Construct stability of an instrumented 2-level cervical corpectomy model following fatigue testing: biomechanical comparison of circumferential antero-posterior instrumentation versus a novel anterior-only transpedicular screw–plate fixation technique
A high rate of complications in multilevel cervical surgery with corpectomies and anterior-only screw-and-plate stabilization is reported. A 360°-instrumentation improves construct stiffness and fusion rates, but adds the morbidity of a second approach. A novel ATS-technique (technique that used anterior transpedicular screw placement) was recently described, yet no study to date has analyzed its performance after fatigue loading. Accordingly, the authors performed an analysis of construct stiffness after fatigue testing of a cervical 2-level corpectomy model reconstructed using a novel anterior transpedicular screw-and-plate technique (ATS-group) in comparison to standard antero-posterior instrumentation (360°-group).
Materials and methods
Twelve fresh-frozen human cervical spines were mounted on a spine motion tester to analyze restriction of ROM under loading (1.5 Nm) in flexion–extension (FE), axial rotation (AR), and lateral bending (LB). Testing was performed in the intact state, and after instrumentation of a 2-level corpectomy C4 + C5 using a cage and the constructs of ATS- and 360°-group, after 1,000 cycles, and after 2,000 cycles of fatigue testing. In the ATS-group (n = 6), instrumentation was achieved using a customized C3–C6 ATS-plate system. In the 360°-group (n = 6), instrumentation consisted of a standard anterior screw-and-plate system with a posterior instrumentation using C3–C6 lateral mass screws. Motion data were assessed as degrees and further processed as normalized values after standardization to the intact ROM state.
Specimen age and BMD were not significantly different between the ATS- and 360°-groups. After instrumentation and 2,000 cycles of testing, no specimen exhibited a ROM greater than in the intact state. No specimen exhibited catastrophic construct failure after 2,000 cycles. Construct stiffness in the 360°-group was significantly increased compared to the ATS-group for all loading conditions, except for FE-testing after instrumentation. After 2,000 cycles, restriction of ROM under loading in FE was 39.8 ± 30 % in the ATS-group vs. 2.8 ± 2.3 % in the 360°-group, in AR 60.4 ± 25.8 vs 15 ± 11 %, and in LB 40 ± 23.4 vs 3.9 ± 1.2 %. Differences were significant (p < 0.05).
360°-instrumentation resembles the biomechanical standard of reference for stabilization of 2-level corpectomies. An ATS-construct was also shown to confer high construct stiffness, significantly reducing the percentage ROM beyond that of an intact specimen after 2,000 cycles. This type of instrumentation might be a clinical valuable and biomechanically sound adjunct to multilevel anterior surgical procedures.
KeywordsCervical spine Biomechanical testing Cyclic loading 360° instrumentation Anterior transpedicular Corpectomy
Conflict of interest
- 10.Steinmetz MP, Stewart TJ, Kager CD, Benzel EC, Vaccaro AR (2007) Cervical deformity correction. Neurosurg 60(Suppl):S90–S97Google Scholar
- 14.Sembrano JN, Mehbod AA, Garvey TA, Denis F, Perra JH, Schwender JD, Transfeldt EE, Winter RB, Wroblewski M (2009) A concomitant posterior approach improves fusion rates but not overall reoperation rates in multilevel cervical fusion for spondylosis. J Spinal Disord Tech 22:162–169CrossRefPubMedGoogle Scholar
- 16.Schlenk RP, Kowalski RJ, Benzel EC (2003) Biomechanics of spinal deformity. Neurosurg Focus 14:Article 2Google Scholar
- 18.Setzer M, Eleraky M, Johnson WM, Aghayev K, Tran ND, Vrions FD (2012) Biomechanical comparison of anterior cervical spine instrumentation techniques with and without supplemental posterior fusion after different corpectomy and discectomy combinations. J Neurosurg Spine 16:579–584CrossRefPubMedGoogle Scholar
- 19.A N, Hussain M, Natarajan RN, An HS, Gunnar BJ, Andersson GB (2011) 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 11:324–330CrossRefGoogle Scholar
- 20.Shamji MF, Cook C, Pietrobon R, Tackett S, Brown C, Isaacs RE (2008) Impact of surgical approach on complications and resource utilization of cervical spine fusion: a nationwide perspective to the surgical treatment of diffuse cervical spondylosis. Spine J 9:10–16Google Scholar
- 23.Koller H, Acosta F, Tauber M, Fox M, Martin H, Forstner R, Augat P, Penzkofer R, Pirich C, Kässmann H, Resch H, Hitzl W (2008) Cervical anterior transpedicular screw fixation (ATPS)—Part II. Accuracy of manual insertion and pull-out strength of ATPS. Eur Spine J 17:539–555PubMedCentralCrossRefPubMedGoogle Scholar
- 41.Koller H, Schmidt R, Mayer M, Hitzl W, Zenner J, Midderhoff S, Graf N, Resch H, Wilke HJ (2010) The stabilizing potential of anterior, posterior and combined techniques for the reconstruction of a 2-level cervical corpectomy model: biomechanical study and first results of ATPS prototyping. Eur Spine J 19:2137–2148PubMedCentralCrossRefPubMedGoogle Scholar
- 48.Hussain M, Natarajan RN, Fayyazi AH, Braaksma BR, Anderson GBJ, An HS (2009) Screw angulation affects bone-screw stresses and bone graft load sharing in anterior cervical corpectomy fusion with a rigid screw plate construct: a finite element model study. Spine J 9:1016–1023CrossRefPubMedGoogle Scholar
- 49.Schlenk RP, Stewart T, Benzel EC (2003) The biomechanics of iatrogenic spinal destabilization and implant failure. Neurosurg Focus 15 (3):Article 2Google Scholar