A spinal stabilization device positionable between separated but neighboring vertebral bodies to stabilize a spinal column which has been rendered unstable by disease. The device includes a vertebral body prosthesis containing at least one pair of oppositely disposed anchoring pins which are advanced out of the prosthesis into the abutting vertebral bodies to secure the prosthesis to and between them. On its anterior side the prosthesis has an opening communicating with the pins inside the prosthesis. A wrench is inserted into the opening until it engages the pair of pins, and then the wrench is rotated to advance the pins into the abutting vertebral bodies. Detent pins bias the anchoring pins against the wrench and lock the anchoring pins in place when in their fully extended anchoring positions. Spacer members can be attached to the ends of the prosthesis thereby elongating it to accommodate separations between neighboring vertebral bodies of varying dimensions.