Newest knowledge of the growth plate.

Recent research, both clinical and basic science, has improved our understanding of the growth plate. New technological advances in surgical technique, tissue preparation, light and electron microscopy, tissue culture, immunology, and imaging allow a better appreciation of this complex function of growing bone. The differing functions and environments of each of the areas of the physis are becoming clear. The resting zone is one of protein synthesis and physical structure. The proliferative zone appears to be the area that propels the physis by ordered, rapid cell duplication. The hypertrophic zone readies the physis for calcification by sequestering calcium and producing calcium-tolerating Type X collagen. The degenerative zone is very active in the process of calcification of the cartilage matrix by releasing calcium into the matrix and stimulating metaphyseal vascular ingrowth and collagen breakdown. Control of growth of the physis seems to come from both systemic (active in the proliferative zone) and local (active in the hypertrophic zone) growth factors.