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

Abstract

We recently evaluated the peak pullout loads for anchors made from our new copolymeric swelling-type material compared with anchors made of a nonswelling material. In vitro and in vivo peak pullout loads of these anchors were evaluated after different intervals of implantation in the lateral femoral condyles of New Zealand White rabbits. Scanning electron microscopy and energy dispersive x-ray analyses were additionally performed on selected retrieved samples after pullout to examine the characteristics of bone attachment to the implant. The mean peak pullout load was greater for 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 was significantly greater for the swelling anchors than for the nonswelling controls (177.7 +/- 41.3 compared with 53.7 +/- 17.5 N, p = 0.0024). The peak 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 swelling implants tended to induce bone deposition at the bone-implant interface. Results from this investigation reveal that the new family of dynamic implants has potential for applications requiring fixation to cancellous or osteoporotic bone.

Fixation strength of swellable bone anchors in low-density polyurethane foam

“…The results presented here demonstrate clearly the existence of an optimal swelling strain beyond which the fixation strength of the swellable anchor does not increase appreciably with an increase in the swelling strain (see Figs. [5][6][7][8].…”

“…(Note that the holding power of traditional metallic anchors are known to be strongly influenced by the cortical layer thickness. 9 ) Gualtieri et al 8 studied the biological and mechanical characteristics of the interface between the swellable anchor and bone in the lateral femoral condyles of New Zealand white rabbits. It was reported that (1) the swellable smooth cylindrical anchors produced from P(MMA-AA) induced radial bone growth, and (2) an average pullout force of 177 N at 4.7% swelling strain and an average pullout force of 102 N at 6.9% swelling strain.…”

Preparation and characterization of crosslinked poly(methylmethacrylate‐acrylic acid sodium salt)‐modified bone cement

“…The swelling of the copolymer was constrained by the surrounding bone, and consequently, an interfacial pressure was developed at the bone–polymer interface. This interfacial pressure, in turn, increased the frictional resistance and improved significantly the fixation strength of the implants 6–11. Thus, crosslinked poly(MMA‐AA‐AMA)‐modified bone cement could compensate the shrinkage of bone cement during polymerization.…”

Studies of the mechanical and thermal properties of cross‐linked poly(methylmethacrylate‐acrylic acid‐allylmethacrylate)‐modified bone cement

“…From our previous studies of crosslinked poly(methylmethacrylate‐acrylic acid‐allylmethacrylate) (poly(MMA‐AA‐AMA)), it is found that this copolymer exhibits the ability to absorb body fluids and swell in a controlled manner 9–13. Gualtieri et al have reported that crosslinked poly(MMA‐AA‐AMA) copolymer is able to induce bone ingrowths in the interface of bone and this copolymer 14. By introducing crosslinked poly(MMA‐AA‐AMA) copolymer into bone cement, the fixation strength in the interface of bone and cement can be improved by the controllable swelling of the modified bone cement, to compensate the shrinkage of the cement during polymerization 15.…”