The Impact of Cervical Pedicle Screws for Primary Stability in Multilevel Posterior Cervical Stabilizations

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Abstract
Study Design. A total of 12 human cervical spines were tested in vitro in a biomechanical nondestructive set-up to compare the primary stability of different posterior cervical instrumentations after a bilevel corpectomy. Objective. To evaluate the primary 3-dimensional stability with special focus on the impact of cervical pedicle screws. Summary of Background Data. Cervical pedicle screw fixation gains popularity due to supposed higher stability. However, biomechanical studies are rare. Especially the impact of a combination of lateral mass and pedicle screws on stability in multilevel posterior stabilizations has not been evaluated until now. Methods. A total of 12 human cervical specimens were loaded with pure moments and unconstrained motion between C4 and C7 was measured. The specimen were tested in the intact state, all lateral mass screws (all LMS) from C4–C7, cervical pedicle screws (CPS) C4 and C7 left, LMS C4–C7 right, C5+C6 left, CPS C4+C7 bilateral, LMS C5+C6, and a anterior–posterior instrumentation (360°). Results. All instrumentations showed a higher stability compared with the intact state. No difference was found for uni- or bilateral applied CPS. The all LMS showed comparable stability than the CPS instrumentations. Conclusion. From a biomechanical primary stability point it seems unnecessary to add CPS in a bilevel corpectomy model. If CPS are added, the unilateral application seems sufficient.