Table 3.

Incidence rates and incidence rate ratios (IRR) of spinal surgery for the AS cohort and comparison cohort, with and without stratification by sex (n=20,772)

Variable	Sex	AS cohort			Comparison cohort			IRR (95% CI)
Events	Person	IR	Events	Person	IR
Spine surgery	Total	149	22,275	668.91	315	109,969	286.44	2.34 (1.92–2.84)
	Male	78	13,853	563.05	162	68,785	235.52	2.39 (1.82–3.13)
	Female	71	8423	842.93	153	41,184	371.50	2.27 (1.71–3.01)
Cervical surgery	Total	32	22,275	143.66	67	109,969	60.93	2.36 (1.55–3.59)
	Male	20	13,853	144.37	34	68,785	49.43	2.92 (1.68–5.08)
	Female	12	8423	142.47	33	41,184	80.13	1.78 (0.92–3.44)
Lumbar surgery	Total	108	22,275	484.85	229	109,969	208.24	2.33 (1.85–2.93)
	Male	51	13,852	368.15	119	68,785	173	2.13 (1.53–2.96)
	Female	57	8423	676.72	110	41,184	267.09	2.53 (1.84–3.49)

Abbreviation: AS, ankylosing spondylitis.