Predicting Outstanding Results Following Primary Total Hip Arthroplasty Using The Maximal Outcome Improvement Threshold.

Background: The delta difference between baseline patient-reported outcome measure scores (PROMS) and postoperative scores is used to measure success following primary total hip arthroplasty (THA). However, statistical improvement is not necessarily equal to clinical benefit. The percentage of the maximal improvement (MOI) is a psychometric tool to determine clinical improvement. This study aimed to determine thresholds for the MOI for the Forgotten Joint Score (FJS), the Harris Hip Score (HHS), and the Visual Analog Scale for Pain (VAS) following THA for osteoarthritis.

Methods: Data were retrospectively reviewed for all patients who underwent primary THA for hip osteoarthritis between October 2014 and July 2020. Patients who answered an anchor question for satisfaction and had baseline and minimum two-year follow-up scores were included. Receiver operating characteristic curve analyses were performed to determine the MOI thresholds with the area under the curve (AUC).

Results: In total, 584 patients were included, 53.1% women and 46.9% men, who had a mean age of 57 years (± 10.4). Improvement was reported for all PROMS (P < 0.0001). The AUC values for MOI for the FJS, HHS, and VAS were 0.788, 0.839, and 0.805, respectively. The MOI for the FJS, the HHS, and the VAS were 54.2, 65, and 67.1%, respectively.

Conclusion: Following primary THA for hip osteoarthritis, percentage thresholds for achieving the MOI for the FJS, the HHS, and the VAS for pain were 54.2, 65, and 67.1%, respectively. No preoperative predictors of achieving the MOI were identified.