title: Biomechanical assessment of bone ingrowth in porous hydroxyapatite.
abstract: Porous hydroxyapatite (Endobon) specimens were implanted into the femoral condyle of New Zealand White rabbits for up to 6 months. After sacrifice, specimens were sectioned for histology and mechanical testing, where the extent of reinforcement by bony ingrowth was assessed by compression testing and fixation was assessed by push-out testing. From histological observations, it was established that the majority of bone ingrowth occurred between 10 day and 5 weeks after implantation and proceeded predominantly from the deep end of the trephined defect, with some integration from the circumferential sides. At 3 months, the implants were fully integrated, exhibiting bony ingrowth, vascularization and bone marrow stroma within the internal macropores. After 5 weeks, the mean ultimate compressive strength of retrieved implants (6.9 MPa) was found to be greater than that of the original implant (2.2 MPa), and by 3 months the fully integrated implants attained a compressive strength of approximately 20 MPa. Push-out testing demonstrated that after 5 weeks in vivo, the interfacial shear strength reached 3.2 MPa, increasing to 7.3 MPa at 3 and 6 months.
authors.affiliation: IRC in Biomedical Materials, Queen Mary and Westfield College, Mile End Road, London E1 4NS, UK.
authors.forename: K A
authors.initials: KA
authors.lastname: Hing
authors.forename: S M
authors.initials: SM
authors.lastname: Best
authors.forename: K E
authors.initials: KE
authors.lastname: Tanner
authors.forename: W
authors.initials: W
authors.lastname: Bonfield
authors.forename: P A
authors.initials: PA
authors.lastname: Revell