Amounts of bone ingrowth into porous cobalt-chromium plugs were compared between male and female dogs, and among sham-operated and ovariectomized female dogs, with or without estrogen treatment, to investigate the effect of gender and estrogen therapy on biologic fixation. Each group consisted of eight skeletally mature dogs. Plugs were implanted bilaterally in the distal femur at 6 months after ovariectomy or sham operation. Estrogen treatment group received estradiol 20 microg/kg/day subcutaneous injection. Three months after implantation, histological examination showed significantly more bone ingrowth in areas with cortical bone contact than in areas with cancellous bone contact (P<0.001 for all groups). Bone ingrowth was essentially the same in male and female control dogs. Ovariectomized dogs showed less overall bone ingrowth than male and female controls (P=0.007). Bone ingrowth in areas with cortical bone contact did not decrease significantly, whereas bone ingrowth in areas with cancellous bone contact was significantly impaired (P<0.001) in ovariectomized dogs compared with female controls. Short-term, high-dose estradiol treatment did not increase bone ingrowth volume fraction. Mechanical tests did not show any statistical differences among groups.
Conclusion: Type of bone contact is the key factor affecting the amount and pattern of bone ingrowth into the porous surface. Ovariectomy results in decreased bone ingrowth in areas with cancellous bone contact, but does not compromise bone ingrowth in areas with cortical bone contact. Short-term, high-dose estradiol treatment does not enhance bone ingrowth into the porous surface. Extensively coated or full-coated porous prostheses are recommended to achieve enough cortical bone contact and ingrowth for post-menopausal patients.