Biological and mechanical characteristics of the interface between a new swelling anchor and bone

We recently evaluated the peak pullout loads for anchors made from our new copolymeric swelling-type material compared with anchors made of a nonswell ing material. In vitro and in vivo peak pullout loads of these anchors were evaluated alter different intervals of implantation in the lateral femoral condyles of New Zealand White rabbits. Scanning electron microscopy and en ergy dispersive x-ray analyses were additionally performed on selected retr ieved samples after pullout to examine the characteristics of bone attachme nt to the implant. The mean peak pullout load was greater fur the swelling anchors than for the nonswelling anchors after 48 hours in vitro (46.0 +/- 15.8 compared with 10.8 +/- 9.1 N, p = 0.0541). After 2 weeks in vivo, it w as significantly greater for the swelling anchors than for the nonswelling controls (177.7 +/- 11.3 compared with 53.7 +/- 17.5 N, p = 0.0024). The pe ak pullout load was also greater for the swelling anchors after 8 weeks in vivo: however, this difference was less pronounced than at 2 weeks (101.8 /- 35.0 compared with 58.9 +/- 9.7 N, p = 0.0508). Furthermore, the swellin g implants tended to induce bone deposition at the bone-implant interface. Results from this investigation reveal that the new family of dynamic impla nts has potential for applications requiring fixation to cancellous or oste oporotic bone.