Design and validation of a minimally invasive adjustable titanium prosthesis as a vertebral body replacement

Unstable vertebral body compression fractures, spinal tumors and post-traumatic deformities require a vertebral body replacement (VBR). Usually, the reconstruction of the lumbar spinal column requires metallic implants, also called cages, which are inserted after a total corpectomy in combination with an internal spinal fixation device. These implants show several complications, including a low bone fusion rate, localized contact between prosthetic endplates and vertebral endplate, and eventually overload the vertebral body due to the excessive insertional force. Creation of a misalignment between prosthetic and bone endplate sometimes causes the subsidence and collapse of the VBR. Then, the ability of the prosthesis/bone interface to support vertebral loading is crucial to the successful implantation of these devices. Recently developed additive manufacturing techniques (i.e. EBM) allow the production of trabecular titanium structures which provides better biomechanics and customized solutions. Furthermore, most of vertebral body implants are currently designed and produced in batches with standard dimensions, that are not able to meet the patient peculiar features. This work aims to design, optimize and validate a new 3D printed trabecular titanium prosthesis with adjustable height for lumbar VBR. The work focused on the durability of the implant considering the lumbar spinal fatigue loadings acting on the porous cage, with the aims to improve bone ingrowth and, at the same time, to minimize the effects of the surgical treatment on the sagittal alignment of the patient. In order to achieve better performances in terms of spinal stabilization and fatigue life resistance, the design of this new customized prosthesis takes into account the most critical factors of the vertebral body resection, with the aim to ensure minimally invasive surgical procedure.