The biomechanics of vertebroplasty in multiple myeloma and metastatic bladder cancer: A preliminary cadaveric investigation - Laboratory investigation

Object. The vertebral column is the most common site for secondary bone metastases and lesions arising from hematological malignancies such as multiple myeloma (MM). These infiltrations can be lytic in nature and cause severe weakening of the vertebral body, an increased risk of fracture, and spinal cord compression leading to neurological deficit. Qualitatively it is apparent that increasing infiltration of these lytic lesions will have a deleterious effect on the mechanical behavior of the vertebrae. However, there is little quantitative information about the relationship between tumor deposits and the impact on the mechanical behavior of the vertebrae. In addition, there have been limited biomechanical assessments of the use of vertebroplasty in the management of these malignancies. The purpose of this preliminary study was to evaluate the mechanical behavior of lesion-infiltrated vertebrae from 2 malignant cancers and to investigate the effectiveness of vertebroplasty with and without tumor debulking. Methods. Individual vertebrae from 2 donor spines - one with MM and another with bone metastases secondary to bladder cancer - were fractured under an eccentric flexion load, from which failure strength and stiffness were derived. Alternate vertebrae defined by spinal level were assigned to 2 groups: Group 1 involved removal of lesion material with Coblation (ArthroCare Corp.) preceding vertebroplasty; Group 2 received no Coblation prior to augmentation. All vertebrae were fractured postaugmentation under the same loading protocol. Micro-CT assessments were undertaken to investigate vertebral morphology, fracture patterns, and cement distribution. Results. Multiple myeloma involvement was characterized by several small lesions, severe bone degradation, and multiple areas of vertebral shell compromise. In contrast, large focal lesions were present in the vertebrae with metastatic bladder cancer, and the shell generally remained intact. The mean initial failure strength of the vertebrae with metastases secondary to MM was significantly lower than in vertebrae with bone metastases secondary to bladder cancer (Load = 950 ± 300 N vs 2200 ± 750 N, p < 0.0001). A significant improvement in relative fracture strength was found postaugmentation for both lesion types (1.4 ± 0.5, p < 0.001). Coblation provided a marginally significant increase in the same parameter postaugmentation (p = 0.08) and qualitatively improved the ease of injection and guidance of cement. Conclusions. In the vertebral column, metastatic lesions secondary to bladder cancer and MM showed variations in the pattern of infiltration, both of which led to significant reductions in fracture strength. Account should be taken of these differences to optimize the vertebroplasty intervention in terms of the cement formulation, delivery, and any additional surgical procedure.