Background: Concern for increased risk of osteonecrosis in hips with an absent ossific nucleus has led some surgeons to delay reduction in the treatment of developmental dysplasia of the hip (DDH) until the ossific nucleus is present. A previous meta-analysis reported a potential protective effect against high-grade osteonecrosis (II to IV) when the ossific nucleus was present. With a greater number of publications on this topic, revisiting this analysis is warranted. The aim of this meta-analysis was to systematically review and analyze the best clinical evidence regarding the association between the status of the ossific nucleus and development of osteonecrosis following the treatment of DDH.
Methods: MEDLINE, Embase, and Cochrane databases were systematically searched for studies including the status of the ossific nucleus and rate of osteonecrosis after open and closed reductions for the treatment of DDH. Study characteristics and risk estimates were extracted. Study quality was assessed using the Newcastle-Ottawa Scale. Pooled effect estimates were calculated using a random-effect model. Meta-regression assessed the relationships of reduction method, study quality, mean age at reduction, surgical approach, method of ossific nucleus assessment, and duration of follow-up to the odds of osteonecrosis.
Results: In the 21 observational studies (18 retrospective, 3 prospective) that were included, osteonecrosis developed in 20.4% of the hips in which the ossific nucleus was present at reduction compared with 21.2% of the hips in which the ossific nucleus was absent. Presence of the ossific nucleus was not associated with decreased odds of any grade of osteonecrosis (odds ratio [OR] = 0.70, 95% confidence interval [CI] = 0.43 to 1.12) or of more severe osteonecrosis of Grades II to IV (OR = 0.70, 95% CI = 0.30 to 1.17). Meta-regression did not show any effect of the mean age at reduction, reduction method, surgical approach, study quality, minimum or mean duration of follow-up, method of ossific nucleus imaging, or osteonecrosis classification system on the relationship between presence of the ossific nucleus and the risk of osteonecrosis.
Conclusions: The current literature does not support the hypothesis that presence of the ossific nucleus at reduction is associated with lower risk of osteonecrosis. Prospective studies with long-term follow-up and blinded assessors are warranted to optimally evaluate the relationship between potential risk factors and the development of osteonecrosis.
Level of evidence: Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.