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The Development of the Aliform Memory Alloy Intrasegmental Fixation Instrument for Lumbar Spondylolysis

Author: ZhangXiBing
Tutor: ZhuLiXin
School: Southern Medical University,
Course: Orthopedics
Keywords: Lumbar spondylolysis Applied anatomy Memory alloy Intrasegmental fixation Biomechanics
CLC: R687.3
Type: Master's thesis
Year: 2012
Downloads: 19
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Abstract


Lumbar spondylolysis is the fatigue fracture of the isthmus between superior and inferior articular process,when the lumbar vertebrae is doing the hyperextension, flexion and rotation movements.,and the essence of lumbar spondylolysis is the forming of pseudarthrosis. The disease which was discovered by Lambel in1865is a common disease of orthopedics and it is a common reason of low back pain. Most experts believe that the lumbar spondylolysis can be controlled with non-surgical treatments, and only small part of patients with persistent pain or spondylolisthesis trend need operation. At early stage, Kimura treated lumbar spondylolysis with bone graft and plaster external fixation and the effect was not satisfied with postoperative pseudarthrosis rate of18%-81%, moreover, patients needed to be on bed rest with plaster external fixation for months. Some experts tried bone graft with cross-section of internal fixation, and found that it would produce stress shielding of the fixed area and significantly increased the stress of the adjacent segments. Thus, all of this accelerate intervertebral disc degeneration of the fixed area and the adjacent segments.Now, most experts adopt intrasegmental fixation and create many intrasegmental fixation methods including Buck’s technique of screw fixation, Nicol’s technique of intrasegmental wire fixation, Hefti’s technique of hook-screw fixation and A variety of improved methods. Buck used a screw to transfix the isthmus to restore the continuity of the isthmus while grafted bone in the gap, and this was the first time to adopt intrasegmental fixation in spine operation. Because Buck’s screw can provid vertical pressure on the fracture which was comply with the biomechanical requirements of the isthmus, it can promote fracture healing. But the screw went through the isthmus directly, it significantly reduced the amount of graft bone and affect bone healing. In addition, screws are sometimes unable or perforation of the lamina into the spinal canal, resulting in the injury of the cauda equina or nerve root, and screw loosening and fatigue fracture maybe occur from time to time because of rigid fixation. Nicol used steel wires to fix the transverse process and spinous process together for the treatment of lumbar spondylolysis. This method commonly used the18th stainless steel wire wrapped around the root segment of transverse process, through the edge of the spinous process of the same segment, tied to the root segment of transverse process at the other side, so the vertebral body and lamina can be together as a whole. However, Nicol method needed to be exposed to the transverse process, to wear around the wire, and the operation was complicated and risk of injury nerve root. In addition, the transverse processes of L5are different from other lumbar segments, sometimes they are near to the ilium and the narrow gap under the transverse processes made it difficult to wear around the wire. Moreover, the exposure of the L5transverse process needs to cut off the iliolumbar ligament which has an important role in maintain lumbosacral stability. Hefti used a screw and a hook to connect the bottom of superior facet with the lower edge of lamina. The clinical efficacy of the surgical reported were discrepancy, and the method required a certain equipment and technology. If improper operated, this method could easily lead to serious complications. From1998, we began to design memory alloy intrasegmental fixation instrument for lumbar spondylolysis and invented two side semiring memory alloy intrasegmental fixation instrument. The instrument with the powerful restoring force of the memory alloy can restore the continuity of the isthmus and can also generate dynamic pressure on the graft bone to promote bone healing of the isthmic. But there are some disadvantages with the instrument:(1) The indications are narrow and it can not be used when the lamina requires to be removed because there is no place for hook.(2) Because of the circle blunt-shaped root segment of transverse process and the independent instrument of the bilateral segment, there is no horizontal compression, which makes it easy to slide to the transverse process lateral and pull off the transverse process.(3) The instrument can not prevent the adjacent intervertebral disc degeneration.In order to overcome the above disadvantages, and to promote the application of shape memory alloy intrasegmental fixation instrument, we developed a aliform memory alloy intrasegmental fixation instrument (AMAIFI), which closely integrate the isthmus anatomical features and made full use of the material advantage of the shape memory alloy. Then, we conducted a biomechanical test to provide a theoretical basis for clinical applications of the aliform memory alloy intrasegmental fixation instrument.Objective1. To explore anatomic features of L1~5,S1vertebraes, and provide parameters for the development of the aliform memory alloy intrasegmental fixation instrument2.To develop a intrasegmental fixation instrument for lumbar spondylolysis basing on anatomical measurements and a series of advantages of shape memory alloy, which is in line with the morphological features of lumbar spine, easy to operate in clinical application and can provide reliable fixation.3.To evaluate the effect of the aliform memory alloy intrasegmental fixation instrument in rebuilding the lumbar stability through comparing three-dimensional motional stability of different groupsMethods1.20sets of antisepsis lumbar specimens (L1~5, S1) of Chinese normal adults were provided by Institute of Clinical Anatomy of Southern Medical University, with the name and sex unknown. Domestic electronic vernier caliper (accuracy0.01mm), protractor (accuracy1°), compasses, soft copper and pins were used to measure the relevant parameters of the L1~5,S1. The parameters basing on which AMAIFI were designed were analyzed by spss13.02. Based on morphological parameters measured aboved and advantages and disadvantages of traditional fixation instruments, we redesigned the intrasegmental fixation instrument and determined the structure and specifications of AMAIFI. The fixer samples produced by a company were then fixed in specimens to evaluate its feasibility.3.6fresh lumbar spine specimen (L2~L6) were seleeted from6pig cadavers (4-5months old). As self-control experiment, the specimens were divided into intact group, lumbar spondylolysis group, Buck’s screw group, Nicol’s wire fixation group and AMAIFI group to test the three-dimensional stability. The top of the embedded specimens were conneeted with three-dimensional spine loading disc drive and the base of the embedded specimens were fixed lower working platform in the testing machine. The movement was applied with±8Nm loads in flexion/extension, left/right lateral bending, and left/right axial rotation on the three-dimension motion stability test. The zero load and maximum load state images of spinal movement were pictured by six infrared cameras placed around lumbar specimen. The angular variations between the spinal segments were calculated by computer image processing system to analyze the range of motion between L4/L5. The results obtained above analyzed by spssl3.0to compare the stability of lumbar spine among intact group, lumbar spondylolysis group, Buck’s screw group, Nicol’s wire fixation group and AMAIFI group.Results1. As L4/L5for example:DITR (the distance from the intersection of the lateral margin of the lowersurface of the lumbar spinous process and lamina of vertebra to the superior border of the root segment of transverse process) was about (35.30±2.38) mm, AFR (the angle between the front and rear side sitting at the superior border of the root segment of transverse process)(30.47±6.38)°, WRT (the width of the root segment of transverse process)(11.43±1.76)mm, DTAP (the distance from one side of the junction of the transverse process, superior articular process and pedicle of vertebral arch to the other)(46.44±2.55)mm5,TSP (the thickness of the spinous process)(9.04±1.12)mm, DAP (the distance between adjacent spinous process)(7.10±1.83)mm, ATL (the angle between two lines(one is the line between the intersection of the lateral margin of the lowersurface of the lumbar spinous process and lamina of vertebra and the junction of the transverse process,superior articular process and pedicle of vertebral arch,the other is the lateral margin of the lowersurface of the spinous process))(58.31±7.02)°, and LSP (the length of the spinous process)(20.40±2.80)mm respectively. AMAIFI is composed of a "U" shaped body and two lateral wings including large, medium and small types.2. AMAIFI is composed of a "U" shaped body and two semi-circular lateral wings. The "U" shaped body includes a C-shaped top and two level "arms" called U-shaped wings, and two fixed slots were placed on the U-shaped wings away from the C-shaped top which are used to fix the "U" shaped body at two adjacent spinous processes. Two semi-circular lateral wings extend from the junction of C-shaped top and U-shaped wing, and there are two hooks at the end of the semi-circular lateral wings which are used to hook the root segment of transverse process. AMAIFI is made of NiTi by ximai memory alloy company, and the content of nickel is50.8%to51.8%. The morphology restoring temperature is (36±4)℃, which is consistent with the body temperature. The AMAIFI samples produced by ximai memory alloy company were then fixed in specimens easily when simulated surgical procedure and they can provid enough holding force.3. The ROM of lumbar vertebrae in flexion/extension and left/right axial rotation was significantly increased after bilateral isthmus fracture and the difference compared with normal lumbar vertebrae was significant(P<0.05). After fixed with Buck’s screw, Nicol’s wire and AMAIFI, the ROM of lumbar vertebrae recovered in flexion/extension and left/right axial rotation, and the difference compared with normal lumbar vertebrae was not significant (P>0.05). In addition, the difference among Buck’s screw group, Nicol’s wire fixation group and AMAIFI group was not significant either (P>0.05). The ROM of lumbar vertebrae in left/right lateral bending was increased after bilateral isthmus fracture, but the difference compared with normal lumbar vertebrae was not significant (P>0.05). After fixed with Buck’s screw, Nicol’s wire and AMAIFI, the ROM of lumbar vertebrae in flexion/extension and left/right axial rotation was almost the same compared with intact lumbar vertebrae, and the difference among Buck’s screw group, Nicol’s wire fixation group and AMAIFI group was not significant (P>0.05).Conclusions1.The aliform memory alloy intrasegmental fixation instrument is morphological feasible which is confirmed by the parameters provided by exploring anatomic features of L1~5,S1vertebraes.2. The design of AMAIFI is feasible anatomically, and every part of the fixation instrument has different sizes. AMAIFI can provid enough holding force and it is easy to operate.3. The stability of lumbar vertebrae is significantly reduced especially in flexion/extension and left/right axial rotation after bilateral isthmus fracture; The stability of lumbar vertebrae provided by AMAIFI has no significant difference compared with that provided by Buck’s screw and Nicol’s wire,and AMAIFI can restore the stability of lumbar vertebrae which is bilateral spondylolysis.

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CLC: > Medicine, health > Surgery > Orthopaedic Surgery ( movement system diseases,orthopedic surgery ) > Orthopedic surgery and surgery > Bone surgery
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