Does pedicle screw fixation of the subaxial cervical spine provide adequate stabilization in a multilevel vertebral body fracture model? An in vitro biomechanical study
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.
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2021, World NeurosurgeryCitation 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
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