Osteolysis or bone loss after total knee replacement (TKR) can be a problem. Tiny flecks of bone and debris from the backside of the implant lead to osteolysis. Over time the implant can come loose or the bone can fracture. This study reports two changes that were made to reduce the risk of osteolysis.
The first step was to polish the baseplate surface of the tibial (lower leg bone) implant. Before that a grit-blasted surface finish was used. The second step was to change the way the implant was sterilized. Before 1993 implants were sterilized with gamma radiation in air. Later this was changed to radiation in nitrogen or gas plasma.
Results were measured by taking X-rays of the implants. The amount of osteolysis was measured. Knee alignment was also viewed. They found the amount of osteolysis was lowered from 34 percent to 6 percent when these two changes were made. Osteolysis was also more severe in the grit-blasted group.
The authors report several other risk factors as well. For example men were 3.6 times more likely to have osteolysis when compared to women. Risk of osteolysis went up when inserts had a longer shelf-life. Knees with a hyperextended angle were more likely to have osteolysis even with the two new changes.
The authors suggest polishing the baseplate reduces loss of polyethylene from the back of the insert. Using a different sterilization process seems to make the surface more fatigue-resistant. A shorter shelf life improves the quality of the polyethylene. Taken together these factors reduced osteolysis. Researchers aren't sure if all three steps are needed. Future studies will look at each one separately.
Matthew B. Collier, MS, et al. Osteolysis After Total Knee Arthroplasty: Influence of Tibial Baseplate Surface Finish and Sterilation of Polyethylene Insert. In The Journal of Bone and Joint Surgery. December 2005. Vol. 87-A. No. 12. Pp. 2702-2708.'