Titanium implants in rabbit knee joints.

The subchondral bone, cartilage, and synovial tissue adjacent to nonalloyed titanium screws were morphologically evaluated 2, 4, and 6 weeks after insertion in rabbit knee joints. The titanium screws were in direct contact with the surrounding bone. Two weeks postoperatively, bone resorption, as well as formation of new bone on the titanium surface, was evident. The observed inflammatory process was transient, and the amount of bone within the screw threads increased progressively with time. The articular cartilage regenerated and covered the titanium screws. Synovial tissue also regenerated and covered the screws when inserted into a noncartilaginous area of the joint. These findings, together with recent findings in soft tissues, indicate that titanium provides an inert surface for the proliferation of differentiating tissues in vivo. These data, supported by the observation that no inflammation was present in the synovial tissue, suggest that nonalloyed titanium can be used safely intraarticularly.