Artikel
Comparison of one screw with two screw fixation of Anderson type II DENS fractures – a biomechanical study
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Veröffentlicht: | 21. Oktober 2010 |
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Gliederung
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Objective: The type II odontoid fracture is the most common type of odontoid fracture, it is inherently unstable. Anterior screw fixation is the best treatment for type II odontoid fracture. Both one- and two-screw techniques have their own merits and demerits. The objective the study is to compare the stability between one and two screw fixation.
Methods: 14 fresh cadaver axes were randomly divided into two groups and fixed with one- or two-screw respectively. Implantation was in the usual technique under radiographic control. The stiffness of intact specimens and after screw fixation in six directions was tested on the universal mechanical testing machine (Zwick) and the corresponding data compared with each other. SPSS v16 was used after the consultation of a biometric statistician.
Results and conclusions: There was no statistically significant difference in any direction between the one and the two screw technique. The results showed that the torque load transmitted to the odontoid by ligaments is around 1/3 (0.53±0.38 Nm) of the maximum physiological load (1.5 Nm) in axial rotation. The torque acting on the occipito-altanto-axial complexes is dominated by the odontoid at smaller rotational angles. At larger rotational angles, the other ligaments that do not attach to the odontoid will join in and react against the torque more. The bone mineral density has statistical significant correlation with shear stiffness loading from anterior and posterior, torsional stiffness loading from left and right of intact specimen.
Both one- and two-screw fixation for type II odontoid fracture can gain the same shear and torsional stiffness. The result indicates that anterior odontoid fixation with one- or two-screw offers similar stability. Both the techniques cannot restore the normal shear and torsional stiffness. The stiffness of the odontoid after one- or two-FCS fixation is much less than that of normal.