physes

Physes are the growth plates of long bones, cartilaginous regions located between the epiphysis and metaphysis that enable longitudinal bone growth during childhood and adolescence. They are present in most long bones, such as the femur, tibia, humerus, and radius, and their activity accounts for increases in bone length until skeletal maturity is reached.

Anatomy and function: Each physis comprises several histologic zones arranged from the epiphyseal to the metaphyseal side. These zones include the resting (reserve) zone, the proliferative zone, the hypertrophic zone, and the zone of calcification, sometimes described alongside the tidemark. Chondrocytes within these zones divide, mature, and are eventually replaced by bone through endochondral ossification, allowing the bone to lengthen. Growth at the physes is regulated by systemic hormones such as growth hormone and sex steroids, as well as thyroid hormones and mechanical factors.

Closure and maturity: With puberty, increased sex steroid production accelerates the ossification process, leading to gradual closure of the physes. Once the physes fuse, typically leaving an epiphyseal line, longitudinal growth ceases and final bone length is established.

Clinical relevance: Physes are relatively vulnerable in children because they are cartilaginous and weaker than surrounding bone and ligaments. Physeal injuries, classified by Salter-Harris systems, are common in pediatric trauma and can lead to growth disturbances, angular deformities, or limb-length discrepancies if the physis is damaged or its function is disrupted.

Imaging and assessment: On radiographs, physes appear as radiolucent growth plates between the metaphysis and epiphysis. Assessment focuses on physis integrity, signs of displacement, and potential arrest lines, which guide treatment to minimize long-term growth complications.