Study Design. Combined prospective randomized controlled trial and observational cohort study of degenerative spondylolisthesis (DS) with an as-treated analysis.
Objective. To determine modifiers of the treatment effect (TE) of surgery (the difference between surgical and nonoperative outcomes) for DS using subgroup analysis.
Summary of Background Data. Spine Patient Outcomes Research Trial demonstrated a positive surgical TE for DS at the group level. However, individual characteristics may affect TE.
Methods. Patients with DS were treated with either surgery (n = 395) or nonoperative care (n = 210) and were analyzed according to treatment received. Fifty-five baseline variables were used to define subgroups for calculating the time-weighted average TE for the Oswestry Disability Index during 4 years (TE = [INCREMENT] Oswestry Disability Indexsurgery− [INCREMENT] Oswestry Disability Indexnonoperative). Variables with significant subgroup-by-treatment interactions (P< 0.05) were simultaneously entered into a multivariate model to select independent TE predictors.
Results. All analyzed subgroups that included at least 50 patients improved significantly more with surgery than with nonoperative treatment (P< 0.05). Multivariate analyses demonstrated that age 67 years or less (TE −15.7 vs.−11.8 for age >67, P= 0.014); female sex (TE −15.6 vs.−11.2 for males, P= 0.01); the absence of stomach problems (TE −15.2 vs.−11.3 for those with stomach problems, P= 0.035); neurogenic claudication (TE −15.3 vs.−9.0 for those without claudication, P= 0.004); reflex asymmetry (TE −17.3 vs.−13.0 for those without asymmetry, P= 0.016); opioid use (TE −18.4 vs.−11.7 for those not using opioids, P< 0.001); not taking antidepressants (TE −14.5 vs.−5.4 for those on antidepressants, P= 0.014); dissatisfaction with symptoms (TE −14.5 vs.−8.3 for those satisfied or neutral, P= 0.039); and anticipating a high likelihood of improvement with surgery (TE −14.8 vs.−5.1 for anticipating a low likelihood of improvement with surgery, P= 0.019) were independently associated with greater TE.
Conclusion. Patients who met strict inclusion criteria improved more with surgery than with nonoperative treatment, regardless of other specific characteristics. However, TE varied significantly across certain subgroups.
Level of Evidence: 3
Surgical treatment effect (TE) modifiers were evaluated in the Spine Patient Outcomes Research Trial degenerative spondylolisthesis cohort. All subgroups improved more with surgery than with nonoperative treatment. Neurogenic claudication, opioid use, not taking antidepressants, dissatisfaction with symptoms, and anticipating a high likelihood of success with surgery most strongly predicted greater TE.
*Geisel School of Medicine at Dartmouth, Hanover, NH
†Dartmouth-Hitchcock Medical Center, Lebanon, NH; and
‡The Dartmouth Institute for Health Policy and Clinical Practice, Lebanon, NH.
Address correspondence and reprint requests to Adam M. Pearson, MD, MS, Dartmouth-Hitchcock Medical Center, One Medical Center Drive, Lebanon, NH 03756; E-mail: firstname.lastname@example.org or email@example.com
Acknowledgment date: January 22, 2013. Revision date: May 6, 2013. Acceptance date: May 13, 2013.
The manuscript submitted does not contain information about medical device(s)/drug(s).
NIH/NIAMS grant funds were received in support of this work.
Relevant financial activities outside the submitted work: consultancy, grants.