gms | German Medical Science

Objective: Junctional regions of the human spine are usually difficult to judge concerning stabilisation procedures. There is a need for biomechanical knowledge if we have to deal with different types of defects and different types of surgical implants. Thus, the objective of the study was to create a model including an isolated anterior osseous defect within the cervicothoracic junction (CTJ) in which we analyse mechanics and sagittal profile following decompensation of the defect.

Methods: 5 human cervicothoracic junctions were removed from fresh human cadavers. The segments C5-T2 were used, frozen until the experiment was done. Soft tissue was removed; however every discoligamentous structures were preserved. A standard computer assisted tomography (CAT) – to measure bone mineral density (BMD) within C7 and to analyse depth of spinal canal spinal-, as well as a lateral x-ray were performed. A standardized wedge-shaped-defect was created within C7. Specimen was forced in flexion –compression using a material testing machine until failure. Lateral x-ray, CAT. We checked: Correlation of load to failure versus BMD, stiffness before and after failure. Cobb´s angle C6-T1, translation C6-T1, spinal encroachment at C7, each parameter before and after failure. All data are given as mean and standard deviation, significance assumed for p = 0,05. Software package used for digitizing images: Spineview 2.4, Surgiview, Paris, France (program gives distances as pixels).

Results: Mean BMD was 299 mg/cm³, mean load to failure 1363 ± 662 N. There was no significant correlation of load to failure versus BMD. (r = 0,346, p = 0,568). Mean stiffness before failure occurred: 441 ± 237 N/mm, after: 256 ± 218 N/mm (Wilcoxon Test, p = 0,043). Sagittal profile between C6 -T1 was lordotic for intact, (2,1° ± 5,3°) kyphotic for defect (6,1° ± 6,4°), which is significant (Wilcoxon Test, p = 0,043). Translation between C6-T1: no significant change (Wilcoxon Test, p = 0,285). NO significant change in depth of spinal canal at C7 (Wilcoxon Test, p = 0,715).

Conclusions: An anterior wedge-shaped-defect with intact posterior ligaments was created in CTJ. With this defect, load to failure is not depending on BMD – which might be a sign for a massive destruction, in which the remaining bone does not contribute to stability. Failure results in significant change of stiffness and sagittal profile from lordosis to kyphosis, however does not result in translation or spinal canal encroachment.