US Patent 7641690 Bone fixation and fusion device

Disclosed is a bone fusion cage that contains bone graft and is implanted between bones in a skeletal system. The cage bears structural loads that are transmitted through the bones of the skeletal system and at least partially shields the contained bone graft from the structural loads. The cage is configured to provide a secondary load to the bone graft independent of the structural load to promote fusion of the bone graft to adjacent bones.