Previous studies have reported on the minimum clinically important difference (MCID), a threshold of improvement that is clinically relevant for lumbar degenerative disorders. Recent studies have shown that pre- and postoperative health-related quality of life (HRQOL) measures vary among patients with different diagnostic etiologies. There is also concern that a patient's previous care experience may affect his or her perception of clinical improvement. This study determined if MCID values for the Oswestry Disability Index (ODI), 36-Item Short-Form Health Survey (SF-36), and back and leg pain are different between patients undergoing primary or revision lumbar fusion.
Prospectively collected preoperative and 1-year postoperative patient-reported HRQOLs, including the ODI, SF-36 physical component summary (PCS), and numeric rating scales (0–10) for back and leg pain, in patients undergoing lumbar spine fusion were analyzed. Patients were grouped into either the primary surgery or revision group. As the most widely accepted MCID values were calculated from the minimum detectable change, this method was used to determine the MCID.
A total of 722 patients underwent primary procedures and 333 patients underwent revisions. There was no statistically significant difference in demographics between the groups. Each group had a statistically significant improvement at 1 year postoperatively compared with baseline. The minimum detectable change–derived MCID values for the primary group were 1.16 for back pain, 1.36 for leg pain, 12.40 for ODI, and 5.21 for SF-36 PCS. The MCID values for the revision group were 1.21 for back pain, 1.28 for leg pain, 11.79 for ODI, and 4.90 for SF-36 PCS. These values are very similar to those previously reported in the literature.
The MCID values were similar for the revision and primary lumbar fusion groups, even when subgroup analysis was done for different diagnostic etiologies, simplifying interpretation of clinical improvement. The results of this study further validate the use of patient-reported HRQOLs to measure clinical effectiveness, as a patient's previous experience with care does not seem to substantially alter an individual's perception of clinical improvement.