An Experimental Study Of Pedicle Screw Fixation System On The Spine Growth

Background: Pedicle screw fixation was first used in the treatment of fractures in 1970. Today, pedicle screw instrumentation is in widespread use in the treatment of various spinal disorders,trauma,tumor, and obtain the excellent results.Spinal deformity is a very severe disease, and it really does great harm to the health. Surgical treatment is the main method of correcting spinal deformity, but while getting great advancements in correcting, they have been deprived of partial functions. Furthermore, transpedicular instrumentation affected the further growth of the vertebra for the immature spine.Objective: To observe the process of further spinal growth after implanting the pedicle screw fixation system and morphological changes of vertebrae and intervertebral discs in the fixed segments.Methods: 1.Six fresh specimens of the vertebrae(L1～L3) in pigs(age 4～6 months) were used to detect the anatomy characteristic of each vertebrae, including the transverse diameter of pedicle, sagittal pedicle angle, distance between two pedicles, the distance from the posterior cortex of pedicle to the anterior cortex of the vertebral body. According to these measurements, the transpedicular instrumentation were designed: 3.5 mm in outer diameter and 22 mm in length of the pedicle screw, 40 mm in length,9mm in width and 3 mm in thickness of the plate. 2. A total of 23 normal pigs(9 males, 14 females, age 6 weeks, weight 8.5±1.7kg, body length 51±4cm) were randomly assigned into 4 groups: group A( 3 pigs), blank control group, not performing operation; group B( 3 pigs), control group, only exposing posterior lamellar of L1～L3; group C( 5 pigs), control group, penetrating through neurocentral cartilage(NCC) structure and leaving the pedicle screws in two sides of the pedicle and vertebral body of L1～L3; group D(12 pigs), test group, implanting pedicle screw fixation system in two sides of L1～L3 The objective vertebras were L1～L3. X-ray and Spiral Computerized tomography(SCT) was used to measure the morphology of the vertebras in serial three months: the transverse dimension,sagittal dimension,area of the spinal canal and the sagittal dimension,transverse dimension,height of vertebra body. 3. Gross anatomy and histology study: All pigs were sacrificed after three months. The gross changes of spine in fixed segments were observed and the histological changes of vertebral bodies and discs in fixed segments were observed after HE staining.Results: 1. Among the 23 pigs, 2 pigs died for overdose of anesthesia in group D, 2 pigs had infection of incisional wound in group C, 1 pig died and 1 pig healed. Weight was 40.4±8.0kg, and body length was 89±7cm . Three months after operation, Of all implants, there were no loosening,breaking,drawing during three months after operation observed with X-ray and SCT. The symptom of spinal cord and nerve root (claudication,amyotrophy,neurogenic ulcer) didn't happened. 2. Three months after operation, in test group, the height of vertebra body and the length of L1～L3 were significantly smaller than that in the control groups (P<0.05), and the transverse dimension,sagittal dimension,area of the spinal canal and the sagittal dimension,transverse dimension of vertebra body were no remarkable differences than the control groups (P>0.05), while there were no remarkable differences between the control groups (P>0.05). In group D, height of vertebra body of L2 was significantly smaller than height of vertebra body of L1 and L3 (P<0.05), and wedge vertebrae appeared on L2. Of the 20 pigs, no one developed scoliosis, and in group D, seven developed lordosis,two decrease in kyphosis and one increase in kyphosis.3. Gross anatomy and histology study: Wedge vertebrae appeared on L2 in test group. Histologic sections of vertebrae revealed that the height of epiphyseal and discs in fixed segments in test group were lower than that in control groups. Abnormal morphology and disarrangement of epiphyseal cartilage cells were observed.Conclusions: Pedicle screw fixation system has significant effect on the growth of vertebra bodies and discs and lead to significant reduction in height of vertebra body and intervertebral space, while it has no significant effect on the growth of spinal canal and does not lead to significant iatrogenic spinal stenosis and noticeable lesion of spinal cord and nerve root.