Causes of titanium release from plate and screws implanted in rabbits.

To investigate the mechanism behind the release of metal from titanium implants in vivo, bone-plate-screw sets consisting of pure titanium were implanted into the legs of rabbits for 48 weeks. Four groups of experiments containing control were conducted: (1) The tibia cut artificially was fixed by one set of bone plate and screws, (2) the same set was implanted separately into muscles in the leg, (3) the set was fixed on the tibia and immediately retrieved, and (4) no implantation was performed. The amounts of titanium in all tissues from knee to ankle were quantified using atomic adsorption spectrometry. The ratio of amounts of titanium detected in the groups (1), (2), and (3) was 100 : 10 : 43. No titanium was detected in the group (4). Causes of the release of titanium in the group (1) include that in the groups (2) and (3). Major causes of titanium release were surgical handling in implantation and wear and/or fretting during experimental-term for 48 weeks. Titanium was also released in the absence of wear. No morphological abnormality was observed around tissue of the implant by biopsy at post-operation week 48.