ≥6000 steps/day. This benchmark is known to discriminate people with knee OA who develop functional limitation over time from those who do not.

Methods: Using data from the Osteoarthritis Initiative, we quantified daily walking as average steps/day from an accelerometer (Actigraph GTM1) worn for >10 hours/day over one week. Physical function was quantified using three performance-based clinical tests: five times sit to stand test, walking speed (tested over 20 meters) and 400-meter walk test. To identify minimum performance thresholds for daily walking, we calculated physical function values corresponding to high specificity (80 to 95%) to predict walking ≥6000 steps/day.

Results: Among 1925 participants (age [mean±sd] 65.1±9.1 years, BMI 28.4±4.8 kg/m2 , 55% female) with valid accelerometer data, 54.9% walked ≥6000 steps/day. High specificity thresholds of physical function for walking ≥6000 steps/day ranged from 11.4 to 14.0 sec on the five times sit to stand test, 1.13 to 1.26 meters/sec for walking speed, or 315 to 349 sec on the 400-meter walk test.

Conclusions: Not meeting these minimum performance thresholds on clinical tests of physical function may indicate inadequate physical ability to walk ≥6000 steps/day for people with knee OA. Rehabilitation may be indicated to address underlying impairments limiting physical function. This article is protected by copyright. All rights reserved.