Developmental dysplasia of the hip: A special pathology.

Developmental dysplasia of the hip (DDH) is one of the most common congenital disorders in childhood. Its diverse pathological changes require different treatments and result in different outcomes. Although many studies have been conducted on DDH, some special pathology is still unrecognized. We here presented a rare case of a one-year and eleven-month old girl with DDH; a half-free intra-articular osteocartilaginous tissue was found in her right hip joint. X-ray, computer assisted tomography (CT) and magnetic resonance imaging (MRI) were performed to evaluate the pathological changes. MRI revealed some positive findings. The patient experienced open reduction and histopathological examination of the small tissue. Through gross anatomy it is a half-free intra-articular osteocartilaginous tissue, which can fully match a fossa observed at the femoral head. Histopathological examination found that the tissue was composed of collagenous fiber and cartilage-like tissue. Interestingly, we found the expression of type I collagen according to immunohistochemical analysis, which indicated that the cartilage-like tissue was formed due to laceration of the articular cartilage. This kind of disorder should be included as one of the pathologies of DDH. The most possible origin of this tissue is the femoral head which we speculate may have been fractured before.