Patient demographics.
| Demographics | N = 1019 |
| Age at surgery, y, mean (SD) (range) | 68.1 (12.2) (16–96) |
| Women, n (%) | 644 (63.2) |
| Rheumatoid arthritis, n/N (%)a | 53/1007 (5.3) |
| Osteoporosis, n/N (%)a | 126/1007 (12.5) |
| Smoking, n/N (%)b | 43/789 (5.4) |
| Body mass index, mean (SD) (range) | 27.5 (5.1) (16.2–52) |
| Previous lumbar surgery, mean (SD) (range) | 0.8 (1.1) (0–8) |
| Duration of follow-up, mo, mean (SD) (range) | 51.7 (30.0) (18–172) |