Challenges in the Analysis of Longitudinal Pain Data: Practical Lessons from a Randomized Trial of Annular Closure in Lumbar Disc Surgery

Table 1

Unadjusted and integrated VAS pain scores with ACD and controls at each follow-up visit.

Follow-up Interval	Unadjusted			Integrated
	ACD	Control	p-value	ACD	Control	p-value
Pre-treatment	81±15	81±15	0.97	81±15	81±15	0.97
6 weeks	13±19	19±25	0.001	14±21	22±29	<0.001
3 months	12±20	15±22	0.08	14±23	19±27	0.02
6 months	11±18	15±23	0.03	13±22	22±32	<0.001
1 year	11±19	14±21	0.13	16±27	26±34	<0.001
2 years	12±21	14±21	0.33	19±30	29±36	<0.001

Notes:values represent patient-reported VAS scores (mean±SD) recorded at scheduled follow-up visits; values represent adjusted VAS scores (mean±SD) where the baseline VAS pain score was substituted for patient-reported VAS score at the time of symptomatic reherniation and at each subsequent follow-up visit through 2 years using the BOCF approach to represent clinical failure. ACD, annular closure device; BOCF, baseline observation carried forward; SD, standard deviation; VAS, visual analogue scale.