Should discontinuity of the osteotomy site 1 year after periacetabular osteotomy be diagnosed as delayed union and not non-union?

Background: Discontinuity at the site of osteotomy is a complication after periacetabular osteotomy. The objectives of this study were to assess whether discontinuity is owed to delayed union or non-union and to clarify the risk factors associated with discontinuity >1 year after periacetabular osteotomy.

Methods: We performed a retrospective review of 104 hips in 95 consecutive patients who underwent periacetabular osteotomy between 2017 and 2021. Pre- and post-periacetabular osteotomy radiographs of 97 hips in 89 patients were finally evaluated. Radiographic evaluations included the occurrence of stress fractures in the inferior pubic ramus and posterior column, incidence of discontinuity at osteotomy sites and stress-fractured bones, centre-edge angle, acetabular roof obliquity, and Tönnis grade. Clinical evaluations included the age at surgery, body mass index, and Harris hip score.

Results: The incidence of discontinuity at the pubic osteotomy site and stress-fractured posterior column improved from 16.5 % to 2.1 % at 1 year postoperatively to 5.2 % and 0 % at the final follow-up, respectively. Multivariate analysis revealed that postoperative stress fracture in the inferior pubic ramus was significantly more common in patients with discontinuity of the stress-fractured inferior pubic ramus at the final follow-up.

Conclusions: The present study demonstrated that even if discontinuity is present at the osteotomy site or stress-fractured inferior pubic ramus and posterior column 1 year post-periacetabular osteotomy, continuity can subsequently occur at these sites. The findings suggest that discontinuity 1 year postoperatively should be defined as delayed union rather than non-union. We also identified postoperative stress fracture in the inferior pubic ramus as a risk factor for discontinuity at the pubic osteotomy site at a mean time of 3.2 years after periacetabular osteotomy.