An understanding of the orientation of posterior cruciate ligament (PCL) fibres can contribute to current knowledge of PCL biomechanics and potentially improve the effectiveness of PCL surgical reconstruction. In this paper, the orientation of PCL fibres with respect to the tibia and femur was analysed by means of a new computer method. The antero-lateral (AL) and postero-medial (PM) bundles of the PCL showed an increasing slope with respect to the tibial plateau during flexion and a statistically significant difference between them (AL: 37-65 degrees, PM: 47-60 degrees). PCL bundles showed similar orientation with respect to the femur and varied 14 degrees average during flexion. The study also measured 84 degrees twisting of PCL bundles during passive range of motion.

Abstract. D ifferent technologies have been used for computer assisted orthopaedic surgery for acquisition of surfaces and motions, but the most efficient are optical and mechanical [2]. In this study we compared two specific systems of these categories: FlashPoint TM 5000 (Image Guided Technologies, USA) and FAROArm TM (FARO Technologies, USA). FARO Arm showed an intrinsic uncertainty of 0.1mm overcoming FlashPoint (0.2mm). However their use in noisy conditions resulted in similar application-uncertainty. FARO Arm can track motion at 31Hz while FlashPoint at 17Hz, therefore FlashPoint spatial resolution m ay be critical during fast m ovements. I n simulated medical applications FARO Arm showed some difficulties (i) when used for passive motion with negligible forces, because the surgeon has to compensate its weight and (ii) during sample trajectory, because it has isolated singularities within its workspace. FlashPoint was affected by reflected light and required complete visibility during tracking of large trajectories. H owever its use in in-vivo conditions is more promising than FARO-Arm's.

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