Elsevier

The Spine Journal

Volume 10, Issue 4, April 2010, Pages 313-320
The Spine Journal

Clinical Study
Minimum acceptable outcomes after lumbar spinal fusion

https://doi.org/10.1016/j.spinee.2010.02.001Get rights and content

Abstract

Background Context

Defining success after spinal surgery remains problematic. The minimal clinically important difference (MCID) in pain or functional outcomes is a common metric often calculated independent of perceived risk and morbidity, which is an important consideration in large procedures such as spinal fusion and instrumentation.

Purpose

The purpose of this study was to describe a method of assessing treatment success based on prospective, patient-reported “minimum acceptable” outcome for which they would undergo a procedure. These goals can then be compared at follow-up to gauge how frequently patient goals are met and determine correlation with patient satisfaction.

Study Design

This is a clinical descriptive study of the patient-reported minimum acceptable outcomes for spinal fusion surgery.

Outcome Measures

Minimum acceptable outcomes were determined by patients on preoperatively administered standard questionnaires regarding ultimate pain intensity, functional outcome (Oswestry Disability Index [ODI]), medication usage, and work status. Satisfaction with outcomes was assessed at 2-year follow-up.

Methods

One hundred sixty-five consecutive patients undergoing lumbar fusion for either isthmic spondylolisthesis or disc degeneration were asked to preoperatively define on standard questionnaires their minimum acceptable outcomes after surgery. Two-year outcomes and satisfaction were subsequently reported and compared with the preoperatively determined minimum acceptable outcomes.

Results

Both the spondylolisthesis and the degenerative disc disease (DDD) groups reported that a high degree of improvement was the minimum acceptable threshold for considering spinal fusion. A large majority indicated that the minimum acceptable outcomes included at least a decrease in pain intensity to 3/10 or less, an improvement in ODI of 20 or more, discontinuing opioid medications, and return to some occupational activity. Achieving the minimum acceptable outcome was strongly associated with satisfaction at 2 years after surgery. Patients with compensation claims, psychological distress, and other psychosocial stressors were more likely to report satisfaction in the absence of achieving their minimum acceptable outcome.

Conclusions

Patients with spondylolisthesis and DDD both have relatively high minimum acceptable outcomes for spinal fusion. In these cohorts, few subjects considered more commonly proposed MCIDs for pain and function as an acceptable outcome and report that they would not have surgery if they did not expect to achieve more than those marginal improvements. Although there was good concordance between achieving the minimum acceptable outcomes and ultimate satisfaction, patients with significant psychosocial factors (compensation claims, psychological distress, and others) are less likely to associate satisfaction with outcomes with actually achieving these improvements.

Introduction

Evidence & Methods

Minimal clinically important differences (MCID) based upon post-hoc anchors or “standard error of measurement” are commonly employed to determine successful clinical outcomes following therapeutic interventions. Often MCID levels put forth in the literature (generated by various methods) do not appear to commensurate with patient expectations or the risks/morbidity of surgical treatments.

As an alternative to minimum clinically important difference (MCID), the authors described a patient and intervention-specific “Minimum-Acceptable Outcome” (MAO) and found patients undergoing surgery for disc degeneration or spondylolisthesis required much larger improvements than suggested by commonly calculated MCID's. The authors report that achieving a MAO across four clinical dimensions (pain, function, medication usage, and work status) was highly predictive of patient satisfaction in subjects without psychosocial comorbidities.

The applicability of commonly calculated MCIDs in accessing surgical outcomes is still open to debate. The validity of MCIDs based solely on a patient's remote assessment of satisfaction or the test's standard error has methodological shortcomings. The concept of MAO, employing both subjective and objective outcome goals established before the intervention, may be a better measure of “success” and, possibly, a useful tool for pre-operative patient education. Further study is needed to substantiate the role of MAO in surgical decision-making.

The Editors

Although many measures have been developed to quantify objective outcomes (eg., fusion integrity, adjacent disc degeneration grades, etc) and subjective patient reports (eg., visual analog scores [VAS], satisfaction ratings, etc), the use of these measures to define clinical success remains problematic. Even global satisfaction ratings are often internally inconsistent and are not specific as to what “satisfaction” means. Furthermore, there may be an inherent bias toward reporting satisfaction after choosing certain “preferred” interventions, regardless of outcome. [1], [2], [3], [4].

Some measures of “success” have been focused on demonstration of statistical improvement in a measure such as pain, function, medication usage, return-to-work status, and so forth. These measurements, however, usually focus on the group level and not the individual level. It is difficult to interpret these results because calculated changes, which appear statistically significant at the group level, may not necessarily translate into significant changes for the individual (eg., one or two points on a 10-point VAS scale for back pain).

More recent trends have suggested a “composite” score combining minimum thresholds for success in several dimensions. The most common suggested dimensions are pain, function, medication requirements, and work status. The magnitude of improvement in each area that qualifies as significant has been the subject of controversy: not everyone will have the same ultimate goal and not all interventions are equally morbid, hazardous, or costly to the patient.

As an alternative, we propose here a method of assessing intervention success based on prospective minimum goals. In this method, patients individually establish what they consider to be a “minimum acceptable” outcome for which they would undergo a procedure using standard metrics. These “minimum acceptable goals” can then be compared at follow-up to gauge how frequently patient goals were met. Patient-determined minimum acceptable outcomes can also serve as a validity check against post hoc patient satisfaction or surgeon assessment scores.

This is a descriptive study of this method using “minimum acceptable” outcomes for common lumbar fusion procedures as assessed in a large cohort of patients with isthmic spondylolisthesis or presumed primary degenerative back pain preparing to undergo posterior lumbar fusions. The outcomes at 2 years were subsequently compared with the preoperative minimum acceptable outcomes.

Section snippets

Patient demographics

Consecutive subjects were enrolled at a single institution between 1995 and 2000 and underwent operations by the senior author. There were 71 isthmic spondylolisthesis patients (40 men, 31 women) and 94 degenerative disc disease (DDD) patients (38 men, 56 women).

Patients were included only if they were seen in the outpatient spinal surgery clinic before surgery. Patients were excluded if they were admitted through the Emergency Department, were seen as inpatient consults and undergoing surgery

Feasibility

Of the 185 subjects solicited to the study, all agreed to participate. Of these, 155 completed the mailed questionnaires before arriving in clinic, 22 were given new forms in clinic, and 8 subjects brought in questionnaires on the day of surgery. The median time before surgery for completion, as indicated by the patient's dating the forms, was 3 days (range 1–7 days). No subject complained to the investigators of the burden to complete the questionnaire.

Baseline characteristics

The baseline results for both groups are

Discussion

Various tools have been devised to assess individual responses with regard to pain level or functional capacity. Benchmarks for outcomes studies have included the VAS, Roland-Morris Disability Questionnaire [9], and the ODI. When comparing one outcomes measure to another, however, markedly inconsistent results can be found. Some studies have shown that despite measures indicating improvement in pain and purported patient satisfaction after fusion for lumbar spondylosis, there continued to be

Conclusion

The minimum acceptable improvements for patients undergoing spinal fusion for isthmic spondylolisthesis and DDD of the lumbar spine are substantial for pain reduction, four or more points on a 10-point scale, good physical functioning (ODI improvement of more than 20), and resuming occupational duties. Continued occupational disability or chronic dependency on opioid medications was not considered acceptable by 90% of the surveyed subjects. In these large cohorts, few subjects considered the

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    Citation Excerpt :

    Therefore, we proposed clean cutoff values for MCID on the basis of the results of two anchor-based methods and both absolute point-change and percentage-change. As some previous reports regarding MCIDs have targeted patients with mixed interventions, including lumbar decompression without fusion, comparing the differences between our proposed values and those estimated in previous studies is not easy. [1,4,6,7] Moreover, some of the previously calculated MCID values were based on the distribution-based method, which is considered more comparable with the “minimal detectable change” than MCID [5,27].

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Author disclosures: EJC (stock ownership, including options and warrants, Simpirica, Bioassetts, Cytonics; private investments, including venture capital, start-ups, Simpirica; consulting, Medtronic, Synthes, Well-Point B/C B/S; trips/travel, US Army; scientific advisory board, Intrinsic Orthopedics, Cytonics; other office, Bioassetts; grants, AO Foundation; fellowship support, DePuy Spine; other relationships, Orthopaedic Surgeon); IC (speaking/teaching arrangements, Stryker Spine; grants, Medtronic, Stryker Spine).

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