60 50 40 30 20 10 0 Acta Orthopaedica 2009; 80 (4): 445–450 447 DPQ score – non-instrumented fusion 70 DPQ score – instrumented fusion 70 Daily activity Work/leisure Anxiety/depression Social interest Daily activity Work/leisure Anxiety/depression Social interest 60 50 40 30 20 10 0 Preoperatively 1 2 Preoperatively 1 2 3–4 5–7 Follow-up (year) 3–4 5–7 Follow-up (year) Figure 1. Dallas pain questionnaire (DPQ) scores according to follow-up time point in the 2 study groups. each for back and leg pain (pain now, worst and average pain in the last 14 days), which are added to give a response scale ranging from 0 to 60 (Manniche et al. 1994). Both the DPQ and the LBPRS pain index were completed preoperatively, at the 1- and 2-year follow-up, and at the mailed follow-up. Furthermore, the patients who answered the mailed follow-up completed the SF-36 generic health survey measure (Ware 2000). As subjective global evaluation, the patient’s answer to the question “Now that you know the result, would you undergo the procedure again?” was used. This question was also asked in the mailed intermediate follow-up question- naire. Fusion was assessed by the surgeon at 1- and 2-year follow- up using plain anteroposterior and lateral radiographs and the criteria suggested by Christensen et al. (2001). Patients were asked to list their pain medication on a sepa- rate page in the questionnaire. Doses were summarized using defined daily dose (DDD) (www.whocc.no). The DDD is the assumed average maintenance dose per day for a drug used for its main indication in adults. Furthermore, drug use was clas- sified as no use, occasional use, or daily use. Statistics All data were analyzed using non-parametric statistics. Between-group comparisons of continuous variables were done using the Mann-Whitney rank-sum test for unpaired data or the Kruskal-Wallis test for equality of groups, when comparing more than 2 groups (without correction for ties). Significance of proportions was calculated using χ2-test. Sig- nificance level was 5% using two-tailed testing. Results are presented as mean (95% CI) unless otherwise stated. Inter- cooled Stata version 9.2 for Windows was the software used for the statistical analysis. Results Both the non-instrumented and instrumented group improved from preoperatively to 1-year follow-up, with a much smaller improvement after that. With respect to the two activity-based DPQ scores, improvement was greatest in the instrumented group (Figure 1). Outcome was better in the instrumented group in all outcome parameters and reached statistical sig- nificance in 6 of 7 parameters (Figure 2). The SF-36 subscale outcome was still better in the instrumented group, although it was only statistically significant in the Bodily Pain (BP) cat- egory: 56 (48–65) vs. 41 (33–50) (p = 0.01). Controlling for differences in age and sex between the groups by using norm- adjusted scores of the SF-36, results were similar. Using the norm-adjusted score, there was a statistically significant dif- ference in favor of the instrumented group in the BP subscale, 75 (64-87) vs. 56 (45-67) (p = 0.01), and in the physical component summary (PCS) scale, 85 (76-93) vs. 72 (64-81) (p = 0.02). With respect to subjective evaluation at the mailed follow- up, 20/29 patients were positive in the instrumented group as compared to 14/30 in the non-instrumented group (p = 0.083). There was no difference between the groups with respect to use of pain medication. It was used on a daily basis by 20/35 and 18/32 in the non-instrumented and instrumented groups, respectively. Doses were slightly higher in the non-instru- mented group, with a median DDD of 0.7 (0.1–1.33) as com- pared to 0.3 (0.1–1.0) in the instrumented group (p = 0.9). Fusion rate was higher in the instrumented group with 35/43 patients fused as compared to 34/50 in the non-instrumented group (p = 0.1). Solid fusion was associated with a better functional outcome at long-term follow-up, although it only reached statistical significance in DPQ Daily activity, 34 (27–