Table 1 Baseline characteristics of patients and clinical details at trial entry. Values are numbers of patients unless otherwise indicated

Characteristic
Surgery (n=176)
Rehabilitation (n=173)

Male
79 (44.9)
93 (53.8)

Female
97 (55.1)
80 (46.2)

Age:

    <30 years
24 (13.6)
20 (11.6)

    30-39 years
63 (35.8)
67 (38.7)

    40-49 years
56 (31.8)
66 (38.1)

     $≥$ 50 years
33(18.8)
20 (11.6)

Centre:^*

    A
55 (31.3)
54 (31.2)

    B
28 (15.9)
27 (15.6)

    C
45 (25.6)
43 (24.9)

    D
48 (27.3)
49 (28.3)

Mean duration of back pain years (range) in years
8 (1-35)
8 (1-35)

Current smokers
76 (43.2)
74 (42.8)

Litigation
25 (14.2)
21 (12.1)

Currently in paid employment
88 (50.0)
94 (54.3)

Back pain interfered patient's ability to work:
149 (84.7)
149 (86.1)

    Had to give up job
65 (43.6)
67 (45.0)

    Had to change job
19 (12.7)
10 (6.7)

    Had to reduce hours
17 (11.4)
12 (8.0)

    Had to take sick leave
59 (39.6)
69 (46.3)

Clinical details

Clinical classification:

    Spondylolisthesis
20 (11.4)
18 (10.4)

    Post-laminectomy
14 (8.0)
14 (8.1)

    Chronic low back pain
142 (80.6)
141 (81.5)

Planned surgery type:

    Graf
27 (15.3)
28 (16.2)

    Fusion
149 (84.7)
144 (83.2)

    Missing
0
1 (0.6)

Planned fused level:

    Single level
100 (56.8)
109 (63.0)

    >1 level
70 (39.8)
62 (35.8)

    Missing
6 (3.4)
2 (1.2)

Mean score (SD)

Oswestry disability index
46.5 (14.6)
44.8 (14.8)

Shuttle walking test in metres
254 (209)
247 (185)

SF-36 physical component score
19.4 (8.8)
20 (9.7)

SF-36 mental component score
43.2 (10.9)
44.2 (12.6)

Modified somatic perception questionnaire
9.0 (6.4)
7.7 (5.7)

Zung self rating depression scale
31.8 (10.4)
31.2 (11.8)

Distress and risk assessment method:

    Normal
14 (8.0)
14 (8.1)

    At risk
65 (36.9)
85 (49.1)

    Distressed depressive
87 (49.4)
69 (39.9)

    Distressed somatic
9 (5.1)
2 (1.2)

    Missing
1 (0.6)
3 (1.7)