Time to Minimal Clinically Important Difference in Patients Undergoing Conversion Total Hip Arthroplasty After Femoral Neck Fracture: A Propensity Score Matched Study

Background: Conversion total hip arthroplasty (cTHA) is commonly used for patients with persistent osteoarthritis or failed fixation following femoral neck fracture (FNF). There are limited data comparing patient-reported outcomes between patients undergoing cTHA after FNF and primary THA (pTHA) patients. This study aimed to compare the time to reach the minimal clinically important difference for improvement (MCID) for the Hip Disability and Osteoarthritis Outcomes Score-Physical Function Short Form, Patient-Reported Outcomes Measurement Information System (PROMIS) Global Physical, and PROMIS Physical Function short form 10a (PF-10a). Methods: Patients undergoing cTHA for FNF between 2016 and 2022 were identified from an institutional database and propensity score matched 1:4 to pTHA patients by age, sex, body mass index, and Charlson Comorbidity Index. Demographic and MCID achievement rates were compared. To assess the time to achieve MCID, survival curves with and without interval censoring were used. Results: A total of 258 THAs (52 FNF cTHA and 206 pTHA) were analyzed. All FNFs were managed surgically. The rate of achieving MCID was similar between the FNF cTHA and pTHA cohorts for all three PROMs. For PROMIS PF-10a, FNF cTHA had a markedly longer median time to MCID at 9.8 months (95% confidence interval [CI], 6.5 to 12.1) compared with 4.2 months (95% CI, 3.3 to 6.0) for pTHA ( P < 0.001). Interval censoring revealed that FNF cTHA achieved MCID for PROMIS PF-10a between 5.07 and 5.34 months, whereas pTHA achieved MCID between 1.37 and 1.37 months ( P < 0.001). Conclusion: The time to achieve MCID was markedly slower for FNF cTHA patients compared with pTHA patients. This delay in achieving MCID should be factored into shared decision-making discussions to enhance preoperative expectation management and patient education. Future research is needed to identify modifiable factors that could improve recovery outcomes for FNF cTHA patients.