gms | German Medical Science

Objective: Effective treatment of traumatic vertebral body fractures in osteoporosis is discussed very controversially. In addition to classical instrumentation, the literature also includes clinical reports on the possibility of successful treatment of incomplete burst fractures with kyphoplasty. However, this effect can’t be explained biomechanically so far. The aim of the present study is the biomechanical evaluation of kyphoplasty and its capability to stabilize the posttraumatic segmental instability of an incomplete burst fracture.

Methods: The study was performed on 14 osteoporotic spine post mortem samples (Th11 - L3). First, the acquisition of the "normal" multisegmental kinematics in our robot based spine tester with 3D motion analysis with and without preload was set as a baseline for each sample. This was followed by the generation of an incomplete burst fracture according to a standardized protocol in the vertebral body LWK 1 with renewed kinematic testing. After subsequent kyphoplasty of the fractured vertebral body under X-ray control, the primary stability was examined again.

Results: Initially, a significant increase in the range of motion (RoM) after experimental fracture generation in all three directions of motion (extension / flexion, lateral tilt, axial rotation) could be detected as a proof of posttraumatic instability in the target motion segment. There were no significant changes to the native state in the terminal segments. Radiologically a significant loss of height in the fractured vertebral body was also shown. This loss of height could be clearly erected by kyphoplasty. The individual traumatic instability could also be significantly reduced. However, the native kinematics were not restored. In this case, the range of movement remains significantly increased compared to the native state.

Conclusion: Although post-traumatic segmental instability can be significantly reduced in our ex vivo model by kyphoplasty, native kinematics have not been reconstructed and significant instability has remained. The present experimental data provide a biomechanical explanation that isolated kyphoplasty is partial able to reduce segmental instability but was not able to restore native conditions. However, the question of what degree of stabilization of the passive musculoskeletal system is necessary for a good clinical outcome cannot be answered by this study.