EVALUATION OF BONE INGROWTH IN PROXIMALLY AND EXTENSIVELY POROUS-COATED ANATOMIC MEDULLARY LOCKING PROSTHESES RETRIEVED AT AUTOPSY

Three proximally (40 per cent) and five extensively (80 per cent) porous-coated anatomic medullary locking femoral components were retrieved from seven cadavera at autopsy, Each component (with the surrounding, intact femur), was sectioned transversely at one-centimeter intervals. Backscattered scanning electron microscopy was used to evaluate circumferentially the interface between the bone and the porous surface of each section, Bone ingrowth was considered to be present within a field when bone was in contact with the outermost layer of the sintered beads, it was detected within the porous space, and it had penetrated the porous space to a depth of at least one bead diameter. All eight components had some bone growth into the porous space, A mean of 35 per cent of the surface of the implants had bone ingrowth, In the areas where bone was present, 67 per cent of the available porous space on the extensively coated stems and 74 per cent on the proximally coated stems contained bone. With both types of implants, the greatest amount of compact bone ingrowth was found at the level where the porous coating ended. Transverse sections obtained at this level frequently demonstrated that bone ingrowth had occurred circumferentially and that the ingrowth was continuous with and an integral part of the femoral cortex, These direct connections to the cortex could be predicted from the appearance of the radiographs. In the most proximal transverse sections of both types of implants, bone was most frequently connected to the medial side and corners of the implant. In areas where the implant was not in direct contact with the cortex, ingrown areas were joined to the outer cortex by hypertrophied cancellous trabeculae, which usually were not visible on clinical radiographs. These porous-coated prostheses, obtained after the death of patients in whom the arthroplasty had been a long-term success, contained substantially more ingrown bone than has been reported in association with similar prostheses that were removed operatively because of malfunction.