Seventeen cases of focal endosteal femoral osteolysis around cementless porouscoated femoral components of total hip replacements that were judged not to be loose on the radiographs were identified and analyzed. Fourteen of these cases were from a retrospective review of 474 cementless total hip replacements with a minimum two-year follow-up done by the authors. The incidence of the osteolysis was approximately 3% for femoral components made of both titanium-based alloys and cobalt-chrome-based alloys.
Four of the patients underwent reoperations for osteolysis. All four femoral components were found to be rigidly fixed to the skeleton at surgery. Three of these showed extensive bony ingrowth into the porous coatings on histology. The tissue in the region of osteolysis had a fibrous stroma. However, it contained focal aggregates of macrophages and rare giant cells. On light microscopy, evidence of fine intracellular particulate polyethylene and metallic debris was found in three of the cases. In the fourth, there was a fine fibrous membrane lining a cystic cavity. Although the tissue in the fourth case contained occasional macrophages, foreign material could not be identified on light microscopy. On electron microscopy, however, fine electron-dense particles consistent with metal were noted within the macrophages of this case.
Although these findings represent a small number of cases, they caution against the assumption that femoral osteolysis can be eliminated by using uncemented components. The precise cause for the osteolysis around uncemented porous-coated femoral components is not known. However, it seems that particulate debris from implanted biomaterials, such as metal and or polyethylene, seems to play an important role in the production of osteolysis around prosthetic components. The debris is much smaller and less frequent than that previously observed with cemented components.