Elsevier

Clinical Biomechanics

Volume 53, March 2018, Pages 72-78
Clinical Biomechanics

Does pedicle screw fixation of the subaxial cervical spine provide adequate stabilization in a multilevel vertebral body fracture model? An in vitro biomechanical study

https://doi.org/10.1016/j.clinbiomech.2018.02.009Get rights and content

Highlights

  • Cervical fracture is corrected by 360° fusion using lateral mass screws with corpectomy spacer/plate

  • 360° fusion may be unnecessary as navigational techniques lower complication rates associated with cervical pedicle screws

  • Biomechanical comparisons between 360° fusion (C3 to C7) and pedicle screw reconstruction (C3 and C7 only) are made

  • Surgical constructs significantly reduced intact; no significant differences were observed between constructs

Abstract

Background

Cervical vertebral body fractures generally are treated through an anterior-posterior approach. Cervical pedicle screws offer an alternative to circumferential fixation. This biomechanical study quantifies whether cervical pedicle screws alone can restore the stability of a three-column vertebral body fracture, making standard 360° reconstruction unnecessary.

Methods

Range of motion (2.0 Nm) in flexion-extension, lateral bending, and axial rotation was tested on 10 cadaveric specimens (five/group) at C2–T1 with a spine kinematics simulator. Specimens were tested for flexibility of intact when a fatigue protocol with instrumentation was used to evaluate construct longevity. For a C4–6 fracture, spines were instrumented with 360° reconstruction (corpectomy spacer + plate + lateral mass screws) (Group 1) or cervical pedicle screw reconstruction (C3 and C7 only) (Group 2).

Findings

Results are expressed as percentage of intact (100%). In Group 1, 360° reconstruction resulted in decreased motion during flexion-extension, lateral bending, and axial rotation, to 21.5%, 14.1%, and 48.6%, respectively, following 18,000 cycles of flexion-extension testing. In Group 2, cervical pedicle screw reconstruction led to reduced motion after cyclic flexion-extension testing, to 38.4%, 12.3%, and 51.1% during flexion-extension, lateral bending, and axial rotation, respectively.

Interpretation

The 360° stabilization procedure provided the greatest initial stability. Cervical pedicle screw reconstruction resulted in less change in motion following cyclic loading with less variation from specimen to specimen, possibly caused by loosening of the shorter lateral mass screws. Cervical pedicle screw stabilization may be a viable alternative to 360° reconstruction for restoring multilevel vertebral body fracture.

Introduction

Posterior cervical spine instrumentation is commonly used to treat regional spinal instability resulting from trauma, tumor, infection, or degenerative disease. Lateral mass screw placement remains a “gold standard” for posterior cervical instrumentation, with excellent results reported (Grob and Magerl, 1987; Jeanneret et al., 1991; Roy-Camille and Saillant, 1972). However, use of lateral mass screws is precluded at a vertebral level with a facet fracture, and this approach provides limited stabilization in patients with poor bone quality, including those with severe osteoporosis. Placement of cervical pedicle screws (CPS) offers an alternative to standard lateral mass screw fixation (Abumi et al., 1994; Abumi and Kaneda, 1997; Hasegawa et al., 2008; Jeanneret et al., 1994; Reinhold et al., 2007; Richter et al., 2000). Use of CPS has not been widely adopted despite very low reported complication rates, because of associated technical difficulty and perceived risk of nerve root or vertebral artery (VA) injury (Abumi et al., 2000; Richter et al., 2004). However, CPS placement is a procedure of interest, as it affords distinct advantages over standard lateral mass screw placement (Dunlap et al., 2010; Johnston et al., 2006; Jones et al., 1997; Kowalski et al., 2000). The pullout strength of a CPS is approximately twice to quadruple that of a lateral mass screw (Ito et al., 2014; Jones et al., 1997). Moreover, three-column fixation can be realized through a single posterior approach and may involve instrumentation at the level of an articular fracture.

Multilevel cervical vertebral body fracture (VBF) from trauma or other pathology generally is treated by anterior reconstruction, often supplemented by posterior stabilization (Memtsoudis et al., 2011). However, because multilevel anterior instrumentation introduces the potential for significant morbidity, it may be preferable to consider treating patients with multilevel cervical VBF through a single posterior approach with CPS placement. Although such reconstruction is plausible, the basic biomechanics of a CPS construct have not been explored, and the effectiveness of CPS placement in restoring three-column stability after disruption has not been examined.

This study looks at biomechanical aspects of two possible surgical solutions for multilevel anterior cervical VBF. Investigators compared the relative stability of a posteriorly placed CPS construct alone versus 360° reconstruction (with anterior cage/plate and posterior lateral mass screw construct) before and after a simulated period of repetitive bending (cyclic loading). Researchers hypothesized that CPS fixation, which should maintain adequate anterior column support through increased screw length, may be comparable with more invasive front-back reconstruction. A clinical case of multilevel VBF, which could have been treated by either of these surgical techniques, is presented later to describe the CPS technique as used in clinical practice.

Section snippets

Specimen preparation

Ten fresh-frozen cadaveric cervical spines (two groups of five specimens) at C2–T1 were used in this study. The medical history of each donor was reviewed along with radiographic images to exclude specimens with spinal trauma, malignancy, deformity, or fracture that would otherwise affect the outcome of the test. Specimens were then carefully dissected, leaving only ligaments, vertebral bodies, and intervertebral discs of desired segments. Specimens were fixed at the C2 body proximally and at

Range-of-motion

A summary of raw and normalized ROM values for 360° reconstruction (Table 1, Table 2), raw and normalized ROM values for CPS reconstruction (Table 3, Table 4), and normalized ROM comparisons before and following cyclic loading with significant relationships (Fig. 4) are presented.

Group 1 (360°) intact specimens have average intact motion values of 23.3° (SD 10.4°) of FE, 8.3° (SD 4.2°) of LB, and 21.6° (SD 9.2°) of AR. After 360° reconstruction, motion was significantly reduced to 1.8° (SD

Discussion

This study was conducted to explore the stability of two different surgical reconstruction options for treatment of multilevel, multicolumn cervical fracture. Range-of-motion baseline values indicate that Group 1 (three-level corpectomy spacer + plate + lateral mass screws) was stiffer than Group 2 (terminal pedicle screws at C3 and C7 with no anterior reconstruction) in FE. After cyclic loading (see Fig. 4), these effects were somewhat neutralized, as the initially greater stiffness in Group 1

Conclusions

Multilevel anterior cervical fractures are devastating injuries that generally are treated by corpectomy, interbody cage, and anterior plate, followed by posterior fixation with lateral mass screws. Cervical pedicle screw reconstruction may simplify surgery and provide adequate stabilization for bone fusion, with acceptable risk to neurovascular structures. Pedicle screws provide better screw purchase and the need for fewer fixation points. Immediate range of motion, range of motion after

Author conflict of interest and funding statement

JD, RTD, and LB have no financial relationships to disclose. MMH, NK, JAH, SSY, and BSB are salaried employees of the Musculoskeletal Education and Research Center (MERC), A Division of Globus Medical, Inc. Funding for this biomechanical study was provided by the Musculoskeletal Education and Research Foundation (MERC), A Division of Globus Medical, Inc. MERC provided all equipment and testing apparatus such as the six-degrees-of-freedom spine motion simulator. MERC employees performed all

Acknowledgments

The authors would like to acknowledge editorial assistance provided by Ms. Dolores Matthews, MEd, ELS, in preparation of the manuscript.

References (56)

  • T.Y. Wang et al.

    Rates of anterior cervical discectomy and fusion after initial posterior cervical foraminotomy

    Spine J.

    (2015)
  • M.S. Yeager et al.

    Anterior lumbar interbody fusion with integrated fixation and adjunctive posterior stabilization: A comparative biomechanical analysis

    Clin. Biomech. (Bristol, Avon)

    (2015)
  • K. Abumi et al.

    Pedicle screw fixation for nontraumatic lesions of the cervical spine

    Spine

    (1997)
  • K. Abumi et al.

    Transpedicular screw fixation for traumatic lesions of the middle and lower cervical spine: description of the techniques and preliminary report

    Clin. Spine Surg.

    (1994)
  • K. Abumi et al.

    Complications of pedicle screw fixation in reconstructive surgery of the cervical spine

    Spine

    (2000)
  • A.H. Barnes et al.

    Biomechanical pullout strength and stability of the cervical artificial pedicle screw

    Spine

    (2009)
  • M.T. Benke et al.

    Biomechanical comparison of transpedicular versus intralaminar C2 fixation in C2–C6 subaxial constructs

    Spine

    (2011)
  • C. Bolger et al.

    Image-guided surgery: applications to the cervical and thoracic spine and a review of the first 120 procedures

    J. Neurosurg.

    (2000)
  • C. Bolger et al.

    Frameless stereotaxy and anterior cervical surgery

    Comput. Aided Surg.

    (1999)
  • A.G. Brantley et al.

    The effects of pedicle screw fit. An in vitro study

    Spine

    (1994)
  • J.K. Burkhardt et al.

    A comparative effectiveness study of patient-rated and radiographic outcome after 2 types of decompression with fusion for spondylotic myelopathy: anterior cervical discectomy versus corpectomy

    Neurosurg. Focus.

    (2013)
  • B.J. Dunlap et al.

    Load sharing properties of cervical pedicle screw-rod constructs versus lateral mass screw-rod constructs

    Eur. Spine J.

    (2010)
  • M.B. Frenkel et al.

    Fusion rates in multilevel, instrumented anterior cervical fusion for degenerative disease with and without the use of bone morphogenetic protein

    J. Neurosurg. Spine

    (2013)
  • S.E. Gould et al.

    Cellular contribution of bone graft to fusion

    J. Orthop. Res.

    (2000)
  • D. Grob et al.

    Dorsal spondylodesis of the cervical spine using a hooked plate

    Orthopade

    (1987)
  • D.W. Hallager et al.

    Use of supplemental short pre-contoured accessory rods and cobalt chrome alloy posterior rods reduces primary rod strain and range of motion across the pedicle subtraction osteotomy level: an in vitro biomechanical study

    Spine (Phila Pa 1976)

    (2016)
  • K. Hasegawa et al.

    Indications for cervical pedicle screw instrumentation in nontraumatic lesions

    Spine

    (2008)
  • T.P. Hedman et al.

    Design of an intervertebral disc prosthesis

    Spine (Phila Pa 1976)

    (1991)
  • Cited by (14)

    • Robotic Assistance for Minimally Invasive Cervical Pedicle Instrumentation: Report on Feasibility and Safety

      2021, World Neurosurgery
      Citation Excerpt :

      Its biomechanical advantages include increased bony purchase in the pedicle, and spanning of all 3 columns of the vertebra. It is a more effective technique in restoring segmental lordosis and global cervical lordosis compared with lateral mass fixation.14-17 Abumi et al.18 were the first to introduce this technique in 1994, and there have been many other reports since.19,20

    • Cervical fixation in the elderly

      2020, Seminars in Spine Surgery
      Citation Excerpt :

      Fig. 2) In the literature, biomechanical studies on cervical pedicle screws have shown that the pull-out strength is significantly higher with initial flexion/extension stability as well as stability after cyclic loading compared to lateral mass screw fixation by 2 to 4 times, and comparable stability of pedicle screw-only construct to a 360° reconstruction model (corpectomy spacer with anterior plating and posterior lateral mass screws from C3 to C7).15–17 Although the biomechanical reports are limited in that they are cadaveric studies that do not consider dynamic stabilizing factors, cervical pedicle screw does appear to provide greater stability than lateral mass screws, and may therefore be justified in patients with poor bone quality or highly unstable conditions that require more rigid fixation than the usual clinical settings.18

    • Guidelines for cortical screw versus pedicle screw selection from a fatigued decompressive lumbar laminectomy model show similar stability and less bone mineral density dependency

      2020, Clinical Biomechanics
      Citation Excerpt :

      Following ROM testing of the instrumented spine (TLIF Pre-Fat), each specimen underwent a specimen-specific displacement-controlled simulated in vivo fatigue protocol. The dynamic cyclic loading testing protocol, and fixtures used, have been previously reported (Duff et al., 2018). Specimens were mounted in a neutral position upon an MTS® 858 mini bionix servo-hydraulic machine (MTS Systems Corporation, Eden Prairie, MN, USA) (Fig. 2C).

    • Stabilizing effect of the rib cage on adjacent segment motion following thoracolumbar posterior fixation of the human thoracic cadaveric spine: A biomechanical study

      2019, Clinical Biomechanics
      Citation Excerpt :

      Data were collected during the third cycle to minimize the viscoelastic behavior of the tissues. The dynamic cyclic loading testing protocol, and fixtures used, has been previously reported (Duff et al., 2018). An MTS® 858 Mini Bionix servo-hydraulic machine (MTS Systems Corporation, Eden Prairie, MN, USA) was used to simulate long-term stability in flexion-extension of the intact rib cage condition with T4–L2 instrumentation.

    View all citing articles on Scopus
    View full text