The effect of pedicle screw insertion through the neurocentral cartilage on the growth of immature canine vertebra

Abstract

To explore the influence of pedicle screw insertion through the neurocentral cartilage (NCC) on the development of vertebrae and spinal canal in an animal experiment. Sixteen dogs were randomly assigned to three groups: in group 1, posterior muscles at the surgery site were dissected; in group 2, the pedicles were drilled through the NCC by screws; in group 3, screws were placed in the pedicles through the NCC. Vertebrae of T8, T10, T12, L2, L4 and L6 were studied with the average data of the adjacent two vertebrae serving as controls. Spiral computerized tomography (CT) was used to assess the morphologic parameters of studied vertebrae and their controls. Measurements were made by an independent radiologist on the first post-operative day and 3 months after operation. Paired Student's t-tests of studied vertebrae and their controls were performed to evaluate the effect of pedicle screw insertion. In group 3, 3 months after operation the area, transverse diameter and anterior-posterior diameter of the vertebral canal and length of pedicle of studied vertebrae were significantly smaller than those of control vertebrae (P < 0.05). There were no significant differences in morphologic parameters between the studied vertebrae and the control vertebrae in groups 1 and 2 (P > 0.05). (i) Pedicle screw placement has a significant impact on the growth of the canine vertebra canal, and may lead to iatrogenic spinal stenosis, but their placement has no significant effect on the vertebral bodies; and (ii) the NCC can repair itself automatically. Drilling pedicle bone through the NCC with a screw and then removing the screw has no obvious impact on the growth of vertebrae.