Connective tissues: matrix composition and its relevance to physical therapy.

In the last 2 decades, the understanding of CT structure and function has increased enormously. It is now clear that the cells of the various CTs synthesize a variety of ECM components that act not only to underpin the specific biomechanical and functional properties of tissues, but also to regulate a variety of cellular functions. Importantly for the physical therapist, and as discussed above, CTs are responsive to changes in the mechanical environment, both naturally occurring and applied. The relative proportions of collagens and PGs largely determine the mechanical properties of CTs. The relationship between the fibril-forming collagens and PG concentration is reciprocal. Connective tissues designed to resist high tensile forces are high in collagen and low in total PG content (mostly dermatan sulphate PGs), whereas CTs subjected to compressive forces have a greater PG content (mostly chondroitin sulphate PGs). Hyaluronan has multiple roles and not only provides tissue hydration and facilitation of gliding and sliding movements but also forms an integral component of large PG aggregates in pressure-resisting tissues. The smaller glycoproteins help to stabilize and link collagens and PGs to the cell surface. The result is a complex interacting network of matrix molecules, which determines both the mechanical properties and the metabolic responses of tissues. Patients with CT problems affecting movement are frequently examined and treated by physical therapists. A knowledge of the CT matrix composition and its relationship to the biomechanical properties of these tissues, particularly the predictable responses to changing mechanical forces, offers an opportunity to provide a rational basis for treatments. The complexity of the interplay among the components, however, requires that further research be undertaken to determine more precisely the effects of treatments on the structure and function of CTs.