Abstract
Background: No previous studies have created and validated prediction models for outcomes in patients receiving
spinal manipulation for care of chronic low back pain (cLBP). We therefore conducted a secondary analysis
alongside a dose-response, randomized controlled trial of spinal manipulation.
Methods: We investigated dose, pain and disability, sociodemographics, general health, psychosocial measures,
and objective exam findings as potential predictors of pain outcomes utilizing 400 participants from a randomized
controlled trial. Participants received 18 sessions of treatment over 6-weeks and were followed for a year. Spinal
manipulation was performed by a chiropractor at 0, 6, 12, or 18 visits (dose), with a light-massage control at all
remaining visits. Pain intensity was evaluated with the modified von Korff pain scale (0–100). Predictor variables
evaluated came from several domains: condition-specific pain and disability, sociodemographics, general health status,
psychosocial, and objective physical measures. Three-quarters of cases (training-set) were used to develop 4
longitudinal models with forward selection to predict individual “responders” (≥50 % improvement from baseline) and
future pain intensity using either pretreatment characteristics or post-treatment variables collected shortly after
completion of care. The internal validity of the predictor models were then evaluated on the remaining 25 % of cases
(test-set) using area under the receiver operating curve (AUC), R2, and root mean squared error (RMSE).
Results: The pretreatment responder model performed no better than chance in identifying participants who became
responders (AUC = 0.479). Similarly, the pretreatment pain intensity model predicted future pain intensity poorly with
low proportion of variance explained (R2 = .065). The post-treatment predictor models performed better with AUC = 0.665
for the responder model and R2 = 0.261 for the future pain model. Post-treatment pain alone actually predicted future
pain better than the full post-treatment predictor model (R2 = 0.350). The prediction errors (RMSE) were large (19.4 and
17.5 for the pre- and post-treatment predictor models, respectively).
Conclusions: Internal validation of prediction models showed that participant characteristics preceding the start of care
were poor predictors of at least 50 % improvement and the individual’s future pain intensity. Pain collected shortly after
completion of 6 weeks of study intervention predicted future pain the best.
Keywords: Chronic low back pain, Prediction model, Spinal manipulation, Chiropractic, Dose–response, Randomized
controlled trial
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