Biomechanical comparison of the pull-down strength between TARP system and posterior atlantoaxial screw fixation system on the axis

Objective　To compare the pull-down strength on axis between anterior transoral atlantoaxial reduction plate (TARP) system and posterior atlantoaxial transarticular screw fixation (ATSF) system so as to provide a biomechanical basis for clinical application. Methods　Six fresh human cadaveric atlantoaxial specimens (C0-C3) with intact ligaments were instrumented with TARP system and ATSF system respectively to simulate the reduction procedure of operation, the same stretch strength were loaded on anterior and posterior parts of the atlas and axis (60, 80 and 100N). The pull-down strength on the axis and the degree of displacement of atlantoaxial detachment were measured respectively and then analyzed statistically. Results　When loaded with the stretch strength of 60, 80 and 100N, the pull-down strength on the axis generated by TARP system were 26.11±2.08, 36.08±2.40 and 45.01±2.26N, and those generated by ATSF system were 22.09±1.45, 29.77±2.36 and 40.80±3.41N, respectively; the atlantoaxial detaching displacement generated by TARP system was 0.87±0.07, 1.07±0.07 and 1.14±0.06mm respectively, and those generated by ATSF system were 0.82±0.07, 1.01±0.08 and 1.06±0.08mm respectively. The pull-down strength on both the axis and atlantoaxial detaching displacement showed a significant difference between the two groups (P<0.05). Conclusion　The pull-down strength on the axis and atlantoaxial detaching displacement generated by TARP system was significantly superior to those generated by ATSF system, suggesting that the TARP system could be a better fixation system for basilar invagination combined with atlantoaxial dislocation. DOI: 10.11855/j.issn.0577-7402.2014.07.04

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