Clinical StudyMinimum clinically important difference in lumbar spine surgery patients: a choice of methods using the Oswestry Disability Index, Medical Outcomes Study questionnaire Short Form 36, and Pain Scales
Introduction
Spinal surgery studies rely on patient's answers to health-related quality-of-life questionnaires (HRQOL) to assess treatment effect. Three commonly used HRQOLs are pain scales, the Oswestry Disability Index (ODI) [1], [2], [3], and the physical component summary (PCS) of the Short Form of the Medical Outcomes Study (SF-36) [4]. A difficulty in using HRQOL measures is that their numerical scores lack immediate meaning or clinical importance [5]. The concept of minimum clinically important difference (MCID) has been proposed as a critical threshold to measure treatment effectiveness. Treatment effect reaching MCID would impart significance to study results and might justify clinicians' decision to treat. The original conceptualization of MCID included an implicit ratio of benefits to costs and risks of treatment [6] but research in the field of MCID has mainly focused on the benefit side of this ratio and most commonly considers MCID to be “the smallest change that is important to patients” [7].
MCID values are instrument dependent. Efforts have been made to determine MCID for a variety of instruments such as the Roland-Morris Back Pain Questionnaire[7], [8], the Chronic Heart Failure Questionnaire [6], [9], the Chronic Respiratory Disease Questionnaire [6], [10], the SF-36 [9], [10], Visual Analog pain scales [11], and ODI [11]. Several methods have been used to calculate MCID; those methods are usually classified into anchor-based methods (comparing HRQOL scores to another measurement) and distribution-based methods (built on the variability of the HRQOL scores). A major limitation in the pursuit of MCID stems from the fact that the different calculation methods produce different MCID values [5], [12]. There is, so far, no agreed upon method to calculate an optimal MCID and no definite MCID has been established for the three commonly used HRQOL scales in spinal surgery patients: pain scales, ODI, and SF-36 (PCS).
The choice of a calculation method and, hence, of an MCID value has important implications for the evaluation of treatment. Obviously, a lower MCID value would put any given treatment in a more favorable light, because a greater proportion of patients would be able to reach a lower threshold. On the other hand, an artificially high MCID would not appropriately credit the value of the intervention. No study so far has examined the range of possible MCID values in lumbar spine surgery patients that can be obtained by different calculation methods.
This study has three purposes. First, to illustrate the variability of values obtained by the common anchor-based and distribution-based methods to calculate MCID [13]. We purposely adhered to calculation methods as found in the MCID literature without attempt to revise those methods. Second, to determine an MCID value for each HRQOL that is both statistically sound and clinically meaningful for patients undergoing spinal surgery. Although it is possible that MCID values may differ by treatment and pathology, we aimed to describe MCID values for a general lumbar spine surgery population, encompassing a broad range of diagnostic entities. Third, to validate the discriminative ability of a global health assessment as anchor by comparing it with another anchor, specifically, a scale based on the patient satisfaction with the outcomes of their surgery.
Section snippets
Patient sample
Physicians from the Lumbar Spine Study Group collaborate in prospectively collecting outcomes data on their patients. The Lumbar Spine Study Group database contained 948 patients; of the 948 patients, 460 were retained for this study because they had answered the “satisfaction with results” questions. These patients were contributed by 11 different surgeons at three medical centers. The following numbers of patients had both baseline and 1-year scores: 457 for ODI, 460 for PCS, 427 for back
Baseline, 1-year, and change scores
Table 1 reports baseline and 1-year scores for ODI, PCS, and pain scales. The change scores broken down by the patient answers to the HTI and the Satisfaction scales are reported in Table 2. Analysis of variance and Bonferroni post hoc tests showed that the average change scores are different between HTI and Satisfaction answers except for the following: the ODI score of the “Somewhat Worse” is not different from the “About the same” and the “Much Worse.” The ODI score of the “Dissatisfied” is
Choice of MCID value
In this study, we evaluated a range of statistical parameters with potential relevance in identifying an optimal MCID value for each of the HRQOL measures studied. It is clear that the different calculation methods yielded widely different threshold values. These ranged from 2.92 to 15.36 for ODI, 1.26 to 5.95 for PCS, 0.28 to 2.88 for back pain, and 0.53 to 2.85 for leg pain. These constitute five- to 10-fold variations. The smallest value consistently resulted from the effect size
Conclusions
MCID is a quantitative assessment of clinical relevance for a given magnitude of HRQOL score change. HRQOL scores above MCID would be indicative of a potentially important change. A given treatment would then be justified when a large proportion of patients report changes above MCID. This study determined an MCID value for the four common HRQOL measures used for the surgical treatment of lumbar spine patients. Amongst a variety of threshold values, the MDC was selected as an appropriate MCID
Acknowledgement
The authors thank the members of the Lumbar Spine Study Group for their support.
References (29)
Distribution-based and anchor-based approaches provided different interpretability estimates for the Hydrocephalus Outcome Questionnaire
J Clin Epidemiol
(2006)- et al.
Measurement of health status. Ascertaining the minimal clinically important difference
Control Clin Trials
(1989) - et al.
Further evidence supporting an SEM-based criterion for identifying meaningful intra-Individual changes in health-related quality of life
J Clin Epidemiol
(1999) - et al.
Understanding the minimum clinically important difference (MCID). A review of concepts and methods
Spine J
(2007) - et al.
Determining a minimal important change in a disease-specific Quality of Life Questionnaire
J Clin Epidemiol
(1994) - et al.
Relative responsiveness of condition-specific and generic health status measures in degenerative lumbar spine stenosis
J Clin Epidemiol
(1995) - et al.
Methodological problems in the retrospective computation of responsiveness to change: the lesson of Cronbach
J Clin Epidemiol
(1997) - et al.
The Oswestry Low Back Pain Disability Questionnaire
Physiotherapy
(1980) - et al.
The Oswestry Disability Index
Spine
(2000) - et al.
The Roland-Morris Disability Questionnaire and the Oswestry Disability Questionnaire
Spine
(2000)
SF-36 health survey update
Spine
Sensitivity to change of the Roland-Morris Back Pain Questionnaire: Part 1
Phys Ther
Sensitivity to change of the Roland-Morris Back Pain Questionnaire: Part 2
Phys Ther
Linking clinical relevance and statistical significance in evaluating intra-individual changes in health-related quality of life
Med Care
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The authors acknowledge a financial relationship (research support from Medtronic [AGC, BRS] and consultants [BRS, TCS, and SDG] for Medtronic Sofamor Danek) that may indirectly relate to the subject of this research.