Primary and secondary outcomes in all follow-up assessments
| Surgical (n=297) | Control (n=73) | Difference | |
|---|---|---|---|
| NASS back pain*, mean (95% CI) | |||
| 6 weeks | 4.4 (4.0 to 4.7) | 5.3 (4.5 to 6.2) | −1.0 (−1.9 to −0.1) |
| 12 weeks | 4.8 (4.4 to 5.1) | 5.1 (4.2 to 6.0) | −0.3 (−1.3 to 0.6) |
| 1 year | 4.5 (4.1 to 4.9) | 4.7 (3.8 to 5.6) | −0.2 (−1.2 to 0.8) |
| 2 years | 4.4 (4.0 to 4.8) | 4.5 (3.5 to 5.5) | −0.1 (−1.2 to 1.0) |
| Response to treatment, % (95% CI) | |||
| 6 weeks | 48 (36 to 60) | 17 (8 to 25) | 34 (16 to 47) |
| 12 weeks | 35 (24 to 46) | 24 (13 to 35) | 9 (−6 to 27) |
| 1 year | 42 (30 to 55) | 35 (15 to 54) | 3 (−15 to 30) |
| 2 years | 44 (30 to 58) | 49 (21 to 77) | −17 (−36 to 26) |
| NASS neurogenic†, mean (95% CI) | |||
| 6 weeks | 16.5 (14.8 to 18.2) | 20.0 (16.2 to 23.9) | −3.5 (−7.7 to 0.7) |
| 12 weeks | 14.7 (13.0 to 16.4) | 18.2 (14.3 to 22.0) | −3.5 (−7.7 to 0.7) |
| 1 year | 14.0 (12.2 to 15.7) | 17.1 (12.7 to 21.5) | −3.1 (−7.9 to 1.6) |
| 2 years | 14.1 (12.2 to 16.0) | 15.4 (10.6 to 20.2) | −1.3 (−6.3 to 3.7) |
| NASS function‡, mean (95% CI) | |||
| 6 weeks | 17.9 (16.5 to 19.4) | 17.3 (14.1 to 20.5) | 0.7 (−2.8 to 4.2) |
| 12 weeks | 13.7 (12.4 to 14.9) | 17.0 (13.6 to 20.3) | −3.3 (−6.9 to 0.3) |
| 1 year | 11.5 (10.2 to 12.9) | 15.3 (11.9 to 18.6) | −3.7 (−7.4 to −0.1) |
| 2 years | 12.5 (10.9 to 14.0) | 13.6 (9.8 to 17.4) | −1.1 (−5.2 to 2.9) |
| SF-36 physical function§, mean (95% CI) | |||
| 6 weeks | 33.2 (31.8 to 34.6) | 36.3 (33.4 to 39.1) | −3.1 (−6.4 to 0.1) |
| 12 weeks | 38.0 (36.7 to 39.3) | 37.8 (34.4 to 41.2) | 0.2 (−3.5 to 3.8) |
| 1 year | 41.0 (39.4 to 42.5) | 40.3 (36.7 to 43.8) | 0.7 (−3.2 to 4.6) |
| 2 years | 42.1 (40.3 to 44.0) | 42.8 (39.1 to 46.4) | −0.6 (−4.7 to 3.5) |
| SF-36 mental function§, mean (95% CI) | |||
| 6 weeks | 47.9 (45.8 to 49.9) | 48.2 (44.3 to 52.2) | −0.4 (−4.9 to 4.1) |
| 12 weeks | 49.3 (47.6 to 51.0) | 47.5 (43.6 to 51.3) | 1.8 (−2.3 to 6.0) |
| 1 year | 50.3 (48.7 to 51.9) | 47.9 (43.9 to 51.8) | 2.4 (−1.9 to 6.7) |
| 2 years | 49.1 (47.0 to 51.1) | 47.7 (43.5 to 52.0) | 1.3 (−3.5 to 6.1) |
Possible NASS subscale scores range from *0 to 10, †0 to 30 and ‡0 to 45; lower scores indicate lower severity of symptoms.
§Possible score range for both SF-36 subscales is 0 to 100; higher scores indicate lower severity of symptoms.
NASS, North American Spine Society lumbar spine outcome assessment instrument; SF-36, 36-Item Short-Form Health Survey.