Do medical factors predict disability in older adults with persistent low back pain?

Persistent low back pain (LBP) is one of the most common and challenging persistent pain conditions in older adults. Medical comorbidity also is common in these individuals, but its impact on disability has not been examined. The purpose of this study was, using a cross-sectional design, to examine the functional impact of pain-related and general medical comorbidity on 100 community dwelling older adults (mean age 74.3) with persistent mechanical LBP. Subjects received a structured history and physical examination, lumbosacral spine X-rays, and standardized tests of physical function. Pain-related variables included intensity, duration, extent, and lumbar motion-induced pain. General medical variables included age, comorbidity, number of medications, depressive symptoms, back range of motion, body mass index, and severity of radiographic pathology. Function/disability measures included self-reported disability, gait speed, and mean number of static lifts and amount of work performed during a dynamic lifting task. Structural equation modeling was used to evaluate the influence of pain and medical variables on function/disability. The overall regression model indicated pain and medical variables were significantly associated with function/disability measures (R2=0.45, P<0.01). Individual regression coefficients, however, indicated that only pain duration (r=-0.36, P<0.05) and pain severity (r=0.37, P<0.001) were significantly associated with function/disability. Despite the prevalence of medical co-morbidities in older PLBP subjects, they appear to be of limited utility in understanding level of disability. These findings also underscore the need to optimize pain treatment in independent older adults to optimize physical function and delay the onset of dependent living status.