Bone Remodelling in a Conservative Femoral Component for Hip Replacement Surgery

This study investigated a conservative femoral component for hip replacement surgery. Re-surfacing implants with two hydroxyapatite-coated pins were inserted into the right femoral necks of eight adult goats for one year. Radiographic analysis revealed bone loss directly beneath the prosthetic cup with increased amounts of bone at the distal end of the pins. Microscopic analysis revealed localised areas of bone formation adjacent to the implant. Oxytetracycline bone markers demonstrated significantly decreased bone formation rates (p<0.05) in bone adjacent to the implant in the operated compared to the control hips. Image analysis results demonstrated an average bone attachment of 30.94% to the implant surface. Attachment varied regionally, with greatest bone attachment at the end of the pins (78.99%) contributing 22% of total bone attachment to the implant. Least bone attachment (13.82%) was measured beneath the prosthetic cup and adjacent to the medial aspect of the pin. This contributed 4% of total bone attachment. Image analysis results demonstrated that in four of five comparable regions of operated and control hips, bone area was greater in control hips. Values were significant in three regions adjacent to the implant (p=0.002, p=0.008, p<0.05). Results revealed no significant correlation between bone attachment to the implant pins and bone area beneath the prosthetic cup. However, these findings do suggest that this conservative design led to stress shielding resulting in unfavourable bone remodelling despite the osteoconductive hydroxyapatite coating.