EP248 Increased risk of post-operative stress fractures in second side surgery for patients undergoing bilateral periacetabular osteotomies.

Abstract Background Post-operative stress fractures following periacetabular osteotomy can prolong the healing process, with some cases resulting in non-union. The purpose of this study was to characterize the incidence of stress fracture following PAO in a cohort of patients who underwent bilateral PAO and identify the subsequent risk of second side stress fracture if there had been a stress fracture on the first side. Methods A total of 112 patients (224 procedures) who underwent bilateral PAO between 2013-2023 to treat symptomatic acetabular dysplasia or retroversion were identified from the Northumbria Hip Preservation Unit patient database. In addition to demographic data and anatomical measurements (acetabular index, centre edge angle, acetabula version, femoral version) post operative radiographs were reviewed for evidence of stress fractures. Results Mean follow-up was 5.2 years (Range: 1.0 – 10.8). The average age was 31.6 years (range: 14.7-50.6) and 89% were female (108/112). The mean time between procedures was 2.0 years (range: 0.4-8.0). The mean BMI was 26.6 kg/m2 (SD: 4.4). The risk of sustaining a stress fracture following a 1st side procedure was 11.6 % (13/112). The risk of sustaining a stress fracture following a 2nd side procedure was 25 % (28/112). The risk of sustaining a stress fracture on the 2nd side PAO after sustaining stress fracture on 1st was 76.9% (10/13). The risk of sustaining a stress fracture in second side after not sustaining it on first was (18/98) =18.2%. Conclusions This study highlights that there is an increased risk with 25.0% of patients undergoing their 2nd side periacetabular osteotomy having a stress fracture. If patients had a stress fracture following their 1st procedure, then this risk was even higher with 79.6% patients having a further stress fracture. These findings highlight the importance of addressing modifiable risk factors prior to undertaking PAO and in cases of where there has been a stress fracture to revisit the risk profile assessment prior to undertaking a further PAO on the second side.