growth plate

The growth plate consists of organized zones of chondrocytes: the resting zone, proliferative zone (chondrocyte division), hypertrophic zone (chondrocyte enlargement and matrix calcification), and zone of ossification (cartilage replaced by bone via endochondral ossification). Growth hormone (via IGF-1) and thyroid hormone stimulate chondrocyte proliferation, while estrogen ultimately triggers growth plate closure/fusion in both sexes at the end of puberty—explaining why children with precocious puberty may have early closure and shorter final height, while those with delayed puberty or estrogen deficiency (e.g., aromatase deficiency, estrogen receptor mutations) have continued linear growth. Growth plates are radiolucent on X-ray, appearing as a lucent line, and are weaker than surrounding bone/ligaments, making them susceptible to fracture (more common in children than sprains, unlike adults). The Salter-Harris classification (SALTR mnemonic) grades physeal fractures: Type I (Straight through the physis), Type II (Above the physis, involving metaphysis—most common), Type III (Lower, through epiphysis), Type IV (Through both metaphysis and epiphysis), Type V (Rammed/crush injury, worst prognosis due to growth arrest risk). Growth plate injuries can lead to growth disturbances, limb length discrepancy, or angular deformity if the blood supply or germinal layer is damaged. Conditions affecting growth plates include rickets (widened, irregular growth plates due to defective mineralization), achondroplasia (defective endochondral ossification due to FGFR3 mutation causing early growth plate senescence), and slipped capital femoral epiphysis (SCFE) in adolescents.