The prevalence and risk factors for delayed union of the superior pubic ramus at one year after curved periacetabular osteotomy: its risk factor and outcome.

Purpose: Curved periacetabular osteotomy (CPO) has been developed for the treatment of acetabular dysplasia. While several studies have reported its good clinical results, the complications of CPO include delayed union and nonunion of the superior pubic ramus. The purpose of this study is to investigate the prevalence of delayed union of the pubis one year after CPO, and to determine the risk factors for this complication.

Methods: The study examined 113 hips that underwent CPO between 2008 and 2012. Delayed union was assessed based on the anteroposterior radiography one year after CPO. A superior pubic ramus union group (U group) and a delayed union group (D group) were retrospectively compared regarding patient characteristics, clinical evaluations, and radiographic parameters.

Results: Delayed union rate was 16.8%. The D group contained a significantly greater proportion of smokers (p < 0.001). The gap at the pubic osteotomy site on CT coronal images was significantly larger in the D group (p < 0.001), and the cut-off value for the risk of nonunion was larger than 5.1 mm. Multivariate regression analysis indicated that smoking (OR 10.7, 95% CI 2.1-55.4) and a gap at the superior pubic ramus >5.1 mm (OR 16.5, 95% CI 3.7-73.7) were significantly associated with delayed union as independent risk factors.

Conclusion: The prevalence of delayed union one year after CPO was 16.8%. Smoking and a gap larger than 5.1 mm at the pubic osteotomy site are risk factors for delayed union after CPO.