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| ORIGINAL ARTICLE |
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| Ahead of print publication |
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Functional and radiological outcome after cervical arthrodesis using polyetheretherketone or tricortical iliac bone graft for degenerative and traumatic spine pathologies: A single-center experience
Jithin Veliyath Thankaraj1, Geo Senil Kidangan1, Bijukrishnan Rajagopala Warrier1, Pranav Veepanattu2
1 Department of Neurosurgery, Government Medical College, Thrissur, Kerala, India
2 Department of Infectious Disease, Amrita Institute of Medical Science, Kochi, Kerala, India
| Date of Submission | 22-Mar-2022 |
| Date of Decision | 02-Apr-2022 |
| Date of Acceptance | 08-Apr-2022 |
| Date of Web Publication | 29-Nov-2022 |
Correspondence Address:
Jithin Veliyath Thankaraj,
Veliyath House, N Aduvassery, S Aduvassery P O, Aluva, Kerala 683578
India
 Source of Support: None, Conflict of Interest: None DOI: 10.4103/jmms.jmms_43_22
Introduction: Anterior cervical discectomy and fusion (ACDF) is the most common surgical procedure used for decompression and fusion of adjacent cervical vertebral bodies. Iliac bone graft was widely accepted for fusion during ACDF to the introduction of polyetheretherketone (PEEK) spacers. Even though PEEK spacers have the advantage of reducing donor-site complications, in cases with doubtful supporting ligament continuity, the long-term outcome of cervical spine stability is not confirmed. In this study, we are comparing the clinical and radiological outcomes of both substitutes. Materials and Methods: We did a retrospective analysis of 111 patients who underwent single-level ACDF using PEEK or tricortical iliac bone graft for various disc pathologies at our institution in the past 10 years along with clinical and radiological presentations and outcome of the procedure at 3 weeks, 6 months, and after 1 year. The study population was divided into two groups: Group “P” (PEEK spacer) and Group “G” (bone graft spacer). Distribution of clinical presentation in terms of radiculopathy, myelopathy, and myeloradiculopathy was evaluated and correlated with the demographic parameters. The standard deviation and P value of the radiological variables were calculated. “Mann–Whitney U-test” for the Japanese Orthopaedic Association score at 1-year follow-up and “Pearson's Chi-square” value for the Odom's score of both groups were used to analyze the correlation. Results: All the radiological parameters were analyzed by the Wilcoxon signed-rank test after checking for normality distribution. The improvements reported above in all domains were found to be statistically significant at P < 0.001. When analyzing the radiographic evidence of bony fusion at 1 year by Bridwell fusion grading, only two patients in Group P had poor fusion and all the patients in Group G had Grade 1 or 2 fusion. The clinical improvement analyzed by evaluating the ODOMS score after 1-year follow-up showed significant improvements in both groups. Conclusions: In our study, PEEK spacers have got definite advantage over iliac bone grafts in maintaining the disc segmental height, segmental angle, cervical lordosis, and fusion segment height without adding any donor-site morbidity.
Keywords: Cervical arthrodesis, iliac bone graft, polyetheretherketone spacer
How to cite this URL:
Thankaraj JV, Kidangan GS, Warrier BR, Veepanattu P. Functional and radiological outcome after cervical arthrodesis using polyetheretherketone or tricortical iliac bone graft for degenerative and traumatic spine pathologies: A single-center experience. J Mar Med Soc [Epub ahead of print] [cited 2023 Mar 24]. Available from: https://www.marinemedicalsociety.in/preprintarticle.asp?id=361395 |
| Introduction | |  |
Anterior cervical discectomy and fusion (ACDF) is the most common surgical procedure used for decompression and fusion of adjacent cervical vertebral bodies for various indications, including disc herniation, ossification of the posterior longitudinal ligament, spondylodiscitis, and spondylolisthesis[1]. Since Smith and Robinson[2] introduced the anterior approach for subaxial cervical spine in 1955, several modifications of the technique were developed over time to improve the clinical outcome in patients with cervical spine diseases. Despite excellent clinical outcomes with ACDF using autograft, there were continuous modifications of various cervical spacer substitutes, including animal allograft (xenograft), polyetheretherketone (PEEK) cage, titanium cage, ceramic spacers, bone morphogenetic proteins, and artificial discs.
Smith and Robinson gave emphasis for stabilization of the pathologic vertebrae after removing the anterior part of the disc using a horseshoe-shaped graft obtained from the iliac crest. They postulated that graft will increase the height of the disc space so that the nerve root is secondarily decompressed and existing osteophytes would regress over time with stabilization of the involved motion segment. The Cloward technique[3] modified the concept in 1958 by removing the compressive elements at the level of the involved disc space and the superior and inferior vertebral bodies along with the augmented stabilization using a round dowel of bicortical iliac graft. Even though the surgical techniques, retractors, disc space distractors, intraoperative imaging techniques, spacer substitutes, and each and every contributing factor were revolutionized over time, tricortical iliac graft is still preferred as the spacer substitute for many of the surgeons.
Even though the iliac bone graft has got excellent fusion capacity, few complications such as pseudarthrosis, subsidence, collapse, angular deformation, protrusion of the bone graft, infection, pain, or bleeding at the donor site resulted in the continued search for other alternatives.[4] For the past several decades, PEEK spacers have gained popularity among all alternative implant options due to its favorable theoretical advantages including biocompatibility, radiolucency, favorable elasticity, and ease of procurement and storage.[5],[6],[7] However, its bioinert property warranted surface enhancements such as cancellous bone filling options or impregnation with bioactive materials such as hydroxyapatite to improve bone integration.[8],[9] Hence, the purpose of this study is to compare the clinical and radiological results of PEEK spacers filled with cancellous bone graft versus tricortical iliac bone graft by retrospectively analyzing the data of single-level cervical disc pathologies surgically managed in our institute.
| Materials and Methods | | |
Study setting
This was a retrospective analysis of 111 patients who underwent single-level ACDF using PEEK or tricortical iliac bone graft for various disc pathologies at our institution from January 1, 2010, to December 31, 2019. All patients were between the ages of 18 and 60 years with at least 1-year follow-up after the surgical procedure. The study population was divided into two groups: Group “P” includes patients who had undergone arthrodesis with PEEK spacer and Group “G” includes patients who underwent arthrodesis with autologous tricortical iliac bone graft. Patients with other neurological diseases or major unrelated disabilities were excluded from our study.
Surgical technique
In all cases, pathological disc space is approached by the method described by Smith and Robinson. Disc removal was done after applying Caspar pin cervical distracters and both endplates are prepared for graft placements. Patients who underwent ACDF with bone grafts, the tricorticate bone grafts were harvested from the iliac crest after getting the dimensions of the disc space. Patients who had undergone ACDF with PEEK spacer, sterile spacers of all dimensions were made available and selected according to the perfect fit trail. Adjacent vertebral bodies were stabilized using titanium plates and screws [Figure 1]. All patients were given three doses of low-dose steroids and Philadelphia collar for 3 weeks. Physiotherapy was started after 6 weeks postoperatively and regular operative follow-up was done for at least 1 year. | Figure 1: (a and b) Sagittal MRI images of single-level cervical disc prolapse with severe kyphotic deformity, (c and d) Postoperative X-rays of the same patient. MRI: Magnetic resonance imaging
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Data collection and analysis
Epidemiological details, clinical presentations, and radiological and clinical outcomes were analyzed in this study. Relevant preoperative clinical and investigation details were collected from the hospital records. Postoperative clinical and radiological outcomes at 3 weeks, 6 months, and 1 year were collected from the patient's outpatient records. Clinical outcomes were assessed by ODOMS score at 1 year and the modified Japanese Orthopaedic Association (JOA) score at 3 weeks, 6 months, and 1 year intervals. Radiological details taken into consideration are C2–C7 Cobb angle, disc segment height, fusion segment height (FSH), segmental Cobb angle at the pathological level, and range of neck movements during flexion and extension [Figure 2]. Interbody fusion was defined by meeting the following criteria. (1) Grade 1 or 2 on the Bridwell fusion grading system, (2) <2° movements and <2 mm widening of interspinous distance between the fused end plates as evidenced by the dynamic lateral X-rays, (3) bridging trabecular bone between the endplates on radiographs, (4) <50% radiolucency in the perimeter surrounding the cage, and (5) lack of implant failure signs of the anterior plate system. Spacer subsidence was also analyzed by measuring the change in the FSH through the midpoint of the graft over 1 year. | Figure 2: Radiological parameters studied with lateral radiographs. Black – c2-c3 Cobb angle, red – disc segment height, yellow – fusion segment height, green – segmental angle
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Distribution of clinical presentation in terms of radiculopathy, myelopathy, and myeloradiculopathy was evaluated and correlated with the demographic parameters. The standard deviation and P value of the radiological variables were calculated. “Mann–Whitney U-test” for the JOA score at 1-year follow-up and “Pearson Chi-square” value for the ODOMS score of both groups were used to analyze the correlation.
| Results | | |
After excluding the patients who lost follow-up within 1 year, a total of 111 patients were evaluated, of which 58 (52.3%) were operated with a PEEK spacer (Group P) and 53 (47.7%) used an autologous tricortical iliac bone graft (Group G). The total population included 76 males (68.5%) and 35 females (31.5%). Among these 111 patients, 50 patients presented with radiculopathy (45.04%), 31 patients with myelopathy (27.9%), and 30 patients with myeloradiculopathy (27.02%) [Table 1].
In Group P, out of 58 patients, 38 (65.5%) were male and 20 (34.5%) were female. The clinical presentation of patients in this group was (1) radiculopathy – 27 cases (46.6%), (2) myelopathy cases – 16 (27.6%), and (3) myeloradiculopathy cases – 15 (25.9%). Forty-one patients had Bridwell Grade 1 fusion (70.7%) and 15 patients had Grade 2 fusion (25.9%), while two patients were having poor Bridwell Grade with unipolar or bipolar pseudarthrosis.
Among 53 patients in Group G, 38 (71.7%) were male and 15 (28.3%) were female. In these groups, 23 patients presented with radiculopathy (43.4%), 15 with myelopathy (28.3%), and 15 with myeloradiculopathy (28.3%). The ODOMS score was excellent for 15 patients (28.3%), good for 24 patients (45.3%), fair for 12 patients (22.6%), and poor for two patients (3.8%). Thirty-six patients had Bridwell Grade 1 fusion (67.9%) and 17 patients had Grade 2 fusion (32.1%).
Radiological outcome
Cobb angle
Cervical lordosis is measured between the inferior endplate of C2 to the inferior endplate of C7. A lordotic curve denoted as positive value and kyphotic angle denoted as negative value. The mean preoperative Cobb angle between C2 and C7 in Group P was 12.15 ± 2.28 and the same in Group G was 12.14 ± 2.09. At 3-week, 6-month, and 1-year follow-up, Cobb angle measurements in Group P were 15.76 ± 2.04, 15.42 ± 2.02, and 14.61 ± 2.04, respectively, and that in Group G were 13.44 ± 1.97, 12.20 ± 2.08, and 11.90 ± 2.08, respectively.
Disc space height
Disc space height (DSH) was measured at the midpoint of endplates in lateral radiographs. The mean preoperative DSH in Group P was 3.60 ± 0.73 and the same in Group G was 3.59 ± 0.75. At 3-week, 6-month, and 1-year follow-up, DSH measurements in Group P were 6.87 ± 0.37, 6.41 ± 0.35, and 6.13 ± 0.34, respectively, and that in Group G were 6.65 ± 0.38, 5.63 ± 0.39, and 4.08 ± 0.51, respectively.
Fusion segment height
FSH was measured from the superior endplate of the upper vertebral body to the inferior endplate of the lower vertebral body. The mean preoperative FSH in Group P was 37.63 ± 0.94 and the same in Group G was 37.57 ± 0.95. At 3-week, 6-month, and 1-year follow-up, FSH measurements in Group P were 41.89 ± 0.99, 40.79 ± 01.03, and 39.64 ± 1.10, respectively, and that in Group G were 41.67 ± 1.03, 39.27 ± 1.27, and 37.88 ± 1.03, respectively.
Range of movements
The range of movements (ROM) of the global cervical spine was determined as the difference between the lordotic and kyphotic angle in neck extension and flexion. The mean preoperative ROM in Group P was 45.66 ± 4.46 and the same in Group G was 45.32 ± 4.24. At 3-week, 6-month, and 1-year follow-up, ROM measurements in Group P were 40.11 ± 4.90, 43.03 ± 4.85, and 42.71 ± 4.63, respectively, and that in Group G were 40.62 ± 4.68, 43.02 ± 4.73, and 43.88 ± 4.76, respectively.
Segmental angle
Segmental angle (SA) is the angle measured between the inferior endplate of the upper vertebral body and superior endplate of the lower vertebral body. Normal lordotic angle is considered a positive value. The mean preoperative SA in Group P was 1.67 ± 1.72 and the same in Group G was 1.59 ± 1.57. At 3-week, 6-month, and 1-year follow-up, SA measurements in Group P were 6.60 ± 1.22, 5.18 ± 1.02, and 4.83 ± 1.12, respectively, and that in Group G were 5.57 ± 1.07, 3.36 ± 0.68, and 2.86 ± 0.65, respectively.
All the values were analyzed by the Wilcoxon signed-ranks test after checking for normality distribution. The improvements reported above in all domains were found to be statistically significant at P < 0.001 [Table 2] and [Table 3]. We can conclude that there is a statistically significant difference between preoperative values and the same 1 year after surgery in both Group P and Group G. | Table 2: Group P – Comparison between preoperative and 1-year follow-up of radiological and clinical data
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 | Table 3: Group G – Comparison of clinical and radiological data between preoperative and postoperative follow-up at 1 year
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Quality of fusion between the adjacent levels
While analyzing the radiographic evidence of bony fusion at 1 year by Bridwell fusion grading, only two patients in Group P were having poor fusion and all the patients in Group G were having Grade 1 or 2 fusion [Table 4]. None of the patients were having clinical or radiological evidence of implant failure and all were having acceptable changes in SA and interspinous distance during the dynamic radiographic study. Three patients (5.17%) in Group P and 44 patients (83.01%) in Group G showed reduction of more than 3 mm in FSH at 1 year compared with immediate postoperative values, but there were no related clinical deficits.
Clinical outcome
The clinical improvement analyzed by evaluating the ODOMS score after 1-year follow-up showed significant improvements in both groups [Table 4]. In Group P, ODOMS score was excellent for 21 patients (36.2%), good for 11 patients (19%), fair for 22 patients (37.9%), and poor for four patients (6.9%). In Group G, ODOMS score was excellent for 15 patients (28.3%), good for 24 patients (45.3%), fair for 12 patients (22.6%), and poor for two patients (3.8%). All the six patients who had poor clinical improvements at follow-up were having severe weakness or paraplegia at the time of presentation and were having low JOA scores.
The JOA score for both PEEK and autologous graft spacer were analyzed by the Mann–Whitney U-test after checking for normality distribution. Even though the JOA score was observed to be high among patients who had undergone surgery using autologous graft spacer (mean rank: 56.02) compared to PEEK spacer (mean rank: 55.98), it can be concluded that patients who had been operated with PEEK spacer and graft spacer were not statistically significant [Table 5]. The ODOMS score for both PEEK and analogous graft spacer was significantly different for both groups (X2 (1) = 154.287, P < 0.000). | Table 5: Comparison of polyetheretherketone spacer and autologous bone graft spacer using the Japanese Orthopaedic Association score and ODOMS score
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| Discussion | | |
Anterior cervical approach is already proved to be the gold standard technique proposed for managing single-level cervical disc disease pathologies.[10],[11] Using this approach, we can selectively decompress the involved roots secondary to degenerative disc disease. Even though biomechanical studies have proven that posterior instrumentation has a better stability among trauma victims, those cases with lateral mass fractures and grossly disrupted discs, th anterior approach has got a definite role as a primary or adjuvant treatment.[12],[13] It is extremely useful in managing kyphotic deformities where the posterior approach will not be able to provide adequate correction and decompression. Additional anterior plate stabilization provides good immobilization and support for the proper fusion of the graft. There are evidence for reduction of a graft collapse rate and pseudarthrosis while using plate and screw stabilization after discectomy and graft placement.[14] In our study, the overall stabilization of the surgical procedure is comparable to the previously available data which range from 80% to 100%.[15],[16],[17]
While choosing a material for fusion of the adjacent vertebral bodies after anterior cervical discectomy, the most important properties that are taken into consideration are osteoconductive, osteoinductive, and osteogenic properties. Tricortical iliac bone autograft has got a definite advantage of the abovestated properties to get nearly 92%–97% bone fusion rates.[6],[7] Even though cortical edges of the graft give structural support to the cancellous core, 28% graft collapse and loss of disc segment height were reported while using the autologous iliac grafts. Immediate donor-site complications are reported to be 16%–20%[1],[2],[18] and 50% of patients who had significant donor-site pain experienced it up to 5 years after surgery.[3] The alternatives to iliac tricortical bone graft to evade donor-site complications were frozen irradiated allograft and fibular allograft. Their biomechanical properties were extensively studied. The lack of live cells in the frozen irradiated bone allografts makes them an inferior alternative even if they have better osteoinduction properties. Even better alternative is the fibular allografts which also proved to have fewer fusion capabilities and increased cage subsidence when compared with iliac autografts[7] and it is not easily available in the market.
Apart from the biological materials, synthetic spacers with provisions for natural bony trabeculae formation between the adjacent vertebral surfaces are more frequently used nowadays. The commonly used synthetic materials are titanium, carbon, and PEEK. Titanium spacers are cheaper options with 88% fusion rates in monosegmental surgeries[5] and effective in maintenance of cervical lordosis. Even though the clinical correlation is doubtful, cage migration and spacer subsidence are definitely more prevalent while using the metallic substitutes. As it is radiopaque, further radiographic follow-up to check trabecular formation is not easy. PEEK is a thermoplastic material which has got the ability to retain its shape up to 315°C as well as resistant to water, high-pressure steam, and ionizing radiations. Its elastic modulus is close to bone so that it decreases the stress shielding, thereby improving the fusion between adjacent bone surfaces.[4] Its biocompatibility is well established in many studies.[4],[19],[20] PEEK provides a structural support to resist the spinal loading to get adequate initial time for osteogenesis and calcification to the inner bone fillings.[21] Previous studies those compared the outcome of metallic cage and PEEK have shown that the PEEK has got definite advantage of long-term maintenance of disc height and lower rate of spacer subsidence.
When we compared the radiological parameters of bone graft and PEEK spacers, the DSH and the SA were well maintained at 1 year after surgery in the PEEK group. Even though there are evidence for the significant differences in clinical improvement when using the PEEK spacers, our results did not show much difference in the clinical outcome despite significantly favorable radiological results in the PEEK cage group. Graft collapse was frequently observed in patients who had bone grafts, but none of the patients in both groups were having implant failure as per our definitions.
| Conclusions | | |
In our study, PEEK spacers have got definite advantage over iliac bone grafts in maintaining the disc segmental height, SA, cervical lordosis, and FSH without adding any donor-site morbidity. The osseous fusion observed at 1 year after surgery is comparable in both groups with 0% implant failure. The clinical outcome of both groups was not showing any obvious difference probably because the clinical outcome may be influenced by many other factors such as patient's physical status apart from comparable neurological gradings, unrelated comorbidities, and subjective variation in operative procedure by the various surgical teams.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]
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