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Demographic, clinical, and operative risk factors associated with postoperative adjacent segment disease in patients undergoing lumbar spine fusions: a systematic review and meta-analysis
Department of Orthopaedic Surgery, Keck School of Medicine, University of Southern California, Los Angeles, CA, USADepartment of Orthopaedic Surgery, Menoufia University Faculty of Medicine, Shebin El-Kom, Menoufia, Egypt
Corresponding author. Department of Orthopaedic Surgery, Keck School of Medicine, University of Southern California, 1450 San Pablo St, HC4 - #5400A, Los Angeles, CA 90033, USA
Adjacent segment disease (ASD) is a potential complication following lumbar spinal fusion.
PURPOSE
This study aimed to demonstrate the demographic, clinical, and operative risk factors associated with ASD development following lumbar fusion.
STUDY DESIGN/SETTING
Systematic review and meta-analysis.
PATIENT SAMPLE
We identified 35 studies that reported risk factors for ASD, with a total number of 7,374 patients who had lumbar spine fusion.
OUTCOME MEASURES
We investigated the demographic, clinical, and operative risk factors for ASD after lumbar fusion.
METHODS
A literature search was done using PubMed, Embase, Medline, Scopus, and the Cochrane library databases from inception to December 2019. The methodological index for non‐randomized studies (MINORS) criteria was used to assess the methodological quality of the included studies. A meta-analysis was done to calculate the odds ratio (OR) with the 95% confidence interval (CI) for dichotomous data and mean difference (MD) with 95% CI for continuous data.
RESULTS
Thirty-five studies were included in the qualitative analysis, and 22 studies were included in the meta-analyses. The mean quality score based on the MINORS criteria was 12.4±1.9 (range, 8–16) points. Significant risk factors included higher preoperative body mass index (BMI) (mean difference [MD]=1.97 kg/m2; 95% confidence interval [CI]=1.49–2.45; p<.001), floating fusion (Odds ratio [OR]=1.78; 95% CI=1.32–2.41; p<.001), superior facet joint violation (OR=10.43; 95% CI=6.4–17.01; p<.001), and decompression outside fusion construct (OR=1.72; 95% CI=1.25–2.37; p<.001).
CONCLUSIONS
The overall level of evidence was low to very low. Higher preoperative BMI, floating fusion, superior facet joint violation, and decompression outside fusion construct are significant risk factors of development of ASD following lumbar fusion surgeries.
Low back pain caused by lumbar spondylosis is a common problem with an estimated prevalence of 5.7% and 4.5% of adult population in Europe and North America, respectively [
]. The degenerative changes associated with ASD include disc degeneration or herniation, osteophyte formation, canal stenosis, spondylolisthesis, or scoliosis [
]. ASD is believed to be caused by disturbance of normal biomechanics of the adjacent unfused segments, including increased mobility and loading and elevated intradiscal pressure, leading to accelerated degenerative changes [
Adjacent-level biomechanics after single-level anterior cervical interbody fusion with anchored zero-profile spacer versus cage-plate construct: a finite element study.
Risk factors of adjacent segment disease requiring surgery after lumbar spinal fusion: comparison of posterior lumbar interbody fusion and posterolateral fusion.
Adjacent segment degeneration after lumbar interbody fusion with percutaneous pedicle screw fixation for adult low-grade isthmic spondylolisthesis: minimum 3 years of follow-up.
]. This variation is possibly due to differences in populations, pathologies, or fusion procedures. The onset of ASD was reported following different lumbar fusion approaches including, posterior lumbar interbody fusion (PLIF), posterolateral fusion (PLF), transforaminal lumbar interbody fusion (TLIF), anterior lumbar interbody fusion (ALIF), and lateral lumbar interbody fusion (LLIF) [
Several risk factors have been reported to be associated with the development of ASD, including age, gender, high body mass index (BMI), pre-existing spinal stenosis; however, inconsistencies and controversies exist between different studies [
Risk factors of adjacent segment disease requiring surgery after lumbar spinal fusion: comparison of posterior lumbar interbody fusion and posterolateral fusion.
The current systematic review and meta-analysis study was conducted to evaluate the epidemiological, clinical, and operative risk factors associated with the development of ASD following lumbar spine fusion.
Methods
Conducting and reporting this systematic review was accomplished adhering to the Preferred Reporting Items for Systematic Reviews and Meta‑Analyses (PRISMA) statement guidelines and the current recommendations of the Cochrane Collaboration [
The PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate health care interventions: explanation and elaboration.
Firstly, we used a broad search terminology that included “adjacent segment” or “adjacent level” and “fusion” without filters. The retrieved studies were then divided into different groups to be included in each systematic review.
A thorough literature search using PubMed, Embase, Medline, Scopus, and the Cochrane library databases from the commencement to December 2019 was conducted to find relevant studies. Additionally, references of the retrieved studies were screened for relevant articles that could meet the inclusion criteria. The MeSH terms for PubMed and EMTREE terms for Embase were utilized during the search.
Studies selection
Screening and evaluation of the titles and abstracts of studies identified through the search process against the eligibility criteria were conducted by three independent reviewers (M.M., N.L., and B.Y.) for qualification for full-text review. Irrelevant or duplicate studies were excluded. The full-text assessment was then conducted for inclusion according to the study goals.
Inclusion and exclusion criteria
The inclusion criteria for this systematic review were: (1) Studies that included adult patients with lumbar spine pathology who underwent lumbar spine fusion. (2) Studies that reported and compared two groups of patients with and without ASD regarding the clinical risk factors. (3) Studies published in the English language with available full text. (4) Studies with a minimum of 10 patients per treatment group and a minimum follow-up period of 12 months.
Exclusion criteria included: (1) Studies with congenital or traumatic pathologies, infection, or malignancy. (2) Studies with radiological risk factors only. (3) Studies that focused solely on the incidence of ASD without evaluating the clinical risk factors. (4) Nonclinical studies, animal studies, systematic reviews and meta-analysis, case reports, biomechanical studies, conference abstracts (Table 1).
Table 1Inclusion and exclusion criteria
Study component
Inclusions
Exclusions
Participants
Patients with lumbar spine pathology
Congenital or traumatic pathologies, infection, or malignancy
Intervention
Lumbar spine surgery
Thoracolumbar surgeries
Comparators
Patients with and without postoperative adjacent segment disease (ASD)
•
ASD vs. subclinical ASD
•
Early ASD vs. late ASD
Outcomes
Clinical risk factors for developing ASD
•
Nonclinical risk factors, including radiological risk factors
•
Treating ASD without reporting risk factors
Study design
•
Prospective
•
Retrospective
•
Randomized controlled trials
•
Nonclinical studies or animal studies
•
Narrative reviews
•
Systematic reviews and meta-analysis
•
Abstracts, editorials, letters, posters, or erratum
•
Case reports
•
Biomechanical studies
•
Single reports from multicenter trials
•
Comparative studies with <10 patients per treatment group
Publication
•Full paper•English language
•
Duplicate publications of the same study without reporting on different outcomes
•
Studies reporting on the technical aspects of biologics use in fusion surgeryWhite papersArticles identified as preliminary reports when results are published in later versions
•
Papers that mentioned ASD as one of the complications but do not focus on it
Any dispute over the inclusion qualification of the studies was settled by a discussion between the three reviewers with the involvement of two other reviewers (Z.B. and A.A.).
Data extraction
After the final selection of the included studies, the pertinent details were extracted in a custom data extraction sheet. Three reviewers (M.M., N.L., and B.Y.) independently extracted data from each study, including the author's last name, the study year and type, the demographics, the spine pathology, the surgery, the number of levels, the ASD diagnostic tool, the definition of ASD, and the follow-up period. Moreover, the data related to the impact of each clinical risk factor on the occurrence of ASD was extracted in a specified table.
Quality assessment
Three reviewers, M.M., N.L., and B.Y., independently assessed the quality and risk of bias of the selected studies according to the criteria of the methodological index for non‐randomized studies (MINORS) [
]. Each criterion was given a score of 0, 1, or 2 if the item is not reported, inadequately reported, or adequately reported, respectively, with a maximum of 16 points for noncomparative studies and 24 points for comparative studies.
The certainty of evidence assessment
Three reviewers, M.M., N.L., and B.Y., independently evaluated the certainty of the evidence utilizing the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) tool, with five domains of risk of bias, inconsistency of results, indirectness of evidence, imprecision, and publication bias [
]. The quality of evidence was graded as high, moderate, low, or very low. Any disagreements about the quality assessment or the certainty of the evidence were settled by a discussion with the other reviewers (Z.B. and A.A.).
Outcome measures
The primary outcome measure was the demographic, clinical, and operative risk factors associated with increased risk of development of ASD following lumbar spine fusions. When analyzing each risk factor, a number of studies were included in the meta-analysis if they reported and compared that risk factor in patients with and without ASD.
Statistical analysis
The Review Manager software (RevMan V.5.2.3), the Nordic Cochrane Centre, Copenhagen, Denmark, was used for meta-analysis, which was performed when adequate data on a specific risk factor was available from at least two studies. The dichotomous data were expressed as odds ratio (OR) with corresponding 95% confidence interval (CI), and continuous data were expressed as mean difference (MD) and 95% CI. The I2 test was used to assess the statistical heterogeneity. The variables were pooled utilizing the fixed effects model when the I2 value was<50% and random effects models when the I2 value was>50%. The significance level was set at a p value of less than .05.
Results
Search results and study selection
Initially, searching the whole databases resulted in obtaining a total of 6,850 unique articles. Out of them, screening by titles and abstracts resulted in 114 articles for full-text review for inclusion. Finally, 35 papers [
Risk factors of adjacent segment disease requiring surgery after lumbar spinal fusion: comparison of posterior lumbar interbody fusion and posterolateral fusion.
Adjacent segment degeneration after lumbar interbody fusion with percutaneous pedicle screw fixation for adult low-grade isthmic spondylolisthesis: minimum 3 years of follow-up.
Symptomatic adjacent segment degeneration at the L3-4 level after fusion surgery at the L4-5 level: evaluation of the risk factors and 10-year incidence.
The efficacy of lumbar hybrid stabilization using the DIAM to delay adjacent segment degeneration: an intervention comparison study with a minimum 2-year follow-up.
Risk factors related to adjacent segment degeneration: retrospective observational cohort study and survivorship analysis of adjacent unfused segments.
Symptomatic adjacent segment degeneration following posterior lumbar arthrodesis: retrospective analysis of 26 patients experienced in 10-year of periods.
Analysis of risk factors for adjacent segment degeneration occurring more than 5 years after fusion with pedicle screw fixation for degenerative lumbar spine.
Risk factors for adjacent segment pathology requiring additional surgery after single-level spinal fusion: impact of pre-existing spinal stenosis demonstrated by preoperative myelography.
Adjacent segment degeneration after lumbar interbody fusion with percutaneous pedicle screw fixation for adult low-grade isthmic spondylolisthesis: minimum 3 years of follow-up.
Symptomatic adjacent segment degeneration at the L3-4 level after fusion surgery at the L4-5 level: evaluation of the risk factors and 10-year incidence.
The efficacy of lumbar hybrid stabilization using the DIAM to delay adjacent segment degeneration: an intervention comparison study with a minimum 2-year follow-up.
Analysis of risk factors for adjacent segment degeneration occurring more than 5 years after fusion with pedicle screw fixation for degenerative lumbar spine.
Based on the MINORS criteria, the mean score of the included studies was 12.4±1.9 (range, 8–16) points, Supplement 1. As none of the included studies were comparative, only the first 8 items of the MINORS criteria were used with the maximum score of 16 points.
Risk factors of adjacent segment disease requiring surgery after lumbar spinal fusion: comparison of posterior lumbar interbody fusion and posterolateral fusion.
Adjacent segment degeneration after lumbar interbody fusion with percutaneous pedicle screw fixation for adult low-grade isthmic spondylolisthesis: minimum 3 years of follow-up.
Symptomatic adjacent segment degeneration at the L3-4 level after fusion surgery at the L4-5 level: evaluation of the risk factors and 10-year incidence.
The efficacy of lumbar hybrid stabilization using the DIAM to delay adjacent segment degeneration: an intervention comparison study with a minimum 2-year follow-up.
Risk factors related to adjacent segment degeneration: retrospective observational cohort study and survivorship analysis of adjacent unfused segments.
Symptomatic adjacent segment degeneration following posterior lumbar arthrodesis: retrospective analysis of 26 patients experienced in 10-year of periods.
Analysis of risk factors for adjacent segment degeneration occurring more than 5 years after fusion with pedicle screw fixation for degenerative lumbar spine.
Risk factors for adjacent segment pathology requiring additional surgery after single-level spinal fusion: impact of pre-existing spinal stenosis demonstrated by preoperative myelography.
]. The remaining 33 studies included 3,714 (60.6%) females and 2,412 (39.3%) males.
The incidence of ASD in the included studies ranged from 2.6% to 62.5%, with a total of 1,266 (17.2%) patients who developed ASD following lumbar spine fusions. The follow-up period widely varied between the included studies and ranged from at least 12 months to a mean of 165.6 months.
Regarding the number of levels that were operated on, twenty-two studies [
Risk factors of adjacent segment disease requiring surgery after lumbar spinal fusion: comparison of posterior lumbar interbody fusion and posterolateral fusion.
Symptomatic adjacent segment degeneration at the L3-4 level after fusion surgery at the L4-5 level: evaluation of the risk factors and 10-year incidence.
Risk factors related to adjacent segment degeneration: retrospective observational cohort study and survivorship analysis of adjacent unfused segments.
Symptomatic adjacent segment degeneration following posterior lumbar arthrodesis: retrospective analysis of 26 patients experienced in 10-year of periods.
Analysis of risk factors for adjacent segment degeneration occurring more than 5 years after fusion with pedicle screw fixation for degenerative lumbar spine.
Adjacent segment degeneration after lumbar interbody fusion with percutaneous pedicle screw fixation for adult low-grade isthmic spondylolisthesis: minimum 3 years of follow-up.
Risk factors for adjacent segment pathology requiring additional surgery after single-level spinal fusion: impact of pre-existing spinal stenosis demonstrated by preoperative myelography.
The efficacy of lumbar hybrid stabilization using the DIAM to delay adjacent segment degeneration: an intervention comparison study with a minimum 2-year follow-up.
] did not report the number of levels. The demographics, pathologies, types of surgery, number of operated levels, ASD diagnostic tools, and the ASD diagnostic criteria in each study are reported in Table 2. Analysis of clinical risk factors for ASD in each individual study is summarized in Table 3.
Table 2Demographics, pathologies, operation, number of operated levels, ASD diagnostic tools, and ASD diagnostic criteria of the included studies
No.
Author/year,Study designRoB
Demographics (mean or %)
Spine pathology diagnosis
Operation
No. of operated levels
ASD diagnostic tools
ASD diagnostic criteria
1.
Ma 2019
-
Retrospective
-
RoB: 13/16
N=71 Age: 62.2 y Female: 37 (52%) Male: 34 (48%) N ASD/No ASD=29 (40.9%)/42 (59.1%) F/U: 36 m
Degenerative lumbar stenosis
PLF/PLIF
1–4 levels
Radiological (lateral X-ray)
•
>20% disc height reduction
•
>3 mm slippage distance
•
>3 mm osteophyte
2.
Olvera 2015
-
Retrospective
-
RoB: 9/16
N=179 Age: 60 y (ASD) Female: Not reported Male: Not reported N ASD/No ASD=20 (11.2%)/159 (88.8%) F/U: 39 m
N=490 Age: 53 y Female: 307 (62.7%) Male: 183 (37.3%) N ASD/No ASD=24 (4.9%)/466 (95.1%) F/U: 51 m
Spinal stenosis, degenerative or spondylolytic spondylolisthesis, herniated intervertebral disc with segmental instability and/or advanced disc degeneration, degenerative disc disease with severe back pain
PLF/PLIF
Single or multiple (≤ 3)
Clinical Radiological (X-rays)
Clinical: Radiculopathy Radiological: Degenerative lesions, such as spinal stenosis, segmental instability, or deformity
10.
Lee 2015
-
Retrospective
-
RoB: 13/16
N=115 Age: 58.2±10.0 y Female: 71 (61.7%) Male: 44 (38.3%) N ASD/No ASD= 42 (36.5%)/73 (63.5%) F/U: 46.1 m
N=630 Age: 61.37±4.12 y (ASD), 62.37±3.9 y (No ASD) Female: 327 (51.91%) Male: 303 (48.09%) N ASD/No ASD=76 (12.1%)/554 (87.9%) F/U: 51±2.2 m (ASD), 52±2.3 m (No ASD)
Degeneration with clinical symptoms requiring revision surgery
19.
Chen 2011
-
Retrospective
-
RoB: 12/16
N=109 Age: 53.4 y Female: 60 (55%) Male: 49 (45%) N ASD/No ASD=24 (22%)/85 (78%) F/U: 39.3 m
L4–L5 degenerative instability
PLIF
Single (L4–L5)
Radiological (lateral dynamic X-rays)
•
>3 mm disc height
•
>5° intervertebral space angulation
•
>3 mm L3 slippage
20.
Choi 2014
-
Retrospective
-
RoB: 13/16
N=49 Age: 50.7±9.4 y (ASD), 48.9±9.4 y (No ASD) Female: 35 (71.4%) Male: 14 (28.6%) N ASD/No ASD=19 (38.8%)/30 (61.2%) F/U: 134.2 m
Low-grade isthmic spondylolisthesis
ALIF with percutaneous PSF
Single (L4–L5 or L5–S1)
Clinical Radiological (lateral dynamic X-rays, CT and MRI)
Clinical:
•
Development of new clinical symptoms
•
VAS pain score of≥6 for back or legs
•
ODI score of more than 40%
Radiological:
•
>3 mm olisthesis (anterolisthesis or retrolisthesis)
•
>10% disc height loss
•
>10° angular motion
•
>3 mm osteophyte formation
•
Disc herniation or spinal stenosis
•
Disc degeneration≥grade 2
•
Facet arthropathy≥grade 2
•
Scoliosis
•
Compression fracture
21.
Disch 2008
-
Retrospective
-
RoB: 14/16
N=102 Age: 54±14.7 y Female: 69 (67.6%) Male: 33 (32.4%) N ASD/No ASD=27 (26.5%)/75 (73.5%) F/U: 165.6 m
Degenerative disease or isthmic spondylolisthesis
ALIF/ALIF & PLIF
Single or two (L4–S1)
Radiological (AP, lateral dynamic X-rays)
•
>20% disc space narrowing
•
≥3 mm dynamic translation
22.
Ghiselli 2004
-
Retrospective
-
RoB: 12/16
N=215 Age: 50 y Female: 126 (58.6%) Male: 89 (41.4%) N ASD/No ASD=59 (27.4%)/156 (72.6%) F/U: 80.4 m
Progressive spondylolisthesis, degenerative or iatrogenic spondylolisthesis in patients with spinal stenosis, progressive lumbar scoliosis, iatrogenic instability from extensive decompression, two or more episodes of disc herniation at the same level, and incapacitating nonradicular back pain after failure of nonoperative treatment
Symptomatic adjacent segment degeneration at the L3-4 level after fusion surgery at the L4-5 level: evaluation of the risk factors and 10-year incidence.
] with 501 ASD patients and 2,299 non-ASD patients were included in the meta-analysis for age at the time of surgery as a possible risk factor for ASD. Patients who developed ASD were slightly older than patients without ASD with no statistical significance (mean difference [MD]=0.17 years; 95% confidence interval [CI]=-0.60 to 0.94; p=.67; I2=79%).
Adjacent segment degeneration after lumbar interbody fusion with percutaneous pedicle screw fixation for adult low-grade isthmic spondylolisthesis: minimum 3 years of follow-up.
Symptomatic adjacent segment degeneration at the L3-4 level after fusion surgery at the L4-5 level: evaluation of the risk factors and 10-year incidence.
The efficacy of lumbar hybrid stabilization using the DIAM to delay adjacent segment degeneration: an intervention comparison study with a minimum 2-year follow-up.
Analysis of risk factors for adjacent segment degeneration occurring more than 5 years after fusion with pedicle screw fixation for degenerative lumbar spine.
] were included in the meta-analysis. The incidence of ASD was not significantly different between males and females (Odds ratio [OR]=0.91; 95% CI=0.75–1.11; p=.36; I2=0%).
] with 197 ASD patients and 663 non-ASD patients. Patients with ASD had a statistically significant higher BMI than patients without ASD (MD=1.97 kg/m2; 95% CI=1.49–2.45; p<.001; I2=83%) (Fig. 2).
Fig. 2Forest plots of meta-analysis of age, gender, and BMI.
] compared the incidence of ASD in smokers and nonsmokers. Overall, the incidence of ASD was higher in smokers than nonsmokers with no statistical significance (OR=1.26; 95% CI=0.94–1.68; p=.12; I2=0%).
Analysis of diabetes was available in five studies [
], and the incidence of ASD was not statistically different between osteoporotic and nonosteoporotic patients (OR=1.00; 95% CI=0.64–1.57; p=.99; I2=0%).
The T-score representing the bone mineral density (BMD) was analyzed in two studies [
With pooled data from different studies, three operative variables were found to be significant risk factors for ASD. Lumbar fusions excluding the sacrum (floating fusions), was associated with a statistically significant risk of developing ASD compared to distal fusions including the sacrum (OR=1.78; 95% CI=1.32–2.41; p<.001; I2=48%) as assessed in nine studies [
Adjacent segment degeneration after lumbar interbody fusion with percutaneous pedicle screw fixation for adult low-grade isthmic spondylolisthesis: minimum 3 years of follow-up.
Symptomatic adjacent segment degeneration at the L3-4 level after fusion surgery at the L4-5 level: evaluation of the risk factors and 10-year incidence.
] found that iatrogenic superior facet joint violation during screw placement was associated with a statistically significant high incidence of ASD (OR=10.43; 95% CI=6.4–17.01; p<.001; I2=95%). Decompression outside fusion construct was also found to be a significant risk factor for ASD (OR=1.72; 95% CI=1.25–2.37; p<.001; I2=46%) as assessed in three studies [
Analysis of risk factors for adjacent segment degeneration occurring more than 5 years after fusion with pedicle screw fixation for degenerative lumbar spine.
] did not find a statistically significant difference between PLF versus PLIF (OR=1.28; 95% CI=0.65–2.51; p=.48; I2=0%) and PLIF versus TLIF (OR=1.45; 95% CI=0.59–3.56; p=.42; I2=15%), respectively.
Similarly, there was no statistically significant difference when comparing single versus multiple-level procedures (OR=0.87; 95% CI=0.50–1.51; p=.62; I2=0%) as assessed in four studies [
Analysis of risk factors for adjacent segment degeneration occurring more than 5 years after fusion with pedicle screw fixation for degenerative lumbar spine.
The quality of evidence for each risk factor analyzed was low to very low. Such quality precludes a definitive conclusion regarding the impact of those risk factors for increasing the incidence of ASD following lumbar fusion surgeries. Regarding the risk of bias domain, there were serious limitations for all the risk factors. Moreover, some of the risk factors had moderate or considerable unexplained heterogeneity or inconsistency of results. There were also serious limitations in the imprecision domain in some risk factors. All these factors led to low to very low-quality evidence (Table4).
Lumbar fusion surgeries are among the most frequent surgical procedures with an increasing yearly trend with the development of new fusion procedures and better imaging modalities [
In the current systematic review, the overall rate of ASD following lumbar fusions was 17.2%. The pooled results of the meta-analysis showed that higher BMI, floating fusion, violation of the superior facet joint, and decompression outside fusion construct were associated with a significant risk of development of ASD. Other factors including age, gender, smoking, diabetes, hypertension, osteoporosis, preoperative JOA score, approach, number of levels, intra-operative blood loss, and operative time were not associated with a significant increase in the rate of ASD.
BMI is widely used in the preoperative assessment prior to spine surgeries, and obesity is associated with higher complication and reoperation rates following lumbar spine surgeries [
] reported that high BMI was a significant risk factor for developing ASD following posterior lumbar fusion after comparing 50 patients with ASD and 50 patients without ASD. Similarly, Ou et al. [
] reported a significantly higher incidence of ASD in patients with high BMI undergoing different lumbar fusions, including PLIF, TLIF, and PLF, with a 67.6% increase in ASD rate for each 1 mean value increase in BMI. With lumbar fusion, there is a significant elevation in the intradiscal pressure, motion, and mechanical stress to the adjacent levels [
]. Consequently, perioperative body weight control is crucial to improve the fusion outcomes and reduce the incidence of ASD.
The lumbosacral segment (L5–S1), a transitional zone between the mobile lumbar spine and the fixed sacrum, is a region of increased stress and degenerative changes [
]. Our meta-analysis found that including the sacral segment in the fusion construct is associated with a lower incidence of ASD compared to floating fusion.
] compared the incidence of ASD following floating fusions versus distal fusions ending at the sacrum in 511 patients who had undergone posterolateral instrumented fusion and found a higher rate of ASD requiring reoperation following floating lumbar fusions than fusions including the sacrum, 19.14% and 12.16%, respectively. The increased incidence of ASD with floating fusion may be due to the fact that fusing L5–S1 level eliminates the possibility of ASD development caudally, as the sacrum is developmentally fused. Bydon et al. [
] reported that all patients with ASD in the distal fusion cohort had ASD at the cephalad level, and 90% of patients with ASD in the floating fusion cohort had ASD at the cephalad level.
] reported a 45.5% incidence of ASD following L4/L5 fusion compared to 19.6% incidence in patients who had L5/S1 fusion after an average follow-up period of 14 years. In the L4–L5 cohort, 9 levels were cranial, and 4 were caudal out of 13 levels affected with ASD [
However, with fusions including the sacrum, the sacroiliac joint is considered an adjacent joint to the fused segment, and the same biomechanical principles of ASD could apply [
], sacroiliac joint degeneration was more frequent in patients with fusion down to S1 compared to patients with fusion down to L5. Therefore, in fusions including the sacrum, the reduced risk of ASD compared to floating fusions should be weighed against the increased risk of sacroiliac joint degeneration.
During lumbar fusion, simultaneous decompression outside the fusion construct may be performed in some circumstances, such as the presence of mild degenerative stenosis in an adjacent level as a prophylactic measure [
Risk factors for adjacent segment disease after posterior lumbar interbody fusion and efficacy of simultaneous decompression surgery for symptomatic adjacent segment disease.
] reported that decompression at an adjacent level is a significant risk factor for ASD development, following treatment of 154 patients with different interbody fusion approaches, including PLF, TLIF, ALIF, or LLIF. Similarly, Maragkos et al. [
] reported that decompression outside the fusion construct was associated with a significant increase in the incidence of ASD following treatment of 568 patients with different instrumented lumbar fusion approaches. Accordingly, it is advisable not to extend the decompression too far to the next level to avoid increased incidence of ASD.
One of the underestimated consequences of pedicle screw insertion during lumbar fusion procedures is superior facet joint violation, which may alter the load-bearing capability and induce degenerative changes in the facet joint leading to the development of ASD [
Computed tomography evaluation of superior-segment facet-joint violation after pedicle instrumentation of the lumbar spine with a midline surgical approach.
] considered the superior facet joint violated if the pedicle screw or screw head is obviously within the facet joint, or the pedicle screw or screw head is within 1 mm or abutting the facet joint on CT scans. Percutaneous minimally-invasive screw placement is associated with a higher incidence of superior joint violation than open techniques [
] reported that intraoperative superior facet joint violation was a significant risk factor for ASD in their retrospective study of 630 patients who had PLIF. Wang et al. [
] reported the same finding after treating 237 patients with PLIF or TLIF.
During fusion surgery, meticulous facet joint identification, exposure and proper pedicle screw insertion technique help prevent superior facet joint violation and consequently reduce the incidence of ASD. Chung et al. [
Facet joint violation during pedicle screw insertion: a cadaveric study of the adult lumbosacral spine comparing the two pedicle screw insertion techniques.
], in a cadaveric study, reported a statistically significant higher incidence of superior facet joint violation during pedicle screw insertion using the mammillary process technique compared to the intersection technique.
As the number of lumbar fusions continues to increase each year, long-term postoperative adverse consequences such as ASD must be identified and adequately managed by spine surgeons. The findings in the current meta-analysis are beneficial for the spine surgeons and patients as preoperative addressing the modifiable risk factors for ASD such as high BMI can reduce the incidence of ASD, improving the operative outcomes, and reducing medical costs associated with the second surgery.
Despite the strength of this meta-analysis, this study has some limitations. The majority of studies included in the meta-analysis were retrospective studies. No randomized controlled trials have met the inclusion criteria and were included in the study. Additionally, there were heterogeneities in the included studies regarding the preoperative diagnosis, the number of fused levels, and the location of the fusion within the lumbar spine. Also, the definition of ASD, whether clinically or radiographically, was to some extent variable between the included studies, and some studies analyzed ASD based on the need for revision surgery. Moreover, some of the risk factors had only two or three studies for the meta-analysis. Also, there was considerable heterogeneity between the studies that were included for meta-analysis for BMI and superior facet joint violation.
Conclusion
The level of evidence was for all studies was low to very low. The current meta-analysis showed that higher preoperative BMI, floating fusion, concurrent decompression outside the fusion construct, and superior facet joint violation were significant risk factors for ASD after lumbar fusion surgeries. Given the lack of high level of evidence, prospective studies are needed to better understand the development of ASD after lumbar fusion surgery.
Declaration of competing interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Acknowledgments
The authors received no financial support for the research, authorship, and/or publication of this article. This study was organized by AO Spine through the AO Spine Knowledge Forum Degenerative, a focused group of international spine degenerative experts. AO Spine is a clinical division of the AO Foundation, which is an independent medically guided not-for-profit organization.
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Degenerative lumbar spine disease: estimating global incidence and worldwide volume.
Adjacent-level biomechanics after single-level anterior cervical interbody fusion with anchored zero-profile spacer versus cage-plate construct: a finite element study.
Risk factors of adjacent segment disease requiring surgery after lumbar spinal fusion: comparison of posterior lumbar interbody fusion and posterolateral fusion.
Adjacent segment degeneration after lumbar interbody fusion with percutaneous pedicle screw fixation for adult low-grade isthmic spondylolisthesis: minimum 3 years of follow-up.
The PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate health care interventions: explanation and elaboration.
Symptomatic adjacent segment degeneration at the L3-4 level after fusion surgery at the L4-5 level: evaluation of the risk factors and 10-year incidence.
The efficacy of lumbar hybrid stabilization using the DIAM to delay adjacent segment degeneration: an intervention comparison study with a minimum 2-year follow-up.
Risk factors related to adjacent segment degeneration: retrospective observational cohort study and survivorship analysis of adjacent unfused segments.
Symptomatic adjacent segment degeneration following posterior lumbar arthrodesis: retrospective analysis of 26 patients experienced in 10-year of periods.
Analysis of risk factors for adjacent segment degeneration occurring more than 5 years after fusion with pedicle screw fixation for degenerative lumbar spine.
Risk factors for adjacent segment pathology requiring additional surgery after single-level spinal fusion: impact of pre-existing spinal stenosis demonstrated by preoperative myelography.
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