Epiphysis

An epiphysis is the rounded end of a long bone, located at the proximal and distal ends of the bone. In developing bones, each epiphysis is separated from the diaphysis by the epiphyseal plate, a thin layer of cartilage that provides longitudinal growth. During later maturation the growth plate ossifies and is replaced by an epiphyseal line when growth ceases.

Anatomically, the epiphysis consists mainly of cancellous (spongy) bone, surrounded by a thin shell of compact bone, and is capped with articular cartilage where it forms a joint surface. The internal marrow cavity typically contains red bone marrow in children and may transition to fatty yellow marrow in adults. The epiphysis receives blood supply through the epiphyseal arteries that travel with surrounding vessels, and it houses the secondary ossification center that forms during endochondral ossification.

The epiphysis participates in articulation with adjacent bones, distributing load and absorbing stress through its spongy lattice. Growth and remodeling of the epiphysis are coordinated with the diaphysis and metaphysis, with growth occurring at the physis until closure.

Clinical relevance: physeal injuries, such as Salter-Harris fractures, affect growth and may require prompt management. In adults, the epiphysis remains the site of articulation and may be involved in conditions such as osteoarthritis affecting the joint surface.