Determinants of hip and knee flexion range: Results from the San Antonio Longitudinal Study of Aging

Objective. We analyzed data from the San Antonio Longitudinal Study of Agin g, a neighborhood-based study of community-dwelling elderly people, to iden tify factors that determine the flexion range (FR) of hips and knees. Methods. The FR of hips and knees was measured in a cohort of 687 subjects aged 65 to 79 years. We used multivariate models to examine the association s among the FR of hips and knees, and between these and age, gender, ethnic ity, body mass index (BMI), pain and its location, self-reported arthritis, and diabetes mellitus. The functional relevance of hip and knee FR was tes ted by measuring its association with 50-foot walking velocity. Results. More than 90 degrees of flexion in both hips and both knees was ob served in 619 subjects (90.1%). Correlations among the FR of hips and knees ranged from 0.54 to 0.80 (P < 0.001 for Spearman r values). Multivariate a nalysis revealed a pattern of significant associations between each of the joints and its contralateral mate and ipsilateral partner joints that was c onsistent for both hips and both knees. Using each individual joint as the unit of analysis, the following variables were independently associated wit h hip or knee FR in multivariate models: rising BMI and female sex with red uced FR of both hips and knees, a Mexican American ethnic background with d ecreased hip FR, and knee pain with decreased knee FR. The functional impor tance of the FR of these two important joints was supported by its signific ant association with walking velocity in a model that adjusted for age, gen der, ethnic background, BMI; and hip or knee pain. Conclusions. Most community-dwelling elderly people have a FR of hips and k nees that can be considered functional. The ipsilateral and contralateral h ip or knee are significant independent determinants of the FR of each of th ese joints. Obesity, a health problem potentially amenable to preventive an d therapeutic interventions, is a factor significantly associated with decr eased FR of hips and knees.