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Measuring clinically relevant improvement after lumbar spine surgery: is it time for something new?
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Measuring Clinically Relevant Improvement After Lumbar Spine Surgery: Is It Time for Something New? Anthony M. Asher BA , Emily Oleisky , Jacquelyn Pennings PhD , Inamullah Khan MD , Ahilan Sivaganesan MD , Cinton J. Devin MD , Mohamad Bydon MD , Anthony L. Asher , Kristin R. Archer PhD, DPT PII: DOI: Reference:
S1529-9430(20)30022-X https://doi.org/10.1016/j.spinee.2020.01.010 SPINEE 58100
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The Spine Journal
Received date: Revised date: Accepted date:
29 July 2019 22 January 2020 23 January 2020
Please cite this article as: Anthony M. Asher BA , Emily Oleisky , Jacquelyn Pennings PhD , Inamullah Khan MD , Ahilan Sivaganesan MD , Cinton J. Devin MD , Mohamad Bydon MD , Anthony L. Asher , Kristin R. Archer PhD, DPT , Measuring Clinically Relevant Improvement After Lumbar Spine Surgery: Is It Time for Something New?, The Spine Journal (2020), doi: https://doi.org/10.1016/j.spinee.2020.01.010
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Measuring Clinically Relevant Improvement After Lumbar Spine Surgery: Is It Time for Something New?
Anthony M. Asher, BA,a,b Emily Oleisky,a,b Jacquelyn Pennings, PhD,a,b Inamullah Khan, MD,a,b Ahilan Sivaganesan, MD,c Cinton J. Devin, MD,a,d Mohamad Bydon, MD,e Anthony L. Asher,f Kristin R. Archer, PhD, DPTa,b,g,h
a Department
of Orthopaedic Surgery, Vanderbilt University Medical Center,
Nashville, TN, United States b Vanderbilt
Center for Musculoskeletal Research, Vanderbilt University Medical
Center, Nashville, TN, United States c Department d Steamboat
Orthopaedic and Spine Institute, Steamboat Springs, CO, United States
e Department f Carolina
of Neurological Surgery, Vanderbilt University Medical Center, TN, United States
of Neurologic Surgery, Mayo Clinic, Rochester, Minnesota, United States
Neurosurgery and Spine Associates, Charlotte, NC, United States
g Department
of Physical Medicine & Rehabilitation, Vanderbilt University Medical
Center, Nashville, TN United States h
Osher Center for Integrative Medicine, Vanderbilt University Medical
Center, Nashville, TN United States
Corresponding Author: Kristin R. Archer, PhD, DPT, Department of Orthopaedic Surgery, Center for Musculoskeletal Research, 1215 21st Avenue South, Medical Center East, South Tower, Suite 4200, Nashville, TN 37232-8774, Phone: 615-322-2732, Fax: 615-936-8500, [email protected],
Conflicts of Interest: None
Funding: None
Background Context. Minimum clinically important difference (MCID) for patient-reported outcome measures is commonly used to assess clinical improvement. However, recent literature suggests that an absolute point-change may not be an effective or reliable marker of response to treatment for patients with low or high baseline patient-reported outcome scores. The multitude of established MCIDs also makes it difficult to compare outcomes across studies and different spine surgery procedures. Purpose. To determine whether a 30% reduction from baseline in disability and pain is a valid method for determining clinical improvement after lumbar spine surgery. Study Design. Retrospective analysis of prospective data from a national spine registry, the Quality Outcomes Database (QOD). Patient Sample. There were 23,280 participants undergoing elective lumbar spine surgery for degenerative disease who completed a baseline and follow-up assessment at 12 months. Outcome Measures. Patient-reported disability (Oswestry Disability Index: ODI), back and leg pain (11-point Numeric Rating Scale: NRS), and satisfaction (NASS scale). Methods. Patients completed baseline and a 12-month postoperative assessment to evaluate the outcomes of disability, pain, and satisfaction. The change in ODI and NRS pain scores was categorized as met (≥ 30%) or not met (< 30%) percent reduction MCID. The 30% reduction from baseline was compared to a wide range of well-established absolute point-change MCID values. The relationship between 30% reduction and absolute change values and satisfaction were primarily compared using receiver operating characteristic (ROC) curves, area under the curve (AUROC), and logistic regression analyses. Analyses were conducted for overall scores and for disability and pain severity categories and by surgical procedure. Results. Thirty percent reduction in ODI and back and leg pain predicted satisfaction with more
accuracy than absolute point-change values for the total population and across all procedure categories (p < 0.001), except for when compared to the highest absolute point-change threshold for leg pain (3.5-point reduction). The largest AUROC differences, in favor of 30% reduction, were found for the lowest disability (ODI 0-20%: 21.8%) and bed-bound disability (ODI 81100%: 13.9%) categories. For pain, there was a 3.4% to 12.4% and 1.3% to 9.8% AUROC difference for mild back and leg pain (NRS 1-4), respectively, in favor of a 30% reduction threshold. Conclusions. A 30% reduction MCID either outperformed or was similar to absolute pointchange MCID values. Results indicate that a 30% reduction (baseline to 12 months after surgery) in disability and pain is a valid method for determining clinically relevant improvement in a broad spine surgery population. Furthermore, a 30% reduction was most accurate for patients in the lowest and highest disability and lowest pain severity categories. A 30% reduction MCID allows for a standard cut-off for disability and pain that can be used to compare outcomes across various spine surgery procedures. Keywords. Lumbar spine, patient reported outcome measures, elective spine surgery, disability, pain, satisfaction, minimum clinically important difference
Introduction
Lumbar spine surgery is one of the most prevalent and fastest-growing medical interventions in the United States (U.S.). The rates of elective lumbar spine surgery have increased 300% in recent decades [1-3]. In 2011, spinal fusions cost the U.S. healthcare system a total of $12.8 billion, more than any other procedure type [4]. Due to the prevalence, incidence, and cost of these procedures along with the shift towards value-based care, accurate and efficient assessment of patient benefit from lumbar spine surgery is imperative. Minimum clinically important difference (MCID) [5] represents the smallest, clinically relevant change in a patient-reported outcome (PRO) score such as the Oswestry Disability Index (ODI) [6, 7] and numerical rating scales (NRS) for back pain and leg pain [8]. MCID thresholds in spine surgery are used to determine whether interventions benefit patients [9-13] and to develop predictive calculators to facilitate informed medical decision making [14-16]. The most widely used MCID values in lumbar spine surgery for ODI, NRS back pain and NRS leg pain are 12.8, 1.2 and 1.6 points, respectively [17]. These values were determined by Copay et al. in patients with diverse lumbar pathologies undergoing various surgical procedures [17]. Other studies have defined MCID point-change values for a wide range of lumbar surgical subpopulations, including transforaminal lumbar interbody fusion for degenerative lumbar spondylolisthesis [18], neural decompression and fusion for same level recurrent lumbar stenosis [19], and revision fusion for symptomatic pseudarthrosis [20]. While MCID is an accepted classification strategy for clinical effectiveness, the literature suggests that an absolute change from baseline, as opposed to relative or proportional, may not be an effective or reliable marker of response to treatment for patients with low or high baseline PRO scores [21, 22]. Studies in the chronic pain literature that compare absolute change measures to thresholds of clinical relevance defined by percent reduction from baseline show
improved performance with the percent reduction measurements [23]. Furthermore, Ostelo et al. developed recommendations on back pain outcome measures based on literature review, expert panel, and a workshop and concluded that a 30% change from baseline can be considered clinically meaningful improvement [24]. To date, one study in the spine surgery literature has calculated percent improvement thresholds for various PROs [25]. However, these values were developed with the goal of identifying thresholds for substantial clinical benefit, which is a higher change threshold than MCID, and from a single center study. The primary objective of this study was to determine whether a percent reduction from baseline in disability and back and leg pain is a valid method for determining MCID after lumbar spine surgery. We hypothesized that a 30% reduction would more accurately represent clinical improvement than established MCIDs that utilize absolute point- change values. Percent reduction from baseline may be a more clinically relevant method for identifying response to treatment among spinal surgery populations by accounting for baseline PRO score.
Materials and Methods Study Design and Population This study is a retrospective analysis of data from a prospective surgical spine registry collected between January 2012 and March 2018 and located at 74 sites in the United States, Quality Outcomes Database (QOD) [26]. A standardized enrollment process for patients undergoing elective surgery for degenerative conditions is used at the QOD participating sites that include both academic and private clinics. Lower volume clinical sites enroll patients continuously; higher volume centers follow a 6-patient a week enrollment process designed to produce random, representative sampling of their total eligible spine population [27]. The QOD lumbar module
enrolls patients undergoing lumbar surgery for primary stenosis, disc herniation, spondylolisthesis (Grade I), and symptomatic mechanical disc collapse and revision surgery for recurrent same-level disc herniation, pseudarthrosis and adjacent segment disease (Grade II). Exclusion criteria include age less than 18 years and spine surgery for infection, tumor, or trauma. Site-based data coordinators identify eligible patients by reviewing the operative case log. Demographic and clinical characteristics, such as age, gender, body mass index (BMI), smoking status, employment, education, insurance, comorbidities, American Society of Anesthesiologists (ASA) grade, and surgical procedure, are collected from the medical record and patient interviews or web-based surveys. Baseline disability and pain are assessed prior to surgery or up to 1 week after surgery through validated questionnaires. Follow-up patient-reported outcomes of disability, pain, and satisfaction are collected at 3 and 12 months following surgery through similar methods that include patient interviews or web-based surveys. For this study, we included patients who had complete 12-month follow-up data.
Patient-Reported Outcomes Disability was measured with the 10-item ODI [6, 7], which rates each item from 0 (high functioning) to 5 (low functioning). The ODI has demonstrated reliability, validity, and good internal consistency in both surgical spine and chronic low back pain populations [28, 29]. The ODI classifies patients into 6 categories based on a percentage score that ranges from 0 to 100. These categories are minimal disability (0 to 20%), moderate disability (21 to 40%), severe disability (41 to 60%), crippled (61 to 80%), and bed bound or exaggerated symptoms (81 to 100%) [7]. Back and leg pain were measured with an 11-point NRS [8, 30, 31]. Patients are
asked to rate their pain on a scale of 0 to 10, with 0 signifying no pain and 10 signifying the worst pain imaginable. NRS optimal cut-points for pain have been found to be no/mild (0-4), moderate (5-6), and severe (7-10) [32]. Satisfaction at 12 months after surgery was measured with 1-item from the North American Spine Society (NASS) lumbar spine outcome assessment [33, 34]. Participants are asked to rate their satisfaction with spine surgery using the following choices from 1 to 4: 1) The treatment met my expectations, 2) I did not improve as much as I had hoped, but I would undergo the same treatment for the same outcome, 3) I did not improve as much as I had hoped, and I would not undergo the same treatment for the same outcome, or 4) I am the same or worse than before treatment. For this study, patients were classified as either “satisfied” based on answer choices 1 and 2 or “not satisfied” based on answer choices 3 and 4.
Statistical Analysis Descriptive statistics, mean and standard deviation, for continuous variables and frequencies and proportions for categorical variables, were calculated for patient demographic and clinical characteristics. Patients were classified into disability and pain severity categories using established ODI score cut-offs of 0-20%, 21%-40%, 41%-60%, 61%-80%, and 81%-100% and NRS score cut-offs of 0-4, 5-6, and 7-10 [7, 32]. Patients were identified as having met percent reduction MCID (percent change ≥ 30%) or not met percent reduction MCID (percent change < 30%) in disability and pain. A 30% threshold was chosen based on the international consensus paper of Osteo et al. that established 30% change from baseline as clinically meaningful improvement for back pain outcome measures [24]. Various statistical methods were used to examine the validity of using a 30%
reduction from baseline compared to well-established absolute point-change values. The primary comparison was with MCID values determined by Copay et al. of 12.8-point reduction in disability and 1.2 and 1.6-point reduction in back and leg pain, respectively, in patients after spine surgery [17]. Additional comparisons were also made using absolute change values identified by Parai et al. in patients undergoing surgery for degenerative lumbar conditions [35], Solberg et al. in patients undergoing lumbar disc surgery [36], and Asher et al. in patients having surgical treatment for degenerative lumbar spondylolisthesis [37] in order to make comparisons across a broad range of point-reduction MCIDs. Three different absolute point-change values were compared to 30% reduction for each of the outcomes of ODI (12.8, 14, 20-point reduction), NRS back pain (1.2, 2.9, and 3.5-point reduction), and NRS leg pain (1.6, 2.7, and 3.5-point reduction) [17, 35-37]. Receiver operating characteristic (ROC) curves were primarily used to compare the accuracy of 30% reduction from baseline and absolute point-change when predicting satisfaction12-months after lumbar spine surgery [38]. After calculating the area under the ROC (AUROC) curve for 30% reduction and each of the point-change values, the AUROC differences were computed along with the 95% confidence interval (CI) to obtain p-values for the differences between the two methods [38]. Additionally, McNemar’s tests and separate logistic regression analyses predicting satisfaction from 30% change and absolute point-change values were computed and the odds ratios (OR) with 95% CI, Nagelkerke R2, and the difference between the R2 were reported to further describe the differences between the two methods. Analyses were conducted for overall ODI and NRS scores and for disability and pain severity categories. In addition, comparisons between all MCID values for the satisfaction outcome were examined by surgical procedure (i.e., fusion, laminectomy only, and microdiscectomy). Sensitivity, specificity, positive predictive values
(PPV), and negative predictive values (NPV) for the 30% reduction from baseline and absolute point-change MCIDs were also calculated. SPSS version 26 was used for the descriptive statistics and regression analyses and the roc.test package in R and MedCalc were used for the AUROC curve analysis and the calculation of the sensitivity, specificity, PPV, and NPV values. Statistical significance was set at p < 0.05.
Results A total of 23,280 patients, 47% female and mean age 59.2 (SD: 14.1), were included in this study (Table 1). Patients with private insurance comprised 50.1% of the sample, and 46.4% had public insurance or were uninsured. The percentage of patients who were current smokers was 16% and patients presented with a variety of preexisting medical conditions, including diabetes mellitus (18.5%), coronary artery disease (11.5%), anxiety/depression (36.8%) and osteoporosis (4.4%). Approximately 36% of patients underwent a lumbar fusion, while 27.5% had a laminectomy without fusion. The average preoperative ODI score for patients was 46.5 (SD: 17.2) and pain scores were 6.5 (SD: 2.8) and 6.8 (SD: 2.7) for back and leg pain, respectively (Table 2). The majority of patients reported severe (41.5%) and moderate disability (32%) and severe back and leg pain (59.9% and 63.5%). McNemar’s test was used to compare the proportion of patients who achieved a 30% reduction to the proportion achieving the three levels of absolute point reduction for disability and pain (Table 3). The proportion of patients achieving a 30% reduction in ODI (69.9%) was significantly higher than the proportion who achieved a 12.8- (69.5%, p = 0.036), 14- (67.4%, p < 0.001), and 20- (57.1%, p < 0.001) point reduction. Results were similar for patients
undergoing laminectomy; however, for fusion, the proportion of patients achieving 30% reduction (67.1%) was significantly lower than the proportion achieving 12.8-point reduction (67.9%, p = 0.007) but significantly higher than the proportion achieving 14- (65.7%, p < 0.001), and 20- (54.3%, p < 0.001) point reduction in ODI. For microdiscectomy, the proportion achieving 30% reduction (76.4%) was significantly higher than the proportion achieving 14- and 20-point reductions (74.9% and 65.7%, p < 0.001) but not significantly different that patients achieving a 12.8-point reduction in ODI (76.6%, p = 0.58). For back pain and leg pain, the proportion of patients achieving 30% reduction was significantly lower than the proportion achieving a 1.2-point reduction (back pain) and 1.6-point reduction (leg pain; all p-values < 0.001). However, the proportion achieving a 30% reduction in pain was significantly higher than the proportion achieving a 2.9- and 3.5-point reduction in back pain and the proportion achieving a 2.7- and 3.5-point reduction in leg pain (p-values < 0.001). This pattern was consistent across procedure types for both back and leg pain (p-values < 0.001). As shown in Table 4, when MCIDs were compared using ROC curves, the 30% reduction threshold in ODI and NRS back and leg pain predicted satisfaction with more accuracy than the absolute point-change thresholds (p < 0.001), except for the 3.5-point reduction in leg pain. The 30% reduction for ODI predicted satisfaction at 12-months with 77% accuracy compared to an accuracy of 73% to 74% for absolute point reduction. The 30% reduction for NRS back and leg pain predicted satisfaction at 12-months with 73% and 70% accuracy, respectively, compared to an accuracy of 68% to 70% for back pain and 67% to 70% for leg pain for absolute point-change values. AUROC differences and odds ratios (ORs) were even more pronounced, in favor of 30% reduction, for the lowest and highest disability categories and the lowest back pain and leg pain categories. The largest AUROC differences for 30% reduction compared to an absolute point-
change for ODI was found for patients with minimal disability (21.8% higher) and bed-bound disability (13.9% higher). For pain, there was a 3.4% to 12.4% and 1.3% to 9.8% AUROC difference for mild back and leg pain (NRS 1-4), respectively, in favor of a 30% reduction threshold. No significant differences were found between 30% reduction and absolute pointchange values for moderate disability and moderate back pain, except when compared with the largest point reduction (p < 0.001). For moderate leg pain, no significant differences were found between the different MCID values. Results varied for severe back and leg pain, with the most accurate MCID depending on the specific point-reduction comparison. MCID comparisons by surgical procedure are presented in Table 5. AUROC and ORs were higher for 30% reduction in disability and back pain compared to absolute point reduction across all three categories of fusion, laminectomy, and microdiscectomy (p < 0.001). For leg pain, the 30% reduction MCID threshold predicted satisfaction with more accuracy than the absolute point-change thresholds in patients undergoing fusion, laminectomy, and microdiscectomy (p < 0.001), except for when compared to 3.5-point reduction in patients treated with fusion or microdiscectomy. Sensitivity, specificity, PPV, and NPV results are presented for the entire sample, by disability and pain categories, and by surgical procedure in a supplemental table.
Discussion The purpose of this study was to determine whether a 30% reduction from baseline in disability and pain is a valid method for determining clinical improvement following lumbar spine surgery. Thirty percent reduction was compared to a wide range of established absolute point-change values to assess validity. Results from the ROC curves and logistic regression models
demonstrated that a 30% reduction in disability and back pain had a higher accuracy for predicting satisfaction as compared with absolute point reduction values for patients undergoing lumbar spine surgery. Results were consistent when analyzed by surgical procedure. For leg pain, 30% reduction predicted satisfaction with more accuracy in the entire sample and by surgical procedure, except when compared to the highest threshold, a 3.5-point reduction. The largest differences in favor of a 30% reduction were found for patients in the lowest and highest disability and lowest pain severity categories. Overall, a 30% reduction MCID either outperformed or was similar to absolute point-change MCID values. We found support for our hypothesis that a 30% reduction threshold would be a more accurate method for determining clinical improvement when compared to established absolute point-change values. Our findings indicate that 30% reduction is a valid method for determining clinical improvement in patients undergoing lumbar spine surgery, which is supported by the use of percent change measures in the chronic pain literature [39-42]. Salaffi et al. and Farrar et al. found that a percent change pain score of approximately 30% was associated with the concept of “much better” improvement in patients with chronic musculoskeletal pain [23, 40]. A 2008 systematic review by Ostelo et al. compared distribution-based and anchor-based approaches for measuring change in scores for patients with low back pain, and proposed a 30% reduction from baseline in ODI, in addition to other measures, as a more effective cutoff for clinically significant change compared to specific point-change values [24]. The use of percent reduction for PROs appears most relevant for patients with low or high disability and low pain at baseline. Prior research has shown that baseline disability and pain are among the most important predictors of success in lumbar spine surgery, [14, 15, 43, 44] and magnitude of change in pain and disability outcomes is associated with baseline score [45].
Patients with higher baseline disability may be at risk for lower satisfaction, since these patients are likely to achieve MCID regardless of self-assessed improvement [45]. In 2010, Copay et al. highlighted this discrepancy and found their previously calculated absolute change MCID values were not consistent or effective predictors of post-hoc surgical success and patient satisfaction [46]. In our study, the 30% reduction threshold consistently outperformed absolute point reduction MCIDs when patients were placed in the mild and severe ODI and mild NRS pain categories. These findings are supported by literature that has found absolute change values ineffective and unreliable markers of response to treatment for patients with a low or high baseline PRO score and underscore the clinical utility of a percent reduction measure to assess patients at highest risk for poor outcomes [47, 48]. Our findings indicate that 30% reduction is an accurate MCID cut-off in a lumbar spine surgery population as well as in sub-groups based on surgical procedure, and can replace the use of different point-change MCID values across instruments. Two systematic reviews in the orthopaedic literature cited six [48] and eleven [49] different absolute change MCID values that have been calculated for the same PRO measures. A survey of trends in published spine literature found eleven studies from 2011 to 2015 that calculated new MCID values for lumbar patients [50]. Chung and colleagues found two- to three- fold ranges in recommended values for the same scoring systems, including absolute chamge MCID values ranging from 5.3 to 14.9 points for ODI [46]. Parker and colleagues established four distinct MCID ODI point reduction values based on specific types of lumbar surgical procedures [18-20, 51]. A year later, Carreon et al. published different absolute change MCID ODI values for both primary and revision lumbar fusions [52]. While MCID is generally defined as the smallest difference in score correlating with clinically relevant change in a given PRO [53, 54], the study specific nature of valid cutoffs
has resulted in the current multiplicity of MCID values. A 30% reduction from baseline provides a standard cut-off for all patient-reported outcomes that can be used across various spine surgery procedures. This allows for broad comparison across studies, which aligns with recommendations for standardized outcome reporting in low back pain clinical research [55, 56].
Limitations Several limitations exist for this study. This was a retrospective analysis using data from a prospective spine registry. Satisfaction was the only anchor method used to validate MCID, as data for other anchors, such as the SF-36 health transition item was unavailable for our cohort. In addition, MCID comparisons were only conducted for the outcomes of disability and pain. Future prospective work is needed to determine whether a 30% reduction from baseline is a valid MCID approach for other outcomes such as physical function and general health in a spine surgery population.
Conclusion Findings demonstrate that a 30% reduction (baseline to 12 months after surgery) in PRO measures of disability and pain is a valid method for determining clinically relevant improvement in a broad spine surgery population. A 30% reduction either outperformed or had a similar accuracy for predicting satisfaction as compared with a wide range of established absolute point-change MCID values. In particular, results highlight that a 30% reduction MCID is most accurate for patients in the lowest and highest disability and lowest pain severity categories. A 30% reduction from baseline MCID allows for a standard cut-off for patientreported outcomes that can be used across various spine surgery procedures. Additional
prospective work is needed to validate 30% reduction as the optimal percentage cut-off for clinical improvement in patients undergoing lumbar spine surgery.
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Table 1. Patient Demographic and Clinical Characteristics (N=23,280) N (%) Age, mean [SD]
59.2 [14.1]
Female sex BMI, mean [SD] Current Smoker Education: Some college or higher Insurance Type
10940 (47.0%) 30.5 [6.25] 3727 (16.0%) 11737 (50.4%)
Worker’s compensation Private
804 (3.5%) 11660 (50.1%)
Public/Uninsured ASA Grade Grade 1 Grade 2 Grade 3 Grade 4 Comorbidities
10807 (46.4%)
1388 (6.0%) 12460 (53.5%) 9047 (38.9%) 265 (1.1%)
Diabetes mellitus
4299 (18.5%)
Coronary artery disease
2670 (11.5%)
Anxiety disorder
3837 (16.5%)
Depression disorder
4718 (20.3%)
Osteoporosis Procedure Type
Microdiscectomy Fusion Laminectomy without fusion
1013 (4.4%)
8418 (36.2%) 8462 (36.3%) 6400 (27.5%)
N = number of patients; BMI = body mass index; SD = Standard Deviation; ASA = American Society for Anesthesiologists.
Table 2. Preoperative Disability and Pain by Average Score and Severity Category (N=23,280) Patient-Reported Outcome ODI, mean ± SD
N (%) 46.5 ± 17.2
Minimal disability (0-20%)
1534 (6.6%)
Moderate disability (21%-40%)
7430 (32.0%)
Severe disability (41%-60%)
9667 (41.5%)
Crippled (61%-80%)
4105 (17.6%)
Bed-bound/exaggerated (81%-100%) NRS Back Pain, mean ± SD
544 (2.3%) 6.5 ± 2.8
No/low leg pain (0-4)
4953 (21.3%)
Moderate leg pain (5-6)
4381 (18.8%)
Severe leg pain (7-10) NRS Leg Pain, mean ± SD
13946 (59.9%) 6.8 ± 2.7
No/low leg pain (0-4)
4230 (18.2%)
Moderate leg pain (5-6)
4253 (18.3%)
Severe leg pain (7-10) 14797 (63.5%) N = number of patients; SD = Standard Deviation; ODI = Oswestry Disability Index; NRS = Numeric Rating Scale.
Table 3. Comparison of 30% Reduction and Absolute Point-Change MCID Values for All Patients and by Surgical Procedure Overall (N=23,280) N (%)
Fusion (N=8,462) N (%)
Laminectomy (N=6,400) N (%)
Microdiscectomy (N=8,418) N (%)
Disability (ODI) 30% reduction 16,272 (69.9%) 5,675 (67.1%) 4,164 (65.1%) 6,433 (76.4%) 12.8-point reduction 16,183 (69.5%)* 5,747 (67.9%)** 3,989 (62.3%)*** 6,447 (76.6%) 14-point reduction 15,685 (67.4%)*** 5,559 (65.7%)*** 3,822 (59.7%)*** 6,304 (74.9%)*** 20-point reduction 13,286 (57.1%)*** 4,591 (54.3%)*** 3,164 (49.4%)*** 5,531 (65.7%)*** Back pain (NRS) 30% reduction 15,368 (66.0%) 5,713 (67.5%) 4,010 (62.7%) 5,645 (67.1%) 1.2-point reduction 16,059 (69.0%)*** 6,122 (72.3%)*** 4,180 (65.3%)*** 5,757 (68.4%)*** 2.9-point reduction 13,594 (58.4%)*** 5,246 (62.0%)*** 3,530 (55.2%)*** 4,818 (57.2%)*** 3.5-point reduction 11,186 (48.0%)*** 4,300 (50.8%)*** 2,903 (45.4%)*** 3,983 (47.3%)*** Leg pain (NRS) 30% reduction 16,808 (72.2%) 5,920 (70.0%) 4,411 (68.9%) 6,477 (76.9%) 1.6-point reduction 17,360 (74.6%)*** 6,123 (72.4%)*** 4,570 (71.4%)*** 6,667 (79.2%)*** 2.7-point reduction 15,583 (66.9%)*** 5,445 (64.3%)*** 4,049 (63.3%)*** 6,089 (72.3%)*** 3.5-point reduction 13,775 (64.3%)*** 4,797 (56.7%)*** 3,568 (55.8%)*** 5,410 (64.3%)*** MCID = minimum clinically important difference; ODI = Oswestry Disability Index; NRS = Numeric Rating Scale. *p < 0.05; **p < 0.01; ***p < 0.001.
Table 4. Predicting Satisfaction from 30% Reduction and Absolute Point Reduction for Disability and Pain Nagelkerke R2 Most acurate R2 differencea reduction type
AUROC (95% CI)
AUROC difference (95% CI)
OR (95% CI)
30% reduction
0.77 (0.76, 0.78)
--
11.1 (10.2, 12.0)
26.3%
12.8-point reduction
0.74 (0.73, 0.74) 0.034 (0.029, 0.039)***
7.8 (7.2, 8.4)
20.4%
5.9%
30%
14-point reduction
0.74 (0.73, 0.74) 0.032 (0.027, 0.037)***
7.9 (7.3, 8.5)
20.4%
5.9%
30%
20-point reduction
0.73 (0.73, 0.74) 0.034 (0.029, 0.040)***
8.5 (7.8, 9.3)
19.8%
6.5%
30%
30% reduction
0.73 (0.72, 0.73)
6.9 (6.4, 7.5)
18.4%
1.2-point reduction
0.68 (0.68, 0.69) 0.041 (0.030, 0.047)***
4.8 (4.5, 5.2)
Oswestery Disability Index
Back Pain NRS 12.7%
5.7%
30%
2.9-point reduction
0.7 (0.69, 0.7)
0.027 (0.023, 0.030)***
5.5 (5.1, 6.0)
14.1%
4.3%
30%
3.5-point reduction
0.69 (0.69, 0.7)
0.033 (0.027, 0.039)***
6.3 (5.8, 7.0)
14.0%
4.4%
30%
30%
Leg Pain NRS 30% reduction
5.9 (5.4, 6.3)
15.6%
1.6-point reduction
0.67 (0.67, 0.68) 0.027 (0.021, 0.032)***
0.7 (0.7, 0.71)
4.9 (4.5, 5.2)
12.4%
3.2%
2.7-point reduction
0.69 (0.68, 0.7)
0.012 (0.008, 0.015)***
5.0 (4.6, 5.4)
13.2%
2.4%
30%
3.5-point reduction
0.7 (0.69, 0.7)
0.003 (-0.003, 0.009)
5.4 (5.0, 5.9)
14.0%
1.6%
30% = 3.5pts
10 (6.7, 15)
20.4%
Oswestery Disability Index Minimal disability (0-20%) 30% reduction
0.75 (0.73, 0.77)
12.8-point reduction
0.65 (0.62, 0.67) 0.104 (0.075, 0.132)*** 12.3 (5.7, 26.4)
10.9%
9.5%
30%
14-point reduction
0.62 (0.59, 0.64) 0.136 (0.107, 0.165)*** 10.4 (4.6, 23.6)
8.0%
12.4%
30%
20-point reduction
0.54 (0.51, 0.56) 0.218 (0.187, 0.249)***
14.2 (2, 102.5)
2.4%
18.0%
30%
Moderate disability (21%-40%) 30% reduction
0.78 (0.77, 0.79)
12.8 (10.8, 15.2)
26.5%
12.8-point reduction
0.78 (0.77, 0.79)
0.001 (-0.007, 0.009)
14.1 (11.7, 17)
26.2%
0.3%
30% = 12.8pts
14-point reduction
0.78 (0.77, 0.79)
0.004 (-0.005, 0.013)
14 (11.5, 16.9)
25.4%
1.1%
30% = 14pts
0.74 (0.73, 0.75) 0.041 (0.028, 0.053)*** 15.8 (12.3, 20.4)
21.0%
30% reduction
0.78 (0.77, 0.78)
11.9 (10.5, 13.5)
28.1%
12.8-point reduction
0.76 (0.75, 0.77) 0.012 (0.006, 0.018)*** 11.1 (9.8, 12.5)
26.8%
1.3%
30%
14-point reduction
0.77 (0.76, 0.78)
0.005 (-0.001, 0.01)
11.5 (10.2, 13.1)
27.7%
0.4%
30% = 14pts
20-point reduction
0.78 (0.78, 0.79)
0.008 (0.001, 0.016)* 13.7 (11.9, 15.8)
29.0%
-0.9%
20 pts
30%
20-point reduction
5.5%
30%
Severe disability (41%-60%)
Crippled (61%-80%) 30% reduction
0.76 (0.75, 0.77)
10.1 (8.5, 12.1)
27.3%
12.8-point reduction
0.72 (0.7, 0.73)
0.044 (0.03, 0.057)***
8.7 (7.4, 10.4)
22.6%
4.7%
14-point reduction
0.73 (0.71, 0.74)
0.032 (0.02, 0.044)***
9 (7.6, 10.7)
23.9%
3.4%
30%
0.76 (0.74, 0.77) 0.003 (-0.001 to 0.008)
9.9 (8.3, 11.8)
26.8%
0.5%
30% = 20pts
30% reduction
0.75 (0.71, 0.78)
11.1 (7, 17.6)
28.6%
12.8-point reduction
0.61 (0.57, 0.65) 0.139 (0.093, 0.185)*** 14.5 (6.6, 31.7)
14.8%
13.8%
30%
14-point reduction
0.62 (0.57, 0.66) 0.133 (0.088, 0.179)***
9.8 (5.1, 18.8)
13.6%
15.0%
30%
20-point reduction
0.69 (0.65, 0.73)
10.2 (6.2, 16.9)
22.4%
6.2%
30%
20-point reduction Bed-bound/exaggerated (81%-100%)
0.056 (0.021, 0.09)**
Back Pain NRS Mild Back Pain 30% reduction
0.66 (0.65, 0.68)
1.2-point reduction
0.63 (0.62, 0.64) 0.034 (0.023, 0.044)***
4.8 (3.8, 6)
8.7%
4.4 (3.3, 5.7)
2.9-point reduction
0.58 (0.56, 0.59)
6.3%
2.4%
30%
4.4 (3, 6.5)
3.7%
5.0%
30%
0.54 (0.53, 0.55) 0.124 (0.107, 0.142)***
6.4 (3.1, 12.9)
2.1%
6.6%
30%
30% reduction
0.76 (0.75, 0.78)
10.6 (8.7, 12.9)
24.5%
1.2-point reduction
0.76 (0.75, 0.78)
0 (<-0.001, <0.001)
10.6 (8.7, 12.9)
24.5%
0.0%
30% = 1.2pts
2.9-point reduction
0.76 (0.74, 0.77)
0.006 (-0.006, 0.019)
10.5 (8.4, 13.1)
22.5%
2.0%
30% = 2.9pts
3.5-point reduction
0.73 (0.72, 0.74) 0.035 (0.018, 0.052)*** 12.3 (9.2, 16.4)
19.5%
5.0%
30%
0.75 (0.74, 0.75)
24.3%
3.5-point reduction Moderate Back Pain
0.085 (0.07, 0.101)***
Severe Back Pain 30% reduction
9.1 (8.2, 10)
1.2-point reduction
0.71 (0.7, 0.72)
0.04 (0.032, 0.047)***
8.2 (7.4, 9)
20.5%
3.8%
30%
2.9-point reduction
0.75 (0.74, 0.75)
0 (<-0.001, <0.001)
9.1 (8.2, 10)
24.3%
0.0%
30% = 2.9 pts
3.5-point reduction
0.76 (0.75, 0.76)
0.008 (0.002, 0.015)*
9.9 (8.9, 11)
24.7%
-0.4%
3.5 pts
Leg pain NRS Mild Leg Pain 30% reduction
0.64 (0.63, 0.65)
3.3 (2.8, 4.1)
7.0%
1.6-point reduction
0.63 (0.61, 0.64)
0.013 (0.002, 0.024)*
3.4 (2.7, 4.2)
6.3%
0.7%
30%
2.7-point reduction
0.59 (0.57, 0.6)
0.052 (0.038, 0.067)***
2.9 (2.3, 3.7)
3.8%
3.2%
30%
3.5-point reduction
0.54 (0.53, 0.56) 0.098 (0.081, 0.115)***
2.4 (1.7, 3.3)
1.5%
5.5%
30%
30% reduction
0.73 (0.71, 0.74)
7.6 (6.3, 9.1)
19.0%
1.6-point reduction
0.73 (0.71, 0.74)
0 (<-0.001, <0.001)
7.6 (6.3, 9.1)
19.0%
0.0%
30% = 1.6pts
2.7-point reduction
0.72 (0.71, 0.74)
0.003 (-0.008, 0.014)
6.7 (5.6, 8.2)
17.2%
1.8%
30% = 2.7pts
3.5-point reduction
0.73 (0.71, 0.74)
0.003 (-0.013, 0.019)
7.7 (6.2, 9.5)
17.9%
1.1%
30% = 3.5pts
7.8 (7.1, 8.6)
19.7%
7.7 (7, 8.5)
17.1%
2.6%
30%
7.8 (7.1, 8.6)
19.7%
0.0%
30% = 2.7pts
8.4 (7.6, 9.2)
21.9%
-2.2%
3.5pts
Moderate leg pain
Severe leg pain 30% reduction
0.71 (0.71, 0.72)
1.6-point reduction
0.68 (0.67, 0.69) 0.034 (0.028, 0.041)***
2.7-point reduction
0.71 (0.71, 0.72)
3.5-point reduction
0.74 (0.73, 0.75) 0.024 (0.018, 0.030)***
0 (<-0.001, <0.001)
Note: MCID = minimum clinically important difference; AUROC = area under the receiver operator characteristic curve; OR = odds ratio; NRS = numeric rating scale
Table 5. Predicting Satisfaction from 30% Reduction and Absolute Point Reduction for Disability and Pain by Surgical Procedure AUROC (95% CI)
AUROC difference (95% CI)
OR (95% CI)
Nagelkerke R2 Most accurate R2 difference reduction type
Oswestry Disability Index Fusion 30% reduction
0.76 (0.75, 0.77)
10.1 (8.8, 11.5)
24.9%
12.8-point reduction
0.72 (0.72, 0.73)
0.036 (0.027, 0.045)***
7 (6.1, 7.9)
18.8%
6.1%
30%
14-point reduction
0.73 (0.72, 0.74)
0.033 (0.024, 0.041)***
7.2 (6.3, 8.1)
19.2%
5.7%
30%
20-point reduction
0.72 (0.71, 0.73)
0.038 (0.029, 0.046)***
7.8 (6.7, 9.1)
18.4%
6.5%
30%
Laminectomy 30% reduction
0.76 (0.75, 0.77)
10.4 (8.9, 12.1)
26.0%
12.8-point reduction
0.73 (0.72, 0.75)
0.029 (0.020, 0.038)***
7.7 (6.6, 8.9)
20.6%
5.4%
30%
14-point reduction
0.73 (0.72, 0.74)
0.031 (0.022, 0.040)***
7.7 (6.6, 9)
20.3%
5.7%
30%
20-point reduction
0.72 (0.71, 0.73)
0.045 (0.035, 0.055)***
8.5 (7.1, 10.1)
18.8%
7.2%
30%
Microdiscectomy 30% reduction
0.78 (0.77, 0.78)
12.7 (11, 14.7)
27.5%
12.8-point reduction
0.74 (0.73, 0.75)
0.038 (0.029, 0.048)***
8.8 (7.6, 10.1)
20.9%
6.6%
30%
14-point reduction
0.74 (0.73, 0.75)
0.034 (0.025, 0.044)***
8.7 (7.6, 10)
21.0%
6.5%
30%
20-point reduction
0.75 (0.74, 0.76)
0.025 (0.015, 0.034)***
9.1 (7.8, 10.6)
21.1%
6.4%
30%
Back Pain NRS Fusion 30% reduction
0.73 (0.72, 0.74)
7.4 (6.5, 8.4)
19.8%
1.2-point reduction
0.69 (0.68, 0.70)
0.038 (0.029, 0.047)***
5.5 (4.9, 6.2)
14.7%
5.1%
30%
2.9-point reduction
0.71 (0.70, 0.72)
0.021 (0.016, 0.026)***
6 (5.3, 6.8)
16.1%
3.7%
30%
3.5-point reduction
0.71 (0.70, 0.72)
0.025 (0.016, 0.035)***
6.9 (5.9, 8)
15.9%
3.9%
30%
Laminectomy 30% reduction
0.71 (0.70, 0.72)
6.2 (5.4, 7.2)
17.3%
1.2-point reduction
0.67 (0.66, 0.68)
0.041 (0.032, 0.051)***
4.3 (3.7, 4.9)
11.5%
5.8%
30%
2.9-point reduction
0.69 (0.68, 0.70)
0.025 (0.018, 0.031)***
5.1 (4.4, 5.9)
13.6%
3.7%
30%
3.5-point reduction
0.68 (0.67, 0.69)
0.033 (0.022, 0.044)***
5.8 (4.9, 6.9)
13.3%
4.0%
30%
Microdiscectomy 30% reduction
0.73 (0.72, 0.74)
7.2 (6.3, 8.3)
17.8%
1.2-point reduction
0.69 (0.68, 0.70)
0.044 (0.034, 0.054)***
4.8 (4.2, 5.5)
11.9%
5.9%
30%
2.9-point reduction
0.7 (0.69, 0.71)
0.033 (0.026, 0.040)***
5.5 (4.7, 6.4)
12.9%
4.9%
30%
3.5-point reduction
0.69 (0.68, 0.7)
0.041 (0.030, 0.051)***
6.4 (5.4, 7.6)
12.8%
5.0%
30%
4.5 (4, 5.1)
12.0% 30%
Leg Pain NRS Fusion 30% reduction
0.68 (0.67, 0.69)
1.6-point reduction
0.66 (0.65, 0.67)
0.019 (0.011, 0.027)***
4 (3.5, 4.5)
9.9%
2.1%
2.7-point reduction
0.67 (0.66, 0.68)
0.009 (0.003, 0.015)**
4 (3.6, 4.5)
10.4%
1.6%
30%
3.5-point reduction
0.68 (0.67, 0.69)
0.003 (-0.007, 0.013)
4.5 (4, 5.2)
11.6%
0.4%
30% = 3.5pts
Laminectomy 30% reduction
0.7 (0.69, 0.71)
5.5 (4.8, 6.3)
15.4%
1.6-point reduction
0.67 (0.66, 0.69)
0.024 (0.015, 0.032)***
4.6 (4, 5.3)
12.4%
3.0%
30%
2.7-point reduction
0.68 (0.67, 0.69)
0.016 (0.010, 0.022)***
4.6 (4, 5.2)
12.6%
2.8%
30%
3.5-point reduction
0.68 (0.67, 0.69)
0.017 (0.007, 0.027)**
4.6 (4, 5.4)
12.3%
3.1%
30%
30%
Microdiscectomy 30% reduction
0.73 (0.72, 0.74)
8.3 (7.2, 9.5)
19.9%
1.6-point reduction
0.69 (0.68, 0.70)
0.038 (0.029, 0.047)***
6.3 (5.5, 7.2)
14.9%
5.0%
2.7-point reduction
0.72 (0.71, 0.73)
0.012 (0.007, 0.018)***
6.7 (5.8, 7.7)
16.8%
3.1%
30%
3.5-point reduction
0.73 (0.72, 0.74)
0.002 (-0.009, 0.012)
7.5 (6.4, 8.6)
18.0%
1.9%
30% = 3.5pts
Note: MCID = minimum clinically important difference; AUROC = area under the receiver operator characteristic curve; OR = odds ratio; NRS = numeric rating scale
Measuring Clinically Relevant Improvement After Lumbar Spine Surgery: Is It Time for Something New? Anthony M. Asher BA , Emily Oleisky , Jacquelyn Pennings PhD , Inamullah Khan MD , Ahilan Sivaganesan MD , Cinton J. Devin MD , Mohamad Bydon MD , Anthony L. Asher , Kristin R. Archer PhD, DPT PII: DOI: Reference:
S1529-9430(20)30022-X https://doi.org/10.1016/j.spinee.2020.01.010 SPINEE 58100
To appear in:
The Spine Journal
Received date: Revised date: Accepted date:
29 July 2019 22 January 2020 23 January 2020
Please cite this article as: Anthony M. Asher BA , Emily Oleisky , Jacquelyn Pennings PhD , Inamullah Khan MD , Ahilan Sivaganesan MD , Cinton J. Devin MD , Mohamad Bydon MD , Anthony L. Asher , Kristin R. Archer PhD, DPT , Measuring Clinically Relevant Improvement After Lumbar Spine Surgery: Is It Time for Something New?, The Spine Journal (2020), doi: https://doi.org/10.1016/j.spinee.2020.01.010
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier Inc.
Measuring Clinically Relevant Improvement After Lumbar Spine Surgery: Is It Time for Something New?
Anthony M. Asher, BA,a,b Emily Oleisky,a,b Jacquelyn Pennings, PhD,a,b Inamullah Khan, MD,a,b Ahilan Sivaganesan, MD,c Cinton J. Devin, MD,a,d Mohamad Bydon, MD,e Anthony L. Asher,f Kristin R. Archer, PhD, DPTa,b,g,h
a Department
of Orthopaedic Surgery, Vanderbilt University Medical Center,
Nashville, TN, United States b Vanderbilt
Center for Musculoskeletal Research, Vanderbilt University Medical
Center, Nashville, TN, United States c Department d Steamboat
Orthopaedic and Spine Institute, Steamboat Springs, CO, United States
e Department f Carolina
of Neurological Surgery, Vanderbilt University Medical Center, TN, United States
of Neurologic Surgery, Mayo Clinic, Rochester, Minnesota, United States
Neurosurgery and Spine Associates, Charlotte, NC, United States
g Department
of Physical Medicine & Rehabilitation, Vanderbilt University Medical
Center, Nashville, TN United States h
Osher Center for Integrative Medicine, Vanderbilt University Medical
Center, Nashville, TN United States
Corresponding Author: Kristin R. Archer, PhD, DPT, Department of Orthopaedic Surgery, Center for Musculoskeletal Research, 1215 21st Avenue South, Medical Center East, South Tower, Suite 4200, Nashville, TN 37232-8774, Phone: 615-322-2732, Fax: 615-936-8500, [email protected],
Conflicts of Interest: None
Funding: None
Background Context. Minimum clinically important difference (MCID) for patient-reported outcome measures is commonly used to assess clinical improvement. However, recent literature suggests that an absolute point-change may not be an effective or reliable marker of response to treatment for patients with low or high baseline patient-reported outcome scores. The multitude of established MCIDs also makes it difficult to compare outcomes across studies and different spine surgery procedures. Purpose. To determine whether a 30% reduction from baseline in disability and pain is a valid method for determining clinical improvement after lumbar spine surgery. Study Design. Retrospective analysis of prospective data from a national spine registry, the Quality Outcomes Database (QOD). Patient Sample. There were 23,280 participants undergoing elective lumbar spine surgery for degenerative disease who completed a baseline and follow-up assessment at 12 months. Outcome Measures. Patient-reported disability (Oswestry Disability Index: ODI), back and leg pain (11-point Numeric Rating Scale: NRS), and satisfaction (NASS scale). Methods. Patients completed baseline and a 12-month postoperative assessment to evaluate the outcomes of disability, pain, and satisfaction. The change in ODI and NRS pain scores was categorized as met (≥ 30%) or not met (< 30%) percent reduction MCID. The 30% reduction from baseline was compared to a wide range of well-established absolute point-change MCID values. The relationship between 30% reduction and absolute change values and satisfaction were primarily compared using receiver operating characteristic (ROC) curves, area under the curve (AUROC), and logistic regression analyses. Analyses were conducted for overall scores and for disability and pain severity categories and by surgical procedure. Results. Thirty percent reduction in ODI and back and leg pain predicted satisfaction with more
accuracy than absolute point-change values for the total population and across all procedure categories (p < 0.001), except for when compared to the highest absolute point-change threshold for leg pain (3.5-point reduction). The largest AUROC differences, in favor of 30% reduction, were found for the lowest disability (ODI 0-20%: 21.8%) and bed-bound disability (ODI 81100%: 13.9%) categories. For pain, there was a 3.4% to 12.4% and 1.3% to 9.8% AUROC difference for mild back and leg pain (NRS 1-4), respectively, in favor of a 30% reduction threshold. Conclusions. A 30% reduction MCID either outperformed or was similar to absolute pointchange MCID values. Results indicate that a 30% reduction (baseline to 12 months after surgery) in disability and pain is a valid method for determining clinically relevant improvement in a broad spine surgery population. Furthermore, a 30% reduction was most accurate for patients in the lowest and highest disability and lowest pain severity categories. A 30% reduction MCID allows for a standard cut-off for disability and pain that can be used to compare outcomes across various spine surgery procedures. Keywords. Lumbar spine, patient reported outcome measures, elective spine surgery, disability, pain, satisfaction, minimum clinically important difference
Introduction
Lumbar spine surgery is one of the most prevalent and fastest-growing medical interventions in the United States (U.S.). The rates of elective lumbar spine surgery have increased 300% in recent decades [1-3]. In 2011, spinal fusions cost the U.S. healthcare system a total of $12.8 billion, more than any other procedure type [4]. Due to the prevalence, incidence, and cost of these procedures along with the shift towards value-based care, accurate and efficient assessment of patient benefit from lumbar spine surgery is imperative. Minimum clinically important difference (MCID) [5] represents the smallest, clinically relevant change in a patient-reported outcome (PRO) score such as the Oswestry Disability Index (ODI) [6, 7] and numerical rating scales (NRS) for back pain and leg pain [8]. MCID thresholds in spine surgery are used to determine whether interventions benefit patients [9-13] and to develop predictive calculators to facilitate informed medical decision making [14-16]. The most widely used MCID values in lumbar spine surgery for ODI, NRS back pain and NRS leg pain are 12.8, 1.2 and 1.6 points, respectively [17]. These values were determined by Copay et al. in patients with diverse lumbar pathologies undergoing various surgical procedures [17]. Other studies have defined MCID point-change values for a wide range of lumbar surgical subpopulations, including transforaminal lumbar interbody fusion for degenerative lumbar spondylolisthesis [18], neural decompression and fusion for same level recurrent lumbar stenosis [19], and revision fusion for symptomatic pseudarthrosis [20]. While MCID is an accepted classification strategy for clinical effectiveness, the literature suggests that an absolute change from baseline, as opposed to relative or proportional, may not be an effective or reliable marker of response to treatment for patients with low or high baseline PRO scores [21, 22]. Studies in the chronic pain literature that compare absolute change measures to thresholds of clinical relevance defined by percent reduction from baseline show
improved performance with the percent reduction measurements [23]. Furthermore, Ostelo et al. developed recommendations on back pain outcome measures based on literature review, expert panel, and a workshop and concluded that a 30% change from baseline can be considered clinically meaningful improvement [24]. To date, one study in the spine surgery literature has calculated percent improvement thresholds for various PROs [25]. However, these values were developed with the goal of identifying thresholds for substantial clinical benefit, which is a higher change threshold than MCID, and from a single center study. The primary objective of this study was to determine whether a percent reduction from baseline in disability and back and leg pain is a valid method for determining MCID after lumbar spine surgery. We hypothesized that a 30% reduction would more accurately represent clinical improvement than established MCIDs that utilize absolute point- change values. Percent reduction from baseline may be a more clinically relevant method for identifying response to treatment among spinal surgery populations by accounting for baseline PRO score.
Materials and Methods Study Design and Population This study is a retrospective analysis of data from a prospective surgical spine registry collected between January 2012 and March 2018 and located at 74 sites in the United States, Quality Outcomes Database (QOD) [26]. A standardized enrollment process for patients undergoing elective surgery for degenerative conditions is used at the QOD participating sites that include both academic and private clinics. Lower volume clinical sites enroll patients continuously; higher volume centers follow a 6-patient a week enrollment process designed to produce random, representative sampling of their total eligible spine population [27]. The QOD lumbar module
enrolls patients undergoing lumbar surgery for primary stenosis, disc herniation, spondylolisthesis (Grade I), and symptomatic mechanical disc collapse and revision surgery for recurrent same-level disc herniation, pseudarthrosis and adjacent segment disease (Grade II). Exclusion criteria include age less than 18 years and spine surgery for infection, tumor, or trauma. Site-based data coordinators identify eligible patients by reviewing the operative case log. Demographic and clinical characteristics, such as age, gender, body mass index (BMI), smoking status, employment, education, insurance, comorbidities, American Society of Anesthesiologists (ASA) grade, and surgical procedure, are collected from the medical record and patient interviews or web-based surveys. Baseline disability and pain are assessed prior to surgery or up to 1 week after surgery through validated questionnaires. Follow-up patient-reported outcomes of disability, pain, and satisfaction are collected at 3 and 12 months following surgery through similar methods that include patient interviews or web-based surveys. For this study, we included patients who had complete 12-month follow-up data.
Patient-Reported Outcomes Disability was measured with the 10-item ODI [6, 7], which rates each item from 0 (high functioning) to 5 (low functioning). The ODI has demonstrated reliability, validity, and good internal consistency in both surgical spine and chronic low back pain populations [28, 29]. The ODI classifies patients into 6 categories based on a percentage score that ranges from 0 to 100. These categories are minimal disability (0 to 20%), moderate disability (21 to 40%), severe disability (41 to 60%), crippled (61 to 80%), and bed bound or exaggerated symptoms (81 to 100%) [7]. Back and leg pain were measured with an 11-point NRS [8, 30, 31]. Patients are
asked to rate their pain on a scale of 0 to 10, with 0 signifying no pain and 10 signifying the worst pain imaginable. NRS optimal cut-points for pain have been found to be no/mild (0-4), moderate (5-6), and severe (7-10) [32]. Satisfaction at 12 months after surgery was measured with 1-item from the North American Spine Society (NASS) lumbar spine outcome assessment [33, 34]. Participants are asked to rate their satisfaction with spine surgery using the following choices from 1 to 4: 1) The treatment met my expectations, 2) I did not improve as much as I had hoped, but I would undergo the same treatment for the same outcome, 3) I did not improve as much as I had hoped, and I would not undergo the same treatment for the same outcome, or 4) I am the same or worse than before treatment. For this study, patients were classified as either “satisfied” based on answer choices 1 and 2 or “not satisfied” based on answer choices 3 and 4.
Statistical Analysis Descriptive statistics, mean and standard deviation, for continuous variables and frequencies and proportions for categorical variables, were calculated for patient demographic and clinical characteristics. Patients were classified into disability and pain severity categories using established ODI score cut-offs of 0-20%, 21%-40%, 41%-60%, 61%-80%, and 81%-100% and NRS score cut-offs of 0-4, 5-6, and 7-10 [7, 32]. Patients were identified as having met percent reduction MCID (percent change ≥ 30%) or not met percent reduction MCID (percent change < 30%) in disability and pain. A 30% threshold was chosen based on the international consensus paper of Osteo et al. that established 30% change from baseline as clinically meaningful improvement for back pain outcome measures [24]. Various statistical methods were used to examine the validity of using a 30%
reduction from baseline compared to well-established absolute point-change values. The primary comparison was with MCID values determined by Copay et al. of 12.8-point reduction in disability and 1.2 and 1.6-point reduction in back and leg pain, respectively, in patients after spine surgery [17]. Additional comparisons were also made using absolute change values identified by Parai et al. in patients undergoing surgery for degenerative lumbar conditions [35], Solberg et al. in patients undergoing lumbar disc surgery [36], and Asher et al. in patients having surgical treatment for degenerative lumbar spondylolisthesis [37] in order to make comparisons across a broad range of point-reduction MCIDs. Three different absolute point-change values were compared to 30% reduction for each of the outcomes of ODI (12.8, 14, 20-point reduction), NRS back pain (1.2, 2.9, and 3.5-point reduction), and NRS leg pain (1.6, 2.7, and 3.5-point reduction) [17, 35-37]. Receiver operating characteristic (ROC) curves were primarily used to compare the accuracy of 30% reduction from baseline and absolute point-change when predicting satisfaction12-months after lumbar spine surgery [38]. After calculating the area under the ROC (AUROC) curve for 30% reduction and each of the point-change values, the AUROC differences were computed along with the 95% confidence interval (CI) to obtain p-values for the differences between the two methods [38]. Additionally, McNemar’s tests and separate logistic regression analyses predicting satisfaction from 30% change and absolute point-change values were computed and the odds ratios (OR) with 95% CI, Nagelkerke R2, and the difference between the R2 were reported to further describe the differences between the two methods. Analyses were conducted for overall ODI and NRS scores and for disability and pain severity categories. In addition, comparisons between all MCID values for the satisfaction outcome were examined by surgical procedure (i.e., fusion, laminectomy only, and microdiscectomy). Sensitivity, specificity, positive predictive values
(PPV), and negative predictive values (NPV) for the 30% reduction from baseline and absolute point-change MCIDs were also calculated. SPSS version 26 was used for the descriptive statistics and regression analyses and the roc.test package in R and MedCalc were used for the AUROC curve analysis and the calculation of the sensitivity, specificity, PPV, and NPV values. Statistical significance was set at p < 0.05.
Results A total of 23,280 patients, 47% female and mean age 59.2 (SD: 14.1), were included in this study (Table 1). Patients with private insurance comprised 50.1% of the sample, and 46.4% had public insurance or were uninsured. The percentage of patients who were current smokers was 16% and patients presented with a variety of preexisting medical conditions, including diabetes mellitus (18.5%), coronary artery disease (11.5%), anxiety/depression (36.8%) and osteoporosis (4.4%). Approximately 36% of patients underwent a lumbar fusion, while 27.5% had a laminectomy without fusion. The average preoperative ODI score for patients was 46.5 (SD: 17.2) and pain scores were 6.5 (SD: 2.8) and 6.8 (SD: 2.7) for back and leg pain, respectively (Table 2). The majority of patients reported severe (41.5%) and moderate disability (32%) and severe back and leg pain (59.9% and 63.5%). McNemar’s test was used to compare the proportion of patients who achieved a 30% reduction to the proportion achieving the three levels of absolute point reduction for disability and pain (Table 3). The proportion of patients achieving a 30% reduction in ODI (69.9%) was significantly higher than the proportion who achieved a 12.8- (69.5%, p = 0.036), 14- (67.4%, p < 0.001), and 20- (57.1%, p < 0.001) point reduction. Results were similar for patients
undergoing laminectomy; however, for fusion, the proportion of patients achieving 30% reduction (67.1%) was significantly lower than the proportion achieving 12.8-point reduction (67.9%, p = 0.007) but significantly higher than the proportion achieving 14- (65.7%, p < 0.001), and 20- (54.3%, p < 0.001) point reduction in ODI. For microdiscectomy, the proportion achieving 30% reduction (76.4%) was significantly higher than the proportion achieving 14- and 20-point reductions (74.9% and 65.7%, p < 0.001) but not significantly different that patients achieving a 12.8-point reduction in ODI (76.6%, p = 0.58). For back pain and leg pain, the proportion of patients achieving 30% reduction was significantly lower than the proportion achieving a 1.2-point reduction (back pain) and 1.6-point reduction (leg pain; all p-values < 0.001). However, the proportion achieving a 30% reduction in pain was significantly higher than the proportion achieving a 2.9- and 3.5-point reduction in back pain and the proportion achieving a 2.7- and 3.5-point reduction in leg pain (p-values < 0.001). This pattern was consistent across procedure types for both back and leg pain (p-values < 0.001). As shown in Table 4, when MCIDs were compared using ROC curves, the 30% reduction threshold in ODI and NRS back and leg pain predicted satisfaction with more accuracy than the absolute point-change thresholds (p < 0.001), except for the 3.5-point reduction in leg pain. The 30% reduction for ODI predicted satisfaction at 12-months with 77% accuracy compared to an accuracy of 73% to 74% for absolute point reduction. The 30% reduction for NRS back and leg pain predicted satisfaction at 12-months with 73% and 70% accuracy, respectively, compared to an accuracy of 68% to 70% for back pain and 67% to 70% for leg pain for absolute point-change values. AUROC differences and odds ratios (ORs) were even more pronounced, in favor of 30% reduction, for the lowest and highest disability categories and the lowest back pain and leg pain categories. The largest AUROC differences for 30% reduction compared to an absolute point-
change for ODI was found for patients with minimal disability (21.8% higher) and bed-bound disability (13.9% higher). For pain, there was a 3.4% to 12.4% and 1.3% to 9.8% AUROC difference for mild back and leg pain (NRS 1-4), respectively, in favor of a 30% reduction threshold. No significant differences were found between 30% reduction and absolute pointchange values for moderate disability and moderate back pain, except when compared with the largest point reduction (p < 0.001). For moderate leg pain, no significant differences were found between the different MCID values. Results varied for severe back and leg pain, with the most accurate MCID depending on the specific point-reduction comparison. MCID comparisons by surgical procedure are presented in Table 5. AUROC and ORs were higher for 30% reduction in disability and back pain compared to absolute point reduction across all three categories of fusion, laminectomy, and microdiscectomy (p < 0.001). For leg pain, the 30% reduction MCID threshold predicted satisfaction with more accuracy than the absolute point-change thresholds in patients undergoing fusion, laminectomy, and microdiscectomy (p < 0.001), except for when compared to 3.5-point reduction in patients treated with fusion or microdiscectomy. Sensitivity, specificity, PPV, and NPV results are presented for the entire sample, by disability and pain categories, and by surgical procedure in a supplemental table.
Discussion The purpose of this study was to determine whether a 30% reduction from baseline in disability and pain is a valid method for determining clinical improvement following lumbar spine surgery. Thirty percent reduction was compared to a wide range of established absolute point-change values to assess validity. Results from the ROC curves and logistic regression models
demonstrated that a 30% reduction in disability and back pain had a higher accuracy for predicting satisfaction as compared with absolute point reduction values for patients undergoing lumbar spine surgery. Results were consistent when analyzed by surgical procedure. For leg pain, 30% reduction predicted satisfaction with more accuracy in the entire sample and by surgical procedure, except when compared to the highest threshold, a 3.5-point reduction. The largest differences in favor of a 30% reduction were found for patients in the lowest and highest disability and lowest pain severity categories. Overall, a 30% reduction MCID either outperformed or was similar to absolute point-change MCID values. We found support for our hypothesis that a 30% reduction threshold would be a more accurate method for determining clinical improvement when compared to established absolute point-change values. Our findings indicate that 30% reduction is a valid method for determining clinical improvement in patients undergoing lumbar spine surgery, which is supported by the use of percent change measures in the chronic pain literature [39-42]. Salaffi et al. and Farrar et al. found that a percent change pain score of approximately 30% was associated with the concept of “much better” improvement in patients with chronic musculoskeletal pain [23, 40]. A 2008 systematic review by Ostelo et al. compared distribution-based and anchor-based approaches for measuring change in scores for patients with low back pain, and proposed a 30% reduction from baseline in ODI, in addition to other measures, as a more effective cutoff for clinically significant change compared to specific point-change values [24]. The use of percent reduction for PROs appears most relevant for patients with low or high disability and low pain at baseline. Prior research has shown that baseline disability and pain are among the most important predictors of success in lumbar spine surgery, [14, 15, 43, 44] and magnitude of change in pain and disability outcomes is associated with baseline score [45].
Patients with higher baseline disability may be at risk for lower satisfaction, since these patients are likely to achieve MCID regardless of self-assessed improvement [45]. In 2010, Copay et al. highlighted this discrepancy and found their previously calculated absolute change MCID values were not consistent or effective predictors of post-hoc surgical success and patient satisfaction [46]. In our study, the 30% reduction threshold consistently outperformed absolute point reduction MCIDs when patients were placed in the mild and severe ODI and mild NRS pain categories. These findings are supported by literature that has found absolute change values ineffective and unreliable markers of response to treatment for patients with a low or high baseline PRO score and underscore the clinical utility of a percent reduction measure to assess patients at highest risk for poor outcomes [47, 48]. Our findings indicate that 30% reduction is an accurate MCID cut-off in a lumbar spine surgery population as well as in sub-groups based on surgical procedure, and can replace the use of different point-change MCID values across instruments. Two systematic reviews in the orthopaedic literature cited six [48] and eleven [49] different absolute change MCID values that have been calculated for the same PRO measures. A survey of trends in published spine literature found eleven studies from 2011 to 2015 that calculated new MCID values for lumbar patients [50]. Chung and colleagues found two- to three- fold ranges in recommended values for the same scoring systems, including absolute chamge MCID values ranging from 5.3 to 14.9 points for ODI [46]. Parker and colleagues established four distinct MCID ODI point reduction values based on specific types of lumbar surgical procedures [18-20, 51]. A year later, Carreon et al. published different absolute change MCID ODI values for both primary and revision lumbar fusions [52]. While MCID is generally defined as the smallest difference in score correlating with clinically relevant change in a given PRO [53, 54], the study specific nature of valid cutoffs
has resulted in the current multiplicity of MCID values. A 30% reduction from baseline provides a standard cut-off for all patient-reported outcomes that can be used across various spine surgery procedures. This allows for broad comparison across studies, which aligns with recommendations for standardized outcome reporting in low back pain clinical research [55, 56].
Limitations Several limitations exist for this study. This was a retrospective analysis using data from a prospective spine registry. Satisfaction was the only anchor method used to validate MCID, as data for other anchors, such as the SF-36 health transition item was unavailable for our cohort. In addition, MCID comparisons were only conducted for the outcomes of disability and pain. Future prospective work is needed to determine whether a 30% reduction from baseline is a valid MCID approach for other outcomes such as physical function and general health in a spine surgery population.
Conclusion Findings demonstrate that a 30% reduction (baseline to 12 months after surgery) in PRO measures of disability and pain is a valid method for determining clinically relevant improvement in a broad spine surgery population. A 30% reduction either outperformed or had a similar accuracy for predicting satisfaction as compared with a wide range of established absolute point-change MCID values. In particular, results highlight that a 30% reduction MCID is most accurate for patients in the lowest and highest disability and lowest pain severity categories. A 30% reduction from baseline MCID allows for a standard cut-off for patientreported outcomes that can be used across various spine surgery procedures. Additional
prospective work is needed to validate 30% reduction as the optimal percentage cut-off for clinical improvement in patients undergoing lumbar spine surgery.
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Table 1. Patient Demographic and Clinical Characteristics (N=23,280) N (%) Age, mean [SD]
59.2 [14.1]
Female sex BMI, mean [SD] Current Smoker Education: Some college or higher Insurance Type
10940 (47.0%) 30.5 [6.25] 3727 (16.0%) 11737 (50.4%)
Worker’s compensation Private
804 (3.5%) 11660 (50.1%)
Public/Uninsured ASA Grade Grade 1 Grade 2 Grade 3 Grade 4 Comorbidities
10807 (46.4%)
1388 (6.0%) 12460 (53.5%) 9047 (38.9%) 265 (1.1%)
Diabetes mellitus
4299 (18.5%)
Coronary artery disease
2670 (11.5%)
Anxiety disorder
3837 (16.5%)
Depression disorder
4718 (20.3%)
Osteoporosis Procedure Type
Microdiscectomy Fusion Laminectomy without fusion
1013 (4.4%)
8418 (36.2%) 8462 (36.3%) 6400 (27.5%)
N = number of patients; BMI = body mass index; SD = Standard Deviation; ASA = American Society for Anesthesiologists.
Table 2. Preoperative Disability and Pain by Average Score and Severity Category (N=23,280) Patient-Reported Outcome ODI, mean ± SD
N (%) 46.5 ± 17.2
Minimal disability (0-20%)
1534 (6.6%)
Moderate disability (21%-40%)
7430 (32.0%)
Severe disability (41%-60%)
9667 (41.5%)
Crippled (61%-80%)
4105 (17.6%)
Bed-bound/exaggerated (81%-100%) NRS Back Pain, mean ± SD
544 (2.3%) 6.5 ± 2.8
No/low leg pain (0-4)
4953 (21.3%)
Moderate leg pain (5-6)
4381 (18.8%)
Severe leg pain (7-10) NRS Leg Pain, mean ± SD
13946 (59.9%) 6.8 ± 2.7
No/low leg pain (0-4)
4230 (18.2%)
Moderate leg pain (5-6)
4253 (18.3%)
Severe leg pain (7-10) 14797 (63.5%) N = number of patients; SD = Standard Deviation; ODI = Oswestry Disability Index; NRS = Numeric Rating Scale.
Table 3. Comparison of 30% Reduction and Absolute Point-Change MCID Values for All Patients and by Surgical Procedure Overall (N=23,280) N (%)
Fusion (N=8,462) N (%)
Laminectomy (N=6,400) N (%)
Microdiscectomy (N=8,418) N (%)
Disability (ODI) 30% reduction 16,272 (69.9%) 5,675 (67.1%) 4,164 (65.1%) 6,433 (76.4%) 12.8-point reduction 16,183 (69.5%)* 5,747 (67.9%)** 3,989 (62.3%)*** 6,447 (76.6%) 14-point reduction 15,685 (67.4%)*** 5,559 (65.7%)*** 3,822 (59.7%)*** 6,304 (74.9%)*** 20-point reduction 13,286 (57.1%)*** 4,591 (54.3%)*** 3,164 (49.4%)*** 5,531 (65.7%)*** Back pain (NRS) 30% reduction 15,368 (66.0%) 5,713 (67.5%) 4,010 (62.7%) 5,645 (67.1%) 1.2-point reduction 16,059 (69.0%)*** 6,122 (72.3%)*** 4,180 (65.3%)*** 5,757 (68.4%)*** 2.9-point reduction 13,594 (58.4%)*** 5,246 (62.0%)*** 3,530 (55.2%)*** 4,818 (57.2%)*** 3.5-point reduction 11,186 (48.0%)*** 4,300 (50.8%)*** 2,903 (45.4%)*** 3,983 (47.3%)*** Leg pain (NRS) 30% reduction 16,808 (72.2%) 5,920 (70.0%) 4,411 (68.9%) 6,477 (76.9%) 1.6-point reduction 17,360 (74.6%)*** 6,123 (72.4%)*** 4,570 (71.4%)*** 6,667 (79.2%)*** 2.7-point reduction 15,583 (66.9%)*** 5,445 (64.3%)*** 4,049 (63.3%)*** 6,089 (72.3%)*** 3.5-point reduction 13,775 (64.3%)*** 4,797 (56.7%)*** 3,568 (55.8%)*** 5,410 (64.3%)*** MCID = minimum clinically important difference; ODI = Oswestry Disability Index; NRS = Numeric Rating Scale. *p < 0.05; **p < 0.01; ***p < 0.001.
Table 4. Predicting Satisfaction from 30% Reduction and Absolute Point Reduction for Disability and Pain Nagelkerke R2 Most acurate R2 differencea reduction type
AUROC (95% CI)
AUROC difference (95% CI)
OR (95% CI)
30% reduction
0.77 (0.76, 0.78)
--
11.1 (10.2, 12.0)
26.3%
12.8-point reduction
0.74 (0.73, 0.74) 0.034 (0.029, 0.039)***
7.8 (7.2, 8.4)
20.4%
5.9%
30%
14-point reduction
0.74 (0.73, 0.74) 0.032 (0.027, 0.037)***
7.9 (7.3, 8.5)
20.4%
5.9%
30%
20-point reduction
0.73 (0.73, 0.74) 0.034 (0.029, 0.040)***
8.5 (7.8, 9.3)
19.8%
6.5%
30%
30% reduction
0.73 (0.72, 0.73)
6.9 (6.4, 7.5)
18.4%
1.2-point reduction
0.68 (0.68, 0.69) 0.041 (0.030, 0.047)***
4.8 (4.5, 5.2)
Oswestery Disability Index
Back Pain NRS 12.7%
5.7%
30%
2.9-point reduction
0.7 (0.69, 0.7)
0.027 (0.023, 0.030)***
5.5 (5.1, 6.0)
14.1%
4.3%
30%
3.5-point reduction
0.69 (0.69, 0.7)
0.033 (0.027, 0.039)***
6.3 (5.8, 7.0)
14.0%
4.4%
30%
30%
Leg Pain NRS 30% reduction
5.9 (5.4, 6.3)
15.6%
1.6-point reduction
0.67 (0.67, 0.68) 0.027 (0.021, 0.032)***
0.7 (0.7, 0.71)
4.9 (4.5, 5.2)
12.4%
3.2%
2.7-point reduction
0.69 (0.68, 0.7)
0.012 (0.008, 0.015)***
5.0 (4.6, 5.4)
13.2%
2.4%
30%
3.5-point reduction
0.7 (0.69, 0.7)
0.003 (-0.003, 0.009)
5.4 (5.0, 5.9)
14.0%
1.6%
30% = 3.5pts
10 (6.7, 15)
20.4%
Oswestery Disability Index Minimal disability (0-20%) 30% reduction
0.75 (0.73, 0.77)
12.8-point reduction
0.65 (0.62, 0.67) 0.104 (0.075, 0.132)*** 12.3 (5.7, 26.4)
10.9%
9.5%
30%
14-point reduction
0.62 (0.59, 0.64) 0.136 (0.107, 0.165)*** 10.4 (4.6, 23.6)
8.0%
12.4%
30%
20-point reduction
0.54 (0.51, 0.56) 0.218 (0.187, 0.249)***
14.2 (2, 102.5)
2.4%
18.0%
30%
Moderate disability (21%-40%) 30% reduction
0.78 (0.77, 0.79)
12.8 (10.8, 15.2)
26.5%
12.8-point reduction
0.78 (0.77, 0.79)
0.001 (-0.007, 0.009)
14.1 (11.7, 17)
26.2%
0.3%
30% = 12.8pts
14-point reduction
0.78 (0.77, 0.79)
0.004 (-0.005, 0.013)
14 (11.5, 16.9)
25.4%
1.1%
30% = 14pts
0.74 (0.73, 0.75) 0.041 (0.028, 0.053)*** 15.8 (12.3, 20.4)
21.0%
30% reduction
0.78 (0.77, 0.78)
11.9 (10.5, 13.5)
28.1%
12.8-point reduction
0.76 (0.75, 0.77) 0.012 (0.006, 0.018)*** 11.1 (9.8, 12.5)
26.8%
1.3%
30%
14-point reduction
0.77 (0.76, 0.78)
0.005 (-0.001, 0.01)
11.5 (10.2, 13.1)
27.7%
0.4%
30% = 14pts
20-point reduction
0.78 (0.78, 0.79)
0.008 (0.001, 0.016)* 13.7 (11.9, 15.8)
29.0%
-0.9%
20 pts
30%
20-point reduction
5.5%
30%
Severe disability (41%-60%)
Crippled (61%-80%) 30% reduction
0.76 (0.75, 0.77)
10.1 (8.5, 12.1)
27.3%
12.8-point reduction
0.72 (0.7, 0.73)
0.044 (0.03, 0.057)***
8.7 (7.4, 10.4)
22.6%
4.7%
14-point reduction
0.73 (0.71, 0.74)
0.032 (0.02, 0.044)***
9 (7.6, 10.7)
23.9%
3.4%
30%
0.76 (0.74, 0.77) 0.003 (-0.001 to 0.008)
9.9 (8.3, 11.8)
26.8%
0.5%
30% = 20pts
30% reduction
0.75 (0.71, 0.78)
11.1 (7, 17.6)
28.6%
12.8-point reduction
0.61 (0.57, 0.65) 0.139 (0.093, 0.185)*** 14.5 (6.6, 31.7)
14.8%
13.8%
30%
14-point reduction
0.62 (0.57, 0.66) 0.133 (0.088, 0.179)***
9.8 (5.1, 18.8)
13.6%
15.0%
30%
20-point reduction
0.69 (0.65, 0.73)
10.2 (6.2, 16.9)
22.4%
6.2%
30%
20-point reduction Bed-bound/exaggerated (81%-100%)
0.056 (0.021, 0.09)**
Back Pain NRS Mild Back Pain 30% reduction
0.66 (0.65, 0.68)
1.2-point reduction
0.63 (0.62, 0.64) 0.034 (0.023, 0.044)***
4.8 (3.8, 6)
8.7%
4.4 (3.3, 5.7)
2.9-point reduction
0.58 (0.56, 0.59)
6.3%
2.4%
30%
4.4 (3, 6.5)
3.7%
5.0%
30%
0.54 (0.53, 0.55) 0.124 (0.107, 0.142)***
6.4 (3.1, 12.9)
2.1%
6.6%
30%
30% reduction
0.76 (0.75, 0.78)
10.6 (8.7, 12.9)
24.5%
1.2-point reduction
0.76 (0.75, 0.78)
0 (<-0.001, <0.001)
10.6 (8.7, 12.9)
24.5%
0.0%
30% = 1.2pts
2.9-point reduction
0.76 (0.74, 0.77)
0.006 (-0.006, 0.019)
10.5 (8.4, 13.1)
22.5%
2.0%
30% = 2.9pts
3.5-point reduction
0.73 (0.72, 0.74) 0.035 (0.018, 0.052)*** 12.3 (9.2, 16.4)
19.5%
5.0%
30%
0.75 (0.74, 0.75)
24.3%
3.5-point reduction Moderate Back Pain
0.085 (0.07, 0.101)***
Severe Back Pain 30% reduction
9.1 (8.2, 10)
1.2-point reduction
0.71 (0.7, 0.72)
0.04 (0.032, 0.047)***
8.2 (7.4, 9)
20.5%
3.8%
30%
2.9-point reduction
0.75 (0.74, 0.75)
0 (<-0.001, <0.001)
9.1 (8.2, 10)
24.3%
0.0%
30% = 2.9 pts
3.5-point reduction
0.76 (0.75, 0.76)
0.008 (0.002, 0.015)*
9.9 (8.9, 11)
24.7%
-0.4%
3.5 pts
Leg pain NRS Mild Leg Pain 30% reduction
0.64 (0.63, 0.65)
3.3 (2.8, 4.1)
7.0%
1.6-point reduction
0.63 (0.61, 0.64)
0.013 (0.002, 0.024)*
3.4 (2.7, 4.2)
6.3%
0.7%
30%
2.7-point reduction
0.59 (0.57, 0.6)
0.052 (0.038, 0.067)***
2.9 (2.3, 3.7)
3.8%
3.2%
30%
3.5-point reduction
0.54 (0.53, 0.56) 0.098 (0.081, 0.115)***
2.4 (1.7, 3.3)
1.5%
5.5%
30%
30% reduction
0.73 (0.71, 0.74)
7.6 (6.3, 9.1)
19.0%
1.6-point reduction
0.73 (0.71, 0.74)
0 (<-0.001, <0.001)
7.6 (6.3, 9.1)
19.0%
0.0%
30% = 1.6pts
2.7-point reduction
0.72 (0.71, 0.74)
0.003 (-0.008, 0.014)
6.7 (5.6, 8.2)
17.2%
1.8%
30% = 2.7pts
3.5-point reduction
0.73 (0.71, 0.74)
0.003 (-0.013, 0.019)
7.7 (6.2, 9.5)
17.9%
1.1%
30% = 3.5pts
7.8 (7.1, 8.6)
19.7%
7.7 (7, 8.5)
17.1%
2.6%
30%
7.8 (7.1, 8.6)
19.7%
0.0%
30% = 2.7pts
8.4 (7.6, 9.2)
21.9%
-2.2%
3.5pts
Moderate leg pain
Severe leg pain 30% reduction
0.71 (0.71, 0.72)
1.6-point reduction
0.68 (0.67, 0.69) 0.034 (0.028, 0.041)***
2.7-point reduction
0.71 (0.71, 0.72)
3.5-point reduction
0.74 (0.73, 0.75) 0.024 (0.018, 0.030)***
0 (<-0.001, <0.001)
Note: MCID = minimum clinically important difference; AUROC = area under the receiver operator characteristic curve; OR = odds ratio; NRS = numeric rating scale
Table 5. Predicting Satisfaction from 30% Reduction and Absolute Point Reduction for Disability and Pain by Surgical Procedure AUROC (95% CI)
AUROC difference (95% CI)
OR (95% CI)
Nagelkerke R2 Most accurate R2 difference reduction type
Oswestry Disability Index Fusion 30% reduction
0.76 (0.75, 0.77)
10.1 (8.8, 11.5)
24.9%
12.8-point reduction
0.72 (0.72, 0.73)
0.036 (0.027, 0.045)***
7 (6.1, 7.9)
18.8%
6.1%
30%
14-point reduction
0.73 (0.72, 0.74)
0.033 (0.024, 0.041)***
7.2 (6.3, 8.1)
19.2%
5.7%
30%
20-point reduction
0.72 (0.71, 0.73)
0.038 (0.029, 0.046)***
7.8 (6.7, 9.1)
18.4%
6.5%
30%
Laminectomy 30% reduction
0.76 (0.75, 0.77)
10.4 (8.9, 12.1)
26.0%
12.8-point reduction
0.73 (0.72, 0.75)
0.029 (0.020, 0.038)***
7.7 (6.6, 8.9)
20.6%
5.4%
30%
14-point reduction
0.73 (0.72, 0.74)
0.031 (0.022, 0.040)***
7.7 (6.6, 9)
20.3%
5.7%
30%
20-point reduction
0.72 (0.71, 0.73)
0.045 (0.035, 0.055)***
8.5 (7.1, 10.1)
18.8%
7.2%
30%
Microdiscectomy 30% reduction
0.78 (0.77, 0.78)
12.7 (11, 14.7)
27.5%
12.8-point reduction
0.74 (0.73, 0.75)
0.038 (0.029, 0.048)***
8.8 (7.6, 10.1)
20.9%
6.6%
30%
14-point reduction
0.74 (0.73, 0.75)
0.034 (0.025, 0.044)***
8.7 (7.6, 10)
21.0%
6.5%
30%
20-point reduction
0.75 (0.74, 0.76)
0.025 (0.015, 0.034)***
9.1 (7.8, 10.6)
21.1%
6.4%
30%
Back Pain NRS Fusion 30% reduction
0.73 (0.72, 0.74)
7.4 (6.5, 8.4)
19.8%
1.2-point reduction
0.69 (0.68, 0.70)
0.038 (0.029, 0.047)***
5.5 (4.9, 6.2)
14.7%
5.1%
30%
2.9-point reduction
0.71 (0.70, 0.72)
0.021 (0.016, 0.026)***
6 (5.3, 6.8)
16.1%
3.7%
30%
3.5-point reduction
0.71 (0.70, 0.72)
0.025 (0.016, 0.035)***
6.9 (5.9, 8)
15.9%
3.9%
30%
Laminectomy 30% reduction
0.71 (0.70, 0.72)
6.2 (5.4, 7.2)
17.3%
1.2-point reduction
0.67 (0.66, 0.68)
0.041 (0.032, 0.051)***
4.3 (3.7, 4.9)
11.5%
5.8%
30%
2.9-point reduction
0.69 (0.68, 0.70)
0.025 (0.018, 0.031)***
5.1 (4.4, 5.9)
13.6%
3.7%
30%
3.5-point reduction
0.68 (0.67, 0.69)
0.033 (0.022, 0.044)***
5.8 (4.9, 6.9)
13.3%
4.0%
30%
Microdiscectomy 30% reduction
0.73 (0.72, 0.74)
7.2 (6.3, 8.3)
17.8%
1.2-point reduction
0.69 (0.68, 0.70)
0.044 (0.034, 0.054)***
4.8 (4.2, 5.5)
11.9%
5.9%
30%
2.9-point reduction
0.7 (0.69, 0.71)
0.033 (0.026, 0.040)***
5.5 (4.7, 6.4)
12.9%
4.9%
30%
3.5-point reduction
0.69 (0.68, 0.7)
0.041 (0.030, 0.051)***
6.4 (5.4, 7.6)
12.8%
5.0%
30%
4.5 (4, 5.1)
12.0% 30%
Leg Pain NRS Fusion 30% reduction
0.68 (0.67, 0.69)
1.6-point reduction
0.66 (0.65, 0.67)
0.019 (0.011, 0.027)***
4 (3.5, 4.5)
9.9%
2.1%
2.7-point reduction
0.67 (0.66, 0.68)
0.009 (0.003, 0.015)**
4 (3.6, 4.5)
10.4%
1.6%
30%
3.5-point reduction
0.68 (0.67, 0.69)
0.003 (-0.007, 0.013)
4.5 (4, 5.2)
11.6%
0.4%
30% = 3.5pts
Laminectomy 30% reduction
0.7 (0.69, 0.71)
5.5 (4.8, 6.3)
15.4%
1.6-point reduction
0.67 (0.66, 0.69)
0.024 (0.015, 0.032)***
4.6 (4, 5.3)
12.4%
3.0%
30%
2.7-point reduction
0.68 (0.67, 0.69)
0.016 (0.010, 0.022)***
4.6 (4, 5.2)
12.6%
2.8%
30%
3.5-point reduction
0.68 (0.67, 0.69)
0.017 (0.007, 0.027)**
4.6 (4, 5.4)
12.3%
3.1%
30%
30%
Microdiscectomy 30% reduction
0.73 (0.72, 0.74)
8.3 (7.2, 9.5)
19.9%
1.6-point reduction
0.69 (0.68, 0.70)
0.038 (0.029, 0.047)***
6.3 (5.5, 7.2)
14.9%
5.0%
2.7-point reduction
0.72 (0.71, 0.73)
0.012 (0.007, 0.018)***
6.7 (5.8, 7.7)
16.8%
3.1%
30%
3.5-point reduction
0.73 (0.72, 0.74)
0.002 (-0.009, 0.012)
7.5 (6.4, 8.6)
18.0%
1.9%
30% = 3.5pts
Note: MCID = minimum clinically important difference; AUROC = area under the receiver operator characteristic curve; OR = odds ratio; NRS = numeric rating scale