Correlation between avascular necrosis and the presence of the ossific nucleus when treating developmental dysplasia of the hip

Purpose: This study assessed whether avascular necrosis (AVN) is correlated with the presence or absence of the ossific nucleus (ON) at the initiation of conservative treatment for developmental dysplasia of the hip (DDH). To date, the correlation between the presence of the ON and AVN manifestations remains ambiguous.

Methods: The medical records of 148 patients with 234 dislocated hips who presented at our institution between January 2006 and December 2007 were reviewed. Based on ultrasound examination, the hips were classified according to Graf IIIa, IIIb, and IV criteria. Patients aged >6 months were simultaneously examined by standardized pelvis radiography.

Results: The ON was present in 84 hips (35.9 %) at the beginning of treatment. Treatment was begun at a mean age of 5 months, with overhead traction for 2 weeks followed by arthrography and a spica cast for 4 weeks. Afterwards, we used a Tübingen hip-flexion splint. The mean age at final follow-up was 87 months. Hips were radiographically evaluated at last follow-up according to the Ogden-Bucholz AVN classification scheme. There was no significant difference in AVN prevalence between ON(-) versus ON(+) hips in children aged ≤10 months (P = 0.681), whereas when all age groups were analyzed together, AVN was significantly increased in ON(+) hips (P = 0.002). Clinical examination revealed no differences in limping, leg length inequality, and range of motion of hips in the ON(-) versus ON(+) groups.

Conclusion: We conclude that DDH treatment should be performed early without regard to the presence or absence of the ON. Reduction should not be delayed beyond >10 months of age because any delay in treatment increases the incidence of AVN.