Evaluation of sleeved implant fixation using a rat model.

Cementless hip implants have some osteolysis, stress shielding, and/or revision problems while the cemented ones have cement fracture problems. To overcome these problems, a new concept of implant fixation using a sleeve between the implant and the bone is proposed. This is a cementless fixation using a sleeve in place of the cement with a press-fit stem. The sleeved implant fixation is compared with the conventional cemented fixation by measuring the bone volume fraction and interface strength in a rat model. The tapered implant was manufactured using a stainless-steel Kirschner-wire with a diameter of 1.6mm, and PEEK (polyetheretherketone) was used for the sleeve. The Sprague-Dawley rats had implantations in their bilateral diaphyseal cut femurs using cemented and sleeved fixation, respectively. The rats were sacrificed at 2, 4, and 12 weeks after the implantation, and micro-CT scanning as well as push-out testing were performed. There was no significant difference between the cemented fixation and the sleeved fixation in areas of both BV/TV (bone volume/total volume) (p=0.838) and the apparent interface strength (p=0.530). However, the decrease in the BV/TV over time was significant in the cemented fixation (p=0.021) while not in the sleeved fixation (p=0.603). The sleeved fixation showed a gain in strength with time while the cemented fixation showed a reverse tendency but the difference was not significant (p=0.125). The results showed the feasibility of the sleeved fixation even though the advantage of sleeved fixation was not clearly confirmed because of the small sample size and high variance as well as the suboptimal surface finish of the sleeve.