| Part I , Experimental Study on technique of translaminar facet joint screws25 lumbar spine speciments of cadava were used to measure path length of translaminar facet joint screw(abbreviated TLS), caudal and lateral angles for TLS, superior and inferior laminar thickness, and lamimar height. The results: the path length and candal angle for TLS increased gradually from T12L1 to L5S1 level ( 30mm to 48mm, 38# to 57#, respectively), the lateral angle relative to the coronal plane was 28 -30?, the superior laminar thickness 2.1mm ~ 3.3mm while the inferior laminor thickness 5.4mm ~ 6.5mm, and 14mm ~ 19mm for the laminar height. According to the measured result, we recommend screw of 3.5~4.5mm in diameter and 35~45mm in length for the TLS. Secondly, 18 lumbar spine speciments were used to place TLS, on the left of speciment a designed aim-sighting device used for drilling while on the right drilling by naked eyes. The drilling point located at the crossing of laminar and spinous process, into the counter lateral laminar, across the facet joint, and into the base of the transverse process, screw of 4mm used for placement. The results: the penetration rate of laminar was a little higher on the right than on the left (41.67% ,37.01% , respectively) but no significant difference between the two methods (P>0.05), the penetration amounts was small (within 2mm) on both sides except in L5S1 level. This indicated that both methods were relatively safe and feasible for placement of TLS. Thirdly, a biomechnical stability of lumar spine was carried out in speciment of spine to investigate values of TLS in augment of fusion in degenerative lumbar spine and in supplement ofpedicle screw in thoracolumbar fracture. Each functional unit of spine was tested on the intact, the injury and the fixed groups in succession. Test included compression in flexion, extention and lateral bending, as well as axial rotation, displacement of angle were recorded. The result: Under the torque of 10 Nm compression or 10.8 Nm rotation in the test, the ROM(range of motion ) of the intact speciment fixed with TLS on one side decreased 3.53%~ 10.79% in compression, and 7.75% in rotation. The ROM of speciment fixed with TLS on both sides decresed 4.71%~15.59% in compression, and 20.19% in rotation . The ROM in the group of total disc excion and TLS fixation decresed 6.76%~ 16.98% in compression,and 17.22% in rotation in comparison with the group of total disc excion. When anterior grafting or cage placed alone, the stability of speciment didn't restore to normal level in axial rotation while augmented with Steffee or TLS the stability of speciment restored to normal in all directions. The ROM in the group of PLIF and TLS fixation was smaller than the group of PLIF and Steffee fixation. The ROM in the group of PLIF with TLS and Steffee fixations decresed 3.58%~8.38% in compression and 16.87% in rotation in comparison with the group of PLIF and Steffee fixation. In fracture models of spine , the ROMs of the three pedicle screw fixators from large to small were Roy-cmille, SHSU and RF respectively ; the ROM in the group of SHSU fixation supplementted with TLS decresed 2.15%~3.03% in compression and 13.56% in rotation in comparison with the group of SHSU fixation. This demonstrated that ,as the anterior and middle columns not destabilized (such as degerative lumbar spine), the stabilizing effects of TLS were better in flexion,extension,lateral bending and rotation; As the anterior and middle columns destabilized , its stabilizing effects were less than pedicle screw in flexion, extension and lateral bending. Pedicle screwsupplemented with TLS in thoracolumbar fracture might increase its stability in all directions, especially in rotation . |
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