Table 2.

Area under curve subgroup results from the adjusted^* as-treated Oswestry Disability Index (ODI) outcome analysis for the six significant treatment effect predictors (time weighted average 4 year treatment effects).

SPS Predictors	N	Surgical (n = 413)	Non-operative (n = 221)	Treatment Effect (95% CI) †
Baseline ODI ≤ 56	482	−18.9 (0.8)	−3.9 (0.9)	−15 (−17, −13)
Baseline ODI > 56	150	−28.3 (1.5)	−23.9 (2.2)	−4.4 (−8.7, −0.1)
p-value		<0.001	<0.001	<0.001
Smoker	62	−8.9 (2.2)	−7.4 (2.4)	−1.6 (−6.6, 3.5)
Non-Smoker	566	−20.7 (0.7)	−9 (0.9)	−11.7 (−13.6, −9.9)
p-value		<0.001	0.53	<0.001
No Neuroforaminal Stenosis	427	−19.6 (0.8)	−10.9 (1)	−8.7 (−10.8, −6.5)
Neuroforaminal Stenosis	207	−20 (1.2)	−5.8 (1.3)	−14.2 (−17, −11.3)
p-value		0.80	0.003	0.002
Predominant Back Pain	159	−16.3 (1.4)	−9.1 (1.6)	−7.3 (−10.8, −3.7)
Predominant Leg Pain	456	−20.6 (0.8)	−9.1 (0.9)	−11.5 (−13.5, −9.5)
p-value		0.008	0.97	0.035
No Lifting at Work	324	−20.9 (0.9)	−8.3 (1.1)	−12.5 (−14.9, −10.1)
Lifting at Work	307	−18.1 (1)	−9.5 (1.1)	−8.5 (−11, −6)
p-value		0.039	0.46	0.017
Any Neurological Deficit	349	−21 (0.9)	−7.7 (1.1)	−13.3 (−15.5, −11)
No Neurological Deficit	285	−18 (1)	−10.8 (1.2)	−7.2 (−9.8, −4.6)
p-value		0.037	0.058	<0.001

^*Adjusted for center, age, gender, baseline ODI score, income, treatment preference, duration of symptoms, compensation, smoking status, BMI, baseline Stenosis Bothersomeness, joint, stomach and bowel problems.

^†Treatment effect is the difference between the surgical and non-operative mean change from baseline. Analysis is done using a mixed model with a random subject intercept term. Treatment is a time-varying covariate where a patients’ experience prior to surgery is attributed to the non-operative arm and time is measured from enrollment and his/her post-surgery outcomes are attributed to the surgical arm and time is measured from time of surgery.