How Does the Achievement of Minimum Clinically Important Difference, Substantial Clinical Benefit, and Patient Acceptable Symptom State Change Over Time After Periacetabular Osteotomy?

Abstract

Background: Anchor-based thresholds of the minimum clinically important difference (MCID), substantial clinical benefit (SCB), and patient acceptable symptom state (PASS) were recently defined for the modified Harris hip score (mHHS) and the International Hip Outcome Tool 12 (iHOT-12) among patients undergoing periacetabular osteotomy (PAO). However, the likelihood of meeting these thresholds and the amount of time it takes for patients to achieve them remain unknown. Understanding the probability of achieving the MCID, SCB, and PASS throughout the postoperative course is important for fair preoperative counseling.

Questions/purposes: (1) For patients treated with PAO, what is the probability of achieving the MCID, SCB, and PASS for the mHHS and iHOT-12 at 1, 2, 5, and 10 years postoperatively using threshold values that accurately characterize the perceptions of patients undergoing PAO? (2) Which factors are associated with time to achieving the MCID, SCB, or PASS?

Methods: Between March 2011 and February 2025, a total of 784 patients underwent PAO for symptomatic acetabular dysplasia at one institution. Of these, 0.4% (3 of 784) who underwent conversion THA were excluded, yielding 781 patients as potentially eligible. Patients without minimum 1-year postoperative PROMs were also excluded, leaving 85% (665 of 781) of patients for analysis. The study cohort (in which 94% [622 of 665] were women, with a mean ± SD age at time of surgery of 26 ± 8 years) included 24% (158 of 665) of patients with prior ipsilateral hip surgery and 37% (246 of 665) of patients with a psychiatric diagnosis. Cumulative probabilities were determined using a parametric survival model under a Weibull distribution with interval censoring. Outcome changes of the mHHS and iHOT-12 were evaluated against the anchor-based MCID and SCB thresholds from prior work. Postoperative scores were evaluated against PASS thresholds from prior work. Intervals were constructed for each patient, ranging from the last known point at which a threshold was not achieved to the earliest time point at which a threshold was met. Weibull regression models were used to identify variables associated (p < 0.05) with the time to achieving each outcome threshold.

Results: For the mHHS, the cumulative probability of achieving the MCID, SCB, and PASS was as follows: 61% at 1 year, 71% at 2 years, 83% at 5 years, and 90% at 10 years for the MCID; 53% at 1 year, 63% at 2 years, 76% at 5 years, and 85% at 10 years for the SCB; and 78% at 1 year, 85% at 2 years, 92% at 5 years, and 96% at 10 years for the PASS. For the iHOT-12, the cumulative probability of achieving the MCID, SCB, and PASS was as follows: 69% at 1 year, 78% at 2 years, 88% at 5 years, and 93% at 10 years for the MCID; 52% at 1 year, 63% at 2 years, 76% at 5 years, and 85% at 10 years for the SCB; and 65% at 1 year, 74% at 2 years, 85% at 5 years, and 91% at 10 years for the PASS. Prior ipsilateral hip surgery was associated with a substantially longer time to reach all thresholds. Having a psychiatric diagnosis was associated with a moderately longer time to reach the MCID, and undergoing bilateral surgery was associated with a substantially longer time to reach the MCID and moderately longer time to reach the SCB. Each 1-point increase in preoperative mHHS and iHOT-12 scores was associated with a slightly longer time to achieve the MCID and SCB and a slightly shorter time to achieve the PASS.

Conclusion: We found that at 1 year, the probability of achieving the MCID, SCB, and PASS (61%, 53%, 78% and 69%, 52%, 65% for the mHHS and iHOT-12, respectively) was lower than previously reported rates, indicating that prior research may have minimized the duration of PAO recovery. Thus, patients can be counseled that by 1 year, they may not experience perceptible improvement in their hip pain and function. The probability of achieving all thresholds increased at each subsequent time point, although even at 10 years, 15% of patients were unlikely to consider their improvement to be substantial, and loss to follow-up may cause our estimates of achieving an MCID, SCB, or PASS to be optimistic. Still, the preoperative discussion can also convey that achieving clinically meaningful benefit becomes more likely throughout the postoperative course. Prior ipsilateral surgery, psychological comorbidities, and bilateral surgery were associated with a moderate to substantially longer time to achieve the MCID, SCB, and PASS. These probabilities and factors provide a foundation for setting realistic patient expectations regarding time frames for improvements in pain and function.

Level of evidence: Level III, therapeutic study.