Injury to the acetabular triradiate physeal cartilage is a rare but potentially serious injury. When it occurs in young children acetabular growth may be delayed, leading to incongruency of the hip and subsequent subluxation. This series reviews 5 patients who sustained injury to the triradiate cartilage and subsequently developed acetabular dysplasia. The radiographic appearance of post-traumatic dysplasia is distinctly different than that of developmental dysplasia. In post-traumatic dysplasia the acetabular teardrop width and inner wall of the acetabulum is significantly increased with the femoral head being lateralized. Four patients have undergone acetabular reconstruction, with 3 patients having a periacetabular osteotomy and 1 having a Chiari osteotomy. The remaining patient with posttraumatic dysplasia has severe and symptomatic osteoarthritis and awaits a total hip replacement.