Modeling impairment: Using the disablement process as a framework to evaluate determinants of hip and knee flexion

Elders often present to health care providers with multiple inter-related c onditions that determine an individual's ability to function. The disableme nt process provides a generalized sociomedical framework for investigating the complex pathways from chronic disease to disability. At each stage of t he main pathway, associations may exist among primary physical factors and modifying variables that ultimately have downstream effects on the progress ion toward disability. The purpose of the present analysis is to examine th e inter-relationships between a cohesive set of variables primarily at the level of impairment that may affect hip and knee flexion range of motion (R OM). The San Antonio Longitudinal Study of Aging enrolled 833 community dwe lling Mexican (MA) and European American (EA) elders aged 64-78 years betwe en 1992 and 1996. Of these, 647 had complete data from both a home-based an d performance-based battery of assessments for these analyses. Concerning i mpairments, hip ROM was measured using an inclinometer, and knee ROM using a goniometer. Pain location and intensity were assessed using the McGill Pa in Questionnaire. Peripheral vascular disease was assessed using doppler br achial and ankle systolic blood pressures. Ankle and knee reflexes, and vib ratory sensation were assessed by a standardized neurological examination. As to diseases, diabetes was assessed using a combination of blood glucose levels and self-report, and arthritis by self-report. Concerning modifying variables, height and weight were directly measured and used to calculate B MI. Activity level was assessed with the Minnesota Leisure Time Questionnai re. Analgesic use was assessed by direct observation of medications taken w ithin the past two weeks. We used structural equation modeling to test asso ciations between the variables that were specified a priori. These analyses demonstrate the central role of BMI as a determinant of hip and knee flexi on ROM. For an increase in level of BMI, the coefficients [SEM] for changes in levels of hip and knee ROM were -0.38 [0.05] and -0.26 [0.05], respecti vely. A higher BMI resulted in lower hip and knee ROM. BMI was also directl y associated with prevalent diabetes (0.10[0.05]) and arthritis (0.17 [0.05 ]). However, after adjustment for BMI, diabetes and arthritis did not have direct independent associations with either hip or knee ROM BMI was also in directly associated with knee, but not hip, ROM through paths including low er-leg pain, pain intensity, and neurosensory impairments. Diabetes had an indirect association with hip, but not knee ROM, through a path including p eripheral vascular disease. In conclusion, BMI is ct primary direct determi nant of hip and knee ROM. The paths by which diabetes and arthritis lead to physical disability may be mediated, in part, at the level of impair ment by BMI's association with joint range of motion. Interventions designed to decrease the impact of diabetes and arthritis on disability should track ch anges in BMI and joint ROM to measure the paths that account for the interv ention's success. The observed associations suggest that interventions targ eted to decrease BMI itself may lead to improved function in part through i mproved joint ROM. (C) 2000, Editrice Kurtis. (C) 2000, Editrice Kurtis.