[Histological study of the porous coating of the uncemented acetabulum. Apropos of 11 implants removed at autopsy].

Tissue ingrowth in the porous coating of 11 cementless acetabular components has been studied histologically. These cups were retrieved at autopsy from 8 patients who had undergone a primary total hip arthroplasty. Seven cups had a mean implantation period of 5.1 years, the other 4 had been in place for less than one year. This component was made of commercially pure (cp) titanium, with a porous surface of cp titanium fiber metal. The initial fixation of the cup was achieved by screws. The tissues of the porous coating were studied into 1 mm fields at four levels, and were categorized either as bone, marrow, cartilage or fibrous tissue. The fraction of void space within the porous coating occupied by bone was measured by backscattered scanning electron microscopy. The percentage of 1 mm fields with bony tissue was 20.9% and the fraction of void space occupied by bone was 12%. No regional significant difference was found. The number of fields with bone increased from the interface between the porous coating and the substrate of the cup to the interface between the outer surface of the porous coating and the host bone. All the screw threads were covered with lamellar bone. In the longest term cases, fine metallic and polyethylene debris were observed and their amount increased with time. This study showed that, despite the important variability in bone ingrowth, these cementless cups were able to give entire satisfaction to the patients.