In vitro biomechanical study of flexibility with finite-element simulation to estimate screw stresses.
To compare cervical spinal stability after a standard plated 3-level corpectomy with stability after a plated 3-level “skip” corpectomy where the middle vertebra is left intact (ie, two 1-level corpectomies), and to quantify pullout forces acting on the screws during various loading modes.
Clinically, 3-level cervical plated corpectomy has a high rate of failure, partially because only 4 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.
Quasistatic nonconstraining torque (maximum 1 N m) 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 3-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.
Plated skip corpectomy tended to be more stable than plated standard corpectomy, but the difference was not significant. Compared with standard plated corpectomy, plated skip corpectomy reduced peak screw pullout force during axial rotation (mode of loading of highest peak force) by 15% (4-screw attachment) and 19% (6-screw attachment).
Skip corpectomy is a good alternative to standard 3-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.
*Department of Neurosurgery, Lütfi Kirdar Kartal Teaching and Research Hospital, Istanbul
†Department of Neurosurgery, Medical Faculty, Kahramanmaraş Sütcü Imam University, Kahramanmaras, Turkey
‡Spinal Biomechanics Laboratory, Department of Neurosurgery Research
§Division of Neurological Surgery, St. Joseph’s Hospital and Medical Center, Barrow Neurological Institute, Phoenix, AZ
Supported by the National Institutes of Health, Grant 1R01EB006135.
V.K.H.S. receives royalities from Medtronic; N.R.C. has acted as a consultant for Lanx Inc. and owns stock in Spartek. The remaining authors declare no conflict of interest.
Reprints: Neil R. Crawford, PhD, c/o Neuroscience Publications, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, 350 W. Thomas Rd., Phoenix, AZ 85013 (e-mail: firstname.lastname@example.org).
Received January 12, 2012
Accepted March 27, 2012