Study Design: In vitro biomechanical study of flexibility with finite element simulation to estimate screw stresses.
Objective: To compare cervical spinal stability after a standard plated three-level corpectomy with stability after a plated three-level "skip" corpectomy where the middle vertebra is left intact (i.e., two one-level corpectomies), and to quantify pullout forces acting on the screws during various loading modes.
Summary of Background Data: Clinically, three-level cervical plated corpectomy has a high rate of failure, partially because only four contact points affix the plate to the upper and lower intact vertebrae. Leaving the intermediate vertebral body intact for additional fixation points may overcome this problem while still allowing dural sac decompression.
Methods: Quasistatic nonconstraining torque (maximum 1 Nm) induced flexion, extension, lateral bending, and axial rotation while angular motion was recorded stereophotogrammetrically. Specimens were tested intact and after corpectomy with standard plated and strut-grafted three-level corpectomy (7 specimens) or 'skip' corpectomy (7 specimens). Screw stresses were quantified using a validated finite element model of C3-C7 mimicking experimentally tested groups. Skip corpectomy with C5 screws omitted was also simulated.
Results: Plated skip corpectomy tended to be more stable than plated standard corpectomy, but the difference was not significant. Compared to standard plated corpectomy, plated skip corpectomy reduced peak screw pull-out force during axial rotation (mode of loading of highest peak force) by 15% (4-screw attachment) and 19% (6-screw attachment).
Conclusions: Skip corpectomy is a good alternative to standard three-level corpectomy to improve stability, especially during lateral bending. Under pure moment loading, the screws of a cervical multilevel plate experience the highest pullout forces during axial rotation. Thus, limiting this movement in patients undergoing plated multilevel corpectomy may be reasonable, especially until solid fusion is achieved.
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