Sequential sagittal alignment changes in the cervical spine after occipitocervical fusion

Table 1 Radiological parameters of patients in the occipitocervical fusion and control groups

	OCF (n = 84)			Control (n = 42)
	Pre-op	Post-op	Final follow-up
O-C2a (°)	4.7 ± 15.3	4.6 ± 12.6	4.7 ± 13.3	12.0 ± 8.2a,b,c
O-EAa (°)	101.1 ± 8.5	99.4 ± 7.7	99.0 ± 9.1	92.2 ± 5.4a,b,c
C2Ta (°)	96.5 ± 17.3	94.8 ± 13.5	94.2 ± 13.2	80.0 ± 8.6a,b,c
C2-7a (°)	24.8 ± 18.1	21.7 ± 16.1	21.6 ± 15.8	16.2 ± 9.6a,b,c
T1 slope (°)	23.2 ± 9.5	23.4 ± 8.2	21.5 ± 8.2	21.9 ± 7.2
C2-7 SVA (cm)	1.4 ± 1.1c	1.5 ± 1.1c	1.0 ± 1.0a,b	1.5 ± 0.8c
PIA (°)	91.6 ± 10.3	89.3 ± 10.1	88.8 ± 12.5	97.3 ± 7.5a,b,c

^aP < 0.05 compared with pre-op.

^bP < 0.05 compared with post-op.

^cP < 0.05 compared with final follow-up.

OCF: Occipitocervical fusion; Pre-op: Preoperative; Post-op: Postoperative; O-C2a: O-C2 angle; O-EAa: Occipital and external acoustic meatus to axis angle; C2Ta: C2 tilting angle; C2-7a: C2-7 angle; SVA: Sagittal vertical axis; PIA: Pharyngeal inlet angle.

Table 2 Pearson product moment coefficient (Pearson’s r value) between O-C2 angle and C2-7 angle and other parameters in the occipitocervical fusion and control groups

OCF (n = 84)	r value	P value	Control (n = 42)	r value	P value
O-C2a
O-EAa	0.039	0.728	O-EAa	0.309	0.046
C2Ta	-0.872	0.000	C2Ta	-0.802	0.000
C2-7a	-0.585	0.000	C2-7a	-0.385	0.012
T1 slope	-0.174	0.214	T1 slope	-0.080	0.615
C2-7 SVA	0.067	0.545	C2-7 SVA	0.331	0.032
PIA	0.757	0.000	PIA	0.579	0.000
C2-7a
O-C2a	-0.585	0.000	O-C2a	-0.385	0.012
O-EAa	0.023	0.837	O-EAa	-0.100	0.530
C2Ta	0.540	0.000	C2Ta	0.326	0.035
T1 slope	0.490	0.000	T1 slope	0.523	0.000
C2-7 SVA	-0.013	0.909	C2-7 SVA	-0.239	0.127
PIA	-0.546	0.000	PIA	-0.156	0.324

O-C2a: O-C2 angle; O-EAa: Occipital and external acoustic meatus to axis angle; C2Ta: C2 tilting angle; C2-7a: C2-7 angle; SVA: Sagittal vertical axis; PIA: Pharyngeal inlet angle.

Table 3 Radiological parameters of patients with dysphagia and without dysphagia

		Dysphagia (n = 20)	Without dysphagia (n = 64)	P value
O-C2a (°)	Pre-op	9.7 ± 10.7	3.2 ± 16.2	0.046
	Post-op	0.9 ± 9.3a	5.8 ± 13.3	0.128
	Final follow-up	1.3 ± 9.6a	5.8 ± 14.1	0.182
O-EAa (°)	Pre-op	104.2 ± 7.8	100.2 ± 8.6	0.070
	Post-op	95.1 ± 8.3a	100.8 ± 6.6	0.003
	Final follow-up	96.9 ± 6.5a	99.7 ± 9.7	0.240
C2Ta (°)	Pre-op	94.5 ± 13.1	97.1 ± 18.5	0.478
	Post-op	94.3 ± 14.1	94.9 ± 13.4	0.851
	Final follow-up	95.6 ± 10.6	93.8 ± 14.0	0.598
C2-7a (°)	Pre-op	19.5 ± 14.3	26.4 ± 19.0	0.136
	Post-op	26.9 ± 13.5a	20.0 ± 16.6	0.100
	Final follow-up	27.9 ± 12.6a	19.6 ± 16.2	0.041
T1 slope (°)	Pre-op	21.5 ± 5.7	21.2 ± 11.1	0.340
	Post-op	21.5 ± 6.8	24.4 ± 8.9	0.226
	Final follow-up	22.7 ± 6.5	20.9 ± 9.1	0.436
C2-7 SVA (cm)	Pre-op	0.9 ± 0.9	1.6 ± 1.1	0.028
	Post-op	1.1 ± 1.3	1.6 ± 1.1	0.088
	Final follow-up	0.4 ± 1.1b	1.2 ± 0.9	0.002
PIA (°)	Pre-op	95.0 ± 6.7	90.6 ± 11.0	0.035
	Post-op	82.0 ± 5.7a	91.6 ± 10.2	0.000
	Final follow-up	86.3 ± 6.8a,b	89.5 ± 13.7	0.321

^aP < 0.05 compared with pre-op.

^bP < 0.05 compared with post-op.

Pre: Preoperative; Post: Postoperative; O-C2a: O-C2 angle; O-EAa: Occipital and external acoustic meatus to axis angle; C2Ta: C2 tilting angle; C2-7a: C2-7 angle; SVA: Sagittal vertical axis; PIA: Pharyngeal inlet angle.