| Hangman fracture, or traumatic spondylolisthesis of the axis, is a bilateral fracture of the isthmus of C2 associated with semi-dislocation between C2 and C3. The incidence of Hangman fracture was low, but is on the increase with the development of society and industrialization. There have been controversies about the treatment of the condition. Selection of therapeutic protocols depends on stability of the fracture, concurrent wound and maximal maintenance of cervical mobility. Treatment may be surgical or non-surgical. Non-surgical treatment, mainly indicated for stable fracture, includes cervical traction, cast fixation of the head, neck and chest, and halo-vest fixation; surgical treatment, mainly indicated for unstable fracture, includes anterior and posterior approaches. The posterior approach includes internal fixation with C2 transpedicle screws and the anterior approach includes C2-3 intervertebral fusion and anterior internal fixation. There are also reports in the literature using C3 corpectomy and C2-4 anterior fusion and internal fixation for unstable Hangman fracture,but evaluation on these surgical modalities remains at the stage of clinical observation. There is no report about whether they are able to provide sufficient biomechanical stability. The present study aims to provide theoretical guidelines for clinical selection of therapeutic protocols for Hangman fracture and attempts to achieve the following Objective:1. Comparing the influence of presence of anterior longitudinal ligament injury or disc injury on stability in Hangman fracture; evaluating biomechanical property of C3 corpectomy and C2-4 anterior fusion and internal fixation with Zephir plate in re-constructing stability of the upper cervical vertebrae, and comparing them with conventionally used C2-3 intervertebral fusion and anterior internal fixation with Zephir and posterior internal fixation with C2 transpedicle screws.2. Comparing C2-3 intervertebral fusion and anterior internal fixation with Zephir plate with C3 corpectomy and C2-4 anterior fusion and internal fixation with Zephir plate with respect to three-dimensional motion in six directions after implantation of the screws and the pull-out stress the screws can bear under biological loading, and evaluating the mechanical properties of the modality in physiological settings. 3. Establishing three-dimensional finite elements models of normal C2-4 cervical segment, Hangman fracture and using the above three internal fixation systems, testifying the models by comparing the biomechanics experimentally, and analyzing the practical value of the three-dimensional finite elements in treating Hangman fracture.4. Evaluating the outcome and clinical value of using C3 corpectomy and C2-4 anterior fusion and internal fixation with Zephir plate for unstable Hangman fracture. Materials and Methods1. Using six fresh human upper cervical vertebra specimens (including C2-C4), range-of-motion (ROM) of the C2-3 and C3-4 segments was tested at 0.5Nm, 1.5Nm and 2.5Nm moment in seven groups: the intact specimen group (Intact group), the bilateral osteotomy of the C2 isthmus group (DestablizedI group), separation of the anterior longitudinal ligament C2-3 group (DestablizedII group), the incision of the disk C2-3 group (DestablizedIII group), the posterior internal fixation with C2 transpedicle screws group (Judet group), the C2-3 intervertebral fusion and anterior internal fixation with Zephir plate group (C2-3+graft group), and the C3 corpectomy and C2-4 anterior fusion and internal fixation with Zephir plate group (C2-4+graft group). The data obtained were treated statistically.2. The Hangman fracture model prepared from the six fresh human upper cervical vertebra specimens (including C2-C4) was fixed as was with the case of C2-3+graft group and C2-4+graft group. Using strain electric measure, electric resistance of strain of the fixed fractures was tested at 0.5Nm, 1.5Nm and 2.5Nm moment. Upper left pull-out stress of the screws of the two fixations was calculated and the res...
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