Declines in strength and balance in older adults with chronic knee pain: a 30-month longitudinal, observational study.

OBJECTIVES: To document changes in lower extremity strength and balance over a 30-month period in older adults with chronic knee pain, and to identify relationships among these variables that may prove useful in designing a subsequent clinical intervention trial.

METHODS: This longitudinal, 30-month, observational study was designed to examine the association of physical, psychological, social, and environmental factors with severity and progression of physical disability caused by chronic knee pain. This article will focus on 2 physical measures: strength and dynamic balance. The participants were a cohort of 480 adults 65 years of age or older with chronic knee pain. Measurements included: 1) force platform dynamic balance measure of the center of pressure excursion during a forward and subsequent backward lean, 2) isokinetic strength measures of concentric and eccentric knee flexion and extension, and concentric ankle plantar flexion and dorsiflexion, and 3) body mass index and a knee pain scale to measure obesity and knee pain, respectively.

RESULTS: A maximum-likelihood analysis revealed an overall significant decline in knee (P < 0.001) and ankle (P = 0.012) strength, and balance (P < 0.001) after a 30-month followup period. Participants with greater knee strength at baseline had less expected decline in balance at followup than their weaker counterparts (4.2% versus 7.7% for the 75th versus 25th percentiles of strength; P = 0.023). However, the absolute decline in balance over 30 months was similar regardless of baseline ankle strength.

CONCLUSIONS: Adults age >or=65 years with chronic knee pain experience significant declines in balance and lower extremity strength over a 30-month period. Moreover, greater knee and ankle muscular strength is associated with better balance. Previous studies have shown that weight training is effective in improving balance in older adults with knee osteoarthritis. Taken together, these studies present a strong rationale for incorporating weight training into an exercise prescription for older adults with chronic knee pain.