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Experience With a Modular PEEK System for Cervical Vertebral Body Replacement Stefan A. Ko¨nig, MD and Uwe Spetzger, MD, PhD
Study Design: A retrospective case series. Summary of Background Data: The authors present their experience with the ATHLET vertebral body replacement (VBR) system in combination with the TOSCA plating system for the treatment of cervical spondylotic myelopathy. Methods: Data obtained from 20 cases were reviewed. Corpectomy and VBR with the ATHLET system was performed in all cases. Patients underwent preoperative and postoperative assessment involving the Japanese Orthopedic Association score, Odom criteria, and radiographic studies to determine the position of the implant as well as cervical lordosis. The mean followup period was 20 months (16–28 mo). Results: Implantation of the ATHLET VBR itself was uncomplicated in all cases. The adjustment of the implants’ height could be done in 2 mm steps. With increasing height of the implant, the angle of lordosis increases comparable with physiological conditions. The authors performed 13 one-level and 7 two-level corpectomies; from the latter group there were 2 revision cases (10%) with implant dislocation. Four cases (20%) of secondary subsidence of the implant were observed radiographs 12 months postoperatively; in all cases treatment remained conservative. Ten patients (50%) had excellent, 4 (30%) good, 2 (10%) satisfactory, and 2 (10%) poor outcome according to Odom criteria. The average improvement of the Japanese Orthopedic Association score was 1.6. All cases achieved osseous fusion without complications, 55% of them had an improvement, and 15% of them had no change of the sagittal contour. Conclusions: The ATHLET VBR is easy to implant and avoids bone graft site morbidity. Due to a relatively high rate of secondary subsidence of the implant (20%) and secondary dislocation (10%) in combination to a poor to satisfactory outcome according to Odom criteria in 20%, the authors do not recommend the use of this PEEK implant for cervical VBR. Key Words: cervical spondylotic myelopathy, vertebral body replacement, PEEK (J Spinal Disord Tech 2015;28:E89–E95) Received for publication January 15, 2014; accepted June 9, 2014. From the Neurochirurgische Klinik, Klinikum Karlsruhe, Karlsruhe, Germany. The authors declare no conflict of interest. Reprints: Stefan A. Ko¨nig, MD, Neurochirurgische Klinik, Klinikum Karlsruhe, Moltkestr. 90, Karlsruhe D-76133, Germany (e-mail: [email protected]). Copyright r 2014 Wolters Kluwer Health, Inc. All rights reserved.
J Spinal Disord Tech
Volume 28, Number 2, March 2015
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orpectomy is an effective treatment of various pathologies of the cervical spine.1–5 Several techniques for reconstruction have been described including titanium mesh cages and expandable cylindrical titanium cages to avoid donor site pain, fracture, infection, nerve injury, or postoperative hematoma formation after iliac crest bone harvest.3,6–10 As an alternative, the ATHLET vertebral body replacement (VBR) system which is made of polyetheretherketone (PEEK) has been used in numerous European spine centers. Nevertheless, there is only 1 report about the experience with this system.11 Thus, the authors report about their experience with this PEEK system for the replacement of cervical vertebral bodies.
PATIENTS AND METHODS Patient Population Between January 2010 and December 2011 a total of 20 patients, including 12 men and 8 women with clinical and radiologic proof of cervical spondylotic myelopathy underwent corpectomy and VBR using the ATHLET system (SIGNUS; Medizintechnik GmbH, Alzenau, Germany). The patients’ ages at surgery ranged from 44 to 76 years, with a mean of 62.5 years. Mean follow-up was 20 months (range, 16–28 mo). The leading symptom was cervical myelopathy with radiculopathy in 17 patients and without radiculopathy in 3 patients, respectively. All patients complained of neck pain and were refractory to conservative treatment. Preoperative radiologic examinations included plain functional radiography, magnetic resonance imaging, computed tomography (CT), and myelography. Postoperative standard imaging included CT and lateral functional radiographic images. After surgery, all patients’ neck was immobilized with a soft collar for 6 weeks. The standard follow-up in our institution is a clinical and radiologic examination 6 and 12–24 months after surgery including assessment of Japanese Orthopedic Association (JOA) score, Odom criteria, and radiographic images. In this retrospective study, the JOA scores were compared with those before surgery. The x-ray films were assessed regarding dislocation of the implant, osseous fusion, and degeneration of adjacent levels.
Surgical Procedure Corpectomies were performed using a high-speed drill. In all cases, a vertebral body pin distractor system was used. The posterior longitudinal ligament was removed in www.jspinaldisorders.com |
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J Spinal Disord Tech
Volume 28, Number 2, March 2015
FIGURE 1. ATHLET vertebral body replacement with adjustment in 2-mm steps by combining 2 implant components (A and B). The implant has a lordotic angle (C) similar to physiological conditions and can be filled with bioceramic material (D) and autologous bone graft. The screw threads in the front of the implant were made for the connector screw of the TOSCA plate.
all cases. The cartilage of the endplates was completely removed. The cortical bone was not damaged to avoid a collapse of the implant into the vertebral bodies. The ATHLET VBR system is made of the PEEK. Its height is adjustable in 2-mm steps ranging from 16 to 50 mm by combining 2 different PEEK components. These components are available in different sizes and can be connected by a click mechanism (Figs. 1A–D). The required height of the implant is measured after corpectomy and applying a slight distraction to the adjacent vertebral bodies. The implant is filled with autolougus bone chips and KAINOS bioceramic material (SIGNUS; Medizintechnik GmbH). The vertebral bodies adjacent to the ATHLET system have to be fused with the TOSCA plate (SIGNUS; Medizintechnik GmbH), which has the same lordotic angle as the ATHLET implant. Fixation of the TOSCA plate is done with distal locking tip screws (Fig. 2B). Finally, the TOSCA
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plate has to be connected with the ATHLET implant by a special connector screw (Figs. 2B, 3B).
RESULTS Implantation of the ATHLET VBR itself was uncomplicated in all cases. The adjustment of the implants’ height could be done 2 mm-wise by combining 2 PEEK components from a set (Fig. 1). With increasing height of the implant, the angle of lordosis increases in a manner that is comparable with physiological conditions (Fig. 1C). The teeth at the top and bottom of the ATHLET implant ensure good fixation in the endplates of the adjacent vertebral bodies. Filling the ATHLET implant with KAINOS bioceramic and bone chips can be done easily through the central canal and the side holes (Fig. 1D). This is supposed to provide osseous fusion 3–6 months after surgery. The Copyright
r
2014 Wolters Kluwer Health, Inc. All rights reserved.
J Spinal Disord Tech
Volume 28, Number 2, March 2015
Cervical Vertebral Body Replacement With PEEK
FIGURE 2. A 48-year-old patient with a degenerative spinal stenosis ranging from C4/C5 to C5/C6. Single-level vertebral body replacement with a 26-mm ATHLET implant and fixation with a 40-mm TOSCA plate. A small screw connects both the implants (B). The ATHLET implant is filled with autologous bone chips and KAINOS (bioactive ceramic). Note the expansion screws inside of the vertebral bodies. Preoperative computed tomography scan showing the osseous stenosis at the posterior aspect of the C5 vertebral body (A). Lateral (B) and anteroposterior (C) radiographs 3 days after surgery showing an improved cervical lordosis.
connector screw (Figs. 2B, 3B) between the TOSCA plate and the ATHLET VBR keeps the plate in place, especially before fixing it to the vertebra. Afterwards, it provides increased stability of the whole construct. Corpectomies of 1 level were performed in 13 patients. Seven patients underwent 2-level corpectomy. There was 1 revision case from the 2-level group who had poor bone quality due to renal dialysis but no evidence of osteoporosis in the preoperative CT scans. This patient initially underwent corpectomy of C5 and C6 including anterior plating from C4 to C7, and suffered from a fracture of the adjacent vertebral bodies and a dislocation of the implant 2 months after surgery. Therefore, we had to perform a 4-level corpectomy in the second operation including VBR and anterior plating from C3 to T1 (again with the ATHLET/TOSCA systems) as well as posterior fusion from C3 to T1. Another revision case from the 2-level group was a patient with a degenerative stenosis and normal bone quality. Nevertheless, the implant complex showed a kick-out dislocation 4 months after surgery (Fig. 4). At that time this 69-year-old patient did not have any neurological symptoms nor dysphagia. Therefore, the authors left the anterior implant in place and performed posterior fixation from C3 to T1 (Figs. 4C, D). Thus, there were 2 of 7 (29%) revision cases in the 2-level corCopyright
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2014 Wolters Kluwer Health, Inc. All rights reserved.
pectomy group due to dislocation of the implant. There was no anterior nor posterior dislocation in the 1-level corpectomy group but we observed 4 cases with hardware subsidence into the caudal adjacent vertebral body (Fig. 5). In both the cases JOA and visual analogue scale scores of neck pain improved despite the subsidence. Therefore, the authors did not indicate revision surgery but scheduled radiographic follow-up studies to check secondary osseous fusion. In the whole patient population there was 1 revision surgery (5%) due to a prevertebral hematoma at the day of surgery. According to Odom criteria 10 patients (50%) had excellent, 6 (30%) good, 2 (10%) satisfactory, and 2 (10%) poor outcome after an average follow-up time of 20 months. The average improvement of the JOA score after was 1.6 points. Only the patient with the terminal renal failure and the secondary 4-level corporectomy and posterior fusion had a deterioration of the JOA score. In all of the 14 cases without subsidence or revision surgery fusion was achieved with no signs of instability on flexion/ extension radiographs, and no signs of radiolucency between the implant and the endplate 20 months after surgery. Furthermore, 11 patients (55%) had an improvement, and 3 patients (15%) had no change of the sagittal contour. www.jspinaldisorders.com |
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FIGURE 3. A 71-year-old patient with a degenerative spinal stenosis ranging from C4/C5 to C6/C7 (A). Two-level vertebral body replacement with a 36-mm ATHLET device and fixation with a 56-mm TOSCA plate. A connector screw connects both the implants (B). The ATHLET implant is filled with autologous bone chips and KAINOS (bioactive ceramic). Note the expansion screws inside of the vertebral bodies. Lateral (B) and anteroposterior (C) radiographs 3 days after surgery.
DISCUSSION Cervical VBR with autologous bone graft bears the disadvantage of complications and heavy pain at the superior pelvic straight. To reduce these problems, several types of VBR methods using allograft material were developed.1,6,9,10,13–16 In the authors’ opinion, the distractable titanium cages10 are not the ideal implant for the reestablishment of cervical lordosis when used over long distances. For example, the ADD distractable titanium cage (ulrich medical, Ulm, Germany) allows just 2 different kinds of lordosis (none/0 or 6 degrees). Nevertheless, these implants provide good stability in the cervical spine.6,10,12 The ATHLET VBR is supposed to reestablish cervical lordosis due to its shape (Fig. 1C). A normal sagittal spinal configuration as a desirable clinical outcome was described previously.17–20 Other advantages of this system are the easy intraoperative handling, the side and central holes for autologous bone graft filling, and the easy connection with the anterior TOSCA plate. The negligible effect of side holes on the stress distribution within a cervical cage was shown by Aslani et al.21 Thus, the advantage of being able to fill the cage with bioceramic and autologous bone material prevails. In contrast to those advantages the authors observed 2 cases (10%) of implant kick-out dislocation and 4 cases (20%) of cage subsidence. In one of these 6 complicated cases there was evidence of low bone quality.
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Thus, primary circumferential surgery would have been a better option in this case.22–24 Two other patients from this group were suspicious to have osteoporosis, and one of them had 2-level corpectomy plus 1-level discectomy (Fig. 6). The latter conformed to criteria for primary circumferential fusion.25 In 4 of the 6 complicated cases there were no risk factors for subsidence (normal bone quality, 1-level corpectomy, normal postoperative x-ray studies). Thus, learning curve could be a reason because these patients were among the earliest cases of our series. Attention has to be paid to low bone quality combined with intraoperative overdistraction to avoid anterior dislocation of the implant or subsidence into adjacent vertebral bodies. Another reason for the relatively high rate of subsidence might be the mismatch in the modulus of elasticity between native bone and PEEK although PEEK cages show high reliability when used as spacers after cervical discectomy. It is possible that some of the patients with subsidence of the implant develop persisting pseudoarthrosis. Thus, the primary aim of surgery (restoration of sagittal balance, bony fusion) will not be achieved. With 20% of patients with a poor to satisfactory outcome according to Odom criteria the clinical outcome of the whole patient population is unsatisfying. The small number of patient was enough to demonstrate an unacceptable rate of failure and further use of this technique was thus, discontinued. Copyright
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2014 Wolters Kluwer Health, Inc. All rights reserved.
J Spinal Disord Tech
Volume 28, Number 2, March 2015
Cervical Vertebral Body Replacement With PEEK
FIGURE 4. A 69-year-old patient with a degenerative spinal stenosis ranging from C4/C5 to C6/C7 (insert in A). Two-level vertebral body replacement with a 34-mm ATHLET implant and fixation with a 54-mm TOSCA plate (A). Anterior dislocation of vertebral body replacement, plate, and screws 4 months after surgery (B). Therefore, posterior fixation from C3 to T1 had to be done. Result another 4 months later (C and D).
FIGURE 5. A 60-year-old patient with a previous fusion of C3/C4 and secondary osseous stenosis behind the vertebral body of C4 (A). One-level vertebral body replacement with a 24-mm ATHLET implant and fixation with a 26-mm TOSCA plate (B). Subsidence of the implant complex 15 months after surgery (C). Nevertheless, JOA score and visual analogue scale of neck pain improved. Therefore, the authors did not indicate revision surgery. Copyright
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2014 Wolters Kluwer Health, Inc. All rights reserved.
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FIGURE 6. A 75-year-old patient with a degenerative spinal stenosis ranging from C3/C4 to C5/C6, additional soft disk herniation at C6/C7. Postoperative result 1 day after C4 and C5 replacement with a 42-mm ATHLET implant, interposition of a Shell-Cage (AMT advanced medical technologies, Nonnweiler, Germany) at the C6/C7 level, and anterior plating with a 84-mm TOSCA plate (A). Routine radiographs 14 days after surgery showing subsidence of the screws inside of the C3 vertebra (B and C). Additional posterior fixation at C3–C7 with significant improvement of the patient’s neck pain (D–F).
In the knowledge of those clinical and radiologic results the authors do not recommend the described PEEK implant for the replacement of cervical vertebral bodies. The main advantage is the avoidance of donor site morbidity when harvesting a bone craft from the iliac crest but there are too many disadvantages compared with the use of autologous bone which is still the gold standard in cervical VBR.
CONCLUSIONS The ATHLET VBR is easy to implant and avoids bone graft site morbidity. Because of a relatively high rate of secondary subsidence of the implant (20%) and sec-
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ondary dislocation (10%) in combination with a poor to satisfactory outcome according to Odom criteria in 20% the authors do not recommend the use of this PEEK implant for cervical VBR. REFERENCES 1. Das K, Couldwell WT, Sava G, et al. Use of cylindrical titanium mesh and locking plates in anterior cervical fusion. Technical note. J Neurosurg. 2001;94:174–178. 2. Edwards CC, Riew KD, Anderson PA, et al. Cervical myelopathy. Current diagnostic and treatment strategies. Spine J. 2003;3: 68–81. 3. Kandziora F, Pflugmacher R, Schaefer J, et al. Biomechanical comparison of expandable cages for vertebral body replacement in the cervical spine. J Neurosurg. 2003;99:91–97.
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2014 Wolters Kluwer Health, Inc. All rights reserved.
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4. Mayr MT, Subach BR, Comey CH, et al. Cervical spinal stenosis: outcome after anterior corpectomy, allograft reconstruction, and instrumentation. J Neurosurg. 2002;96:10–16. 5. Medow JE, Trost G, Sandin J. Surgical management of cervical myelopathy: indications and techniques for surgical corpectomy. Spine J. 2006;6(suppl):233S–241S. 6. Auguste KI, Chin C, Acosta FL, et al. Expandable cylindrical cages in the cervical spine: a review of 22 cases. J Neurosurg Spine. 2006;4:285–291. 7. Dorai Z, Morgan H, Coimbra C. Titanium cage reconstruction after cervical corpectomy. J Neurosurg. 2003;99:3–7. 8. Hacker RJ, Cauthen JC, Gilbert TJ, et al. A prospective randomized multicenter clinical evaluation of an anterior cervical fusion cage. Spine. 2000;25:2646–2654. 9. Narotam PK, Pauley SM, McGinn GJ. Titanium mesh cages for cervical spine stabilization after corpectomy: a clinical and radiological study. J Neurosurg. 2003;99:172–180. 10. Woiciechowsky C. Distractable vertebral cages for reconstruction after cervical corpectomy. Spine. 2005;30:1736–1741. 11. Schulz C, Koschel S, Kunz U, et al. PEEK implant or autologous iliac crest graft as vertebral body substitute after anterior cervical corporectomy? Eur Spine J. 2011;20(suppl 4): S421–S464. 12. Arts MP, Peul WC. Vertebral body replacement systems with expandable cages in the treatment of various spinal pathologies: a prospectively followed case series of 60 patients. Neurosurgery. 2008;63:537–544. 13. Burkett CJ, Baaj AA, Dakwar E, et al. Use of titanium expandable vertebral cages in cervical corpectomy. J Clin Neurosci. 2012;19: 402–405. 14. Castellvi AE, Castellvi A, Clabeaux DH, et al. Corpectomy with titanium cage reconstruction in the cervical spine. J Clin Neurosci. 2012;19:517–521.
Copyright
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2014 Wolters Kluwer Health, Inc. All rights reserved.
Cervical Vertebral Body Replacement With PEEK
15. Chen JF, Lee ST. A simple method for making a hollow cylindrical polymethylmethacrylate strut for cervical spinal reconstruction. J Neurosurg Spine. 2011;14:336–340. 16. Yan D, Wang Z, Deng S, et al. Anterior corpectomy and reconstruction with titanium mesh cage and dynamic cervical plate for cervical spondylotic myelopathy in elderly osteoporosis patients. Arch Orthop Trauma Surg. 2011;131:1369–1374. 17. Harrison DD, Janik TJ, Troyanovich SJ, et al. Comparisons of lordotic cervical spine curvatures to a theoretical ideal model of the static sagittal cervical spine. Spine. 1996;21:667–675. 18. Harrison DD, Troyanovich SJ, Harrison DE, et al. A normal sagittal spinal configuration: a desirable clinical outcome. J Manipulative Physiol Ther. 1996;19:398–405. 19. Harrison DE, Harrison DD, Cailliet R, et al. Cobb method or Harrison posterior tangent method: which to choose for lateral cervical radiographic analysis. Spine. 2000;25:2072–2078,15. 20. Lin Q, Zhou X, Wang X, et al. A comparison of anterior cervical discectomy and corpectomy in patients with multilevel cervical spondylotic myelopathy. Eur Spine J. 2012;21:474–481. 21. Aslani FJ, Hukins DW, Shepherd DE. Effect of side holes in cervical fusion cages: a finite element analysis study. Proc Inst Mech Eng H. 2011;225:986–992. 22. Kim PK, Alexander JT. Indications for circumferential surgery for cervical spondylotic myelopathy. Spine J. 2006;6(suppl):299S–307S. 23. Komotar RJ, Mocco J, Kaiser MG, et al. Surgical management of cervical myelopathy: indications and techniques for laminectomy and fusion. Spine J. 2006;6(suppl):252S–267S. 24. Ko¨nig SA. To the editor: cervical stability. J Neurosurg Spine. 2012;16:102. 25. Hussain M, Nassr A, Natarajan RN, et al. Biomechanical effects of anterior, posterior, and combined anterior-posterior instrumentation techniques on the stability of a multilevel cervical corpectomy construct: a finite element model analysis. Spine J. 2011;11:324–330.
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RIGINAL
ARTICLE
Experience With a Modular PEEK System for Cervical Vertebral Body Replacement Stefan A. Ko¨nig, MD and Uwe Spetzger, MD, PhD
Study Design: A retrospective case series. Summary of Background Data: The authors present their experience with the ATHLET vertebral body replacement (VBR) system in combination with the TOSCA plating system for the treatment of cervical spondylotic myelopathy. Methods: Data obtained from 20 cases were reviewed. Corpectomy and VBR with the ATHLET system was performed in all cases. Patients underwent preoperative and postoperative assessment involving the Japanese Orthopedic Association score, Odom criteria, and radiographic studies to determine the position of the implant as well as cervical lordosis. The mean followup period was 20 months (16–28 mo). Results: Implantation of the ATHLET VBR itself was uncomplicated in all cases. The adjustment of the implants’ height could be done in 2 mm steps. With increasing height of the implant, the angle of lordosis increases comparable with physiological conditions. The authors performed 13 one-level and 7 two-level corpectomies; from the latter group there were 2 revision cases (10%) with implant dislocation. Four cases (20%) of secondary subsidence of the implant were observed radiographs 12 months postoperatively; in all cases treatment remained conservative. Ten patients (50%) had excellent, 4 (30%) good, 2 (10%) satisfactory, and 2 (10%) poor outcome according to Odom criteria. The average improvement of the Japanese Orthopedic Association score was 1.6. All cases achieved osseous fusion without complications, 55% of them had an improvement, and 15% of them had no change of the sagittal contour. Conclusions: The ATHLET VBR is easy to implant and avoids bone graft site morbidity. Due to a relatively high rate of secondary subsidence of the implant (20%) and secondary dislocation (10%) in combination to a poor to satisfactory outcome according to Odom criteria in 20%, the authors do not recommend the use of this PEEK implant for cervical VBR. Key Words: cervical spondylotic myelopathy, vertebral body replacement, PEEK (J Spinal Disord Tech 2015;28:E89–E95) Received for publication January 15, 2014; accepted June 9, 2014. From the Neurochirurgische Klinik, Klinikum Karlsruhe, Karlsruhe, Germany. The authors declare no conflict of interest. Reprints: Stefan A. Ko¨nig, MD, Neurochirurgische Klinik, Klinikum Karlsruhe, Moltkestr. 90, Karlsruhe D-76133, Germany (e-mail: [email protected]). Copyright r 2014 Wolters Kluwer Health, Inc. All rights reserved.
J Spinal Disord Tech
Volume 28, Number 2, March 2015
C
orpectomy is an effective treatment of various pathologies of the cervical spine.1–5 Several techniques for reconstruction have been described including titanium mesh cages and expandable cylindrical titanium cages to avoid donor site pain, fracture, infection, nerve injury, or postoperative hematoma formation after iliac crest bone harvest.3,6–10 As an alternative, the ATHLET vertebral body replacement (VBR) system which is made of polyetheretherketone (PEEK) has been used in numerous European spine centers. Nevertheless, there is only 1 report about the experience with this system.11 Thus, the authors report about their experience with this PEEK system for the replacement of cervical vertebral bodies.
PATIENTS AND METHODS Patient Population Between January 2010 and December 2011 a total of 20 patients, including 12 men and 8 women with clinical and radiologic proof of cervical spondylotic myelopathy underwent corpectomy and VBR using the ATHLET system (SIGNUS; Medizintechnik GmbH, Alzenau, Germany). The patients’ ages at surgery ranged from 44 to 76 years, with a mean of 62.5 years. Mean follow-up was 20 months (range, 16–28 mo). The leading symptom was cervical myelopathy with radiculopathy in 17 patients and without radiculopathy in 3 patients, respectively. All patients complained of neck pain and were refractory to conservative treatment. Preoperative radiologic examinations included plain functional radiography, magnetic resonance imaging, computed tomography (CT), and myelography. Postoperative standard imaging included CT and lateral functional radiographic images. After surgery, all patients’ neck was immobilized with a soft collar for 6 weeks. The standard follow-up in our institution is a clinical and radiologic examination 6 and 12–24 months after surgery including assessment of Japanese Orthopedic Association (JOA) score, Odom criteria, and radiographic images. In this retrospective study, the JOA scores were compared with those before surgery. The x-ray films were assessed regarding dislocation of the implant, osseous fusion, and degeneration of adjacent levels.
Surgical Procedure Corpectomies were performed using a high-speed drill. In all cases, a vertebral body pin distractor system was used. The posterior longitudinal ligament was removed in www.jspinaldisorders.com |
E89
Ko¨nig and Spetzger
J Spinal Disord Tech
Volume 28, Number 2, March 2015
FIGURE 1. ATHLET vertebral body replacement with adjustment in 2-mm steps by combining 2 implant components (A and B). The implant has a lordotic angle (C) similar to physiological conditions and can be filled with bioceramic material (D) and autologous bone graft. The screw threads in the front of the implant were made for the connector screw of the TOSCA plate.
all cases. The cartilage of the endplates was completely removed. The cortical bone was not damaged to avoid a collapse of the implant into the vertebral bodies. The ATHLET VBR system is made of the PEEK. Its height is adjustable in 2-mm steps ranging from 16 to 50 mm by combining 2 different PEEK components. These components are available in different sizes and can be connected by a click mechanism (Figs. 1A–D). The required height of the implant is measured after corpectomy and applying a slight distraction to the adjacent vertebral bodies. The implant is filled with autolougus bone chips and KAINOS bioceramic material (SIGNUS; Medizintechnik GmbH). The vertebral bodies adjacent to the ATHLET system have to be fused with the TOSCA plate (SIGNUS; Medizintechnik GmbH), which has the same lordotic angle as the ATHLET implant. Fixation of the TOSCA plate is done with distal locking tip screws (Fig. 2B). Finally, the TOSCA
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plate has to be connected with the ATHLET implant by a special connector screw (Figs. 2B, 3B).
RESULTS Implantation of the ATHLET VBR itself was uncomplicated in all cases. The adjustment of the implants’ height could be done 2 mm-wise by combining 2 PEEK components from a set (Fig. 1). With increasing height of the implant, the angle of lordosis increases in a manner that is comparable with physiological conditions (Fig. 1C). The teeth at the top and bottom of the ATHLET implant ensure good fixation in the endplates of the adjacent vertebral bodies. Filling the ATHLET implant with KAINOS bioceramic and bone chips can be done easily through the central canal and the side holes (Fig. 1D). This is supposed to provide osseous fusion 3–6 months after surgery. The Copyright
r
2014 Wolters Kluwer Health, Inc. All rights reserved.
J Spinal Disord Tech
Volume 28, Number 2, March 2015
Cervical Vertebral Body Replacement With PEEK
FIGURE 2. A 48-year-old patient with a degenerative spinal stenosis ranging from C4/C5 to C5/C6. Single-level vertebral body replacement with a 26-mm ATHLET implant and fixation with a 40-mm TOSCA plate. A small screw connects both the implants (B). The ATHLET implant is filled with autologous bone chips and KAINOS (bioactive ceramic). Note the expansion screws inside of the vertebral bodies. Preoperative computed tomography scan showing the osseous stenosis at the posterior aspect of the C5 vertebral body (A). Lateral (B) and anteroposterior (C) radiographs 3 days after surgery showing an improved cervical lordosis.
connector screw (Figs. 2B, 3B) between the TOSCA plate and the ATHLET VBR keeps the plate in place, especially before fixing it to the vertebra. Afterwards, it provides increased stability of the whole construct. Corpectomies of 1 level were performed in 13 patients. Seven patients underwent 2-level corpectomy. There was 1 revision case from the 2-level group who had poor bone quality due to renal dialysis but no evidence of osteoporosis in the preoperative CT scans. This patient initially underwent corpectomy of C5 and C6 including anterior plating from C4 to C7, and suffered from a fracture of the adjacent vertebral bodies and a dislocation of the implant 2 months after surgery. Therefore, we had to perform a 4-level corpectomy in the second operation including VBR and anterior plating from C3 to T1 (again with the ATHLET/TOSCA systems) as well as posterior fusion from C3 to T1. Another revision case from the 2-level group was a patient with a degenerative stenosis and normal bone quality. Nevertheless, the implant complex showed a kick-out dislocation 4 months after surgery (Fig. 4). At that time this 69-year-old patient did not have any neurological symptoms nor dysphagia. Therefore, the authors left the anterior implant in place and performed posterior fixation from C3 to T1 (Figs. 4C, D). Thus, there were 2 of 7 (29%) revision cases in the 2-level corCopyright
r
2014 Wolters Kluwer Health, Inc. All rights reserved.
pectomy group due to dislocation of the implant. There was no anterior nor posterior dislocation in the 1-level corpectomy group but we observed 4 cases with hardware subsidence into the caudal adjacent vertebral body (Fig. 5). In both the cases JOA and visual analogue scale scores of neck pain improved despite the subsidence. Therefore, the authors did not indicate revision surgery but scheduled radiographic follow-up studies to check secondary osseous fusion. In the whole patient population there was 1 revision surgery (5%) due to a prevertebral hematoma at the day of surgery. According to Odom criteria 10 patients (50%) had excellent, 6 (30%) good, 2 (10%) satisfactory, and 2 (10%) poor outcome after an average follow-up time of 20 months. The average improvement of the JOA score after was 1.6 points. Only the patient with the terminal renal failure and the secondary 4-level corporectomy and posterior fusion had a deterioration of the JOA score. In all of the 14 cases without subsidence or revision surgery fusion was achieved with no signs of instability on flexion/ extension radiographs, and no signs of radiolucency between the implant and the endplate 20 months after surgery. Furthermore, 11 patients (55%) had an improvement, and 3 patients (15%) had no change of the sagittal contour. www.jspinaldisorders.com |
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FIGURE 3. A 71-year-old patient with a degenerative spinal stenosis ranging from C4/C5 to C6/C7 (A). Two-level vertebral body replacement with a 36-mm ATHLET device and fixation with a 56-mm TOSCA plate. A connector screw connects both the implants (B). The ATHLET implant is filled with autologous bone chips and KAINOS (bioactive ceramic). Note the expansion screws inside of the vertebral bodies. Lateral (B) and anteroposterior (C) radiographs 3 days after surgery.
DISCUSSION Cervical VBR with autologous bone graft bears the disadvantage of complications and heavy pain at the superior pelvic straight. To reduce these problems, several types of VBR methods using allograft material were developed.1,6,9,10,13–16 In the authors’ opinion, the distractable titanium cages10 are not the ideal implant for the reestablishment of cervical lordosis when used over long distances. For example, the ADD distractable titanium cage (ulrich medical, Ulm, Germany) allows just 2 different kinds of lordosis (none/0 or 6 degrees). Nevertheless, these implants provide good stability in the cervical spine.6,10,12 The ATHLET VBR is supposed to reestablish cervical lordosis due to its shape (Fig. 1C). A normal sagittal spinal configuration as a desirable clinical outcome was described previously.17–20 Other advantages of this system are the easy intraoperative handling, the side and central holes for autologous bone graft filling, and the easy connection with the anterior TOSCA plate. The negligible effect of side holes on the stress distribution within a cervical cage was shown by Aslani et al.21 Thus, the advantage of being able to fill the cage with bioceramic and autologous bone material prevails. In contrast to those advantages the authors observed 2 cases (10%) of implant kick-out dislocation and 4 cases (20%) of cage subsidence. In one of these 6 complicated cases there was evidence of low bone quality.
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Thus, primary circumferential surgery would have been a better option in this case.22–24 Two other patients from this group were suspicious to have osteoporosis, and one of them had 2-level corpectomy plus 1-level discectomy (Fig. 6). The latter conformed to criteria for primary circumferential fusion.25 In 4 of the 6 complicated cases there were no risk factors for subsidence (normal bone quality, 1-level corpectomy, normal postoperative x-ray studies). Thus, learning curve could be a reason because these patients were among the earliest cases of our series. Attention has to be paid to low bone quality combined with intraoperative overdistraction to avoid anterior dislocation of the implant or subsidence into adjacent vertebral bodies. Another reason for the relatively high rate of subsidence might be the mismatch in the modulus of elasticity between native bone and PEEK although PEEK cages show high reliability when used as spacers after cervical discectomy. It is possible that some of the patients with subsidence of the implant develop persisting pseudoarthrosis. Thus, the primary aim of surgery (restoration of sagittal balance, bony fusion) will not be achieved. With 20% of patients with a poor to satisfactory outcome according to Odom criteria the clinical outcome of the whole patient population is unsatisfying. The small number of patient was enough to demonstrate an unacceptable rate of failure and further use of this technique was thus, discontinued. Copyright
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J Spinal Disord Tech
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Cervical Vertebral Body Replacement With PEEK
FIGURE 4. A 69-year-old patient with a degenerative spinal stenosis ranging from C4/C5 to C6/C7 (insert in A). Two-level vertebral body replacement with a 34-mm ATHLET implant and fixation with a 54-mm TOSCA plate (A). Anterior dislocation of vertebral body replacement, plate, and screws 4 months after surgery (B). Therefore, posterior fixation from C3 to T1 had to be done. Result another 4 months later (C and D).
FIGURE 5. A 60-year-old patient with a previous fusion of C3/C4 and secondary osseous stenosis behind the vertebral body of C4 (A). One-level vertebral body replacement with a 24-mm ATHLET implant and fixation with a 26-mm TOSCA plate (B). Subsidence of the implant complex 15 months after surgery (C). Nevertheless, JOA score and visual analogue scale of neck pain improved. Therefore, the authors did not indicate revision surgery. Copyright
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FIGURE 6. A 75-year-old patient with a degenerative spinal stenosis ranging from C3/C4 to C5/C6, additional soft disk herniation at C6/C7. Postoperative result 1 day after C4 and C5 replacement with a 42-mm ATHLET implant, interposition of a Shell-Cage (AMT advanced medical technologies, Nonnweiler, Germany) at the C6/C7 level, and anterior plating with a 84-mm TOSCA plate (A). Routine radiographs 14 days after surgery showing subsidence of the screws inside of the C3 vertebra (B and C). Additional posterior fixation at C3–C7 with significant improvement of the patient’s neck pain (D–F).
In the knowledge of those clinical and radiologic results the authors do not recommend the described PEEK implant for the replacement of cervical vertebral bodies. The main advantage is the avoidance of donor site morbidity when harvesting a bone craft from the iliac crest but there are too many disadvantages compared with the use of autologous bone which is still the gold standard in cervical VBR.
CONCLUSIONS The ATHLET VBR is easy to implant and avoids bone graft site morbidity. Because of a relatively high rate of secondary subsidence of the implant (20%) and sec-
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ondary dislocation (10%) in combination with a poor to satisfactory outcome according to Odom criteria in 20% the authors do not recommend the use of this PEEK implant for cervical VBR. REFERENCES 1. Das K, Couldwell WT, Sava G, et al. Use of cylindrical titanium mesh and locking plates in anterior cervical fusion. Technical note. J Neurosurg. 2001;94:174–178. 2. Edwards CC, Riew KD, Anderson PA, et al. Cervical myelopathy. Current diagnostic and treatment strategies. Spine J. 2003;3: 68–81. 3. Kandziora F, Pflugmacher R, Schaefer J, et al. Biomechanical comparison of expandable cages for vertebral body replacement in the cervical spine. J Neurosurg. 2003;99:91–97.
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Volume 28, Number 2, March 2015
4. Mayr MT, Subach BR, Comey CH, et al. Cervical spinal stenosis: outcome after anterior corpectomy, allograft reconstruction, and instrumentation. J Neurosurg. 2002;96:10–16. 5. Medow JE, Trost G, Sandin J. Surgical management of cervical myelopathy: indications and techniques for surgical corpectomy. Spine J. 2006;6(suppl):233S–241S. 6. Auguste KI, Chin C, Acosta FL, et al. Expandable cylindrical cages in the cervical spine: a review of 22 cases. J Neurosurg Spine. 2006;4:285–291. 7. Dorai Z, Morgan H, Coimbra C. Titanium cage reconstruction after cervical corpectomy. J Neurosurg. 2003;99:3–7. 8. Hacker RJ, Cauthen JC, Gilbert TJ, et al. A prospective randomized multicenter clinical evaluation of an anterior cervical fusion cage. Spine. 2000;25:2646–2654. 9. Narotam PK, Pauley SM, McGinn GJ. Titanium mesh cages for cervical spine stabilization after corpectomy: a clinical and radiological study. J Neurosurg. 2003;99:172–180. 10. Woiciechowsky C. Distractable vertebral cages for reconstruction after cervical corpectomy. Spine. 2005;30:1736–1741. 11. Schulz C, Koschel S, Kunz U, et al. PEEK implant or autologous iliac crest graft as vertebral body substitute after anterior cervical corporectomy? Eur Spine J. 2011;20(suppl 4): S421–S464. 12. Arts MP, Peul WC. Vertebral body replacement systems with expandable cages in the treatment of various spinal pathologies: a prospectively followed case series of 60 patients. Neurosurgery. 2008;63:537–544. 13. Burkett CJ, Baaj AA, Dakwar E, et al. Use of titanium expandable vertebral cages in cervical corpectomy. J Clin Neurosci. 2012;19: 402–405. 14. Castellvi AE, Castellvi A, Clabeaux DH, et al. Corpectomy with titanium cage reconstruction in the cervical spine. J Clin Neurosci. 2012;19:517–521.
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Cervical Vertebral Body Replacement With PEEK
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