The effects of immobilization on the characteristics of articular cartilage:: current concepts and future directions

Objective: The purpose of this paper is to review current data and concepts concerning the effect of immobilization on articular cartilage in animal models. We also evaluate the methods to measure articular cartilage changes in humans. Methods: Studies looking at the effects of immobilization on morphological, biochemical, and biomechanical characteristics of articular cartilage are reviewed. Results: Articular cartilage changes in immobilized animals include altered proteoglycan synthesis, as well as thinning and softening of the tissue. The overall thickness of articular cartilage in the knee decreases up to 9% after 11 weeks of immobilization and the deformation rate under test load increases up to 42%. Quantitative data about changes in human articular cartilage following immobilization are not available. This is mainly due to the lack of an accurate, reproducible, and non-invasive method to characterize articular cartilage. Discussion: An understanding of the alterations in articular cartilage following short and long term immobilization in humans is essential for the optimization of rehabilitation programs. Refined imaging techniques combined with state-of-the-art visualization tools could allow the systematical monitoring of articular cartilage morphology changes in immobilized humans. (C) 2002 OsteoArthritis Research Society International. Published by Elsevier Science Ltd. All rights reserved.