The exact cause of osteonecrosis in the setting of developmental dysplasia of the hip (DDH) is unknown. However, some pediatric orthopaedists are concerned that DDH treatment in the absence of the ossific nucleus of the femoral head increases the risk of subsequent osteonecrosis. That concern has to be weighed against evidence that delayed DDH treatment may lead to more difficult reduction and potentially necessitate additional procedures.
In the May 3, 2017 issue of JBJS, Chen et al. performed a meta-analysis of cohort and case-control studies to clarify this potential “conflict of interests” in DDH treatment. Twenty-one observational studies were included. Of the 969 hips with an ossific nucleus present before reduction, 198 hips (20.4%) had eventual osteonecrosis events; among the 608 hips without an ossific nucleus, 129 (21.2%) had osteonecrosis events. The authors state that this difference “is neither clinically important nor [statistically] significant.”
A sub-analysis determined that the presence of the ossific nucleus was not associated with significantly decreased odds of osteonecrosis even among patients who later developed more severe (grades II to IV) osteonecrosis. Chen et al. also performed a “meta-regression” of studies with short- and long-term follow-ups, finding “no evidence for a protective effect of the ossific nucleus with either short or long-term follow-up.”
Although 11 of the 21 studies in the meta-analysis were deemed high quality and 10 were of moderate quality, the inherent limitations of a meta-analysis derived predominantly from retrospective data prompted the authors to call for “further prospective studies with long-term follow-up and blinded outcome assessors.” Nevertheless, these findings lend additional support to the belief that treatment for DDH should not be delayed based on the absence of the femoral head ossific nucleus.