Development of a Low-Cost Polymethylmethacrylate Stand-Alone Cervical Cage: Technical Note

Abstract

Background and Study Aims Stand-alone cervical cages aim to provide primary stability, yield solid fusion in the long-term course, and maintain physiologic alignment. However, many implants designed for these purposes fail in achieving these goals. Following implantation, relatively high rates of cage subsidence and failure of disc height maintenance may lead to cervical kyphosis and poor alignment of the cervical spine. At the same time, costs for cage implantation are relatively high compared with their unfavorable radiologic performance. Thus the aim of the study was to develop and test mechanically a low-cost polymethylmethacrylate (PMMA) cage with similar mechanical and procedural properties compared with a commercial polyetheretherketone (PEEK) cage.

Material and Methods Following determination of the cage design, a casting mold was developed for the production of PMMA cages. Nine cages were produced and compared with nine PEEK cages using static compression tests for 0 and 45 degrees according to the recommendations of the American Society for Testing and Materials. Mean compressive yield strength, mean yield displacement, mean tensile strength, and mean stiffness were determined.

Results At 0 degrees axial compression, the mean compressive yield strength, mean displacement, and mean tensile strength of the PMMA cage was significantly higher compared with the PEEK cage (p < 0.001). Stiffness of both implants did not differ significantly (p = 0.903). At 45 degrees axial compression, PEEK cages could not be investigated because slipping of the holding fixture occurred. Under these conditions, PMMA cages showed a mean compressive yield strength of 804.9 ± 60.5 N, a mean displacement of 0.66 mm ± 0.05 mm, a mean tensile strength of 7.92 ± 0.6 N/mm², and a mean stiffness of 1,228 ± 79.4 N/mm.

Conclusions The newly developed PMMA cage seems to show similar to superior mechanical properties compared with the commercial PEEK cage. Considering a preparation time of only 10 minutes and the low price for the PMMA material, the cost-benefit ratio clearly points to the use of the PMMA cage. However, clinical effectiveness has to be proven in a separate study.

Keywords

cervical spine - PMMA - ACDF - cervical cage

Notes

Portions of this work were presented in poster form at the 94th meeting of the German Society for Orthopedics and Orthopedic Surgery (DGOOC; October 22–25, 2008) and the 5th German spine conference (DWG; December 16–18, 2010).

• References

• 1 Bartels RH, Donk RD, Feuth T. Subsidence of stand-alone cervical carbon fiber cages. Neurosurgery 2006; 58 (3) 502-508 ; discussion 502–508
• 2 Yang JJ, Yu CH, Chang BS, Yeom JS, Lee JH, Lee CK. Subsidence and nonunion after anterior cervical interbody fusion using a stand-alone polyetheretherketone (PEEK) cage. Clin Orthop Surg 2011; 3 (1) 16-23
• 3 Kolstad F, Nygaard OP, Andresen H, Leivseth G. Anterior cervical arthrodesis using a “stand alone” cylindrical titanium cage: prospective analysis of radiographic parameters. Spine 2010; 35 (16) 1545-1550
• 4 Jacobs W, Willems PC, Kruyt M , et al. Systematic review of anterior interbody fusion techniques for single- and double-level cervical degenerative disc disease. Spine 2011; 36 (14) E950-E960
• 5 Hamburger C, Festenberg FV, Uhl E. Ventral discectomy with PMMA interbody fusion for cervical disc disease: long-term results in 249 patients. Spine 2001; 26 (3) 249-255
• 6 Barsa P, Suchomel P. Factors affecting sagittal malalignment due to cage subsidence in standalone cage assisted anterior cervical fusion. Eur Spine J 2007; 16 (9) 1395-1400
• 7 Zivic F, Babic M, Grujovic N, Mitrovic S, Favaro G, Caunii M. Effect of vacuum-treatment on deformation properties of PMMA bone cement. J Mech Behav Biomed Mater 2012; 5 (1) 129-138
• 8 Pintar FA, Yoganandan N, Voo L. Effect of age and loading rate on human cervical spine injury threshold. Spine 1998; 23 (18) 1957-1962
• 9 Chen J-F, Wu C-T, Lee S-C, Lee ST. Use of a polymethylmethacrylate cervical cage in the treatment of single-level cervical disc disease. J Neurosurg Spine 2005; 3 (1) 24-28
• 10 Chen JF, Lee ST. The polymethyl methacrylate cervical cage for treatment of cervical disk disease Part III. Biomechanical properties. Surg Neurol 2006; 66 (4) 367-370 ; discussion 370
• 11 Chen JF, Lee ST. A simple method for making a hollow cylindrical polymethylmethacrylate strut for cervical spinal reconstruction. J Neurosurg Spine 2011; 14 (3) 336-340
• 12 Kast E, Derakhshani S, Bothmann M, Oberle J. Subsidence after anterior cervical inter-body fusion. A randomized prospective clinical trial. Neurosurg Rev 2009; 32 (2) 207-214 ; discussion 214
• 13 Wilke HJ, Kettler A, Goetz C, Claes L. Subsidence resulting from simulated postoperative neck movements: an in vitro investigation with a new cervical fusion cage. Spine 2000; 25 (21) 2762-2770
• 14 Barth M, Tuettenberg J, Thomé C, Weiss C, Vajkoczy P, Schmiedek P. Watertight dural closure: is it necessary? A prospective randomized trial in patients with supratentorial craniotomies. Neurosurgery 2008; 63 (4) (Suppl. 02) 352-358 ; discussion 358