metaphyses

Metaphysis is the flared portion of a long bone that lies between the epiphysis at one end and the diaphysis at the other. In a growing bone, the growth plate (epiphyseal plate) sits at the boundary between the metaphysis and the epiphysis and controls longitudinal bone growth through endochondral ossification. The metaphysis contains cancellous (spongy) bone with a lattice of trabeculae and, in children, active red marrow; as a person ages, red marrow in this region is gradually replaced by yellow marrow.

Histologically, the metaphysis is rich in vascular channels that supply the adjacent epiphysis and diaphysis. The region is highly metabolically active during growth, with rapid modeling and remodeling as bones lengthen and change shape in response to mechanical loads. The cortical bone surrounding the metaphysis is relatively thin in developing bone, reflecting its role in growth and remodeling.

Functionally, the metaphysis serves as the site of longitudinal bone growth in children via endochondral ossification at the growth plate. Once growth ceases and the growth plate closes, the metaphysis fuses with the diaphysis to form a single region of mature bone.

Clinical significance includes the propensity for metaphyseal fractures in children, which can affect growth if adjacent physes are damaged. The metaphysis is also a region evaluated in radiographs for metabolic or nutritional bone diseases; changes in trabecular pattern or metaphyseal margins can indicate pathology.