The acetabular cement-bone interface in experimental arthroplasties in dogs.

Increased clinical loosening of total hip arthroplasty acetabular components has been noted in patients with long follow-up and in young active individuals. Evaluation of the acetabular cement-bone interface has been limited to a few human cadaveric specimens and to canine studies in which the data are difficult to interpret. The effects of cement fixation of the acetabular component were investigated in serial observations in 21 dogs with hip surface replacements. The postoperative survival time before evaluation was from two to 46 weeks. Twenty animals were clinically normal before autopsy. Analytic techniques used to examine acetabular fixation included the use of epoxy-embedded specimens to preserve the cement-bone interface and conventional histologic sections. After two weeks, no direct contact between the cement and bone was seen. A correlation between the adequacy of cement fixation and interface membrane thickness was found. Poor acrylic fixation resulted in thick membranes up to 2 mm thick and horizontal trabeculation of the interface woven bone. Good cement intrusion led to a thinner, almost minimal membrane two to three cells in thickness.