Impending fracture of the metastatic spine: risk factors and optimization of preventive vertebroplasty

Background The spine is the most common site for skeletal metastasis, with one third of all cancer patients developing spinal metastases. Since advancements in oncological treatments have improved patients' survival, the prevalence of spinal metastases is bound to increase. Vertebral fractures caused by spine metastases result in pain, deformity, loss of mobility, and/or neurological complications, significantly affecting quality of life. Vertebroplasty is spreading worldwide, with preventive purposes, for patients presenting with vertebral metastases. At present, however, there are no guidelines that allow the appropriate selection of patients as candidates for vertebroplasty. Moreover, although disc degeneration thus appears to be related to the increased fracture risk seen in the elderly spine, the exact pathway from a degenerated disc to this increased fracture risk remains unclear. The ability to predict the occurrence of a fracture is essential in order to intervene promptly and to guide the decision-making process of the medical-surgical team. Aims The aims of this thesis are (1) to evaluate if bone mineral density and intervertebral disc degeneration influence the risk of fracture of a metastatic vertebra (2) to evaluate if bone mineral density and intervertebral disc degeneration influence the risk of fracture of adjacent vertebrae after a prophylactic vertebroplasty. Methods A three-dimensional model of the lumbar segment L3-L5 was isolated from a pre-existing model of a thoraco-lumbo-sacral spine validated in vitro. This is an anatomical model obtained from a high- resolution CT scan of the vertebral column of a cadaver and transformed though several software in order to obtain a working finite element analysis model. A parametric analysis was performed varying bone mineral density and disc degeneration. Three different level of BMD (Normal, Osteopenia and Osteoporosis) were combined with five different levels of disc degeneration (I to V). For each combination of variables, three sub-scenarios were developed: "H", Healthy Spine (L4 with no metastatic lesion) / "M", Metastatic Spine (L4 with a metastatic lesion) / "V", Spine after vertebroplasty (L4 with PMMA core) Results and Conclusion Bone mineral density and disc degeneration significantly influences the risk of vertebral fracture of the metastatic vertebra and fracture of the adjacent vertebral level. These parameters should be taken into account in the evaluation of patients with vertebral metastases, in order to select those who, presenting a greater fracture risk, can benefit from vertebroplasty. In this regard, in fact, it has been shown that this procedure restores vertebral stability to values greater than the physiological ones. However, although the ultimate goal of the procedure is achieved, the presence of a material with physical properties very different from those of bone, can cause fractures of the adjacent levels. This risk is a function of the degree of bone mineral density and disc degeneration.