Peer-Review ReportBiomechanical Comparison of Cervical Fixation via Transarticular Facet Screws without Rods versus Lateral Mass Screws with Rods
Introduction
Posterior cervical spine stabilization and fusion are mandatory when instability results from tumor, trauma, or inflammatory disease as well as from failed lateral mass fixation and revisions. Hadra in 1891 was the first to report successful stabilization by wire of a cervical fracture secondary to Pott disease (9). Since then, many surgical techniques for posterior cervical stabilization and fusion have been developed; at the present time, placement of posterior screw-rod fixation systems is the established technique in cervical spine surgery. These fixation systems include the lateral mass screw-rod (LMSR), transarticular facet screw (TFS) with or without rod, and cervical pedicle screw-rod 1, 2, 7, 8, 10, 11, 18, 21.
LMSR and TFS fixations provide similar biomechanical performances and have similar fixation forces (18). The cervical pedicle screw-rod fixation system has the strongest fixation force among these techniques 12, 14, 15, 20, with the potential for vascular, cord, and nerve root injuries and pedicle perforations as reported for 6.7%–30% of pedicle screw insertions 1, 2, 3, 4. Although TFS systems with rods have relatively weaker fixation forces than cervical pedicle screw systems, they can be placed more easily and have a less probable chance of vascular injury (6). In the present study, we tested and compared the biomechanics of a TFS system without rods versus LMSR fixation for 1-level and 2-level insertions.
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Specimen Preparation
We obtained 6 frozen human cadaveric cervical spines (3 female and 3 male; average age, 63 years; age range, 55–78 years) from Science Care (Phoenix, Arizona, USA) that included cervicothoracic junction vertebrae. The specimens were stored in a refrigerator at −20°C and thawed 2 hours to room temperature before use. Fluoroscopy was performed on each specimen to screen for abnormalities. Surrounding soft tissues and muscles were dissected carefully while preserving facet capsules and midline
Flexion-Extension Mode
For flexion-extension, normal ROM values were 11.8 ± 1.4 (mean ± SE) for the intact C5-C6 levels and 22.7 ± 1.5 for the intact C5-C7 levels (Figure 4). In the 1-level C5-C6 experiment, ROM values were 2.5 ± 0.3 for nonrod TFS fixations and 2.9 ± 0.6 for LMSR fixations. There were no significant differences in ROM between nonrod TFS and LMSR fixation groups in 1-level instrumentation (P = 0.40). In the 2-level experiments at C5-C7, ROM values were 6.1 ± 0.5 for nonrod TFS fixations and 3.1 ± 0.4
Discussion
Cervical pedicle screws and rods fix the spine posteriorly after decompressive surgery, yet they require demanding placement procedures that can produce complications such as vascular and nerve root and cord injuries. Although lateral mass screws are relatively safe and easy to insert, surgeons also inevitably need to dissect the posterior cervical musculature to create sufficient room for screw purchase.
TFS fixation was introduced in 1987 by Magerl and Seeman (16) for atlantoaxial fixation. A
Conclusions
We studied the biomechanical stability of nonrod TFS fixation versus LMSR fixation. Both fixation methods produced a biomechanically stable ROM of the cervical spine comparable to an intact spine. Nonrod TFS fixation can be applied percutaneously and is a feasible alternative in cases with altered anatomy.
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Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.