Sex (female/male) Age at operation (years) Age at follow-up (years) Follow-up time (years) Operation time (min) Blood loss (mL) Hospitalization (days) Diagnosis Degenerative Stenosis Stenosis + deg. olisthesis Stenosis + deg. scoliosis Operated level(s) 1 level 2 levels 3 levels 4 + 5 levels Additional neural decompression None Laminotomy Laminectomy Previous spine surgery Radiographic fusion at last follow-up 1 14 11 9 8 14 7 6 1 8 26 9 3 19 9 5 12 14 8 2 2 10 24 7 P-value 0.5 0.008 0.005 0.3 0.4 0.9 0.4 0.2 0.5 0.004 0.3 P-value 0.3 0.007 0.03 0.02 <0.001 0.1 0.3 0.4 0.4 0.7 0.5 0.3 0 4 1 3 2 2 3 1 0 0 8 5 0 11 3 1 6 5 4 0 0 0 15 1 446 Acta Orthopaedica 2009; 80 (4): 445–450 Characteristics of the study population and drop-outs according to treatment group Follow-up population Instrumented Non-instrumented 26/9 67 (65–68) 71 (69–73) 4.7 (4.3–5.2) 222 (191–254) 898 (558–1238) 13 (11–14) 23/13 70.3 (68.3–72.4) 74.3 (72.3–76.4) 4.0 (3.5–4.4) 154 (136–172) 615 (413–816) 13 (11–15) Drop-outs Instrumented Non-instrumented 3/5 68 (63–72) 72 (68–77) 4.5 (3.4–5.6) 215 (149–280) 1012 (-97–2121) 14 (10–17) 8/7 76 (73–80) 80.3 (77–83) 3.9 (3.1–4.8) 179 (154–205) 672 (375–968) 12 (10–14) 29 (83%) 26 (74%) 6 (75%) 8 (53%) Values are mean (95% CI) or number (%) Patients and methods Patient population The study included all 94 patients (60 women), aged 60 years or older, who underwent a primary lumbar fusion using fresh frozen allograft at our department in the period from January 2001 through December 2005. The mean age was 70 (60– 88) years (Table). They all underwent posterolateral spinal fusion, either as a non-instrumented procedure (51 patients) or as an instrumented procedure using either CD-Horizon (Medtronic Sofamor Danek, Minneapolis, MN) (31 patients) or TSRH pedicle screw systems (Medtronic Sofamor Danek) (12 patients). The allograft used was a fresh frozen femoral head. Main indications for fusion were spinal stenosis sur- gery where fusion was deemed necessary due to instability or the need for extensive decompression, or a high degree of back pain. 91 patients had decompression performed together with the fusion. Central laminectomy was performed in 73 patients; 18 had a laminotomy and 3 patients were fused without decompression of neural structures because of pri- marily back pain. Of the 8 patients in the non-instrumented group who had previous spine surgery, this was discectomy in 4 patients and partial laminectomy in the other 4 patients. In the instrumented group the previous surgeries consisted of 8 discectomies, 5 partial laminectomies, and 1 fusion of the sacroiliac joints. All patients who were still alive were mailed the question- naires described below in November 2007 to assess their func- tional outcome and quality of life at this follow-up. After 1 month, a written reminder was sent and no further contact was made after this. Of the 94 patients, 4 patients had died at the time of the follow-up, 71 patients responded with completed question- naires, and 3 patients stated that they felt unable to complete the questionnaires, 1 because of dementia and 2 because of other significant comorbidities. 16 patients did not respond at all. Thus, available response rate was 74/90 (82%). This resulted in an overall follow-up rate of 76% and an available follow-up rate of 79%. Average length of follow-up was 4.3 years with slightly longer follow-up time in the instrumented group (Table). Characteristics of the drop-outs are given in the Table. Twelve patients missed answering the subjective evaluation question and 4 patients missed listing their medica- tion use. One patient in the non-instrumented group missed her follow-ups at 1 and 2 years and had no radiographs per- formed. Outcome parameters Functional outcome was assessed by the Dallas pain question- naire (DPQ). The DPQ assesses the impact of chronic spinal pain in 4 categories: Daily activities, Work-Leisure activities, Anxiety-Depression and Social interest. A high score indi- cates a high influence of back pain on the daily life of the patient and thus a poor outcome (Lawlis et al. 1989). Back and leg pain was measured using the pain assessment index from the low back pain rating scale (LBPRS). It comprises 3 scales