Risk Factors Associated With Nonunion Following Periacetabular Osteotomy for Treatment of Symptomatic Hip Dysplasia.

Background: Nonunion of an osteotomy site is one of the most reported complications following periacetabular osteotomy (PAO). Identification of risk factors for nonunion is an important area of research as hip preservation has an increasing presence in orthopaedic surgery. Methods: We retrospectively identified patients who underwent PAO between March 2018 and May 2023 with a minimum of 1-year follow-up. Twelve-month postoperative radiographs were reviewed to determine the prevalence of nonunion. Descriptive statistics and mixed-effects logistic regression models were run. Results: Ninety-four hips (84 patients) were included. 84.5% of patients (n = 71) were female, average age was 28.2 (±9.8) years and body mass index (BMI) was 25.4 (±4.3) kg/m2. 15 of 94 hips (16.0%) were nonunited at the superior ramus osteotomy, and 2 of these hips (2.1%) also had an ischial nonunion. All nonunions occurred in female patients. The mean age of healed hips was 26.7 ± 9.5 years compared with 35.7 ± 8.1 years for nonunion (p = 0.016). BMI was higher in the nonunion group (healed 24.8 ± 4.0, nonunion 27.7 ± 4.3 kg/m2; p = 0.048). Hounsfield unit at the femoral neck on preoperative computed tomograpy was 220.7 ± 77.3 in healed hips and 167.6 ± 49.6 for nonunion (p = 0.047). Average distance from the ilioischial line to the most medial aspect of the femoral head was 5.6 ± 5.7 mm in healed hips and 1.7 ± 5.2 mm for nonunion (p = 0.047). Conclusions: Risk factors of nonunion include older age, lower bone mineral density at the femoral neck, greater acetabular fragment medialization, and higher BMI. Our findings reinforce the importance of preoperative risk assessment and patient counseling, particularly for older, higher BMI, female patients. Intraoperative modifications, including making a more lateral superior ramus osteotomy and minimizing excessive acetabular fragment medialization, may help mitigate nonunion risk. Level of Evidence: Level III. See Instructions for Authors for a complete description of levels of evidence.