Are some patients predisposed to avascular necrosis after hip surgery?

Although avascular necrosis (AVN) is believed to be an iatrogenic complication following treatment of developmental dysplasia of the hip (DDH), an investigation in China found 2 characteristics associated with the condition: the likelihood of AVN increases with both the grade of dislocation and of underdevelopment of the ossific nucleus. Furthermore, these factors are themselves positively correlated, investigators found.

The 108 patients (100 girls and 8 boys) in the study had 140 hip dislocations, with the left hip involved in 50 patients, the right in 26, and both in 32. Mean age at treatment was 16.6 months, and average length of follow-up was 10.1 years. All patients underwent closed reduction, followed by application of a spica cast for 3 months and then a second abduction cast.

Investigators scrutinized postoperative radiographs for signs of AVN and graded those that had necrosis. They also evaluated development of the epiphyseal ossific nucleus by measuring the epiphyseal ossific nucleus diameter to the neck diameter ratio (ENR) and classified the patients into 3 groups: those with ENR >50%, ENR <50%, and those with delayed unossification (no ossific nuclei in patients older than 1 year). They also divided patients by age at the time of reduction into 3 groups: <1 year, 1 to <1.5, and 1.5 to 2 years.

Of the 44 of 140 hips (31.4%) that developed AVN, most were Grade I (31 hips, 70%), with Grade II or higher in 14 hips, and some cases of Grade II detected when the patient neared adolescence. Two hips were Grade III and one Grade IV.

Analysis showed that AVN was significantly correlated with development of the ossific nucleus and dislocation grade but was not related to sex, side adductor or iliopsoas tenotomy, and age at the time of reduction. Specifically, AVN was found in only 3.4% of hips with an ENR >50% but in 51% of hips with an ENR <50% and in 50% of hips with delayed unossification.

Thoughts from Dr. Farber

Because the United States does more early screening than other countries, the patients in this study presumably were older at treatment than we would expect in the US, which might have affected the prognosis. However, it’s worth remembering this possible complication in your older children who were treated for DDH.

Reference

Bian Z, Guo Y, Lyu XM, Zhu ZH, Yang Z, Wang YK. Risk factors for avascular necrosis after closed reduction for developmental dysplasia of the hip. J Pediatr Orthop. 2022;42(9):467-473. doi:10.1097/BPO.0000000000002228.