Abstract
Background:
The smallest worthwhile effect (SWE) enables patients to evaluate the expected value of a treatment by weighing its benefits, risks, and costs. It has emerged as an alternative to the minimal clinically important difference (MCID) for interpreting patient-reported outcome measures (PROMs). The purposes of this study were to determine the SWE estimates and MCID thresholds in patients undergoing surgery for adult idiopathic scoliosis (AdIS) and to verify whether meeting or exceeding the SWE estimates correlates with satisfaction at a minimum of 2 years postoperatively.
Methods:
Patients with postoperative satisfaction measured at a minimum of 2 years were prospectively recruited between July 2017 and August 2022. The Scoliosis Research Society-22 revised (SRS-22r) questionnaire was preoperatively administered to estimate the SWE thresholds using the benefit-harm trade-off method. The baseline SRS-22r and the SRS-30 at a minimum of 2 years postoperatively were recorded to determine the MCID estimates using the anchor-based approach, with questions 24 to 30 of the SRS-30 used as anchors. A construct validity assessment was performed to evaluate the association between meeting or exceeding the 50th percentile of the SWE (SWE50) threshold and postoperative satisfaction (defined as a score of ≥4 on both SRS-22r satisfaction questions). Race and ethnicity data were collected from the medical records.
Results:
A total of 119 Asian participants (19 male and 100 female) with a mean age of 26.5 ± 7.2 years were included. The absolute SWE50 estimates for the SRS-22r were 0.8 (interquartile range [IQR], 0.6 to 1.2) for self-image, 0.0 (IQR, 0.0 to 0.2) for function, 0.0 (IQR, 0.0 to 0.6) for pain, 0.4 (IQR, 0.0 to 0.6) for mental health, and 0.4 (IQR, 0.2 to 0.6) for the total score. The MCID thresholds for the corresponding domains or total score were 0.7, 0.1, 0.1, 0.3, and 0.3, respectively. Achieving or exceeding the absolute SWE50 threshold for the total score (p < 0.001) or the self-image (chi-square, 11.3; p < 0.001), function (chi-square, 6.3; p = 0.012), or pain (chi-square, 5.7; p = 0.017) domain was significantly correlated with postoperative satisfaction at a minimum of 2 years.
Conclusions:
The SWE could serve as an effective alternative to the MCID for interpreting PROMs at a minimum of 2 years postoperatively in patients with AdIS.
Level of Evidence:
Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.
Adult idiopathic scoliosis (AdIS) evolves from adolescent idiopathic scoliosis (AIS) as structural spinal changes progress into adulthood1. For patients with AIS, surgical correction primarily aims to ameliorate spinal alignment and to prevent curve progression, whereas adult patients are more likely to seek treatment for cosmetic concerns, chronic back pain, or functional impairment2-9. Additionally, stiffer and larger curves expose adult patients to increased surgical complexity and higher complication rates compared with patients with AIS10-14. Therefore, it is important to quantify patient concerns regarding surgical decision-making and the interpretation of clinical outcomes.
Patient-reported outcome measures (PROMs) are widely used to evaluate patient-centered concerns and clinical outcomes. However, a key challenge is interpreting the clinical relevance of changes in PROM scores. Several methods have been developed to assess the meaningfulness of these changes, including the minimal clinically important difference (MCID)15-19. However, these approaches fail to consider the benefits and risks associated with specific interventions. The smallest worthwhile effect (SWE) refers to the minimum extent of improvement that patients consider valuable for a treatment20-23. Compared with the MCID, the SWE method provides a prospective evaluation that considers the costs, side effects, and benefits of a specific treatment compared with no intervention or alternative interventions24.
The aims of this study were to determine, on the basis of the Scoliosis Research Society-22 revised (SRS-22r) questionnaire, the SWE estimates of patients with AdIS who underwent surgical correction, and to verify the association of the SWE estimates with satisfaction evaluated at least 2 years after surgery. We hypothesized that the SWE could be an effective alternative to the MCID for interpreting PROMs.
Materials and Methods
Participants
A total of 134 consecutive participants with AdIS were prospectively recruited from July 2017 to August 2022 at our orthopaedic center for spine surgery. The eligibility criteria included an age of 18 to 60 years, a diagnosis of idiopathic scoliosis, primary surgery with ≥5 fusion levels, and at least 2 years of follow-up. Patients with degenerative scoliosis, infection, spinal tumors, trauma, or intraspinal anomalies were excluded. The institutional review board approved the study protocol, and written informed consent was obtained from all participants.
Baseline Variables
Demographic data (age, sex, race and ethnicity, body mass index [BMI], income, educational attainment, and preoperative symptoms) and surgical details (fusion levels, surgical duration, osteotomy type, estimated blood loss, complications, and the length of the hospital stay) were collected from the medical records. Radiographic evaluation included the main curve type, Cobb angle, and correction rate.
Clinical Outcome Measures
Chinese versions of the SRS-22r and SRS-30 questionnaires have been adopted25-29. The SRS-22r includes 22 items organized into 5 domains—pain, self-image, function, mental health, and satisfaction—as well as the total score. Each domain is scored on a scale of 1 to 5, with higher scores indicating better outcomes. The SRS-30 contains the 22 items from the SRS-22r and 8 additional questions30. The baseline SRS-22r was utilized to determine the SWE estimates, whereas the SRS-30 at a minimum of 2 years postoperatively was utilized for estimating the MCIDs. The participants were categorized into those who were satisfied and those who were not satisfied with their postoperative outcomes at a minimum of 2 years postoperatively. If both of the SRS-22r satisfaction questions were scored ≥4, the outcome was considered satisfactory.
Determination of the MCID
The last 7 questions of the SRS-30 served as anchors for determining the MCID values. Each item’s response was assigned an ordinal value, with 1 representing the poorest outcome and with the highest value, either 3 or 5, representing the best outcome. The anchor questions and scores are shown in Supplemental File 1 (see Appendix). The MCIDs were determined with use of receiver operating characteristic (ROC) analyses by identifying the change scores that best distinguished (with the best sensitivity and 1 – specificity) between patients with “Unchanged” and “Improved” statuses. The MCID for satisfaction could not be determined because of the lack of relevant anchor questions for this domain.
Estimation of the SWE
The SWE estimates were determined using the benefit-harm trade-off method21,23. Initially, a formatted script, with a standardized description of the estimated benefits, risks, and costs of surgery, as well as the anticipated curve progression, back pain, activity impairment, and mental disturbance without intervention (Supplemental File 2; see Appendix)1,4-9,31-34, was presented to participants by a trained interviewer. This information was provided to participants to evaluate whether the forthcoming surgery was deemed worthwhile.
Subsequently, the participants were asked to estimate the expected magnitude of improvement from baseline to at least 2 years of follow-up in each domain of the SRS-22r. To ensure that the improvement represented the minimum change deemed worthwhile, the interviewer systematically decreased the options corresponding to the postoperative outcomes. The process began by selecting the question for which the patient chose the highest score, and then systematically reducing the option from the highest by 1 point. For example, instead of choosing “pretty good” for appearance in clothes, the participant was asked whether a response of “good” would still be a worthwhile result. This approach was iteratively adopted for each item until participants indicated that the perceived benefits of surgery no longer outweighed the associated risks, costs, or inconveniences.
The SWE estimates are presented as absolute and relative values, indicating the improvements in scores and percentages, respectively, that were deemed worthwhile21. Interquartile ranges (IQRs) are used to describe the distribution of the SWE estimates. The 50th percentile of the SWE (SWE50) reflects the SRS-22r score change that was deemed worthwhile for the median patients, and the 90th percentile (SWE90) represents the SRS-22r score change that was deemed worthwhile by 90% of the patients.
Statistical Analysis
Baseline demographics and clinical variables are described using descriptive statistics. The Wilcoxon signed-rank test for paired samples was used to test the significance of differences in PROMs between the preoperative time point and at least 2 years of follow-up. The standardized response mean (SRM) was calculated to assess the responsiveness of PROMs to surgery. A Mann-Whitney U test was conducted to compare changes in domain scores between groups that were classified according to their responses to the anchor questions. The construct validity of the SWE estimates was tested with use of the continuity-corrected chi-square test for associations between satisfaction status (a score of ≥4 on both SRS-22r satisfaction questions) at a minimum of 2 years of follow-up and meeting or exceeding the SWE50 thresholds in the self-image, function, pain, and mental health domains, or with use of the Fisher exact test for associations between satisfaction status and SWE50 threshold achievement for the total score. A multivariable linear regression analysis was performed to assess the impact of age, educational level, income, main curve type, and curve magnitude on SWE estimates. All statistical analyses were conducted using SPSS (version 29.0; IBM), and significance was defined as p < 0.05.
As no previous studies have investigated the SWE in patients with scoliosis, data to calculate the appropriate sample size were unavailable. The chosen sample size was instead based on comparisons with previous studies on low back pain and osteoarthritis21,22.
Results
Patient Cohort
A total of 134 participants initially met the inclusion criteria, of whom 15 (2 male and 13 female patients; mean age [and standard deviation], 28.3 ± 7.4 years [range, 21 to 39 years]; main Cobb angle, 50.7° ± 12.6°) were lost to follow-up due to failure to contact or refusal to complete questionnaires. A total of 119 Asian participants (19 male and 100 female) with a mean age of 26.5 ± 7.2 years (range, 19 to 54 years) were ultimately included. Participants had a preoperative main Cobb angle of 53.4° ± 13.8°, with a correction rate of 72.2% ± 15.4% (Table I).
TABLE I.
Primary Demographics and Surgical Variables*
| Primary Demographics | |
|---|---|
| Age† (yr) | 26.5 ± 7.2 (19-54) |
| Sex, M/F (no. of patients) | 19/100 |
| BMI† (kg/m2) | 20.2 ± 3.0 |
| Educational level (no. of patients) | |
| High school degree or less | 10 (8.4%) |
| College degree | 98 (82.4%) |
| Graduate degree | 11 (9.2%) |
| Yearly household income (no. of patients) | |
| <$25,000 | 12 (10.1%) |
| $25,000-$100,000 | 78 (65.5%) |
| >$100,000 | 29 (24.4%) |
| Preop. symptoms (no. of patients) | |
| Back pain | 68 (57.1%) |
| Root symptoms | 9 (7.6%) |
| Reduced exercise tolerance | 6 (5.0%) |
| Intermittent claudication | 0 (0.0%) |
| Time from surgery to final follow-up† (mo) | 49.6 ± 17.7 |
| Surgical Details | |
| Curve type (no. of patients) | |
| Main thoracic | 71 (59.7%) |
| Thoracolumbar | 26 (21.8%) |
| Lumbar | 22 (18.5%) |
| Coronal Cobb angle† | |
| Preop. (deg) | 53.4 ± 13.8 |
| Postop. (deg) | 15.7 ± 10.9 |
| Correction (%) | 72.2 ± 15.4 |
| No. of fusion levels† | 10.6 ± 2.9 |
| Surgical duration† (min) | 246.7 ± 64.8 |
| Osteotomy type (no. of patients) | |
| PCO | 80 (67.2%) |
| 3CO | 2 (1.7%) |
| Estimated blood loss† (mL) | 544.9 ± 304.2 |
| Cell salvage (no. of patients) | 109 (91.6%) |
| Cell salvage† (mL) | 288.8 ± 159.1 |
| pRBC (no. of patients) | 20 (16.8%) |
| pRBC† (U) | 2.4 ± 1.1 |
| Periop. complications (no. of patients) | |
| Radicular symptom | 1 (0.8%) |
| Infection | 0 (0.00%) |
| Implant failure | 0 (0.00%) |
| Cerebrospinal fluid leak | 1 (0.8%) |
| Pleural effusion | 2 (1.7%) |
| Postop. length of hospital stay‡ (days) | 8.0 (6.0-9.0) |
Except where indicated, values are given as the count, with or without the percentage in parentheses. BMI = body mass index, PCO = posterior column osteotomy, 3CO = 3-column osteotomy, pRBC = packed red blood cell.
Values are expressed as the mean ± standard deviation, with or without the range in parentheses.
Values are expressed as the median, with the IQR in parentheses.
Clinical Outcome Measures
All SRS-22r domain scores were significantly improved compared with the preoperative scores (Table II). The self-image (SRM = 2.0), function (SRM = 1.0), and mental health (SRM = 1.0) domains, as well as the total score (SRM = 1.5), were strongly responsive to surgery, whereas the pain domain (SRM = 0.4) had relatively little responsiveness (Table II). There were significant differences in the self-image, function, and pain domains and total score across the summed anchor response categories; the difference in the mental health domain was not significant (Table III).
TABLE II.
Paired Comparison of Preoperative and Latest Follow-up Scores*
| Domain | Preop. | Latest Follow-up | Δ PROM† | SRM | P Value‡ |
|---|---|---|---|---|---|
| Self-image (/5) | 2.7 ± 0.4 | 3.7 ± 0.5 | 1.0 ± 0.5 | 2.0 | <0.001 |
| Function (/5) | 3.8 ± 0.5 | 4.1 ± 0.4 | 0.3 ± 0.3 | 1.0 | <0.001 |
| Pain§ (/5) | 4.3 ± 0.7 | 4.6 ± 0.5 | 0.3 ± 0.7 | 0.4 | <0.001 |
| Mental health (/5) | 3.5 ± 0.7 | 4.1 ± 0.4 | 0.6 ± 0.6 | 1.0 | <0.001 |
| Satisfaction (/2) | – | 4.4 ± 0.7 | – | – | – |
| Total# | 3.6 ± 0.4 | 4.2 ± 0.3 | 0.6 ± 0.4 | 1.5 | <0.001 |
Values are given as the mean ± standard deviation, except where noted. PROM = patient-reported outcome measure, SRM = standardized response mean.
Indicates the difference in PROM scores between the preoperative time point and a minimum follow-up of 2 years.
Wilcoxon signed-rank test. Significance (p < 0.05) is indicated with boldface.
Total score was calculated by dividing by either 20 or 22.
TABLE III.
Domain Scores Classified According to the Summed Response to Anchor Questions
| No. (%) of Patients | Δ Domain Score* | P Value† | |
|---|---|---|---|
| Response to self-image anchor | 0.029 | ||
| Worse or the same | 26 (21.8%) | 0.4 ± 0.3 | |
| Improved | 93 (78.2%) | 1.1 ± 0.5 | |
| Response to function anchor | 0.018 | ||
| Worse or the same | 11 (9.2%) | 0.0 ± 0.2 | |
| Improved | 108 (90.8%) | 0.3 ± 0.3 | |
| Response to pain anchor | 0.004 | ||
| Worse or the same | 19 (16.0%) | –0.1 ± 0.4 | |
| Improved | 100 (84.0%) | 0.5 ± 0.5 | |
| Response to mental health anchor | 0.312 | ||
| Worse or the same | 14 (11.8%) | 0.4 ± 0.5 | |
| Improved | 105 (88.2%) | 0.7 ± 0.6 | |
| Response to total score anchor | <0.001 | ||
| Worse or the same | 9 (7.6%) | 0.2 ± 0.2 | |
| Improved | 110 (92.4%) | 0.6 ± 0.3 |
Indicates the difference in SRS-22r scores, for that subscale, between the preoperative time point and a minimum follow-up of 2 years. Values are given as the mean ± standard deviation.
Mann-Whitney U test. Significance (p < 0.05) is indicated with boldface.
MCID Estimates
The MCID was 0.7 for self-image (area under the receiver operating characteristic curve [AUC], 0.77 [95% CI, 0.68 to 0.85]), 0.1 for function (AUC, 0.75 [95% CI, 0.61 to 0.90]), 0.1 for pain (AUC, 0.75 [95% CI, 0.65 to 0.85]), 0.3 for mental health (AUC, 0.60 [95% CI, 0.45 to 0.75]), and 0.3 for the total score (AUC, 0.89 [95% CI, 0.80 to 0.98]) (Table IV).
TABLE IV.
Calculated MCIDs Using the Anchor-Based Method*
| Domain | AUC (95% CI) | Sensitivity | Specificity | MCID |
|---|---|---|---|---|
| Self-image | 0.77 (0.68-0.85) | 0.73 | 0.54 | 0.7 |
| Function | 0.75 (0.61-0.90) | 0.73 | 0.70 | 0.1 |
| Pain | 0.75 (0.65-0.85) | 0.56 | 0.84 | 0.1 |
| Mental health | 0.60 (0.45-0.75) | 0.66 | 0.50 | 0.3 |
| Total | 0.89 (0.80-0.98) | 0.85 | 0.78 | 0.3 |
MCID = minimum clinically important difference, AUC = area under the curve.
SWE Estimates
The largest estimated worthwhile effects were found in the self-image domain, with SWE50 and SWE90 values reaching approximately 0.8 (IQR, 0.6 to 1.2) and 1.4, respectively. The absolute SWE50 estimates were 0.0 (IQR, 0.0 to 0.2) for function, 0.0 (IQR, 0.0 to 0.6) for pain, 0.4 (IQR, 0.0 to 0.6) for mental health, and 0.4 (IQR, 0.2 to 0.6) for the total score. After a minimum of 2 years of follow-up, 83.2%, 61.3%, 61.3%, and 74.8% of patients met or exceeded the SWE50 thresholds for the function, pain, and mental health domains and the total score, respectively. Fifty percent of patients deemed worthwhile changes to equal or exceed 31.3% (IQR, 23.1% to 46.2%) for self-image, 0.0% (IQR, 0.0% to 5.6%) for function, 0.0% (IQR, 0.0% to 13.6%) for pain, 10.0% (IQR, 0.0% to 17.7%) for mental health, and 11.1% (IQR, 5.4% to 17.4%) for the total score (Table V).
TABLE V.
Estimated Absolute and Relative SWE Thresholds*
| Domain | Absolute SWE | Relative SWE (%) | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 10th %ile | 25th %ile | 50th %ile | 75th %ile | 90th %ile | 10th %ile | 25th %ile | 50th %ile | 75th %ile | 90th %ile | |
| Self-image | 0.4 | 0.6 | 0.8 | 1.2 | 1.4 | 14.3 | 23.1 | 31.3 | 46.2 | 58.3 |
| Function | 0.0 | 0.0 | 0.0 | 0.2 | 0.6 | 0.0 | 0.0 | 0.0 | 5.6 | 17.7 |
| Pain | 0.2 | 0.0 | 0.0 | 0.6 | 0.8 | −4.0 | 0.0 | 0.0 | 13.6 | 25.0 |
| Mental health | 0.0 | 0.0 | 0.4 | 0.6 | 1.0 | 0.0 | 0.0 | 10.0 | 17.7 | 38.6 |
| Satisfaction | – | – | – | – | – | – | – | – | – | – |
| Total | 0.2 | 0.2 | 0.4 | 0.6 | 0.9 | 3.9 | 5.4 | 11.1 | 17.4 | 25.5 |
SWE = smallest worthwhile effect, %ile = percentile.
After a minimum of 2 years of follow-up, the SRS-22r satisfaction scores indicated that 110 participants (92.4%) were satisfied with their postoperative outcomes. Achieving or surpassing the absolute SWE50 thresholds for the total score (p < 0.001) or the self-image (chi-square, 11.3; ϕ = 0.31; p < 0.001), function (chi-square, 6.3; ϕ = 0.23; p = 0.012), or pain (chi-square, 5.7; ϕ = 0.22; p = 0.017) domain was significantly associated with postoperative satisfaction at a minimum of 2 years postoperatively, whereas no significant association was found for the mental health domain (chi-square, 0.5; p = 0.467).
SWE50 estimates were calculated for the baseline tertiles of the SRS-22r domain scores and showed that participants with poorer baseline scores exhibited higher estimates, although no test for significance was performed (Table VI). Additionally, age, educational level, income, main curve type, and curve magnitude were not associated with either the SWE50 or SWE90 estimates.
TABLE VI.
Absolute SWE50 Estimates for SRS-22r Domains, Stratified by Baseline Tertile Score*
| SRS-22r Domain | Tertile (score range) | ||
|---|---|---|---|
| 1st (Worst Status) | 2nd (Intermediate Status) | 3rd (Best Status) | |
| Self-image | |||
| Preop. | 0-2.3 | 2.4-2.8 | 2.9-5.0 |
| SWE50 | 1.2 | 1.0 | 0.8 |
| Function | |||
| Preop. | 0-3.5 | 3.6-3.8 | 3.9-5.0 |
| SWE50 | 0.2 | 0.0 | 0.0 |
| Pain | |||
| Preop. | 0-4.1 | 4.2-4.6 | 4.7-5.0 |
| SWE50 | 0.6 | 0.0 | 0.0 |
| Mental health | |||
| Preop. | 0-3.1 | 3.2-3.8 | 3.9-5.0 |
| SWE50 | 0.6 | 0.2 | 0.0 |
| Total | |||
| Preop. | 0-3.4 | 3.5-3.8 | 3.9-5.0 |
| SWE50 | 0.7 | 0.4 | 0.3 |
SWE = smallest worthwhile effect, SWE50 = 50th percentile of the SWE.
Discussion
The primary finding was that median patients with AdIS required score changes of 0.8 (IQR, 0.6 to 1.2) for self-image, 0.0 (IQR, 0.0 to 0.2) for function, 0.0 (IQR, 0.0 to 0.6) for pain, 0.4 (IQR, 0.0 to 0.6) for mental health, and 0.4 (IQR, 0.2 to 0.6) for the total SRS-22r score to perceive the surgery as worthwhile in comparison to not undergoing a surgical intervention. For all domains except mental health, achieving or exceeding the SWE50 estimates was significantly correlated with satisfaction at a minimum of 2 years postoperatively.
The MCID serves as an effective tool for interpreting clinical meaningfulness16,30,35. In the present cohort, the MCIDs and the median changes in SRS-22r scores at a minimum of 2 years postoperatively were comparable for self-image (0.7 and 0.8, respectively), function (0.1 and 0.2), pain (0.1 and 0.0), mental health (0.3 and 0.4), and the total score (0.3 and 0.5). The similarity between the MCID estimates and the score changes indicates that nearly 50% of patients did not perceive themselves as having met the MCID at least 2 years after surgery. This may be attributed to the moderate responsiveness of the SRS-22r.
In addition to overlooking important patient-centered factors, the MCID has inherent limitations that affect its clinical application. One major issue is the heterogeneity arising from the arbitrary selection of cutoff points on the anchors that are used to determine clinically important responses. In addition to the conventional anchor-based method, alternative approaches, such as the 15-point Likert scale and latent class analysis, have also been used to select cutoff values for MCID estimations36,37. Methodologically, the classification of anchor-based responses and the distribution of patients across these response categories may also affect the MCID estimation. Although using the 50th or 90th percentile for SWE estimation is arbitrary, individually determined SWE values are not classified into arbitrarily defined groups for sample-based SWE estimation. Moreover, the ordinal scales of the SRS-22r and SRS-30 introduced bias to the MCID thresholds as well as to the SWE estimates. Although the current Likert scaling of the SRS-22r allows for the same numerical improvement between different scores, the improvement may have different clinical implications depending on the baseline scores. Rasch modeling offers a potential strategy to address this issue effectively38. In addition, recall bias possibly skewed the anchors that were recorded at least 2 years postoperatively39. These limitations raise concerns about the applicability of the MCID for interpreting clinical outcomes.
The SWE method quantifies patient-perceived meaningful improvement, with consideration of the benefits, side effects, and costs, and thus may be theoretically superior to the MCID20-22,24. This method offers the advantages of considering patient-centered factors and eliminating recall bias24. Our study introduced this method in the setting of structural spine disorders, focusing on AdIS. The absolute and relative SWE values were established at different percentiles for the SRS-22r domains and the total score. Moreover, for all domains except mental health, participants who met or exceeded the SWE50 thresholds were more likely to report postoperative satisfaction at a minimum of 2 years of follow-up. Both the SWE and MCID estimates for the self-image domain were higher than those for other domains, and the greatest improvement was in self-image. These findings suggest that, by coincidence, the estimates also aligned with the patients’ primary concern, which was centered on appearance40-42. The SWE50 estimates for self-image and the total score exceeded the corresponding MCID values, indicating that postoperative outcome assessment using the SWE was probably more stringent than that using the MCID. This difference may be attributed to the additional consideration of patient-centered factors in SWE estimation. Furthermore, the predictive ability of the SWE and MCID for postoperative satisfaction could be compared and tested for external validity in future studies. Additionally, the estimated SWEs for self-image and mental health were higher than those for function and pain, likely because some younger patients prioritize appearance, which indirectly influences mental health43. To diminish between-person variation, SWE50 estimates were stratified by preoperative score tertiles. A trend of patients with lower baseline scores tending to have higher SWE50 estimates was observed. This suggests that surgeons should formulate therapeutic strategies that align with the baseline conditions and expectations of patients. Overall, absolute SWE estimates are well-suited for reporting absolute changes in PROMs, whereas relative SWE estimates are more appropriate for evaluating proportional changes. In the present study, the SWE50 estimates were generally applicable for interpreting PROMs in general patients, whereas the SWE90 estimates appeared to be more suitable for patients with higher expectations. However, there is currently no consensus guiding the decision to prefer a specific percentile cutoff when proposing SWE estimates.
This study has limitations. The preoperative script was developed by the spinal deformity specialist team at our orthopaedic center on the basis of previous studies, health-care policies, and our clinical experience. Therefore, this script may be biased by our own opinions and influenced by limited evidence. Additionally, the SWE is possibly affected by patients’ understanding of the script. Theoretically, patient expectations may vary depending on the treatment modality or the time point on which the worthwhile effect estimation is based. However, this study did not refer to specific time points when asking patients to choose a response option for the SWE estimation. Furthermore, this study only estimated the worthwhile effects of surgery compared with no intervention. Therefore, future studies should consider standardized time points for SWE estimation and comparisons with other active treatments. Additionally, a larger sample size is needed in future studies to determine stratified SWE estimates and to investigate the correlation of baseline variables and radiographic parameters with SWE estimates. Moreover, there was variation in the timing of collecting the latest SRS-30 questionnaires, which may have affected the MCID estimation and the correlation of SWE estimates with postoperative satisfaction. Additionally, the results of this study are not applicable to degenerative scoliosis. Finally, the postoperative hospital stay described in our script, and experienced by our patients, was longer than the average to ensure that patients could independently meet the standards for basic daily activities before discharge. This may affect the generalizability of our SWE estimates to settings with shorter stays.
Conclusions
SWE estimates served as effective indicators of the desired magnitude of improvement in patients with AdIS. The MCID was 0.7 for self-image, 0.1 for function, 0.1 for pain, 0.3 for mental health, and 0.3 for the total score. The absolute SWE50 estimates for the SRS-22r were 0.8 (IQR, 0.6 to 1.2) for self-image, 0.0 (IQR, 0.0 to 0.2) for function, 0.0 (IQR, 0.0 to 0.6) for pain, 0.4 (IQR, 0.0 to 0.6) for mental health, and 0.4 (IQR, 0.2 to 0.6) for the total score. Meeting or exceeding the SWE50 estimate for total score, self-image, function, or pain was significantly correlated with patient satisfaction at a minimum of 2 years postoperatively.
Appendix
Supporting material provided by the authors is posted with the online version of this article as a data supplement at jbjs.org (http://links.lww.com/JBJS/I762).
Footnotes
Investigation performed at the Peking Union Medical College Hospital, Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing, People’s Republic of China
Disclosure: This work was funded by the National Key Research and Development Program of China (No. 2023YFC2507700), National High Level Hospital Clinical Research Funding (No. 2022-PUMCH-D-004 and 2022-PUMCH-C-033), and the Chinese Academy of Medical Sciences (CAMS) Innovation Fund for Medical Sciences (CIFMS; No. 2021-I2M-1051 and 2023-I2M-C&T-A-003). The Article Processing Charge for open access publication was funded by the National Key Research and Development Program of China (No. 2023YFC2507700). The Disclosure of Potential Conflicts of Interest forms are provided with the online version of the article (http://links.lww.com/JBJS/I761).
Contributor Information
Di Liu, Email: medic6d@163.com.
Zhengye Zhao, Email: zhaozhengye97@163.com.
Guozhuang Li, Email: Guozhuang_Li@outlook.com.
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Yuanpeng Zhu, Email: zhuyuanpeng2022@163.com.
Ze Liu, Email: liuze1227@163.com.
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Terry Jianguo Zhang, Email: jgzhang_pumch@yahoo.com.
Collaborators: Guixing Qiu, Jianguo Zhang, Nan Wu, Zhihong Wu, Zhongmin Zhang, Peng Liu, Zhen Yang, Yanzheng Gao, Yuntao Lu, Bingwu Wang, Fuzhi Ai, Xuejun Zhang, Xueyang Tang, Xueyu Hu, Qiang Jie, Zhensong Jiang, Wanru Duan, Zhenlei Liu, Hao Wu, Bin Xiao, Liang Wang, Fangcai Li, Guofu Pi, Xinyu Yang, Lian Liu, Lianlei Wang, Xinyu Liu, Yu Wang, Jiaqi Liu, Mao Lin, Chenxi Yu, Jiashen Shao, Yongyu Ye, Shengru Wang, Sen Liu, Na Zhao, Sen Zhao, Zefu Chen, Yuchen Niu, Zhengye Zhao, Guozhuang Li, Guilin Chen, Di Liu, Jihao Cai, Maheshati Aoran, Xiangjie Yin, Xi Cheng, Yaqi Li, Zihui Yan, Yuanpeng Zhu, Jialuo Han, Ze Liu, and Cheng Qiu
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