Table 2.

Multivariate logistic regression model of factors associated with complications (including reoperation within 30 days) due to lumbar spine surgery in Norway from 1999 to 2013 (n=67 855)

	Complications (n=977)	OR	Lower 95% CI	Upper 95% CI
Age (years)
18-39	250	Ref
40-59	460	0.97	0.83	1.13
60-75	198	0.61	0.50	0.74
> 75	69	0.51	0.39	0.67
Missing	152
Gender
Male	510	Ref
Female	467	0.90	0.79	1.02
Missing	152
Length of stay (days)		1.02	1.01	1.02
Type of surgery
Simple	659	Ref
Complex	318	2.34	2.04	2.69
Year of operation
1999	24	Ref
2000	29	0.98	0.57	1.71
2001	29	1.03	0.60	1.77
2002	33	1.31	0.77	2.22
2003	44	1.52	0.92	2.50
2004	41	1.46	0.88	2.43
2005	67	2.23	1.39	3.57
2006	60	2.25	1.40	3.63
2007	58	2.25	1.39	3.64
2008	56	2.29	1.42	3.71
2009	80	3.12	1.97	4.94
2010	89	3.03	1.93	4.78
2011	93	3.03	1.93	4.77
2012	140	4.31	2.79	4.67
2013	134	4.16	2.68	6.44
Missing	134