Anterior Locking Plate Fixation Of Cervical Spine:an Anatomic And Biomechanical Study

Anterior Locking Plate Fixation of Cervical Spine: an Anatomic and Biomechanical Study Abstract Objectives: (1) To measure curvature of human middle and lower cervical spine and determine optimal curve of anterior cervical plate instrumentation. (2) To evaluate the biomechanical stability of a cervical spine butterfly plate (CSBP) for unstable cervical spine in a human cadaveric model. Methods: (1)A. Height, width and depth of human vertebral body were measured on 129 dry Chinese adult cervical vertebrae (C2-.-C 7). B. Lordotic curvature of cervical spine was measured on radiograph in lateral view on 43 normal Chinese adults. (2)A. 14 cervical spine specimens (C3-~-T1), obtained from fresh human cadavers, were divided randomly into two groups, A and B. A flexibility test was conducted on the intact specimens under a maximum 2.ONm moment in flexion-extension, lateral bending and axial rotation using a custom spinal testing machine. For the each specimen, a wedge bone defect was produced in the C5 body, then a compressive load was applied until the wedge defect was closed on MTS material testing machine. The same flexibility test was conducted again on the specimens with a fixation at C4 and C6 using either a new anterior plate (CSBP, Stable Impfant Co. Ltd~ Foshan, China) in the group A or a Orion plate (Sofamor, TN, USA) in the group B. B. A fatigue test was carried on two CSBPs in according to ASTM standard of anterior plates of cervical spine. A cyclic compressive load ranged from 1 ON to 1 OON was applied at 1Hz until failure of the plate occurred. Number of loading cycle at the failure was recorded and failure of the plate was observed. C. A finite element model of CSBP was set up to analyze stress distribution on the plate using ANSYS software. Results: (1)A. The body height and the depth varied little from C3 to C6, and were approximately 10.0mm and 14.6mm respectively. However, the transverse curvature along anterior vertebral body increased evenly from 棗III棗 9.6mm at C3 to 14.6mm at C7, and body width from 19.2mm at C3 to 23.0mm at C6. B. There was a large variation in cervical Lordotic curvature on lateral view of X-ray. (2)A. The ranges of motion following fixation with CSBP and Orion were significantly less than those of control (P<0.05) in flexion, extension, lateral bending and axial rotation, respectively. However, there was no significant different difference of ranges of motion between CSBP and Orion fixation. B. CSBPs were ruptured at lateral rim around screw hole under cyclic loading up to 540,000?50,000 cycles. Finite element model indicated that there was a stress concentration at lateral rim around screw hole on CSBP. Conclusions: (1)A. Transverse curvature of anterior vertebral body of cervical spine decreases caudally. B. Lordotic curvature of cervical spine is difficult to be determined on a lateral radiograph. (2)A. Both CSBP and Orion plate augment spinal stability for unstable cervical spine. B. Lateral rim of screw hole on CSBP is a weak area.