A HISTOMORPHOMETRIC AND HISTOLOGIC ANALYSIS OF THE IMPLANT INTERFACE IN 5 SUCCESSFUL, AUTOPSY-RETRIEVED, NONCEMENTED POROUS-COATED KNEE ARTHROPLASTIES

Five clinically successful, primary uncemented porous-coated anatomic knee implants were retrieved postmortem, 13-56 months after implantati on, and were sectioned and evaluated histologically and histomorphomet rically for bone ingrowth. The prosthesis-bone interface was divided i nto the following four zones: (1) the tissue prosthetic surface interf ace; (2) the beaded area; (3) the immediate beadless area; and (4) the marrow space. Although fibroosseous ingrowth was present in all cases , it varied quantitatively with each case and component. Average compo nent bone ingrowth for the prosthesis interface (Zones 1 and 2) of pat ellae was 29%; tibias, 6%; and femora, 8%. In Zone 3, the percentage o f bone apposed to the prosthesis for the patellae was 53%; tibias 36%; and femora, 32%. Zone 4, the marrow space, was not quantitated. The f ibrous tissue filling nonbone-ingrown porous space in Zone 2 appeared ''ligamentoid,'' connecting bone to beads within Zone 2 and between Zo nes 2 and 3. Zone 3 exhibited a bony plate formation parallel to the p rostheses. No significant inflammation was noted. Overall there was mo re bone ingrowth into Zone 3 than Zones 1 and 2 with greater bone ingr owth found in the patellar components. The implant interface in clinic ally successful noncemented porous-coated prostheses of this design is characterized histologically by a noninflammatory fibroosseous ingrow th of varying degrees, and the fibrous component of this composite str ucture exhibits a highly organized pattern.