Table 1.

Demographic and treatment characteristics of the groups

	Exposed group	Control group
N	37	36
Ø age	67	65
Age range	53–91	46–82
% females	85 %	69 %
N of fused segments on average	4	3
Th7 screw (%)	0 (0)	1 (1)
Th8 screw (%)	1 (3)	1 (1)
Th9 screw (%)	1 (3)	3 (4)
Th10 screw (%)	4 (11)	2 (3)
Th11 screw (%)	0 (0)	6 (8)
Th12 screw (%)	5 (14)	4 (6)
L1 screw (%)	13 (35)	13 (18)
L2 screw (%)	6 (16)	11 (15)
L3 screw (%)	2 (5)	11 (15)
L4 screw (%)	3 (8)	13 (18)
L5 screw (%)	1 (3)	5 (7)
S1 screw (%)	2 (3)	2 (3)