Table 4. Number of screws of each instrumented vertebra and distribution on grades.

Position		Grade 0				Grade 1				Grade 2				Total
		Conventional		3D navigated		Conventional		3D navigated		Conventional		3D navigated
Spinal level	Vertebra	n	%	n	%	n	%	n	%	n	%	n	%	Conventional (n)	3D navigated (n)
Cervical	1/2	0	0	9	90	0	0	0	0	0	0	1	10	0	10
	3	0	0	0	0	0	0	0	0	0	0	0	0	0	0
	4	2	100	2	100	0	0	0	0	0	0	0	0	2	2
	5	4	100	4	100	0	0	0	0	0	0	0	0	4	4
	6	0	0	4	100	0	0	0	0	0	0	0	0	0	4
	7	4	100	6	75	0	0	0	0	0	0	2	25	4	8
Subtotal (n)		10	100	16	89	0	0	0	0	0	0	2	11	10	18
Thoracic	1	2	100	14	88	0	0	1	6	0	0	1	6	2	16
	2	3	75	15	68	0	0	2	9	1	25	5	23	4	22
	3	5	71	32	68	0	0	8	17	2	29	7	15	7	47
	4	6	75	23	59	0	0	9	23	2	25	7	18	8	39
	5	10	83	50	69	1	8	11	15	1	8	11	15	12	72
	6	13	72	41	68	2	11	10	17	3	17	9	15	18	60
	7	15	83	48	65	3	17	11	15	0	0	15	20	18	74
	8	27	75	36	72	5	14	8	16	4	11	6	12	36	50
	9	26	76	42	75	7	21	8	14	1	3	6	11	34	56
	10	32	82	33	79	2	5	7	17	5	13	2	5	39	42
	11	83	73	60	83	19	17	8	11	11	10	4	6	113	72
	12	155	89	76	84	16	9	6	7	4	2	8	9	175	90
Subtotal (n)		377	81	470	73	55	12	89	14	34	7	81	13	466	640
Lumbar	1	145	88	67	88	13	8	5	7	6	4	4	5	164	76
	2	183	94	76	86	9	5	11	13	3	2	1	1	195	88
	3	91	89	39	93	6	6	2	5	5	5	1	2	102	42
	4	67	91	23	96	5	7	0	0	2	3	1	4	74	24
	5	29	73	21	88	5	13	3	13	6	15	0	0	40	24
Subtotal (n)		515	90	226	89	38	7	21	8	22	4	7	3	575	254
Sacral	1	16	89	12	100	0	0	0	0	2	11	0	0	18	12
Total (n)		918	86	724	78	93	9	110	12	58	5	90	10	1,069	934

Abbreviation: 3D, three-dimensionally.

Note: % = percent of all screws of the respective vertebra of each method.