An intervertebral spacer formed of dense cancellous human or animal bone is provided. In one preferred embodiment, the intervertebral spacer includes at least one bore which is dimensioned to receive a plug formed from cortical bone tissue. The cortical bone plug provides increased mechanical strength...http://www.google.co.uk/patents/US6638310?utm_source=gb-gplus-sharePatent US6638310 - Intervertebral spacer and implant insertion instrumentation
