Activity limitations (eg, walking, stair-climbing) are common among individuals with knee osteoarthritis (OA). Muscle
weakness has been hypothesized to be a causal factor in the development of activity limitations.However, the evidence for muscle weakness being a causal factor is limited. The association between muscle strength and activity limitations has been found in cross-sectional studies. Moreover, baseline muscle strength has been found to be a predictor of activity limitations. A causal association, however, requires that a decrease in muscle strength be shown to be associated with an increase in activity limitations. This longitudinal association has been studied in 2 observational studies, which showed conflicting results, and in a clinical trial. The latter study, however, failed to control for
confounding variables. We therefore decided to study the association between change in muscle strength and change in activity limitations in a longitudinal, well-controlled observational study. If muscle weakness is indeed a causal factor in the increase in activity limitations, one would hypothesize a decrease in muscle strength to be associated with an increase in activity limitations. Activity limitations might be affected by several neuromuscular factors. In addition to muscle weakness, poor knee joint proprioception and high knee joint laxity have been hypothesized to contribute to the increase in activity limitations. In these cross-sectional studies, the association between muscle strength and activity limitations was demonstrated to be stronger in patients with knee OAwith poor proprioception than in patients with accurate proprioception, while the results for laxity were conflicting. Longitudinal studies are not available. It has been
hypothesized that the impact of muscle weakness on activity limitations is even greater in the presence of poor proprioception and laxity: Poor proprioception and laxity are hypothesized to lead to instability of the knee, thereby aggravating the impact of muscle weakness on activity limitations.22 However, evidence to support this hypothesis is based on cross-sectional studies only. Whether the longitudinal association between change in muscle strength and change in activity limitations is moderated by poor proprioception and high laxity in patients with knee OA
is unknown. The aims of the study were to determine whether a decrease in muscle strength over 3 years is associated with an increase in activity limitations in persons with early symptomatic knee OA; and to examine whether the longitudinal association between muscle strength and activity limitations is moderated by knee joint proprioception and laxity.
Activity limitations (eg, walking, stair-climbing) are common among individuals with knee osteoarthritis (OA). Muscle
weakness has been hypothesized to be a causal factor in the development of activity limitations.However, the evidence for muscle weakness being a causal factor is limited. The association between muscle strength and activity limitations has been found in cross-sectional studies. Moreover, baseline muscle strength has been found to be a predictor of activity limitations. A causal association, however, requires that a decrease in muscle strength be shown to be associated with an increase in activity limitations. This longitudinal association has been studied in 2 observational studies, which showed conflicting results, and in a clinical trial. The latter study, however, failed to control for
confounding variables. We therefore decided to study the association between change in muscle strength and change in activity limitations in a longitudinal, well-controlled observational study. If muscle weakness is indeed a causal factor in the increase in activity limitations, one would hypothesize a decrease in muscle strength to be associated with an increase in activity limitations. Activity limitations might be affected by several neuromuscular factors. In addition to muscle weakness, poor knee joint proprioception and high knee joint laxity have been hypothesized to contribute to the increase in activity limitations. In these cross-sectional studies, the association between muscle strength and activity limitations was demonstrated to be stronger in patients with knee OAwith poor proprioception than in patients with accurate proprioception, while the results for laxity were conflicting. Longitudinal studies are not available. It has been
hypothesized that the impact of muscle weakness on activity limitations is even greater in the presence of poor proprioception and laxity: Poor proprioception and laxity are hypothesized to lead to instability of the knee, thereby aggravating the impact of muscle weakness on activity limitations.22 However, evidence to support this hypothesis is based on cross-sectional studies only. Whether the longitudinal association between change in muscle strength and change in activity limitations is moderated by poor proprioception and high laxity in patients with knee OA
is unknown. The aims of the study were to determine whether a decrease in muscle strength over 3 years is associated with an increase in activity limitations in persons with early symptomatic knee OA; and to examine whether the longitudinal association between muscle strength and activity limitations is moderated by knee joint proprioception and laxity.
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