A radiological classification of lateral growth arrest of the proximal femoral physis after treatment for developmental dysplasia of the hip

BACKGROUND: After treatment of developmental dysplasia of the hip, lateral growth arrest of the physis of the proximal femur resulting in disturbance of the growth of the capital femoral epiphysis is not uncommon. The changes are usually not apparent until approximately the age of 9 years. The residual deformity has a variable prognosis at skeletal maturity. The purpose of this study was to assess the long-term impact of these proximal femoral changes on the function of the hips. METHODS: We reviewed the natural history of 22 hips in 21 patients who had a lateral growth arrest of the physis of the proximal femur after treatment of developmental dysplasia of the hip. The average age at follow-up was 22 years. The radiographic changes in the proximal femur after the growth arrest were analyzed. Radiographic outcome was assessed using Severin criteria, with classes I and II being graded as satisfactory and classes III and IV being graded as unsatisfactory. The Iowa hip score was used to assess clinical outcome. RESULTS: The consistent radiographic findings were a shortened lateral neck length in comparison with the medial neck length and lateral tilting of the capital femoral epiphysis, both of which were evident by an average age of 9 years. Overall, 41% of hips had a satisfactory radiological outcome according to the Severin classification. Two types of changes were observed in the proximal femur: a varus configuration (pattern A, 12 hips) and a valgus configuration (pattern B, 10 hips). Pattern A hips (varus) had a satisfactory result in 75% of the hips compared with none in pattern B hips (valgus). CONCLUSIONS: Valgus orientation of the proximal femur (pattern B) leads to disruption of the Shenton line, progressive subluxation, and acetabular dysplasia which resulted in class III or class IV Severin grade hips leading to a poorer clinical and radiological outcome at long-term follow-up. LEVEL OF EVIDENCE: Level III-Diagnostic study.