Teaching monograph. The pathophysiology of bone and joint disease

Unlike parenchymal organs, the form and function of the connective tissues are the expression of the extracellular matrices of which they are largely composed. Bone, cartilage, and dense fibrous connective tissue differ in their visible appearance and mechanical properties because of the various compositions of their matrices. Bone also has a structural inhomogeneity. The ends of the long bones and the vertebral bodies are largely composed of an open network of delicate plates and rods, forming cancellous or spongy bone. It is this trabecular bone with its high surface-to-volume ratio which is susceptible to rapid turnover and hence most sensitively reflects alterations in mineral homeostasis. Growth and modeling are intrinsic to the developing skeleton. Growth is the means whereby the skeleton increases in size. Modeling involves the sculpting of bone and its movement through space and is probably influenced by the distribution of skeletal load. It is the combination of growth and modeling which is responsible for the development of a small fetal bone into an identically shaped, yet manyfold larger, adult bone. Remodeling is the process associated with mineral homeostasis and redistribution of load through the skeleton. While minute-to-minute alterations of mineral balance probably do not involve the remodeling process, it certainly has a relationship to long-term homeostatic demands made on bone.