Developmental dysplasia of the hip: open reduction as a risk factor for substantial osteonecrosis.
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.


OBJECTIVE
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.


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.


METHODS
Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
Department of Orthopaedic Surgery, Room 4M12, University of the Witwatersrand Medical School, 7 York Road, Parktown, Johannesburg 2193, South Africa. greg.firth@gmail.com
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Firth
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Robertson
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Schepers
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Fatti
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D016009:Chi-Square Distribution; D002648:Child; D005260:Female; D006618:Hip Dislocation, Congenital / Q000601:surgery*; D006801:Humans; D016015:Logistic Models; D008297:Male; D015588:Observer Variation; D016017:Odds Ratio; D019637:Orthopedic Procedures / Q000009:adverse effects*; D010020:Osteonecrosis / Q000145:classification / Q000000981:diagnostic imaging / Q000209:etiology*; D011237:Predictive Value of Tests; D011859:Radiography; D015203:Reproducibility of Results; D012189:Retrospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D012720:Severity of Illness Index; D013997:Time Factors; D014143:Traction; D016896:Treatment Outcome; D055815:Young Adult