EP1.34 Early Patient-Reported Function Does not Correlate with Improved Contact Stress in Dysplastic Hips Treated with PAO

Abstract Objectives Surgically reorienting the acetabulum of a dysplastic hip using a periacetabular osteotomy (PAO) has been shown to reduce elevated contact stress in dysplastic hips, and patients with failed hips more than 10 years after PAO have significantly higher residual contact stress. The goal of this work was to determine if there is a relationship between high contact stress and poor patient reported outcomes at early-/mid-term follow up. Methods With IRB approval, we recontacted individuals treated for hip dysplasia by a single surgeon who were greater than 2 years after PAO. Patients completed patient-reported outcome measures (PROs) for each operative hip: International Hip Outcomes Tool (iHOT), modified Harris Hip Score (mHHS), PROMIS Bank v2.0 – Physical Function (PF), and PROMIS Bank v1.1 – Pain Interference (PI). Contact stress was calculated for each hip both preoperatively and postoperatively using discrete element analysis on models derived from each patient’s preoperative and postoperative CT scans. Contact stress and contact area were correlated with patient reported outcomes. Results 132 patients provided 2+ year outcomes for 169 dysplastic hips. Postoperative iHOT scores ranged from 10-100 (avg 75±23), and postoperative mHHS ranged from 22-100 (avg 86±15). PROMIS PF scores ranged from 22-100 (avg 51±9.5) and PI ranged from 39-68 (avg 49±8.3). Paired t-tests indicated peak contact stress was significantly lower postoperatively than preoperatively (14.4 vs 15.4 MPa, respectively, p<0.001). Mean contact stress was also lower postoperatively (3.3 vs 3.5, p<0.001), and contact area was higher (p=0.003). Correlation coefficients ranged from R2=0 to 0.01 for the relationship between all contact stress metrics and iHOT or mHHS scores. Correlations between pre-to-postoperative changes in contact stress metrics and PROs improved slightly, but were still negligible (R2=0.01=0.03). Conclusion Despite significant reductions in hip contact stress after PAO, early postoperative PROs only modestly correlated with contact stress. This that suggests high contact stress better relates to longer term joint degeneration and early improvements in patient-reported hip function after PAO are not closely related to contact stress.