Vertebral body replacement
Instrumented implant
Severe compression fractures of a vertebral body or a tumour in the region of the spine sometimes require the replacement of a vertebral body by an implant. The loads on such an implant are not well known. In order to measure these loads, the commercially available vertebral body replacement ‘SYNEX’ was modified. It allows the in vivo measurement of three force components and three moments acting on the implant. The 9-channel telemetry transmitter developed in our biomechanics laboratory was placed into the cylinder of the implant together with 6 load sensors and a coil for the inductive power supply. Usually, the spine is in addition stabilized dorsally by an internal spinal fixation device implanted from the back side.
Coordinate system
The bone-based coordinate system was chosen according to ISO 2631. The x- axis in the median plane points anteriorly, the y-axis in the frontal plane to the left side, and the z-axis cranially.
The forces and moments are presented in the measuring units N and Nm.
Patients
 |  |  |  |  |
| WP1 | WP2 | WP3 | WP4 | WP5 |
Table with basic information about those patients who had vertebral body replacements:
| Patient | Gender | Weight [kg] | Age at Implantation [years] | Indication |
| WP1 | m | 66 | 62 | Fracture L1 |
| WP2 | m | 72 | 71 | Fracture L1 |
| WP3 | f | 64 | 69 | Fracture L1 |
| WP4 | m | 60 | 64 | Fracture L1 |
| WP5 | m | 63 | 67 | Fracture L3 |