Animal Experimental Study In Swine For Spinal Growth Modulation With Unilateral Elastic Fixation

Background:Idiopathic scoliosis is one of the most common deformities of the musculoskeletal system in adolescent. The incidence ranges from1-3%. Surgical management is usually recommended once patient's curve greater than40°-50°. At present, the classic surgical procedure for scoliosis is spinal fusion, which has got good effects on the deformity correction and patients'cosmetic improvement. However, it also brought many negative effects to the patients. For example, spinal fusion will limit the motion of the spine, restrict patient's height growth, limit the thoracic development and affect the function of heart and lung. Nonfusion surgery for the treatment of scoliosis has been the goal pursued by many spine surgeons. Though some of the nonfusion techniques we used have certain effects on patients with early-onset scoliosis and thoracic insufficient scoliosis, such as growing rod and VEPTR. But it requires repeated surgery to extend the rods as the spine grows. Patients have to undergo many times of operations and finally need spinal fusion with internal fixation to maintain the correction effects. The number of surgery and the high incidence of complications will greatly increase the suffering and economic burden of patients. Now, a better nonfusion technique is needed for the treatment of scoliosis, which can not only limit the progression of the spinal deformity, but also won't affect the growth and development of the spine, while avoiding multiple surgical complications and final spinal fusion.Objectives:To observe the spinal growth modulation with the unilateral elastic tether, and compare the impact of unilateral elastic fixation on the range of spine motion, vertebral epiphysis and intervertebral disc from aspects of general anatomy, histology and molecular biology. To demonstrate the efficacy and safety of unilateral elastic fixation on the spinal growth as well as the maintenance of the motion of the spine.Methods:15Tibet immature pigs,3-month-old, were randomly divided into three groups:elastic fixation group, metal rod fixation group and control group. There were5pigs in each group. All the pigs were taken radiographs before the experiment, including posteroanterior and lateral views. Operations were taken on the pigs from the three groups. In the elastic fixation group, the left side of lumbar vertebras from L1to L5were fixed with pedicle screws and connected with a unilateral polyester tether with tension so as to produce a curve on the lumbar spine. The same manipulation was done on the metal rod fixation group. However, the pedicle screws were connected with metal rods. In the control group, the postorier spinal structures of the left side were just exposed from L1to L5, with no instrumentations implanted. Radiographs were taken immediately after the surgery. All pigs in the three groups were breed for8weeks under conventional condition. The radiographs were taken and the spines were harvest after8weeks. The angles of the curves were measured with Cobb method, the ranges of spine motion were observed and the vertebral epiphysis and intervertebral disc were evaluated from aspects of general anatomy, histology and molecular biology.Results:The scoliosis and lordosis in the coronal and sagittal planes were observed both in experimental and control groups after8weeks. Radiographs demonstrated that scoliosis were formed with Cobb angles of12.16°±1.37°and9.10±2.02°P=0.023) in the two groups, also with Cobb angles of17.44°±11.29°and5.32°±3.06°(P=0.049) in lordosis. The vertebras and discs were wedging to the tether side. However, there was no significant difference between the two groups(P>0.05). The motion of the spine was maintained at certain degree in the experimental group. When the elastic tether was removed, the motion increased greatly, especial on the lateral bending. But the elastic tether also increased the spinal stiffness. The thickness of proximal and distal epiphysis were decreased both in the experimental and control groups, but greater decrease in the former (P=0.032and P=0.024). The thickness of discs didn't decrease significantly. There were no gross morphologic differences present between discs evaluated from both experimental and control groups. They were all given a Thompson Grade I. Real time PCR showed that types Ⅰ and Ⅱ collagens decreased and MMP-3increased in both groups. Also, the proteoglycan decreased in the two groups.Conclusions:Unilateral asymmetric elastic tether can modulate spinal growth and result in scoliosis. The elastic fixation can maintain the motion of the spine when modulating its growth. But it also increased the spinal stiffness to some extent. There was no degeneration observed on the discs after the elastic tether fixation in the experimental group. Compared to the rigid fixation, the elastic fixation showed a greater spinal growth modulation and made a larger scoliosis.