What Are the Minimum Clinically Important Difference, Substantial Clinical Benefit, and Patient-Acceptable Symptom State Thresholds for the Modified Harris Hip Score and International Hip Outcome Tool 12 Among Patients Who Undergo Periacetabular Osteotomy?

Abstract

Background

The utility of patient-reported outcome measures (PROMs) has been well established, but their interpretation relies on population-specific definitions of meaningful improvement. As such, the minimum clinically important difference (MCID), substantial clinical benefit (SCB), and patient-acceptable symptom state (PASS) thresholds have become prominent metrics in the orthopaedic evidence to ascribe clinical relevance to numeric PROM scores. Studies assessing outcomes of periacetabular osteotomy (PAO) relative to the MCID and PASS have previously evaluated patients against thresholds defined for hip arthroscopy for the treatment of femoroacetabular impingement or distribution-based MCID calculations. These scores may not accurately reflect the status or expectations of patients with a different symptom profile undergoing open hip preservation surgery.

Questions/purposes

For patients treated with PAO, we sought to (1) define the MCID, SCB, and PASS threshold values for the mHHS (modified Harris hip score) and International Hip Outcome Tool 12 (iHOT-12) using anchor-based methods; (2) assess the validity of MCID and SCB estimates against minimal detectable change (MDC) values; and (3) determine the proportion of patients who achieved a clinically meaningful threshold.

Methods

Between February 2011 and May 2023, a total of 690 patients underwent PAO for symptomatic acetabular dysplasia at one institution and were included in a longitudinally maintained hip preservation registry. The cohort used to define and validate MCID, SCB, and PASS threshold values consisted of those with a completed postoperative anchor questionnaire, which yielded 456 patients as potentially eligible. An additional 139 patients were excluded because of missing mHHS or iHOT-12 scores during the eligibility window (1 to 2 years postoperatively), leaving 70% (317 of 456) of patients to define and validate MCID, SCB, and PASS at a mean ± SD of 1.0 ± 0.3 years of follow-up. A minimum 1-year follow-up was chosen to reduce recall bias. The cohort for defining MCID, SCB, and PASS (94% [298 of 317] women, mean ± SD age at time of surgery 27 ± 8 years) included 21% (68 of 317) of patients with prior ipsilateral surgery. From those registry patients without complete anchor questionnaires, 37% (137 of 373) were identified with pre- and postoperative PROM scores at a mean ± SD of 1.0 ± 0.9 years of follow-up to form the sample for assessing the proportion of patients achieving a clinically meaningful threshold. The MCID, SCB, and PASS thresholds for the mHHS and iHOT-12 were calculated through an anchor-based approach, using area under the receiver operating curve to determine cut points that best identified positive responses, according to quality of life–based anchor questions. The MDC was calculated with confidence intervals (CIs) reflecting 80%, 90%, and 95% certainty to determine the smallest change in the PROM scores that can be considered above the level of measurement error. The validity of MCID estimates was assessed by confirming that they exceeded corresponding MDC values. The validity of SCB estimates were assessed by confirming that they exceeded corresponding MCID values. The proportion of patients achieving a clinically meaningful threshold was determined by calculating the percentage of patients who met the defined anchor-based scores.

Results

The MCID, SCB, and PASS thresholds for the mHHS were 18, 23, and 71, respectively. The MCID, SCB, and PASS thresholds for the iHOT-12 were 26, 42, and 65, respectively. The MDC ranged from 8 to 12 for the mHHS and 10 to 16 for the iHOT-12. The MCID values for the mHHS and iHOT-12 exceeded corresponding values of the MDC at all CIs. The SCB thresholds exceeded all corresponding MDC and MCID values. Across the mHHS and iHOT-12, the proportion of patients who achieved an MCID at the first time point ranged from 60% to 73%, the proportion of patients who achieved the SCB ranged from 49% to 56%, and the proportion of patients who achieved the PASS threshold ranged from 55% to 79%. Among the cohort for defining MCID, SCB, and PASS, the proportion of patients achieving any MCID, SCB, or PASS was 79%, 66%, and 81%, respectively. Among the sample for assessing the proportion of patients achieving a clinically meaningful threshold, the proportion achieving any MCID, SCB, or PASS threshold was 74%, 58%, and 72%, respectively.

Conclusion

We found that using a sample of patients undergoing PAO, the anchor-based values for the MCID and SCB were generally larger than previous distribution- and anchor-based scores that have been defined for hip preservation, whereas PASS threshold scores were similar. All MCID and SCB thresholds exceeded corresponding MDC values, confirming these scores to be valid estimates. These metrics provide more rigorous, procedure-specific definitions for the evaluation of treatment success and failure after PAO. As anchor-based metrics are defined based on patients’ perceptions, they should be used preferentially for postoperative assessment over distribution-based scores.

Level of Evidence

Level III, therapeutic study.

Introduction

Many young patients undergo periacetabular osteotomy (PAO) procedures for symptomatic hip dysplasia to reduce pain and improve quality of life [4, 39, 44]. Determining whether these procedures are effective from the patient’s vantage point is a primary professional obligation of the provider [5]. The utility of patient-reported outcome measures (PROMs) in measuring patient-centered change has been well established [2], but their interpretation relies on population-specific definitions of meaningful improvement. As such, the minimum clinically important difference (MCID), substantial clinical benefit (SCB), and the patient-acceptable symptom state (PASS) thresholds have become prominent metrics to ascribe clinical relevance to numeric PROM scores. The MCID, representing the smallest difference that is perceived as a meaningful change in health to the patient, can be defined using either a distribution- or anchor-based approach [7]. Although both methods have limitations, the anchor-based MCID is generally preferred as it relies directly on patient-reported improvement rather than statistical distributions, which are divorced from individual patient perceptions. Anchor-based calculations have been shown to have superior face validity in some clinical scenarios [21, 25]. The SCB, the change in a PROM score perceived as substantial in size by the patient [12], and the PASS threshold, the postoperative PROM score signifying patient satisfaction [45], can similarly be calculated using anchor-based methods. The MCID and SCB values can be validated through comparison with the minimal detectable change (MDC), defined as the threshold at which a difference reflects more than the measurement error of the instrument [15]. The combined application of these metrics aids the thoughtful use of PROMs in determining postoperative treatment success.

Studies on PAO, including those assessing outcome measures relative to the MCID and PASS, have previously evaluated patients against thresholds defined for hip arthroscopy for the treatment of femoroacetabular impingement or the MCID values determined using distribution-based methods on the study sample [10, 16, 17, 27, 37]. These scores (commonly an MCID of ≥ 8 and a PASS of ≥ 74 for the modified Harris hip score [mHHS] [1, 27, 37, 40]) have been calculated in patients treated with hip arthroscopy at 1-year follow-up using distribution- and anchor-based methods [3, 19, 31]. Few studies have described the psychometric properties of PROMs for PAO [8, 43], only one of which defined the MCID for mHHS as 7.4 using distribution-based methods [43]. To our knowledge, the SCB and PASS thresholds have yet to be defined for this procedure-specific population. Frequently used metrics defined for hip arthroscopy may not accurately reflect the status or expectations of patients with a different symptom profile undergoing open hip preservation surgery. Furthermore, distribution-based estimates for MCID values have no connection to patients’ perceptions about whether they have improved after surgery, and they may systematically over- or underestimate treatment success compared with anchor-based thresholds [21]. As such, we and others [7, 20, 23, 33] believe that anchor-based estimates of MCID are preferable for determining whether a treatment effect is sufficiently large to justify surgery.

Therefore, for patients treated with PAO, we sought to (1) define the MCID, SCB, and PASS threshold values for the mHHS and International Hip Outcome Tool 12 (iHOT-12) using anchor-based methods; (2) assess the validity of MCID and SCB estimates against MDC values; and (3) determine the proportion of patients who achieved a clinically meaningful threshold.

Patients and Methods

Study Design and Setting

This was a retrospective study drawn from a longitudinally maintained hip preservation registry at an urban, tertiary academic medical center. Patients were treated by one senior surgeon (ELS) experienced in performing PAO as part of a referral hip preservation practice.

Patients

Between February 2011 and May 2023, a total of 690 patients underwent PAO for symptomatic acetabular dysplasia at one institution and were included in a longitudinally maintained hip preservation registry. Since March 2016, results from an anchor questionnaire have been collected on enrolled patients. The cohort used to define and validate MCID, SCB, and PASS threshold values consisted of those with a completed postoperative anchor questionnaire, yielding 456 patients as potentially eligible. We included patients with PROM scores and results from the anchor questionnaire completed at a minimum of 1 year and a maximum of 2 years to provide estimates specific to the point at which most patients have recovered from PAO. This follow-up range was chosen as 1 year after PAO, patients typically have achieved radiographic union, completed supervised physical therapy, and resumed functional and recreational activity. For patients with multiple eligible data sets, the earliest PROM scores at a minimum of 1 year were included to reduce recall bias. For those who underwent bilateral surgery, only the second hip was considered as interpretability of PROM scores collected between surgical procedures may be limited by the disability of the second hip. We excluded an additional 139 subjects because of missing mHHS or iHOT-12 scores during the eligibility window (1 to 2 years postoperative), leaving 70% (317 of 456) of patients to define and validate MCID, SCB, and PASS thresholds at a mean ± SD 1.0 ± 0.3 years of follow-up (Fig. 1). From those registry patients without complete anchor questionnaires, 137 were identified with preoperative and a minimum 1-year postoperative PROM scores at a mean ± SD 1.0 ± 0.9 years of follow-up to form the sample for assessing the proportion of patients achieving a clinically meaningful threshold. The cohort for defining MCID, SCB, and PASS and the sample for assessing the proportion of patients achieving a clinically meaningful threshold were combined (n = 454) for the calculation of the MDC.

Fig. 1.

This Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) study flow diagram shows patients who were excluded because of missing anchor questionnaires or hip-specific PROMs.

Descriptive Data

The cohort for defining MCID, SCB, and PASS (94% [298 of 317] women, mean ± SD age at time of surgery 27 ± 8 years, 77% Tönnis grade 0 [243], 21% Tönnis grade 1 [66], 2% Tönnis grade 2 [5]) included 21% (68 of 317) of patients with prior ipsilateral surgery. Of the 68 patients with prior ipsilateral surgery, 72% (49) underwent one prior hip arthroscopy, 12% (8) underwent two hip arthroscopies, 6% (4) underwent three hip arthroscopies, 1% (1) underwent four hip arthroscopies, 8% (5) underwent prior surgical hip dislocation, 1% (1) underwent prior ipsilateral PAO, 1% (1) underwent open reduction and internal fixation, 1% (1) underwent varus osteotomy, 1% (1) underwent tendon transfer to the abductors, 1% (1) underwent iliopsoas lengthening, and 1% (1) underwent shelf acetabuloplasty. There were no differences between the patients included in the cohort for defining MCID, SCB, and PASS and the sample for assessing the proportion of patients achieving a clinically meaningful threshold, and both groups were comparable to all eligible patients in the registry in terms of demographics, preoperative radiographic measurements, and PROMs (Table 1). All patients underwent PAO as described by Ganz et al. [11] with a rectus and abductor sparing approach. A more cosmetic, transverse “bikini” incision was instituted in 2016 and was performed on 277 of the 317 patients in the cohort for defining MCID, SCB, and PASS. Within the cohort for defining MCID, SCB, and PASS, concomitant hip arthroscopy for intraoperative labral repair and/or femoroplasty was performed in 117 patients (Table 2).

Table 1.

Characteristics of the study cohort, test sample, and all registry patients

Characteristic	Cohort for defining MCID, SCB, and PASS (n = 317)	Sample for assessing the proportion of patients achieving a clinically meaningful threshold (n = 137)a	All registry patients (n = 690)a
Demographics
Age in years	27 ± 8	25 ± 8	25 ± 8
Women	94 (298)	91 (125)	93 (626 of 676)a
BMI in kg/m2	23 ± 4	22 ± 3	23 ± 4
Prior ipsilateral surgery	21 (68)	30.9 (38 of 123)a	26.4 (146 of 553)a
Radiographic parameters
Plain radiograph
Lateral center-edge angle in °	18 ± 8	17 ± 6	17 ± 8
Anterior center-edge angle in °	21 ± 11	20 ± 8	21 ± 11
CT
Alpha angle in °	56 ± 10	57 ± 13	56 ± 10
Femoral version in °	17 ± 12	20 ± 14	19 ± 12
Acetabular version at 1 o’clock in °	8 ± 9	8 ± 9	8 ± 9
Acetabular version at 2 o’clock in °	15 ± 8	15 ± 9	15 ± 8
Acetabular version at 3 o’clock in °	21 ± 7	20 ± 7	20 ± 7
PROMs
Baseline modified Harris score	59 ± 15	58 ± 13	58 ± 14
Follow-up modified Harris score	83 ± 15	80 ± 16	81 ± 16
Outcome change modified Harris score	25 ± 18	21 ± 18	23 ± 18
Baseline International Hip Outcome Tool 12	30 ± 17	28 ± 16	29 ± 16
Follow-up International Hip Outcome Tool 12	72 ± 24	67 ± 26	68 ± 26
Outcome change Hip Outcome Tool 12	42 ± 26	39 ± 26	40 ± 27

Data presented as mean ± SD or % (n). There were no differences (p > 0.05) between the groups in any variables presented. Both mHHS and iHOT-12 scores improved (p < 0.001) from baseline to follow-up in all groups.

^aData elements not available for all patients.

Table 2.

Percentage of patients undergoing concomitant procedures

Procedure	Value (n = 317)
Arthroscopy	37 (117)
Femoral osteochondroplasty	24 (77)
Anterior inferior iliac spine resection, subspine resection, or decompression	24 (76)
Femoral osteotomy	3 (10)
Surgical hip dislocation	2 (7)
Osteochondral allograft placement	1 (4)

Data presented as % (n).

Data and Survey Instruments

Demographic, radiographic, and surgical data are regularly recorded by the operating surgeon. These data are subsequently entered into the electronic medical record. Hip-specific PROMs (mHHS and iHOT-12) are administered preoperatively and annually per registry protocol, beginning at the 1-year follow-up through the electronic medical record or by a member of the hip preservation team. Data are automatically queried from the electronic medical record and transferred into the registry. These data were extracted by a member of the hip preservation team (ZAT). The anchor questionnaire, which included two questions (the single-item Patient Global Impression of Change [PGIC] [14] and the single-item Patient-Acceptable Symptom State question [PASS-Q] [41]), was administered to patients who had undergone PAO postoperatively along with the hip-specific PROMs. The PGIC question, “Please circle the response which best describes how your quality of life due to your hip pain and function has changed since surgery,” was modified to make it specific to hip pain after hip surgery; the response variables were modified from “very much improved,” “much improved,” “minimally improved,” “no change,” “minimally worse,” “much worse,” and “very much worse” to “much improved” (response frequency 48% [153 of 317]), “improved” (29% [92]), “slightly improved” (11% [35]), “no change” (6% [18]), “slightly worse” (5% [16]), “worse” (1% [3]), and “much worse” (0% [0]). The PASS question, “Taking into account all of the activities you have during your daily life, your level of pain, and also your functional impairment due to your hip, do you consider that your current state is satisfactory?” was modified to specify functional impairment because of the hip; response variables were modified from “yes” and “no” to “very satisfied” (63% [201 of 317]), “somewhat satisfied” (22% [70]), “somewhat dissatisfied” (11% [35]), and “very dissatisfied” (4% [11]). PGIC responses showed a moderate-to-strong correlation with mHHS and iHOT-12 outcome changes (r = 0.57 [95% confidence interval (CI) 0.49 to 0.64] and r = 0.58 [95% CI 0.49 to 0.65], respectively), and PASS-Q responses showed a moderate-to-strong correlation with postoperative mHHS and iHOT-12 scores (r = 0.63 [95% CI 0.55 to 0.69] and r = 0.64 [95% CI 0.56 to 0.70], respectively).

Primary and Secondary Study Outcomes

Our primary study goal was to define MCID, SCB, and PASS thresholds for the mHHS and iHOT-12 using an anchor-based approach. MCID was determined by anchoring outcome changes of the mHHS and iHOT-12 to positive responses on the PGIC. SCB was determined by anchoring outcome changes of the mHHS and iHOT-12 to only the most positive response on the PGIC. The PASS threshold was determined by anchoring postoperative mHHS and iHOT-12 scores to positive responses on the PASS-Q. Area under the receiver operating curve was used to determine cut points on the mHHS and iHOT-12 that best identified positive responses.

Our secondary study goals were to assess the validity of MCID and SCB estimates and to determine the proportion of patients achieving a clinically meaningful threshold. To assess validity, we defined the MDC at various CIs to determine the smallest change in the mHHS and iHOT-12 that can be considered above the level of measurement error or variability. We compared MCID estimates to corresponding MDC scores to verify that the MCID exceeded the error of the scoring instrument. Additionally, SCB estimates were compared with MCID thresholds. To be considered valid, the MCID should be greater than the MDC, and the SCB should be greater than the MCID. Last, we applied our thresholds to the cohort for defining the MCID, SCB, and PASS and the sample for assessing the proportion of patients achieving a clinically meaningful threshold to determine the percentage of patients who achieved our anchor-based values.

Ethical Approval

This study received approval from the local hip preservation steering committee to use data from an institutional review board–approved, longitudinally maintained hip preservation registry at the Hospital for Special Surgery.

Statistical Analysis

Descriptive Data

We assessed normality using the Shapiro-Wilk test. We used the Student t-test or the Mann-Whitney U test, as necessary, to compare pre- to postoperative PROM scores. We performed ANOVA and chi-square tests to assess differences in demographics, radiographic parameters, and PROMs across the cohort for defining MCID, SCB, and PASS; the sample for assessing the proportion of patients achieving a clinically meaningful threshold; and all registry patients for continuous and categorical variables, respectively. Pearson or Spearman correlations, depending on normality, were assessed between anchor responses and hip-specific PROMs.

Defining MCID, SCB, and PASS Thresholds

Patients who responded “slightly improved,” “improved,” or “much improved” on the PGIC were considered to have achieved an MCID. A response of “slightly improved” was included as meeting the MCID, as 69% (24 of 35) of patients who reported that they were slightly improved on the PGIC also reported that they were somewhat or very satisfied on the PASS-Q. Patients who responded “much improved” were considered to have achieved an SCB. Patients who responded “somewhat satisfied” or “very satisfied” on the PASS-Q were considered to have achieved a satisfactory state as per the definition of the PASS. While there is potential for disagreement between the PGIC and PASS-Q, their responses were strongly correlated (Spearman coefficient 0.75), suggesting that the likelihood of disagreement is negligible.

We determined thresholds for MCID, SCB, and PASS using a receiver operating characteristic (ROC) curve and an area under the curve (AUC) with a 95% CI to assess the model’s ability to discern between patients achieving satisfactory and unsatisfactory outcomes. The AUC was interpreted in a manner consistent with previous orthopaedic evidence; an AUC between 0.70 and 0.80 was considered acceptable and an AUC of ≥ 0.80 was considered excellent [6, 9]. The 95% CI was calculated for the AUC via bootstrapping with 2000 randomly generated samples. The thresholds for achieving MCID, SCB, and PASS were identified using the Youden index to maximize the sensitivity and specificity of the selected threshold on the ROC curve [26, 47]. We performed the ROC analysis using the pROC package in R, version 4.3.3 (The R Foundation for Statistical Computing) [35].

Defining the MDC

The MDC is a distribution-based calculation based on the standard error of measurement (SEM) that indicates the minimal amount of change representing true improvement rather than changes because of measurement errors. The MDC was calculated as follows: MDC = z score × SEM × √2 [21]; and the SEM was calculated as follows: SEM = SD × √(1 – ICC), where SD is the SD of the baseline PROM measurements and ICC is the intraclass correlation coefficient of the PROM determined by previous studies (0.91 for the mHHS and 0.89 for the iHOT-12) [13, 19, 21, 46]. The MDC was calculated at the 80%, 90%, and 95% confidence levels using z scores of 1.28, 1.64, and 1.96, respectively.

Results

Defining MCID, SCB, and PASS Thresholds

The MCID, SCB, and PASS thresholds for the mHHS were 18, 23, and 71, respectively. The MCID, SCB, and PASS thresholds for the iHOT-12 were 26, 42, and 65, respectively (Table 3).

Table 3.

MCID, SCB, and PASS thresholds for the mHHS and iHOT-12

PROM/metric	Threshold value	Sensitivity	Specificity	AUC (95% CI)
mHHS
MCID	18	0.69	0.82	0.85 (0.79-0.90)
SCB	23	0.77	0.63	0.74 (0.69-0.80)
PASS	71	0.89	0.80	0.90 (0.84-0.94)
iHOT-12
MCID	26	0.79	0.82	0.87 (0.81-0.92)
SCB	42	0.77	0.68	0.77 (0.72-0.82)
PASS	65	0.79	0.91	0.92 (0.89-0.95)

Validity of MCID and SCB Estimates

The MDC ranged from 8 to 12 for the mHHS and 10 to 16 for the iHOT-12 (Table 4). The MCID values for mHHS and iHOT-12 exceeded corresponding values of the MDC at all CIs. The SCB thresholds exceeded all corresponding MDC and MCID values.

Table 4.

MDC, MCID, and SCB for the mHHS and iHOT-12

PROM	MDC80	MDC90	MDC95	MCID	SCB
mHHS	8	10	12	18	23
iHOT-12	10	13	16	26	42

The MDC is reported at the 80%, 90%, and 95% CIs (MDC₈₀, MDC₉₀, and MDC₉₅), reflecting the probability that a detected change at the MDC estimate is above measurement error.

Proportion of Patients Achieving MCID, SCB, and PASS Thresholds

Across the mHHS and iHOT-12, the proportion of patients who achieved the MCID at the first time point ranged from 60% to 73%, the proportion of patients who achieved SCB ranged from 49% to 56%, and the proportion of patients who achieved the PASS threshold ranged from 55% to 79% (Table 5). Among the cohort for defining MCID, SCB, and PASS, the proportion of patients achieving any MCID, SCB, or PASS threshold was 79%, 66%, and 81%, respectively. Among the sample for assessing the proportion of patients achieving a clinically meaningful threshold, the proportion achieving any MCID, SCB, or PASS threshold was 74%, 58%, and 72%, respectively.

Table 5.

Proportion of patients achieving the MCID, SCB, and PASS for the mHHS and iHOT-12

PROM/metric	Value	Cohort for defining the MCID, SCB, and PASS, % achieved	Sample for assessing the proportion of patients achieving a clinically meaningful threshold, % achieved
mHHS
MCID	18	64	60
SCB	23	56	50
PASS	71	79	71
iHOT-12
MCID	26	73	69
SCB	42	55	49
PASS	65	69	55

Percentages indicate the proportion within each group that achieved the clinically meaningful threshold (MCD, SCB, PASS).

Discussion

Objective criteria for interpreting PROMs are necessary to ensure that they are applied effectively and responsibly in the clinical setting. Anchor-based MCID, SCB, and PASS values help to provide meaningful thresholds derived from patients’ subjective perceptions of change using a procedure-specific sample. Although these metrics have been used in the assessment of patients undergoing PAO, prior studies used scores that either had been defined for hip arthroscopy and may not have accurately reflected the condition of patients undergoing PAO or were defined on a sample of patients who underwent PAO using distribution-based methods, which do not necessarily have a relationship with patients’ perceptions of the success of the procedure [1, 27, 37, 40]. We found that using a sample of patients undergoing PAO, the anchor-based values for the MCID and SCB were generally larger than previous distribution- and anchor-based scores defined for hip preservation, whereas PASS threshold scores were similar. All MCID and SCB thresholds exceeded corresponding MDC values, confirming these scores to be valid estimates. These metrics provide more appropriate definitions for evaluation of improvement after PAO that should be used preferentially over distribution-based alternatives to give clinicians and clinician scientists a more accurate depiction of patient sentiment after treatment.

Limitations

There are several limitations to this study. The single-surgeon and single-institution nature may have limited the generalizability of these results. This study was conducted at an urban hip preservation center with a large referral volume. Thus, findings from the PAO population in this study may best generalize to other large, urban, referral-based institutions. Second, selection bias may be present, as 30% (139 of 456) of potentially eligible patients treated with PAO within our institutional hip preservation registry were excluded from the cohort for defining MCID, SCB, and PASS because of missing anchor and/or PROM responses at the 1- or 2-year time points. However, the included patients were comparable to all registry patients in terms of demographics, preoperative radiographic parameters, baseline PROMs, and follow-up PROMs, providing confidence that these patients were representative of all patients treated with PAO at this institution (Table 1). Furthermore, there were no differences when comparing baseline characteristics of all included patients (n = 454) to excluded patients (n = 236) (Supplemental Table 1; http://links.lww.com/CORR/B383). Moreover, the absolute number of data points was sufficient to discern thresholds with acceptable AUC values [6, 9].

Next, anchor-based values may be limited by the anchor questions used for the calculations. The anchor question used to determine the MCID and SCB calculations in this study describes changes in quality of life similar to the anchor used to define the MCID and SCB for THA and TKA [21], whereas studies for hip arthroscopy have used an anchor describing changes in physical ability [24, 29, 30]. Studies defining PASS thresholds for hip arthroscopy have used a nearly identical anchor as that in the current study with possible responses as yes/no or a Likert scale [28, 36]. It has been suggested that anchor selection be evaluated by the correlation test, with Revicki et al. [34] recommending 0.30 to 0.35 as a correlation threshold to define an acceptable association between an anchor and change in PROM scores. Responses to the PGIC showed a moderate-to-strong correlation to both the mHHS and iHOT-12 outcome changes, and PASS-Q responses showed a moderate-to-strong correlation with postoperative PROM scores, supporting their use as anchors in this study.

Other limitations pertain to the chosen eligibility window, sample size, and patient heterogeneity. While the minimum and maximum follow-up times were chosen as the earliest point at which patients had recovered from PAO to reduce recall bias, some patients may not yet have achieved their desired activity level by the 1-year postoperative time point. Among patients included in this study, the proportion of those who reached clinical achievement increased at longer follow-up times, indicating that patients may experience further improvements in pain and function after 1 to 2 years after PAO. However, as these observed trends do not include patients missing data on longer follow-up, subsequent research will be necessary to confirm whether this trajectory is the case. The proportion of patients meeting the MCID, SCB, and PASS presented in the current study can be used to advise patients on their expectations for recovery during the 1- to 2-year postoperative period. To provide the most accurate representations of clinical achievement, the proportion of patients meeting the MCID, SCB, and PASS should be evaluated through midterm time points when functional gains can be more thoroughly assessed. While the heterogeneity of the patient sample in terms of demographic, clinical, and radiographic characteristics provides an opportunity for confounders to impact MCID, SCB, and PASS achievement, lack of differences between included and excluded patients suggests that confounding effects were negligible. Subgroup analysis was not possible because of insufficient numbers and fell outside of study aims. Future studies may evaluate the association between baseline characteristics and achieving clinically meaningful thresholds. Last, with the absence of a control group, it is unclear how the results of this study compare with those for patients with symptomatic hip dysplasia who do not undergo surgery.

Defining MCID, SCB, and PASS Thresholds

Our anchor-based values for the MCID and SCB for both the mHHS and iHOT-12 are generally larger than those defined for hip arthroscopy as well as those defined for PAO using distribution-based methods (Table 6) [3, 10, 17, 19, 28-31, 36, 43]. Derived directly from subjective perceptions of change, these scores provide more patient-focused criteria that can be used to delineate those experiencing treatment success and failure. Given the option, more stringent criteria should be used to declare that a patient has improved after PAO, a major surgery with significant recovery time. Our PASS threshold score for the mHHS was 3 points lower than the criteria often used for hip preservation (≥ 74) [3]. This PASS threshold score, in contrast with relatively larger MCID and SCB values, may be attributed to lower preoperative mHHS scores in this PAO sample compared with hip arthroscopy cohorts [24, 28-31, 36]; thus, an equivalent postoperative score may be perceived as a larger change from baseline and the achievement of a satisfactory state. Our PASS threshold score for the iHOT-12 was slightly higher than values defined for hip arthroscopy using a subjective anchor similar to the PASS-Q (59.5 to 64.3) [22, 28, 36]. Our PASS scores may also be explained by the Likert scale grading of the PASS-Q, as answers of “somewhat satisfied” were considered positive responses in addition to “very satisfied” [22, 28, 36]. In future studies, Likert scale grading can serve to identify postoperative thresholds for satisfaction in addition to a minimum score for characterizing those who are not satisfied.

Table 6.

Comparison of the current study and MCID values from selected publications

PROM and author [ref.]	MCID value	Calculation approach	Procedure sample
mHHS	18	Anchor based	PAO
Wasko et al. [43]	7.4	Distribution based	PAO
Jimenez et al. [17]	7.1	Distribution based	PAO
Flemig et al. [10]	9.3	Distribution based	PAO
Kemp et al. [19]	8	Anchor based	Hip arthroscopy
Nwachukwu et al. [31]	8.2	Distribution based	Hip arthroscopy
Nwachukwu et al. [30]	7.9	Distribution based	Revision hip arthroscopy
iHOT-12	26	Anchor based	PAO
Martin et al. [24]	13	Distribution based	Hip arthroscopy
Nwachukwu et al. [28]	13	Distribution based	Hip arthroscopy
Robinson et al. [36]	12.54	Distribution based	Hip arthroscopy

Validity of MCID and SCB Estimates

Anchor-based MCID values defined for the mHHS and iHOT-12 were greater than all corresponding MDC scores, and the SCB exceeded the MCID in both instances, confirming their validity as likely not to have resulted from measurement error. Our MDC score for the mHHS, although comparable to the value defined by Kemp et al. [19] for hip arthroscopy, was larger than the MCID for the mHHS calculated for PAO using distribution-based methods and those identified for hip arthroscopy [19, 31, 42, 43]. Similarly, our MDC score for the iHOT-12, although comparable to the MDC calculated for a sample undergoing hip arthroscopy [18], was larger than the distribution-based MCID thresholds defined for hip arthroscopy [42]. In terms of the PAO population, MCID values below our presented MDC values can be considered unsuitable for postoperative evaluation.

Proportion of Patients Achieving MCID, SCB, and PASS Thresholds

Among our cohort for defining MCID, SCB, and PASS and sample for assessing the proportion of patients achieving a clinically meaningful threshold, the percentage of patients achieving an MCID, SCB, or PASS threshold at a mean 1 year of follow-up ranged from 60% to 73%, 49% to 56%, and 55% to 79%, respectively, according to our anchor-based values. Research on PAO has reported MCID achievement from 78% to 100% for the mHHS and 83% for the iHOT-12, with most studies reporting rates > 85% [1, 10, 16, 17, 27, 32, 37, 38, 40]. Similarly, PASS threshold achievement has ranged from 76% to 100% for the mHHS [1, 17, 32, 37], although these studies also show elevated preoperative scores as high as 72.6. To our knowledge, the PASS has yet to be evaluated after PAO using the iHOT-12. Distribution-based methods have been shown to yield less reliable and more permissive values compared with procedure-specific, anchor-based scores [21, 42]. It is possible that prior studies using either distribution-based thresholds or scores defined for a different population present inflated rates of MCID and PASS achievement after PAO that do not appropriately consider patients’ expectations. Our tools for treating symptomatic hip dysplasia are better than they have ever been [5]; among the cohort for defining MCID, SCB, and PASS, 88% of patients reported that they had improved on PGIC, and 86% reported their current state as satisfactory on the PASS-Q. Despite these advances and expertise, there remains a portion of patients with residual pain and functional limitations who do not meet criteria for clinically meaningful improvement (MCID), achieving a substantial benefit (SCB), or an acceptable level of symptoms (PASS) at the 1- to 2-year time point. Future research may evaluate the achievement of these thresholds at longer postoperative follow-up times or determine factors associated with failure to meet these scores.

Conclusion

Clinical providers hold the responsibility of accurately framing postoperative improvement to inform and guide expectations for surgical candidates. This study presented anchor-based values for the MCID, SCB, and PASS thresholds for the treatment of hip dysplasia with PAO. These thresholds are generally larger than those that have been previously defined for hip preservation, providing more patient-centered, procedure-specific criteria that can be used to evaluate levels of treatment success and failure after PAO. Comparison to MDC values confirms that all MCID and SCB scores did not arise from measurement error. As these anchor-based thresholds relate directly to patient perception, they should be used preferentially over distribution-based alternatives in clinical practice and clinical research. Furthermore, as they were defined using a procedure-specific population, they should be implemented in place of thresholds defined for other surgical procedures. With the widespread usage of PROMs, it is vital to determine valid and reliable definitions of clinical benefit. Future research using larger, nationally representative cohorts will be needed to confirm these results to reach consensus definitions.

Supplementary Material

abjs-483-1275-s001.docx ^{(22.5KB, docx)}