Table 1a.

Patient demographics

Men / women	56 / 53
Mean age	71 (10)
Age groups (years)
30–50	2
50–60	14
60–70	21
70–80	53
> 80	19
Mean dural sac area (mm2) (SD)	43 (17)
Multilevel stenosis	54
Spondylolisthesis, all grade I	35
Smokers	9