Risk factors and clinical significance of posterior slip of the proximal vertebral body after lower lumbar fusion

Table 1 Patient demographic data, mean ± SD

	Nonretrograde group	Retrograde group	t value	P value
Age (year)	51.7 ± 10.6	52.4 ± 11.3	0.258	0.797
Sex (male/female)	18/54	4/15	0.128	0.721
Operation time (minute)	257.3 ± 46.9	264.7 ± 43.8	0.619	0.540
Blood loss (mL)	219.6 ± 49.3	207.7± 56.5	0.907	0.367
Follow-up time (month)	27.4 ± 6.3	26.9 ± 7.0
Fixed segment	2.4 ±0.69	2.5 ± 0.74	0.554	0.581
Fusion segment
1	59	14	0.646	0.421
2	13	5
Fixation of S1
Yes	12	5	0.921	0.337
No	60	14

Table 2 Radiography parameters of the two groups, mean ± SD

	Nonretrograde group	Retrograde group	t value	P value
PI (°)
Preoperative	47.9 ± 9.2	57.8 ± 10.6	4.041	< 0.001
Postoperative	49.2 ± 9.6	58.1 ± 11.4	3.454	0.008
Final follow-up	49.6 ± 10.3	57.2 ± 11.9	2.768	< 0.001
PT (°)
Preoperative	20.5 ± 6.2	21.5 ± 6.4	0.621	0.536
Postoperative	15.6 ± 4.4	14.8 ± 5.6	0.665	0.508
Final follow-up	14.9 ± 3.9	15.3 ± 5.0	0.374	0.709
SS (°)
Preoperative	27.9 ± 8.3	35.1 ± 8.2	3.371	< 0.001
Postoperative	35.8 ± 7.9	42.7 ± 10.8	3.123	0.002
Final follow-up	37.1 ± 9.4	41.9 ± 7.7	2.049	0.043
LL (°)
Preoperative	34.1 ± 10.2	38.9 ± 14.8	1.649	0.103
Postoperative	48.7 ± 12.6	57.1 ± 10.6	2.664	0.009
Final follow-up	48.9 ± 9.7	56.3 ± 9.2	2.988	0.003
lLL (°)
Preoperative	24.9 ± 4.8	27.0 ± 6.8	1.546	0.126
Postoperative	38.1 ± 8.9	38.7 ± 9.9	0.255	0.799
Final follow-up	37.4 ± 9.6	38.9 ± 8.5	0.619	0.537
uLL (°)
Preoperative	8.1 ± 3.4	10.9 ± 4.7	2.934	0.004
Postoperative	12.5 ± 4.3	18.2 ± 6.4	4.605	< 0.001
Final follow-up	12.7 ± 5.6	17.6 ± 5.4	3.417	< 0.001

PI: Pelvic incidence; PT: Pelvic tilt; SS: Sacral slope; LL: Lumbar lordosis; lLL: Lower LL; uLL: Upper LL.

Table 3 Lumbar sagittal images of the patients in the two groups, mean ± SD

	Nonretrograde group	Retrograde group	t value	P value
|PI-LL| (°)
Preoperative	13.9 ± 5.2	15.3 ± 5.8	1.019	0.311
Postoperative	1.9 ± 4.3	1.4 ± 3.6	0.465	0.643
Final follow-up	0.9 ± 2.1	1.2 ± 3.0	0.671	0.504
PI-LL matching
Yes	63	16	0.142	0.706
No	9	3
LDI (%)
Preoperative	75.9 ± 14.9	71.1 ± 16.7	1.217	0.226
Postoperative	75.7 ± 10.4	68.1 ± 11.5	2.772	0.006
Final follow-up	74.3 ± 9.4	67.2 ± 11.9	2.764	0.006
Distribution of LL
LDI < 50%	6	7	49.937	< 0.001
50% ≤ LDI < 80%	64	12
80 ≤ LDI	2	0

PI: Pelvic incidence; LL: Lumbar lordosis; lLL: Lower LL; LDI: Lordosis distribution index.

Table 4 Quality of life of the patients in the two groups, mean ± SD

	Nonretrograde group	Retrograde group	t value	P value
ODI score
Preoperative	41.4 ± 11.9	40.8 ± 10.3	0.201	0.841
Postoperative	21.1 ± 7.2	26.1 ± 7.4	2.677	< 0.001
Final follow-up	18.0 ± 6.3	24.2 ± 4.6	4.009	< 0.001
VAS score
Preoperative	7.0 ± 2.2	7.4 ± 2.5	0.685	0.495
Postoperative	2.2 ± 1.2	3.1 ± 1.6	2.703	0.008
Final follow-up	1.8 ± 1.1	2.9 ± 1.4	3.654	< 0.001

ODI: Oswestry Disability Index; VAS: Visual Analogue Scale.