Disability from chronic illness is a major problem for society, yet the study of its determinants lacks an overall theoretical paradigm. Johnston (1996) has proposed conceptualizing disability as behavior and integrating biomedical and behavioral predictors. Dixon, Johnston, Rowley, and Pollard (2008) tested a model including constructs from the International Classification of Functioning, Disability and Health (ICF) and the theory of planned behavior (TPB) using structural equation modeling; it fitted better and explained more variance than the ICF or TPB alone. We replicated their study with a new sample from the same population (orthopedic patients awaiting joint replacement) and also tested the model after the patients had surgery.
Two weeks before surgery, 342 orthopedic patients who had joint pain (most with arthritis) completed a questionnaire, with 228 completing it again 1 year after surgery. The authors tested Dixon et al.'s best-fit models cross-sectionally (before and after surgery) and assessed the goodness of fit of these imposed models to our data using structural equation modeling.
Findings strongly supported those of Dixon et al. Before surgery, results were very similar to Dixon et al. with all models accounting for significant variance and fitting well, but the integrated model fitted better and accounted for more variance. One year after surgery, Dixon et al.'s models showed even stronger fit to the data.
Although behavioral and biomedical (ICF) models were supported, the integrated model provided a better explanation of disability in this population than either of these models alone and suggests biopsychosocial interventions to reduce disability.