ABSTRACT
BACKGROUND: Kalamchi and MacEwen (K&M) described a four-group scheme for classifying osteonecrosis (ON) following treatment for developmental dysplasia of the hip (DDH). However, the four groups can overlap in radiographic appearance, making assessment difficult. QUESTIONS/PURPOSES: We (1) describe a simplified K&M classification; (2) determined whether the simplified classification was reliable; and (3) assessed whether differences in the type of reduction or age at reduction resulted in different degrees of ON. PATIENTS AND METHODS: We retrospectively reviewed 300 patients with DDH treated with either open or closed reduction. We included 101 of these patients (133 involved hips). Intraobserver and interobserver reliability testing of the original and our simplified classification was performed. ON occurred in 64 hips (48%). Of these, 22 had original K&M Group I disease (classified as simplified Group A), and 42 had original K&M Groups II, III, or IV disease (classified as simplified Group B). The mean age of the patients at final followup was 12.4 years (range, 6-26.3 years). RESULTS: The interobserver reliability of the simplified classification was greater than that of the K&M classification (0.51 vs 0.33, respectively). Closed reduction after skin traction resulted in a lower incidence of Group B ON than open reduction, regardless of age at reduction. CONCLUSIONS: We propose a simplified and more reliable classification of ON after DDH. With the new classification we found type of reduction (closed with traction versus open without femoral shortening) but not age influenced the risk of ON. LEVEL OF EVIDENCE: Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.