Abstract
Aims: To evaluate the effect of tapered pegs in reducing tibial tray tilt and subsidence in closed cell foam. Methods: 1. Foam validation was carried out using a load frame (Instron) to establish its static and fatigue behaviour. 2. Subsidence and tilt tests: Three brass peg sets of varying length and matching surface area were designed. Four identical pegs of each set were fixed with screws to an IBII tibial tray and testing was performed using the load frame and the closed cell foam. Results: Foam validation revealed an average strength of 0.65±0.01 MPa in compression and 1.53±0.02 MPa in tension and an average stiffness of 40.2±1.5 Mpa in compression and 50.4±1.06 Mpa in tension. Subsidence tests revealed a significant increase in the total load producing 0.2mm subsidence with pegs ( p< 0.0053) and no significant difference for 1 and 2mm (p> 0.1). Tilt tests revealed a significant increase in the total load producing 0.2mm tilt with the medium and short pegs ( p < 0.008 & < 0.042 respectively) and no significant difference for 1 and 2mm (p> 0.1). Conclusions: The foam analogue material shows similar behaviour to cancellous bone in both static and dynamic tests and suggests that polymer foams are a good analogue material to cancellous bone. The addition of tapered conical pegs to the tibial tray increases its resistance to initial subsidence while initial tilt resistance is increased only with the medium and short pegs. Combining tilt and subsidence resistance, the medium pegs perform most favourably.
Theses abstracts were prepared by Professor Dr. Frantz Langlais. Correspondence should be addressed to him at EFORT Central Office, Freihofstrasse 22, CH-8700 Küsnacht, Switzerland.
