Effect of porous-coating configuration on tibial osteolysis after total knee arthroplasty.

Porous-coating configuration on the undersurface of tibial components in total knee arthroplasty was evaluated for its effect on tibial osteolysis. Clinical data and radiographic results of 675 Ortholoc II components (range, 4-8 years postoperative) and 236 Ortholoc Modular components (range, 2-4 years postoperative) were compared. The undersurface of the Ortholoc II tibial component is completely covered with porous coating, and that of the Ortholoc Modular is partially porous coated with smooth metal bridges connecting the 4 screw holes and joint cavity to the smooth metal stem. None of the radiographs of the Ortholoc II tibial components showed significant osteolysis around the stem or pegs. Radiographically detectable signs of osteolysis around the distal 1/2 of the stem appeared in 28 of the 124 long-stemmed Ortholoc Modular knees. None had radiographically identifiable osteolysis around the screws or pegs. In the 112 knees with short stems, 19 had radiographically identifiable radiolucency around the stem, but none had radiolucency around the screws or pegs. Despite their substantially shorter followup, cementless tibial components with patches of porous coating connected by smooth metal tracks were more likely to have osteolysis develop than those with uninterrupted porous coating on the undersurface of the tibial tray. The smooth metal tracks appear to conduct debris from the joint cavity to the areas surrounding the stem.