Operative Behandlung von A3-Frakturen im Bereich des thorakolumbalen Übergangs – biomechanische Studie zur Evaluation unterschiedlicher Schraubendesigns unter zyklischer Belastung

Incomplete burst fractures due to high-speed trauma are among the most common fractures of the thoracolumbar junction sustained by young people, whereupon numerous treatment strategies have become established and ongoing debates are underway to establish a uniform treatment guideline. Depending on the hospital and attending staff, type A3 fractures have usually been treated with exclusively posterior or anterior stabilization, or a combination of both, depending on the extent of the defect. Due to a relevant height reduction occurring in the course of the exclusively posterior or anterior stabilization procedures, minimally invasive combined methods are currently increasingly preferred, which are associated with lower complication rates, reduced pain and significantly increased patient satisfaction. The aim of the study is to demonstrate the advantages of combining the newly developed prototype with posterior instrumentation, with additional consideration of implant behavior as a result of cement augmentation. Accordingly, the study serves to further develop existing treatment strategies for type A3 injuries, with a focus on improved height reconstruction and the most accurate possible restoration of the original anatomical and biomechanical condition. Resulting questions 1. Which surgical technique shows in comparison the best vertebral body height preservation? 2. Does the cement augmentation of the prototype affect the stability and the vertebral elevation of the treated vertebral spine segment? After precise preparation and embedding of 21 fresh-frozen human vertebrae, including the eleventh thoracic to the third lumbar vertebral body, different diagnostic techniques were used to compare different diagnostic methods. Among others the DEXA measurement was performed to determine the individual bone density of each vertebral body and the additional computed tomographic imaging allowed a target-oriented classification for a best possible comparability of the results. The subsequently conducted generation of controlled type A3 fractures of the first lumbar vertebral spine was ensured by the use of the freefall tower designed by the Philipps University of Marburg. During the following implementation of the three different combinations of surgical procedures, the proper positioning of the implants was made possible under constant X-ray control. Two trained doctors from Philipps University performed all percutaneous minimally invasive interventions for a better comparability. The prototypes were implanted with and without cement, under additional use of the dorsal instrumentation, which was compared with a pure outcome of the exclusive posterior procedure in the third test group. The implantation was followed by the postoperative loading of all included vertebrae in a hydraulic machine in 100000 cycles, with 3HZ and 600N, while recording a force-displacement diagram. The data documented in the meantime has been included to determine the height loss of the vertebral elevation, in consideration of the height loss of the ventral, medial and posterior columns, and stabilisation. The insignificant results of the height behavior after generating the fractures, which obtained in all three groups, has been used as the evaluation basis of the height reconstruction at different stages of the study. Comparing the methods, there is a significant difference of the height behaviour due to the various techniques, while facing central and dorsal column. After the surgical treatment and cyclical loading a significance can therefore be assumed in relation to the height reconstructions. In contrast, the implantation of the sextant alone achieved only insufficient results and is subject to the combination of the newly designed prototype. Furthermore, the cementation of the prototype proved to be irrelevant, which is why its use should be abandoned due to the side effects. Based on the positive results of the new procedure, it can certainly be considered as an alternative and oriented method for height reconstruction of the central and dorsal column, in comparison to currently existing procedures. In context to the relatively small number of cases and the increased average donor age of the male donors, the comparability of the results is poor in view of the initially affected clientele. The sources of error due to the use of fresh-frozen preparations without soft tissue, the non-standardized computed tomographic evaluation, with possible measurement inaccuracies and the exclusive loading in only one level also belongs to the in vitro conditions of the study and are again accompanied by a questionable transferability to normally presented in vivo occurrences. Consequently, the further extension of the study is to be aimed at, which is accompanied by an increase in number of cases, the extensive additional comparison of common consolidated procedures and the inclusion of different cement types in vitro. After further research, the ultimate goal should be to settle a targeted procedure for the daily clinical setting, in order to achieve best long-term outcomes and to establish a treatment guideline for fractures of the thoracolumbar spine.