Purpose: To determine the effect of the ossific nucleus on avascular necrosis (AVN) of the hip in the treatment of hip dislocation.

Methods: A systematic review was performed in MED-LINE, EMBASE, DARE, and Cochrane Library. Two independent reviewers evaluated all articles. Interrater agreement was determined by the kappa statistic. Quality of evidence was evaluated by the GRADE statement. A meta-analysis was performed on the main outcome, AVN 2 years after reduction.

Results: 6 observational studies met the inclusion criteria. Inconsistency was found in that half of the studies reported a protective effect of the ossific nucleus, whereas half of the studies did not. A meta-analysis of all studies (415 patients) showed no statistical significant effect of the ossific nucleus on the development of AVN, with 42 (17%) cases of AVN in infants with the ossific nucleus present at reduction compared with 47 (28%) in the group without a ossific nucleus (RR 0.60, 95% CI 0.28 to 1.27). If only radiographic changes of grade ≥II were considered AVN, a significant difference in the prevalence of AVN was found, with 15 (6%) cases of AVN in infants with the ossific nucleus compared with 28 (20%) without the ossific nucleus (0.34, 0.17 to 0.67). Subgroup analysis showed that the presence of the ossific nucleus reduced the probability of AVN by 70% (0.30, 0.14 to 0.62) in case of a closed reduction, but no significant effect was found for open reduction (0.87, 0.50 to 1.54). All studies demonstrated methodological weaknesses compromising the quality of evidence.

Conclusion: We could not demonstrate a significant effect of the ossific nucleus on the development of AVN. The meta-analysis suggested that the ossific nucleus might have a protective effect against the development of more severe forms of AVN.