Lumbar fusion with implantation of interbody cage is a common procedure for treatment of lumbar degenerative disease. This study aims to compare the fusion and subsidence rates of titanium (Ti) versus polyetheretherketone (PEEK) interbody cages after posterior lumbar interbody fusion and investigate the effect of clinical and radiological outcomes following fusion on patient-reported outcomes.
A systematic search strategy of 4 electronic databases (MEDLINE, Embase, Web of Science, and Cochrane) was conducted using different MeSH (medical subject headings) terms until January 2020. Pooled odds ratios (ORs) with 95% confidence intervals (CI) were calculated using fixed and random-effect models based upon the heterogeneity (I2) to estimate the association between interbody cages and the measured outcomes.
A total of 1,094 patients from 11 studies were reviewed. The final analysis included 421 patients (38.5%) who had lumbar surgery using a Ti and/or a Ti-coated interbody cage and 673 patient (61.5%) who had lumbar surgery using a PEEK cage. Overall, PEEK interbody devices were associated with a significantly lower fusion rate compared with Ti interbody devices (OR, 0.62; 95% CI, 0.41–0.93; p = 0.02). There was no difference in subsidence rates between Ti and PEEK groups (OR, 0.91; 95% CI, 0.54–1.52; p = 0.71). Also, there were no statistically significant differences in visual analogue scale (VAS)-low back pain (p = 0.14) and Japanese Orthopedic Association scale (p = 0.86) between the 2 groups. However, the PEEK group had lower odds of leg pain after surgery compared to the Ti group (OR [VAS-leg], 0.61; 95% CI, 0.28–0.94; p = 0.003).
Ti and Ti-coated PEEK cages used for posterior lumbar interbody fusion are associated with similar rates of subsidence, but a higher rate of fusion compared to PEEK interbody cages. Randomized controlled trials are needed to better assess the effect of cage materials and potential factors that could influence the outcomes of interbody lumbar fusion.
Symptoms arising from lumbar degenerative disease are common and can be debilitating, leading to surgical intervention to alleviate pain and restore function. The prevalence of low back pain (LBP) due to lumbar spondylosis is estimated at 3.6% worldwide, and 4.5% in North America [
One of the most commonly employed instrumentation techniques for achieving fusion is implantation of an interbody cage. A study from the Nationwide Inpatient Sample database showed as many as 83% of surgeries for degenerative spondylolisthesis involve the use of an interbody cage [
The characteristics and clinical outcomes of Ti and PEEK cages for lumbar spinal fusion were explored in several studies [
We performed a systematic review and meta-analysis in line with the Preferred Reporting Items for Systematic Review and Meta-analysis (PRISMA) guidelines [
Two of the authors (EM and NF) independently identified articles eligible for review with input by the senior author (JHS). Studies were selected for inclusion in the meta-analysis if they evaluated PEEK and Ti interbody cages in spinal lumbar fusion procedures for degenerative spinal disease, intervertebral disc herniation, spondylolisthesis, and spinal stenosis. Studies were included in the meta-analysis if they reported at least one of the following outcomes: (1) fusion rates, (2) subsidence rates, or (3) PROs for Ti and PEEK. Initial screenings of abstracts were performed, followed by full-text reviews. Covidence Systematic Review Software (Veritas Health Innovation, Melbourne, VIC, Australia) [
The primary outcome was fusion rate and we tested the null hypothesis that Ti and PEEK have the same fusion rate in PLIF. Ti and Ti-coated interbody cages were grouped because they bring together the bio-compatible characteristics of Ti important for fusion. We compared patient baseline characteristics (age, sex, and comorbidities) in studies reporting on the primary outcomes to examine if patient characteristics can affect fusion and subsidence rates and could therefore inform the interpretation of nondifferential results. Secondary outcomes included the rate of cage subsidence and PROs that were assessed in the included studies: (1) Oswestry Disability Index; (2) visual analogue scale (VAS) for low back or leg pain; (3) Japanese Orthopedic Association (JOA) score for LBP, and radiologic outcomes when available.
Data were independently extracted by 2 of the authors (EM and NF) using a standardized protocol and reporting electronic sheet. Disagreements between the 2 authors were resolved by arbitration when consensus could not be reached after discussion. Two reviewers independently assessed the quality of the included studies using the Newcastle-Ottawa scale, which allocates each study a quality grade of maximum 9 points based on (1) selection of the study groups, (2) comparability of the groups, and (3) assessment of outcomes [
Continuous data were analyzed by calculating the pooled weighted mean difference with 95% confidence interval (CI). The association between the type of interbody cages and the primary and secondary outcomes were reported using the odds ratio (OR) with 95% CI. Between-study heterogeneity was evaluated using the I2 statistic. A fixed-effect model was used for I2 < 50%, while for I2 > 50% a random-effect model was employed. Statistical tests were 2-sided and p-value < 0.05 was considered statistically significant. We inspected the symmetry of the funnel plots and performed the Egger test to assess publication bias. Also, we used a nonparametric trim-and-fill procedure to identify and correct for funnel plot asymmetry and re-estimate the aggregate results [
Eleven studies involving PLIF with Ti and PEEK cages were included in this meta-analysis. The results of our search strategy are summarized in the PRISMA chart (
The data of 1,094 patients was analyzed in this meta-analysis, of which 673 (61.5%) had lumbar interbody fusion using a Ti or Ti-coated cage and 421 (38.5%) had lumbar interbody fusion using a PEEK cage. The mean follow-up time in the Ti and PEEK groups was 20.5 and 22.3 months respectively (range, 6–84 months). The Ottawa-Newcastle quality assessment tool showed that most studies carry a potential risk of bias (
Demographic characteristics of Ti and PEEK patients extracted from each study are summarized in
Lumbar fusion was performed for a total of 1,094 patients (Ti421, PEEK-673). PLIF was performed in 5 studies [
Early fusion status was assessed most commonly at 12 months and 24 months but as early as 3 months in 1 study by dynamic plain radiographs, computed tomography (CT) scan, and multiplanar reformation (MPR)-CT scan (
Subsidence rates were successfully extracted from 6 studies [
PROs were not reported in most the included studies. VAS-leg and VAS-LBP were reported in only 2 studies [
We found some evidence of publication bias, as suggested by slight asymmetry of the funnel plot (Egger test, z=-3.367; p = 0.009) and association between effect sizes and corresponding sampling variances (Begg test, z=-2.415; p = 0.01). According to the trim-and-fill method to correct for publication bias (
This systematic review and meta-analysis of 11 studies involving 1,094 patients who underwent posterior lumbar fusion demonstrated increased odds of bony fusion with use of Ti and Ti-coated interbody cages in comparison to PEEK interbody cages for posterior lumbar fusion (p = 0.02). Demographic characteristics including age, sex, and BMI were similar between the 2 groups. However, important factors such as smoking status, osteoporosis and bone mineral density (BMD) were not reported in the included studies. Studies investigating posterior lumbar fusion identified low BMI, diabetes mellitus, osteoporosis, loosening of posterior instrumentation, and pear-shaped disc as potential risk factors for subsidence [
Ti and PEEK are the most common materials used for interbody cages. In fact, PEEK implants are widely used for different applications because of their mechanical properties and good chemical resistance. In addition to that, their radiolucent property allows for better assessment of fusion by imaging [
Unlike PEEK that has an elastic modulus similar to bone, Ti material has an elastic mismatch that can lead to stress shielding and bone remodeling around the implant [
In addition to that, this meta-analysis included 5 PLIF studies and 6 TLIF studies. Previous comparative studies revealed that PLIF with bilateral cage placement was shown to be equivalent in fusion to TLIF with a unilateral interbody device. Intraoperative and postoperative complications were shown to be lower in TLIF compared to PLIF procedures [
This meta-analysis is adherent to PRISMA guidelines and includes all relevant articles identified by an extensive literature search to assess the outcomes of interbody fusion in posterior lumbar surgery. According to the Ottawa-Newcastle quality assessment tool the quality of the included studies is low. A heterogeneity between the studies for subsidence rate and PROs was identified in the statistical analysis. The definition criteria, follow-up period and modalities used for assessment of fusion and subsidence were different across studies as shown in
As detailed in this review, the comparison of cage materials between PEEK and Ti revealed a competitive advantage of Ti and PEEK on high fusion and low subsidence respectively. In this meta-analysis, Ti interbody cages demonstrated a significantly higher fusion rate than that of PEEK in posterior spinal fusion. However, PEEK did not show significant superiority to subsidence in posterior spinal fusion. Although our understanding of indications and outcomes is steadily increasing, rigorous evaluation of indications and characterization of risks and outcomes is still required. So far, one pilot RCT compared Ti and PEEK interbody cages for posterior lumbar fusion. Future RCTs are needed to better investigate the implants and the associated factors that influence the outcomes of interbody fusion.
The authors have nothing to disclose.
Elie Massaad, MD research work, and education at Harvard Medical School are supported by a scholarship from the Dubai-Harvard Foundation for Medical Research (DHFMR).
Supplementary Table 1 can be found via
Detailed Newcastle-Ottawa Scale of each included cohort study
PRISMA (Preferred Reporting Items for Systematic Review and Meta-analysis) flow diagram.
Forest plot showing the effect sizes and 95% confidence intervals (CIs) of studies comparing the fusion rates of PEEK vs. Ti. PEEK shows less odds of fusion compared to titanium cage for lumbar interbody fusion (odds ratio, 0.62; 95% CI, 0.41–0.93; p=0.02). PEEK, polyetheretherketone; Ti, titanium; df, degrees of freedom.
Forest plot showing effect sizes and 95% confidence intervals (CIs) of studies comparing subsidence rates for titanium and PEEK interbody cages. Titanium and PEEK have similar odds of subsidence (odds ratio, 0.91; 95% CI, 0.54–1.52; p=0.71). PEEK, polyetheretherketone; Ti, titanium; df, degrees of freedom.
Forest plot showing effect sizes and 95% confidence intervals (CIs) of studies comparing visual analogue scale (VAS) scores for low back pain (A) and leg pain (B), and the Japanese Orthopedic Association (JOA) score for low back pain (C) for titanium and PEEK interbody cages. PEEK, polyetheretherketone; df, degrees of freedom.
Funnel plot to assess for publication bias.
Summary of study design, cage type, total patients, and type of procedure done
Study | Quality of evidence | Study design | Country | No. of patients (%) |
Procedure | Type of cage |
Bone graft used | ||
---|---|---|---|---|---|---|---|---|---|
PEEK | Titanium | Titanium | PEEK | ||||||
Cuzzocrea et al. [ |
Very low | Retrospective | Italy | 20 (50) | 20 (50) | TLIF | - | - | - |
Wrangel et al. [ |
Very low | Retrospective | Germany | 25 (62.5) | 15 (37.5) | PLIF | - | - | No grafting |
Kashii et al. [ |
High | Prospective | Japan | 26 (50) | 26 (50) | PLIF | ProSpace Xp | ProSpace | Yes, local bone |
Schnake et al. [ |
High | Prospective | Germany | 30 (50) | 30 (50) | PLIF | Titanium-coated PEEK cage | - | - |
Tanida et al. [ |
Very low | Retrospective | Japan | 40 (31.2) | 77 (68.8) | TLIF | Crescent shaped: 8 Kidney Bean Mesh cages, 1 Devex cage, and 84 Boomerang II cages | Milestone cages, crescent shaped | Yes, local bone and iliac crest |
Vazifehdan et al. [ |
Very low | Retrospective | Germany | 323 (77.1) | 96 (22.9) | TLIF | - | - | - |
Sakaura et al. [ |
Very low | Retrospective | Japan | 92 (71.8) | 36 (28.2) | PLIF | - | - | Yes, local bone |
Rickert et al. [ |
High | Prospective | Germany | 20 (50) | 20 (50) | TLIF | MectaLIF TiPEEK Oblique | MectaLIF PEEK | Autograft + bone graft substitute |
Nemoto et al. [ |
Very low | Retrospective | Japan | 25 (52.1) | 23 (47.9) | TLIF | Bullet-shaped - Capstone | Bullet-shaped | Autograft |
Liu et al. [ |
Very low | Retrospective | China | 52 (47.2) | 58 (52.8) | PLIF | - | - | - |
Lee et al. [ |
Very low | Retrospective | UK | 20 (50) | 20 (50) | TLIF | 3D porous lamellar | - | - |
Eight of 11 were deemed to have very low quality of evidence. All studies included were from Europe or Asia. A transforaminal lumbar interbody fusion procedure was done in 6/11 studies.
PEEK, polyetheretherketone; PLIF, posterior lumbar interbody fusion; TLIF, transforaminal interbody fusion; 3D, 3 dimensional.
Patient demographic characteristics, surgical indication for lumbar interbody fusion and levels of operated lumbar spine
Study | Males, n (%) |
Age (yr), mean±SD |
BMI (kg/m2), mean±SD |
Surgical Indication |
Lumbar level |
|||||
---|---|---|---|---|---|---|---|---|---|---|
Titanium | PEEK | Titanium | PEEK | Titanium | PEEK | Titanium | PEEK | Titanium | PEEK | |
Cuzzocrea et al. [ |
8 (40) | 9 (45) | 55 (43–64) | 48 (39–57) | - | - | 8 Disc herniation, 5 spondylolisthesis, 7 lumbar stenosis | 12 Disc herniation, 3 spondylolisthesis, 5 lumbar stenosis | - | - |
Wrangel et al. [ |
10 (66.7) | 7 (28) | 63 ± 12 | 69 ± 10 | - | - | Degenerative instability | L2–3 (0%); L3–4 (29%); L4–5 (35%); L5–S1 (35%) | L2–3 (7%); L3–4 (29%); L4–5 (39%); L5–S1 (25%) | |
Kashii et al. [ |
- | - | 67.6 ± 11.2 | 25.4 ± 4.2 | 1 Disc herniation, 14 spondylolisthesis, 11 lumbar stenosis | L2-3 to L4-5 | ||||
Schnake et al. [ |
19 (63.3) | 19 (63.3) | 51 (31-70) | - | - | Lumbar degenerative disease | L2/3 (3%), L3/4 (7%), L4/5 (45%) and L5/S1 (45%) | |||
Tanida et al. [ |
15 (19.4) | 36 (90) | 62.5 (20–86) | 65 (30–82) | - | - | - | - | T11–12 (1%); L2–L3 (9%); L3–L4 (14%); L4–L5 (70%); L5–S1 (22%) | L2–L3 (4%); L3–L4 (8%); L4–L5 (59%); L5–S1 (29%) |
Vazifehdan et al. [ |
- | - | 70.9 ± 11.3 | - | - | Degenerative disc disease, recurrent disc herniation, facet joint arthritis, and spinal stenosis | - | - | ||
Sakaura et al. [ |
19 (52.7) | 44 (47.8) | 65.3 (37–83) | 68.5 (42–85) | - | - | Degenerative lumbar spondylolisthesis | L3–4 (11%), L4–5 (78%), L5–S1 (11%) | L1–2 (1%), L2–3 (1%), L3–4 (16.3%), L4–5 (77%), L5–6 (1%), L5–S1 (3%) | |
Rickert et al. [ |
- | - | 67.7 ± 12.5 | 68.3 ± 10.5 | 27.7 ± 4.9 | 28.5 ± 3.6 | Degenerative disc disease n=9, spinal stenosis n=7, spondylolisthesis with stenosis n=3, and spondylolisthesis with degenerative disc n=1 | Degenerative disc disease n=10; spinal stenosis n=6; isthmic or low dysplastic spondylolisthesis n=2, degenerative spondylolisthesis with stenosis n=2 | L2–3 (4%); L3–4 (38%); L4–5 (58%) | L2–3 (4%); L3–4 (38%); L4–5 (58%) |
Nemoto et al. [ |
23 (100) | 22 (88) | 40.7 ± 10.2 | 42.9 ± 10.4 | 24.6 ± 2.8 | 25.3 ± 5.2 I | Isthmic spondylolisthesis n=6; foraminal stenosis n=3; Disc herniation n=6; degenerative disc disease n=7; canal stenosis n=1 | Isthmic spondylolisthesis n=4; foraminal stenosis n=2; Disc herniation n=7; degenerative disc disease n=9; canal stenosis n=3 | L4–5 (30%); L5–S1 (70%) | L4–5 (40%); L5–S1 (60%) |
Liu et al. [ |
29 (53) | 28 (56) | 40.8 ± 10.6 | 41.8 ± 10.4 | 25.8 ± 2.3 | 25.3 ± 4.2 | Lumbar spinal stenosis, lumbar disc herniation accompanied by lumbar spinal instability after 6 months of formal conservative treatment | L4–5 (63%); L5–S1 (37%) | L4–5 (56%); L5–S1 (44%) | |
Lee et al. [ |
- | - | - | - | - | - | - | - | - | - |
SD, standard deviation; PEEK, polyetheretherketone; BMI, body mass index.
Summary of the definitions of fusion and subsidence rates used in the included studies, the follow-up period, and the modality used for assessment of fusion and subsidence
Study | Fusion definition | Subsidence definition | Follow-up (mo) | Modality |
---|---|---|---|---|
Cuzzocrea et al. [ |
Fusion degrees described by Christensen et al. | - | 12 | CT |
Wrangel et al. [ |
Bony bridging with at least 3 trabeculae was defined as a fused segment. Moreover, the fusion rate was additionally assessed by a fusion score that consisted of 3 parameters: bony bridging, in which at least 3 trabeculae are necessary for fusion (0 or 1 point); radiolucency of none, one, or both end plates (0–2 points); and finally transition in dynamic X-ray images (0–1 points). No fusion (0–1 points), semirigid pseudarthrosis (2 points), potential fusion (3 points), and fusion (4 points) were distinguished via this score | - | 33 | CT |
Kashii et al. [ |
Achievement of fusion was determined to satisfy the 4 criteria as follows: (1) presence of continuous bone bridging across the disc space by CT, (2) absence of screw loosening assessed by CT, (3) absence of a radiolucent area around the cage assessed by functional radiograph and CT, and (4) angular change <3 degrees between the fused vertebrae on functional radiograph | - | 12 | Functional radiograph and CT |
Schnake et al. [ |
- | - | 12 | X-ray and thin-sliced CT scans |
Tanida et al. [ |
Bone union was defined according to the osseous continuity through and/or around the cage in both the sagittal and coronal CT-MPR images | - | 24 | CT-MPR |
Vazifehdan et al. [ |
- | - | 50 | CT |
Sakaura et al. [ |
Solid fusion was defined as the condition in which osseous continuity between the vertebrae and grafted bone was achieved on MPR-CT, with neither loosening of the PSs nor motion at the fused segments on lateral flex- ion-and-extension radiographs. Fusion status was graded as either union in situ (solid fusion without loss of graft height), collapsed union (solid fusion with ≥2-mm cage subsidence into the adjacent vertebral body), or nonunion according to the previously reported criteria | ≥2-mm cage subsidence into the adjacent vertebral body | 12 | CT, MPR-CT |
Rickert et al. [ |
The presence of fusion was based on Bridwell et al.’s criteria which included presence or absence of bony bridging | Loss of disc space height of ≥1 mm with a visible fracture of the vertebral body endplate | 12 | Plain radiograph, CT |
Nemoto et al. [ |
A solid fusion was defined as the presence of bridging bone within and around the cage both on the coronal and sagittal MPR CT images | If a cage was observed to sink into an adjacent vertebral body by ≥2 mm | 24 | MPR CT |
Liu et al. [ |
- | - | 24 | CT |
Lee et al. [ |
- | - | 12 | - |
CT, computed tomography; MPR, multiplanar reformation.