Experiment Study Of Anterior Enlargement Of Cervical Spine Canal And The Clinical Application

Objective:To determinate the feasibility of a new designed anterior enlargement of the cervical spine canal through vertebral body and evaluate the mechamical stability of cervical model with autogenous bone graft and the construction combined with AO cervical spine locking plate and provide a new method for the treatment of the cervical spinal injury and cervical spondylosis. Methods:1) Specimen experiment: Four corps cervical spine, excluding the pathological changes on the radiographs, were used in the experimental study. The anterior surrounding soft tissues were detached and the posterior soft tissues and the intrinsic ligaments were left intact. The vertebral foramina were dissected and a 4mm in diameter latex pipe was inserted as the vertebral artery. The contrast agent was injected into the vertebral artery through the pipe. The C3 to C6 vertebral bodies were split longitudinally along the midline to the posterior longitudinal ligament, and then the gap was separated to 3, 6, 9 and 12 mm in turn and the anterior-posterior, transverse diameter, section area of the canal, the distance between the vertebral arteries and the change of neuroformen were observed on the CT scan respectively.2) Animal experiment: Two adult sheep were used for animal experimental study. The C2 to C4 vertebra were split longitudinally through anterior approach and enlarged the gap to 9 mm under general anesthesia, and then the bone harvested from ipsilateral proximal tibia was grafted in place. The motion of the extremities was observed. Four fresh cervical spine specimens(C3- C7) of young cadaver were used in the biomechanical test. After C4- C6 were given vertebrectomy, ilium autograft and ilium autograft with anterior plate fixation were performed. Their stabilities of flexion, bilateral axial rotation, the lateral bending and the extension were tested. Intact cervical spine specimens served as control group. Four patients with cervical spondylosis myelopathy and eight patients with traumatic cervical fracture were treated by cervical anterior decompression, interbody fusion,and plating was analyzed retrospectively. The outcomes were assessed by clinical criteria and radiographs of the cervical spine. Results:When the gaps were separated to 3, 6, 9mm. the anterior-posterior diameter of the canal were increased by 1.14%, 3.53 %and 5.15%, the transverse diameter increased by 7.92%, 14.62% and22.74%. The section area increased by 8.52%, 17.99% and 25.10% respectively (p<0.05). The vertebral arteries run parallel without distortion and there was no fracture found when the enlargement less than 9 mm. The fracture with minimal displacement were found in the left junction of the lamina and spinous process in 3 of 4 specimens when the gap was enlarged to 12 mm. Animal experiment demonstrated that the animal could move the extremities freely the day after the operation. Ilium autograft improved the stability of the unstable cervical vertebrae and decreased the flexion, the lateral bending or the extension showing a significant difference when compared with control group(P < 0. 05). Whereas, axial rotational motion was decreased insignificantly(P> 0. 05). Ilium autograft with anterior plate fixation improved the stability of the unstable spine and decreased the flexion, the bilateral axial rotation, the lateral bending or the extension, showing a significant difference when compared with control group(P< 0. 05). Twelve patients were followed up for twelve months in average. The rate of excellent and good results was 83 %, The overall fusion rate was83 %. Conclusion:The section area can be increased significantly without damage to spinal cord and surrounding tissues when the vertebral body was separated< 9 mm. Therefore. The anterior enlargement of the canal is safe and feasibility.: Compared with the normal condition, the stability of cervical model under ilium autograft condition are improved significantly during flexion, left / right bending , left / right axial rotation, but is reduced during extension with the combination of AO cervical spine locking plate, the stability of cervical model in all motional direction were improved obviously, and can meet the demand of clinical application. The vertebrectomy and anterior cervical fusion by ilium autograft was the least stable construct of all modes tested, and the ilium autograft implantation is more stable than the intact cervical sample. This study demonstrated that plate fixation can reduce the rate of nonunion and increase the rate of fusion in patients undergoing interbody fusion for cervical spondylosis. The clinical results appear promising.