title: Determination of minimum clinically important difference (MCID) in pain, disability, and quality of life after revision fusion for symptomatic pseudoarthrosis.
abstract: BACKGROUND
  Spinal surgical outcome studies rely on patient reported outcome (PRO) measurements to assess the effect of treatment. A shortcoming of these questionnaires is that the extent of improvement in their numerical scores lacks a direct clinical meaning. As a result, the concept of minimum clinically important difference (MCID) has been used to measure the critical threshold needed to achieve clinically relevant treatment effectiveness. Post hoc anchor-based MCID methods have not been applied to the surgical treatment for pseudoarthrosis.
  
  
  OBJECTIVE
  To determine the most appropriate MCID values for visual analog scale (VAS), Oswestry Disability Index (ODI), Short Form (SF)-12 physical component score (PCS), and European Quality of Life 5-Dimensions (EQ-5D) in patients undergoing revision lumbar arthrodesis for symptomatic pseudoarthrosis. STUDY DESIGN/ SETTING: Retrospective cohort study.
  
  
  METHODS
  In 47 patients undergoing revision fusion for pseudoarthrosis-associated back pain, PRO measures of back pain (BP-VAS), ODI, physical quality of life (SF-12 PCS), and general health utility (EQ-5D) were assessed preoperatively and 2 years postoperatively. Four subjective post hoc anchor-based MCID calculation methods were used to calculate MCID (average change; minimum detectable change; change difference; and receiver operating characteristic curve analysis) for two separate anchors (health transition index (HTI) of SF-36 and satisfaction index).
  
  
  RESULTS
  All patients were available for a 2-year PRO assessment. Two years after surgery, a significant improvement was observed for all PROs; Mean change score: BP-VAS (2.3±2.6; p<.001), ODI (8.6%±13.2%; p<.001), SF-12 PCS (4.0±6.1; p=.01), and EQ-5D (0.18±0.19; p<.001). The four MCID calculation methods generated a wide range of MCID values for each of the PROs (BP-VAS: 2.0-3.2; ODI: 4.0%-16.6%; SF-12 PCS: 3.2-6.1; and EQ-5D: 0.14-0.24). There was no difference in response between anchors for any patient, suggesting that HTI and satisfaction anchors are equivalent in this patient population. The wide variations in calculated MCID values between methods precluded any ability to reliably determine what the true value is for meaningful change in this disease state.
  
  
  CONCLUSIONS
  Using subjective post hoc anchor-based methods of MCID calculation, MCID after revision fusion for pseudoarthrosis varies by as much as 400% per PRO based on the calculation technique. MCID was suggested to be as low as 2 points for ODI and 3 points for SF-12. These wide variations and low values of MCID question the face validity of such calculation techniques, especially when applied to heterogeneous disease and patient groups with a multitude of psychosocial confounders such as failed back syndromes. The variability of MCID thresholds observed in our study of patients undergoing revision lumbar fusion for pseudoarthrosis raises further questions to whether ante hoc or Delphi methods may be a more valid and consistent technique to define clinically meaningful, patient-centered changes in PRO measurements.
authors.affiliation: Department of Neurosurgery, Vanderbilt University Medical Center, Nashville, TN 37232-8618, USA.
authors.forename: Scott L
authors.initials: SL
authors.lastname: Parker
authors.forename: Owoicho
authors.initials: O
authors.lastname: Adogwa
authors.forename: Stephen K
authors.initials: SK
authors.lastname: Mendenhall
authors.forename: David N
authors.initials: DN
authors.lastname: Shau
authors.forename: William N
authors.initials: WN
authors.lastname: Anderson
authors.forename: Joseph S
authors.initials: JS
authors.lastname: Cheng
authors.forename: Clinton J
authors.initials: CJ
authors.lastname: Devin
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: McGirt
mesh_terms: D000328:Adult; D000368:Aged; D001416:Back Pain / Q000209:etiology / Q000601:surgery*; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010147:Pain Measurement / Q000379:methods*; D017060:Patient Satisfaction; D011542:Pseudarthrosis / Q000150:complications / Q000601:surgery*; D011788:Quality of Life; D012086:Reoperation; D012189:Retrospective Studies; D013123:Spinal Fusion; D016896:Treatment Outcome