This was a retrospective observational study.
We identify risk factors, including physical and surgical factors, and comorbidities affecting cage retropulsion following posterior lumbar interbody fusion (PLIF).
Diffuse idiopathic skeletal hyperostosis (DISH) is considered a risk factor for reoperation after PLIF. We evaluated the effect of DISH on cage retropulsion into the spinal canal, which may require surgical revision for severe neurological disorders.
A total of 400 patients (175 men, 225 women) who underwent PLIF were observed for >1 year. Factors investigated included the frequency of cage retropulsion and surgical revision. In addition, physical (age, sex, disease), surgical (fusion and PLIF levels, cage number, grade 2 osteotomy), and comorbid (DISH, existing vertebral fracture) factors were compared between patients with and without cage retropulsion. Factors related to surgical revision during the observation period were also considered.
Cage retropulsion occurred in 15 patients and surgical revision was performed in 11. Revisions included the replacement of pedicle screws (PSs) with larger screws in all patients and supplementary implants in 10. Among the patients with cage retropulsion, the average PLIF level was 2.7, with DISH present in nine patients and existing vertebral fractures in six. Factors affecting cage retropulsion were diagnoses of osteoporotic vertebral fracture, multilevel fusion, single-cage insertion, grade 2 osteotomy, presence of DISH, and existing vertebral fracture. Multivariable analysis indicated that retropulsion of a fusion cage occurred significantly more frequently in patients with DISH and multilevel PLIF.
DISH and multilevel PLIF were significant risk factors affecting cage retropulsion. Revision surgery for cage retropulsion revealed PS loosening, suggesting that implant replacement was necessary to prevent repeat cage retropulsion after revision.
Posterior lumbar interbody fusion (PLIF) has been performed for various clinical conditions, because widespread spinal canal decompression and intervertebral stability can be obtained simultaneously while restoring foraminal height [
Among patients with comorbidities, those with Parkinson’s disease suffer complications frequently during spinal surgery [
A retrospective observational study was conducted in compliance with the tenets of the Declaration of Helsinki. The study was reviewed and approved by the Institutional Review Board for Clinical Research Ethics at Fujita Health University (IRB approval no., HM 19-123) and the requirement for informed consent from some individual participants was omitted because of the retrospective design of this study.
The inclusion criterion was patients with cage retropulsion into the spinal canal over the posterior margin of the vertebral body. DISH was defined as >4 continuous ossification vertebrae per the criteria of Resnick et al. [
As usual, in these procedures, cranial laminectomy and partial facetectomy were performed first. Second, pedicle screws (PSs) were inserted and the PS-attached device was used to perform disc space distraction to prepare the disc, followed by disc space packing with autogenous local bone. Finally, the cage was inserted and the PS systems were fixed. Grade 2 osteotomy was performed after PS insertion to prevent pedicle fracture. Generally, two cages were inserted in each disc space, except in patients with poor overall condition, in whom only one cage was inserted. The implant material used for the cage was polyether ether ketone (PEEK) in all but nine cases. All cages were of the box or bullet type, and the lordosis angle was ≤6°.
All demographics and examination results were compared between the patients with and without cage retropulsion. Demographics, such as age, sex, diagnosis, fusion and PLIF levels, cage number, grade 2 osteotomy, presence of DISH, existing vertebral fracture, and revision surgery, were evaluated. In patients with cage retropulsion, clinical examinations, such as the frequency, period, level, Visual Analog Scale (VAS), surgical examinations for revision, and radiological examinations for osseous union at the cage retropulsion level, were evaluated.
Interbody fusion at the cage retropulsion level was assessed by reconstruction computed tomography (CT) at 1 year postoperatively. Sagittal and coronal CT was used to evaluate the fusion condition for the existence of consecutive bone formation in multiple slices obtained around the cage.
All values are expressed as the mean±standard deviation. Statistical analyses were performed with respect to the presence of cage retropulsion. Continuous variables (age, fusion and PLIF levels, and VAS) were assessed using the Mann-Whitney
The average age of the 175 men and 225 women was 67.7 years. Diagnoses included lumbar canal stenosis (LCS) in 142 patients, degenerative spondylolisthesis (DS) in 116, lumbar disc hernia in 52, degenerative lumbar scoliosis (DLS) in 41, isthmic spondylolisthesis in 20, degenerative kyphosis in 17, and osteoporotic vertebral fracture (OVF) in 12. The average fusion level was 2.1 and the average PLIF level was 1.8. A total of 30 patients received one cage and 370 received two cages. Grade 2 osteotomy was performed in 76 patients, with DISH present in 98, and existing vertebral fracture in 36. Surgical revision was performed in 52 patients, including 22 with adjacent segment disease and 11 with cage retropulsion (
The frequency of cage retropulsion was 3.8% (15/400 patients), and it occurred at 15 of 707 (2.1%) intervertebral levels. The average age of the seven men and eight women was 72.7 years. Five patients had LCS, five had DS, three had OVF, and two had DLS. The average fusion level was 2.9, the average PLIF level was 2.7, and the average retropulsion period was 16.1 days. Retropulsion levels were L4/5 in six patients, L5/S in five, L2/3 in three, and L3/4 in one. The VAS at 1 year postoperatively was 3.2 and 3.6 cm in the groups with and without revision surgery, respectively (the results were not significantly different) (
Eleven patients underwent surgical revision for cage retropulsion. Laboratory values, including the white blood cell count, C-reactive protein, and neutrophil levels were lower at revision than after the initial surgery. The findings at revision included PS loosening in all patients and pedicle fractures in three not present at the initial operation (
On univariate analysis, the average age was 72.7 and 67.6 years in patients with and without cage retropulsion, respectively (not significantly different). There was no significant difference between sexes. The diagnoses of patients with and without cage retropulsion, and with LCS, DS, OVF, and DLS, were significantly different (
On multivariable analysis, the PLIF level (
We identified risk factors affecting cage retropulsion following PLIF. Initially, in the PLIF procedure, an iliac bone autograft was transplanted only into the interbody space after posterior decompression. Therefore, pseudoarthrosis accompanied by retropulsion or collapse of the grafted bone was of great concern [
PLIF performed without PS results in a significantly greater incidence of cage retropulsion [
Limited reports exist of cage retropulsion after lumbar interbody fusion combined with PS fixation [
Factors reportedly related to surgery include multilevel fusion [
Few studies exist on the association between comorbidities and cage retropulsion [
The bone mineral density contributes to pressure between the intervertebral bone graft and endplate [
DISH tends to be associated with osteoporosis when it is accompanied by vertebral fractures [
At reoperation for cage retropulsion, an approach from the same incision is considered high risk because of concern for nerve injury caused by tissue adhesion [
Eleven of our patients underwent reoperation for cage retropulsion. In all approaches, we used the same posterior incision, and the cage could be set up without intraoperative complications, such as nerve injury. We increased the size of the PSs in all patients and, although we set up the same cage as previously, there were no instances of repeat cage retropulsion after reoperation. There is a report that repeat reoperation for recurrent cage retropulsion was necessary to increase the size of the cage or PS when the same size of PS and cage was used at reoperation [
Interbody fusion was recognized after cage retropulsion in 10 of the 11 reoperated patients compared to only one of the four in whom reoperation was not performed. Therefore, in cases of cage retropulsion after PLIF, interbody fusion is expected to be difficult through the natural course of healing. On the other hand, regarding clinical outcomes, the VAS was not different between patients with and without reoperation.
Based on the results, reoperation is considered desirable for cases exhibiting favorable overall conditions if the complication of cage retropulsion occurs during the early postoperative period. Reoperation following PLIF was significantly more likely to occur in patients with cage retropulsion and, thus, its prevention is important. Aggressive treatment of osteoporosis may prevent PS loosening [
Our study had some limitations. This was a single-center, retrospective study. We did not examine the bone mineral density in patients with cage retropulsion. Therefore, the effect of osteoporosis on PS loosening accompanied by cage retropulsion was uncertain. As the follow-up periods varied widely, the frequency of adjacent segment disease, which is the most frequent cause of reoperation, could not be evaluated accurately. We did not examine tissue membrane cultures or pathology in the tract of a loosened PS or retropulsed cage. Therefore, the possibility of subclinical infection cannot be denied. We limited our selection of cage material primarily to PEEK and size to a lordosis angle ≤6°, and these factors may have contributed to cage retropulsion.
Cage retropulsion following PLIF occurred significantly frequently in the presence of DISH and multilevel fusion, particularly when multilevel PLIF was performed. Surgical revision was more frequent in patients with cage retropulsion and was accompanied by PS loosening, suggesting that the replacement of the implant, particularly the PSs, was necessary to prevent repeated cage retropulsion after revision.
No potential conflict of interest relevant to this article was reported.
Shinichi Kato: conception and design, analysis of data, drafting of the manuscript, critical revision; Nobuki Terada: administrative support; Osamu Niwa: data acquisition; and Mitsuko Yamada: administrative support.
Cage retropulsion accompanied by pedicle fracture (arrow) on coronal computed tomography.
Cage retropulsion accompanied with set screw dislocation (arrow) on lateral radiograph.
Patient demographic data
Characteristic | Value |
---|---|
Age (yr) | 67.7±12.2 |
Sex | |
Men | 175 |
Women | 225 |
Diagnosis | |
Lumbar canal stenosis | 142 |
Degenerative spondylolisthesis | 116 |
Lumbar disc hernia | 52 |
Degenerative lumbar scoliosis | 41 |
Isthmic spondylolisthesis | 20 |
Degenerative kyphosis | 17 |
Osteoporotic vertebral fracture | 12 |
Fusion level | 2.1±1.3 |
1 | 167 |
2 | 132 |
3 | 62 |
4 | 19 |
5 | 8 |
≥6 | 12 |
Posterior lumbar interbody fusion level | 1.8±0.9 |
1 | 187 |
2 | 137 |
3 | 60 |
4 | 14 |
5 | 2 |
No. of cages | |
1 | 30 |
2 | 370 |
Grade 2 osteotomy | 76 |
Diffuse idiopathic skeletal hyperostosis presence | 98 |
Existing vertebral fracture | |
Incident VF | TL 0, ML 8 |
Prevalent VF | TL 19, ML 12 |
Duplicate VF cases included | 36 |
Revision surgery | |
Adjacent segment disease | 22 |
Cage retropulsion | 11 |
Infection | 7 |
Implant failure | 3 |
Hematoma | 2 |
Additional vertebral fracture | 2 |
Other | 5 |
Values are presented as mean±standard deviation or number.
VF, vertebral fracture; TL, thoraco-lumbar; ML, middle-lower lumbar.
Characteristics of cage retropulsion patients
Age (yr) | Sex | Fusion level | PLIF level | Cage type | Revision surgery | VAS at 1 year postoperatively (cm) | Retropulsion level/fusion |
---|---|---|---|---|---|---|---|
58 | Man | L2–S | 4 | PEEK | + | 3.5 | L5/S/+ |
70 | Man | L4/5 | 1 | PEEK | − | 4.1 | L4/5/− |
73 | Man | L2–5 | 3 | PEEK | + | 3.7 | L2/3/− |
75 | Man | L3–S | 3 | PEEK | + | 2.5 | L5/S/+ |
75 | Man | L2–iliac | 4 | PEEK | + | 2.8 | L2/3/+ |
81 | Man | L4–S | 2 | PEEK | + | 2.0 | L4/5/+ |
86 | Man | L4–S | 2 | PEEK | + | 3.8 | L5/S/+ |
49 | Woman | L2–S | 3 | PEEK | + | 4.7 | L5/S/+ |
53 | Woman | L4–S | 2 | PEEK | − | 3.1 | L5/S/− |
71 | Woman | L2–5 | 2 | PEEK | + | 2.3 | L4/5/+ |
72 | Woman | L1–4 | 3 | PEEK | + | 2.6 | L3/4/+ |
78 | Woman | L3–5 | 2 | PEEK | − | 3.3 | L4/5/+ |
79 | Woman | L2–iliac | 4 | PEEK | + | 4.3 | L2/3/+ |
81 | Woman | L2–5 | 3 | PEEK | + | 3.3 | L4/5/+ |
89 | Woman | L2–5 | 3 | PEEK | − | 3.7 | L4/5/− |
PLIF, posterior lumbar interbody fusion; VAS, Visual Analog Scale; PEEK, polyether ether ketone.
Univariable and multivariable analysis of cage retropulsion patients versus non-cage retropulsion patients
Variable | Cage retropulsion | Non-cage retropulsion | Univariable |
Multivariable |
---|---|---|---|---|
Age (yr) | 72.7 | 67.6 | 0.11 | - |
Sex | 0.81 | - | ||
Men | 7 | 168 | ||
Women | 8 | 217 | ||
Diagnosis | 0.03 |
0.3436 | ||
Lumbar canal stenosis | 5 | 137 | ||
Degenerative spondylolisthesis | 5 | 111 | ||
Osteoporotic vertebral fracture | 3 | - | ||
Lumbar disc hernia | - | 52 | ||
Degenerative lumbar scoliosis | 2 | 39 | ||
Isthmic spondylolisthesis | - | 20 | ||
Degenerative kyphosis | - | 17 | ||
Osteoporotic vertebral fracture | - | 9 | ||
Fusion level | 2.9 | 2.0 | 0.0098 |
0.2994 |
Posterior lumbar interbody fusion level | 2.7 | 1.7 | <0.0001 |
0.0157 |
No. of cages | 0.0206 |
0.9707 | ||
1 | 4 | 26 | ||
2 | 11 | 359 | ||
Grade 2 osteotomy | 6 | 70 | 0.0388 |
0.2378 |
Diffuse idiopathic skeletal hyperostosis presence | 9 | 89 | 0.0011 |
0.0165 |
Existing vertebral fracture | 6 | 30 | <0.0001 |
0.1377 |
Revision surgery | 11 | 41 | <0.0001 |
<0.0001 |
Statistically significant.
Comparison of selected reports of cage retropulsion
Reference | Age (yr) | Frequency (%) | Diagnosis | Revision surgery (%) | Risk factor |
---|---|---|---|---|---|
Aoki et al. [ |
NA | 4/125 (2.8) | DS 4 | 2/4 (50) | Cage type; disc height |
Kimura et al. [ |
68.2 | 9/1,070 (0.8) | LCS 6; DLS 3 | 3/9 (33) | Pear-shaped disk; disc height; disc ROM; multilevel fusions (L5/S) |
Pan et al. [ |
45.6 | 8/667 (1.2) | LCS 3; LDH 3; DLS 1 | 6/8 (75) | Infection |
Li et al. [ |
45.4 | 18/286 (6.3) | DLS 7; LDH 6; LCS 5 | NA | Surgeons experience; cage type; spondylolisthesis |
Lee et al. [ |
68.3 | 16/1,047 (1.5) | LCS 9; DLS 5 | 0/16 (0) | Low BMI; pear-shaped disc; pedicle screw loosening |
This study | 72.7 | 15/400 (3.8) | LCS 5; DS 5; OVF 3; DLS 2 | 11/15 (73) | DISH; multilevel PLIF |
NA, not available; DS, degenerative spondylolisthesis; LCS, lumbar canal stenosis; DLS, degenerative lumbar scoliosis; ROM, range of motion; LDH, lumbar disc hernia; BMI, body mass index; OVF, osteoporotic vertebral fracture; DISH, diffuse idiopathic skeletal hyperostosis; PLIF, posterior lumbar interbody fusion.