Postmortem retrieved canine THR: femoral and acetabular component interaction

Dogs are the preferred animal model for testing of human total hip replacements (THRs). A postmortem retrieval program for clinical, cemented, canine THR was established to analyze the long-term performance of THRs in dogs and to compare that performance to postmortem retrievals of human THRs. The purpose of the present study was to analyze the interaction between the femoral and acetabular components. Thirty-eight postmortem retrievals from 29 dogs were donated and analyzed. The acetabular components (ACs) were measured for volumetric wear and graded for articulating surface damage. Femoral and acetabular components were mechanically tested for implant stability. Digital image analysis was performed on contact radiographs of transverse femoral slices. Of 14 cases with a firmly implanted femoral component (FC). 6 articulated against loose ACs. Of 24 cases with a loose FC, 16 articulated against loose ACs. Only 4 specimens had both components firmly implanted, and 14 specimens had both components loose. There was a significant positive correlation between AC volumetric wear and FC loosening; however, there was no evidence of osteolysis or wear debris induced osteolysis as seen in human postmortem retrieval studies. There was a significant but weak negative correlation between FC loosening at the cement/bone interface and AC scores reflecting damage to the rim and creep across the entire AC. Although implant-on-implant damage to the AC was expected to positively correlate with FC loosening, this was not found. Researchers need to look at interactions between AC and FC to understand how the failure of one component affects performance of the other.