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.