A cage device for harvesting bone graft material for use in bone fusion surgery, e.g., a spinal fusion. The device has a chamber configured to contain a slurry of morselized bone and blood that effuses from adjacent bones when the device is placed in a space between the bones, and a bone cutter assembly is inserted into the chamber and operated. In one embodiment, the cutter assembly includes an elongated cannula having a bend at a distal end, and a wire arranged to slide inside the cannula so that a cutting tip of the wire can be set to project a desired distance from the distal end. When the cannula is driven to rotate about its long axis, the wire cutting tip strikes and cuts grooves in the facing surfaces of the bones to produce the mentioned slurry which remains inside the chamber to promote a solid and healthy fusion.
