Patient Acceptable Symptom State (PASS) Threshold in the Oxford Hip Score 12 Months Following Primary Total Hip Arthroplasty: Factors Associated with Failure to Achieve the Threshold and the Impact on Hip-Specific Outcomes, Quality of Life, and Satisfaction

Abstract

Background: The Oxford Hip Score (OHS) is a widely used hip-specific patient-reported outcome measure (PROM) following primary total hip arthroplasty (THA). This measure is calculated from answers to a 12-item questionnaire and can provide indices that indicate clinically meaningful success, such as patient acceptable symptom state (PASS). There were three purposes of the present single-cohort retrospective study: first, to determine the threshold PASS; second, to determine the influence of patient characteristics (age, gender, and body mass index (BMI)) and preoperative OHS and other PROMs of patients (namely, EQ-5D-3L, EQ-VAS, and pain VAS) who did not achieve this threshold; and third, to establish whether failure to achieve the PASS could still be associated with meaningful clinical improvement. Methods: This single-centre retrospective cohort study was conducted over 10 years from January 2013 to December 2022, during which 3997 patients completed pre- and postoperative OHS. The mean age was 68.3 years (standard deviation 11.7), and there were 2375 (59.4%) females in the cohort. Patient satisfaction was used as the anchor to define the PASS. Results: An OHS at 12 months postoperative of ≥36 points was identified as the threshold PASS (area under the curve 88.5%, 95% confidence interval [CI] 87.0 to 90.1, p < 0.001). Overall, 3002 (75.1%) achieved the PASS at 12 months. Lower BMI (odds ratio [OR] 0.96, 95% CI 0.95 to 0.98, p < 0.001) and higher preoperative OHS (OR 1.05, 95% CI 1.03 to 1.06, p < 0.001), EQ-5D (OR 1.88, 95% CI 1.33 to 2.65, p < 0.001) and EQ-VAS (OR 1.02, 95% 1.01 to 1.02, p < 0.001) were independently associated with achieving the PASS at 12 months. A total of 995 patients (24.9%) did not achieve this threshold. Patients not achieving the PASS had clinically meaningful worse (p < 0.001) postoperative outcomes and improvement relative to baseline in OHS, EQ-5D and EQ-VAS when compared to those achieving a PASS. Patients achieving the PASS were more likely to be satisfied with their THA (OR 16.8, 95% CI 12.8 to 22.1, p < 0.001); however, patients not achieving the PASS still had significant (p < 0.001) improvements relative to baseline in their OHS (9.6, 95% CI 9.0 to 10.2), EQ-5D (0.254, 95% CI 0.229 to 0.278), EQ-VAS (1.4, 95% CI −0.3 to 3.1) and pain VAS (8.2, 95% CI 6.1 to 10.3) and were more likely to be satisfied (70.8%) than not (29.2%). Conclusions: An OHS of ≥36 at 12 months was defined as the PASS. In total, 995 patients (29.4%) did not achieve this threshold, and in this group, patients were more likely to be female and have a high BMI and low preoperative OHS, EQ-5D, EQ-VAS, and pain VAS. Despite not achieving the PASS, they reported meaningful clinical improvements in OHS, EQ-5D, and pain VAS, and were satisfied with their THA (70.8%).