MRI findings in residual hip dysplasia.

BACKGROUND: Residual subluxation of the hip is a major problem in pediatric orthopaedics. Corrective surgery by Salter innominate osteotomy is performed for residual subluxation before school age. Common indications for corrective surgery are determined based on the clinical condition, x-ray images, and arthrographic images. However, the surgical indications vary among institutions. Thus, further information that can predict acetabular growth with certainty is needed for precise decision- making. This study focused on signal intensity changes on magnetic resonance (MR) images within the weight-bearing portion of the acetabulum to determine whether these signal intensity changes could predict acetabular growth.

METHODS: Thirty-six patients who showed residual subluxation after reduction of developmental dysplasia of the hip and whose MRIs were taken when they were around 3 years old were studied. Corrective surgery was performed in 14 patients, whereas the remaining 22 patients were followed conservatively. The presence of a high-signal intensity area (HSIA) within the weight-bearing portion of the acetabular cartilage on T2-weighted MR coronal section images was investigated, and the correlation between HSIA presence and acetabular growth was examined.

RESULTS: All patients who underwent corrective surgery showed an HSIA within the weight-bearing portion of the acetabular cartilage on T2-weighted MR images before surgery. After surgery, all patients showed HSIA disappearance or decrease. In patients who were followed conservatively, HSIA-positive patients had poor acetabular growth, whereas HSIA-negative patients had favorable acetabular growth.

CONCLUSIONS: HSIAs in the acetabular cartilage may be caused by an extraordinary stress load from the femoral head. The presence of HSIA on MRI may prevent acetabular growth. HSIA on MRI appears to be a significant decision-making tool for corrective surgery.