Examining the consequences of rehabilitation interventions on disease progression and functional decline: Is function really the only thing that matters?

While reading the articles by Mikesky et al (1) and van Dijk et al (2) which appear elsewhere in this issue of Arthritis Care & Research, I was reminded of the ongoing debate concerning whether measurement of radiographic progression of osteoarthritis (OA) or the progression of symptoms and functional decline is more relevant in reflecting the status of patients with knee OA. Mikesky et al examined the effects of strength training on the incidence and progression of knee OA over a 30-month period. This area of study is important because although there have been a number of studies addressing the relationship between strength and physical function (3–6) and the effects of strength training on pain and function (6–9), to my knowledge there have been no clinical trials examining the effects of strength training on the incidence or progression of radiographic knee OA. However, based on the results of the Mikesky et al study (1), the actual training program did not appear to induce a significant amount of muscle strengthening in the short term, and there was actually a decrease in strength over the long term. Despite concerted efforts by the investigators to encourage adherence to the exercise programs, significant problems with subject adherence occurred during the course of the study, which may explain the limited effects of the program on muscle strength. Nevertheless, it is difficult to make any definitive conclusions about the effects of strength training on the incidence or progression of knee OA based on the results of the study by Mikesky et al, when it is not clear that meaningful increases in strength actually occurred. Further work is still needed to determine whether inducing and maintaining significant gains in muscle strength can have either a protective or adverse effect on the progression of knee OA. The article by van Dijk et al (2) is a systematic review of the literature concerning the changes in functional status over time and the identification of predictors of functional change in patients with knee and hip OA. This area of work is also very important because improved understanding of factors that may either contribute to or protect against functional decline can provide insight for developing interventions that might enhance the effectiveness of preventing or minimizing disability. Although van Dijk et al identified a number of factors in the current literature that can either contribute to or protect against functional decline, they correctly point out that the evidence is limited and there is much more room for work in this area. However, van Dijk et al made one statement that caught my attention: “Previous results from cross-sectional studies suggested there was no or only a weak association between radiologic changes and functioning. In this review, this ambiguous relationship was confirmed by the results of longitudinal studies, emphasizing the need to focus on functional rather than radiologic consequences. Such functional focus is furthermore important, because knowledge of functional consequences is essential for the development of optimal rehabilitation programs in patients with OA.” For me, this statement served as the impetus for the topic of this editorial. Although I am in agreement with a significant focus on function (because this has been a very large element in my own work), I am concerned that it is premature to suggest we completely shift the direction of focus away from radiologic consequences, or progression of disease, and direct our efforts mainly on function when evaluating the consequences of rehabilitation interventions for knee OA. It is true that both cross-sectional and longitudinal studies have not demonstrated that radiographic severity correlates with measures of pain and function (10–13). For this reason, it has been suggested that efforts may be better placed in developing interventions that reduce the burden of illness related to OA with respect to pain, limitation of G. Kelley Fitzgerald, PhD, PT: University of Pittsburgh, Pittsburgh, Pennsylvania. Address correspondence to G. Kelley Fitzgerald, PhD, PT, Department of Physical Therapy, University of Pittsburgh, 6035 Forbes Tower, Pittsburgh, PA 15260. E-mail: kfitzger@ pitt.edu. Submitted for publication June 19, 2006; accepted July 13, 2006. Arthritis & Rheumatism (Arthritis Care & Research) Vol. 55, No. 5, October 15, 2006, pp 687–689 DOI 10.1002/art.22243 © 2006, American College of Rheumatology