Failure of Migration by Injected Polyethylene Particles around Press Fit Implants: An Experimental Study in Rabbits

In a rabbit model, we wanted to study the migration of polyethylene particles into the interface between implant and bone, the effect of these wear particles on periimplant tissue, and whether hydroxyapatite coating inhibited particle migration. Non weight bearing implants were inserted into the distal femur of both knees in 14 rabbits. Hydroxyapatite coated implants were inserted on the right side and non coated, polished titanium implants on the left side. Three, four and five weeks after surgery, group 1 (n=7) had bilateral intraarticular knee injections of polyethylene particles, group 2 (n=7) had bilateral sham injections. Histological analysis after six weeks revealed no osteolysis and showed no difference in bone ingrowth between the two groups, but a significantly higher bone ingrowth around hydroxyapatite coated implants. Around implants in both groups, only trace numbers of polyethylene particles were found in the interface close to the joint surface, and no specific inflammatory reaction could be verified. The tip of all implants, against the joint surface were covered by a massive fibrocartilaginous overgrowth. Synovial tissue contained scattered polyethylene particles in group 1, but histology was similar to group 2. The press fit situation and fibrocartilaginous overgrowth most likely closed the entrance to the interface.