| Objective1. To investigate anterior corrective fusion level of adolescent idiopathic scoliosis (AIS) type Lenkel and analysis the relationship between fusion level conservation and trunk balance.2. To discuss the efficacy and fusion strategy of all pedicle screws applied in surgical treatment for adolescent idiopathic scoliosis. To compare with hook-screw system, we evaluate the safety and advantages of all pedicle screw technique in correction of AIS and it's meaning to restore LIV.3. To construct the scoliosis biomechanical model by finite element method and analysis the stress change of the model under all kinds of force suffered.Methods1. Twenty-eight patients of thoracolumbar/lumbar(TL/L) adolescent idiopathic scoliosis (AIS) were retrospectively studied who received anterior correction and followed up at least one year. We applied unified statistics standard and recorded preoperative and postoperative radiographic parameters such as lowest instrumented vertebra(LIV) and distal disc wedging.2. We compared 26 AIS type Lenke 1 patients who received all pedicle screw correction with 54 AIS patients who underwent correction by pedicle hooks, laminar hooks combined with lumbar pedicle screws . The efficacy of all pedicle screw with corrective rate of major curve, spontaneous corrective rate of compensate curve and loss of correction were evaluated. By compared with the LIV of 15 patients in each group with the similar Cobb angle and the same typealong with inappropriate fusion, we analyzed the fusion strategy of thoracic scoliosis applied with all pedicle screw.3. We constructed biomechanical model of mild AIS by application of 3-dimension CT scan combined with reconstruction of radiography and finite element method. We analyzed force parameter like shift, distribution of low end vertebra disc after simulating the stress force of spine under the condition of upright standing , side-bending and rotation.Results1. In the thoracolumbar/lumbar adolescent idiopathic scoliosis patients who recieved anterior correction , the preoperative disc angle was 2.96°± 1.43° and postoperative -3.60°± 1.75°. The change of the disc angle was significantly correlated to the relation of LIV level and LEV. Regressive analysis demonstrated the correlative parameters to the postoperative disc angle to be: preoperative upright disc angle, T12-L2 lordosis, T4-T12 kyphosis, L1-L5 lordosis, Apex-CSVL, Apex-LIV vertebras, LIV tilt. The most significant correlated parameter was preoperative DA. If the disc was close to parallel and LIV was chosen as the proximal vertebra to the LEV, bigger disc wedging occurred in the last follow-up. The correlative parameters to postoperative trunk balance were preoperative LIV translation, fusion levels, preoperative DA, Apex—LIV, LIV tilt, L1 — L5 lordosis, T4-T12 kyphosis and T1—CSVL.2. In the all pedicle screw group of posterior correction of thoracic adolescent idiopathic scoliosis, the corrective rate of major curve was 74.26%, spontaneous corrective rate of lumbar compensated curve was 75.70% , corrective rate of trunk shift was 73.76% and loss of correction was 1.92°, which was better than control group 66.19%, 60.60%, 70.95% and 3.38° respectively. There was no statistically difference between the two groups on the restoration of saggital plane. In the 15 patients whose curve type and curve magnitude were coincidental, there were 11 patients saved 12 segments compared with control group, 4 cases' fusion levelswere identical. Average saving levels were 0.8 segments. When NV was the same to EV or one segment distal to it(8 cases), fused to NV or NV-1(5 cases) acquired satisfactory results.3. We constructed biomechanical model of AIS by applying finite element methods. When simulated vertical load, the relative shift of vertebra increased from thoracic vertebrae to lumbar vertebrae , and reached maximum around LEV. In coronal plane, shift decreased from convexity to concavity around L3. Stress distribution in the L3 plane: stress load of anterior and concave side was less then posterior and convex side significantly. We observed stress concentration at the anteral-lateral side of facet joint in convexity. When simulated rotated load, the conversion stress of disc distribution indicated that surrounding of disc and concave facet beared more stress. When left side-bending load, the relative shift of vertebra decreased from apex to up and down. The distribution of stress in the L3 disc plane demonstrated the different condition to vertical load. Right side of disc, convexity bewared more stress, and there was more stress concentrated in the convex facet. In right side-bending there indicated opposite result, the difference stress between two sides were more the left side-bending.Conclusion1. The possibility of postoperative disc wedging more than 5° increased if LIV distal disc close to parallel preoperative in anterior surgery to AIS. We did not advocate short segments fusion if involved the factors as followed: the disc angle between LEV and upper vertebra is bigger than5°, less segments between LIV and Apex, long distance between LEV and CSVL and more LIV tilt. If fusion didn't contain the parallel disc, the possibility of disc wedging increased.2. Compared with hook-screw correction group, the all pedicle screw group has better coronal correction, spontaneous compensated curve correction and loss of correction. To all types of thoracic scoliosis, fuse to NV or NV-1 could achieve satisfactory spine balance. All pedicle screw technique could efficiently save... |
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