Pedikuloskopisch assistierte transpedikul�re Spongiosaplastik zur interkorporellen Fusion an der lumbalen Wirbels�ule Eine tierexperimentelle Untersuchung am Schafsmodell

Der Unfallchirurg (Impact Factor: 0.65). 07/2002; 105(8):680-687. DOI: 10.1007/s00113-001-0404-1


Objective. Failure of transpedicular bone-grafting in thoracolumbar burst-fractures has been proven. Possible reasons are insufficient disc-removal and difficult decortication of endplates. Methodical improvements are sought to make the procedure succeed in a sheep-model.
Method. 12 sheep with posterior instrumentation L4/L6 and transpedicular disc-removal L4/L5 underwent auto-grafting. Classical surgical technique was modified by bilateral approach and transpedicular endoscopic control. Animals were sacrificed 8 weeks p.op. For evaluation, radiology, histology, histomorphometry, and fluorochrome-analysis were employed.
Results. 10 animals could be evaluated. All revealed sufficient disc-removal and decortication with autograft-impaction into the lower vertebra L4. Main restoration took place before week 4 p.op. Fusion rate was 1/10. For 9/10 animals, defects in the disc-space were filled with metaplastic chondral-tissue; autograft was almost entirely resorbed.
Conclusions. Reason for failure of the method seems to be the insufficient primary stability of the posterior instrumentation, since satisfactory disc-removal and decortication alone cannot successfully modify the method.

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    ABSTRACT: Anteroposterior procedures for lumbar interbody fusion usually combine posterior instrumentation with anterior techniques that achieve primary stability for compressive loading: tricortical strut-graft, anterior plating systems, or cages. In comparison to transpedicular lumbar interbody fusion (TLIF), these methods bear the burden of the additional anterior approach. TLIF with autograft, in contrast, does not prove to be clinically sufficient because of its lack of primary compressive stability. In a sheep model, we therefore developed a TLIF method providing primary stability for axial loading. In 24 sheep, L4-L6 were instrumented posteriorly. An endoscopically assisted L4/L5 TLIF procedure was performed via a bilateral approach. In 12 sheep, the defect was filled with an injectable calcium phosphate cement. After setting, this cement gains a stability against axial loading comparable to healthy vertebrae. Another 12 sheep were treated with autograft. The animals were killed at 8 weeks and evaluated by radiologic (plain X-ray, computed tomography), histologic and histomorphometric analysis, and fluorochrome labeling. Only ten autograft sheep were available for evaluation. Radiologically and histologically, TLIF with calcium phosphate led to a 2/12 fusion rate compared to autograft (1/10 fused) (P=0.70). Semiquantitative radiologic and histologic scoring did not reveal significant differences (P=0.88). In 4/12 calcium phosphate sheep, excessive resorption was responsible for local aseptic inflammation. The findings of this study show that calcium phosphate cement is not superior to autograft, despite enabling primary stability against compressive loading. Biointegration of the osteoconductive cement does not occur fast enough, and shear forces cause early cement fracture, subsequent fragmentation, and gross resorption with the possibility of severe inflammation.
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    ABSTRACT: Porcine and human cervical spine specimens were in vitro biomechanically compared with different instrumentation techniques. To evaluate whether subaxial porcine cervical spines are a valid model for implant testing in a single level corpectomy. Biomechanical in vitro tests are widely used for implant tests, mainly with human spine specimens. The availability of human cadavers is limited and the properties of the specimen regarding age, bone mineral density, and grade of degenerative changes is inhomogeneous. Six porcine and six human cervical specimens were loaded nondestructively with pure moments: 1) in an intact state; 2) after a corpectomy of C5 and substitution by a cage with integrated force sensor; 3) after additional instrumentation with a posterior screw and rod system with: a) lateral mass and b) pedicle screws; 4) after instrumentation with an anterior plate; and 5) with a circumferential instrumentation. The unconstrained motion and the axial loads occurring in the corpectomy gap were measured, as well as the bone mineral density of the specimen before testing. The range of motion in the intact state, as well as for the different instrumentations, was comparable for flexion-extension. In lateral bending and axial rotation, marked differences in the intact state as well as for pedicle screw instrumentations occurred. The subaxial porcine cervical spine is a potential model in flexion-extension because of its biomechanical similarity. For lateral bending and axial rotation, the marked differences severly restrict the comparability.
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