ETIOLOGY OF OSTEOLYSIS AROUND POROUS-COATED CEMENTLESS TOTAL HIP ARTHROPLASTIES

The prosthetic components and tissues retrieved from 12 hips with oste olysis in association with well-fixed cementless porous-coated total h ip prostheses (5 Porous Coated Anatomic, 6 Harris-Galante Porous, and 1 Omniflex) were examined using a variety specific techniques includin g electron microscopy, standard histology, immunohistochemistry, and p article identification. The patients were young and active. Extensive osteolysis developed in all 12 femurs and 3 acetabula between 36 and 8 4 months after arthroplasty (mean, 63 months). All of the polyethylene liners were noted to be worn substantially (mean volumetric wear, 114 0 +/- 810 mm(3)). The wear was unrelated to the head diameter in this small number of cases. In all 12 cases, the articulating surfaces were wear polished and contained numerous fine multidirectional scratches, suggesting 3-body abrasive wear mechanisms in addition to adhesive we ar liberating very small (micron to submicron) wear particles. In 4 ca ses, surface delamination and flaking of polyethylene were also found, suggesting fatigue wear liberating larger wear particles. Nine of 10 cobalt alloy heads showed numerous fine scratches with sharp edges pre sumably from 3-body abrasive wear. Corrosion and fretting at the femor al head-neck junction in 5 cases, burnishing of the femoral stem again st bone in 4 cases, and metal staining of tissues opposite the porous coatings in 7 cases provided evidence for the liberation of fine metal particles from outside the articulation. Histologic and immunohistoch emical studies of tissue in the regions of osteolysis in all cases sho wed numerous focal aggregates of KP1 antibody positive activated macro phages containing large amounts of submicron intracellular particles o f polyethylene (presumably related to the 3-body abrasive wear polishi ng) and giant cells within a fibrous stroma. In 5 cases, some of the m acrophages also contained submicron metal particles but smaller in num bers. T lymphocytes, plasma cells, and mast cells that might indicate hypersensitivity were found in 4 of the 12 cases (33%), and none of th e cases had B lymphocytes. These data suggest that abrasive wear at th e articulation leads to the liberation of abundant fine particulate we ar debris of polyethylene into the tissues around cementless prosthese s. Small amounts of particulate metal debris are also liberated from c orrosion and fretting of the metal components and can contribute to ac celerated 3-body abrasive wear at the articulation. The abundant fine polymeric debris, however, is the most common feature in cases with un cemented components of different alloys and designs, and is the most l ikely agent for the production of osteolysis by giving rise to an aggr essive, foreign-body granulomatous tissue reaction.