Oral Presentations / Gait & Posture 24S (2006) S7–S97 S21 Depending on the subject analysed, differences of up to 12 ◦ in knee joint flexion/extension angle were obtained. After defining the geometrical parameters of the model and attaching the movement analysis data, the initially esti- mated position of the hip joint centre was moved by the optimisation procedure used to match the model, within a range of 5 mm. Skin motion artefacts for the femoral condyle mark- ers were found to reach 22.2 mm for the full range of motion. Since the proposed approach does not use markers at condyles, this source of error was eliminated. 6. Discussion By comparing the joint angles computed from the model and those obtained using the marker on the lateral femoral condyle the highest angular differences, of about 10 ◦ , were found at the stance phase, when full extension of the knee was observed. After being applied in normal subjects, the method showed characteristics that make it adapted for advanced applica- tions, e.g. applications related to skeletal-muscle system char- acterisation, starting from common movement analysis data without increasing the subject preparation complexity. Since the coordinates of the attachment points of the lig- aments on femur and tibia are the most affecting model parameters, anthropometrical variability as well as some other critical points, such as loading conditions, still need to be addressed. Acknowledgements The authors thank Prof. Paolo Crenna and Dr. Eng. A. Marzegan for having made available their competences and their clinical gait analysis laboratory. References [1] Lu T-W, O’Connor JJ. Bone position estimation from skin marker co- ordinates using global optimisation with joint constraints. J Biomechan- ics 1999;32:129–34. [2] Frigo C, Rabuffetti M, Kerrigan DC, Deming LC, Pedotti A. Functionally oriented and clinically feasible quantitative gait analysis method. Med Biol Eng Comput 1998;36(2):179–85. [3] Frigo C, Rabuffetti M. Multifactorial estimation of hip and knee joint centres for clinical application of gait analysis. Gait Posture 1998;8:91–102. [4] Pavan EE, Pascolini G, Zappata A, Frigo C. Determination of knee joint kinematics by means of bio-images and modelling for clinical application of gait analysis. Siamoc 2005 Congress Abstracts. 2005. doi:10.1016/j.gaitpost.2006.11.018 O-11 A single gait cycle as measured by four current protocols Alberto Ferrari a,∗ , Esteban Pavan b , Maria Grazia Benedetti a , Dario Bettinelli c , Carlo Frigo b , Alberto Leardini a a Movement Analysis Laboratory, Istituti Ortopedici Rizzoli, Bologna, Italy b Movement Biomechanics & Motor Control Lab, Bioengineering Depart- ment, Politecnico Milano, Italy c Aurion s.r.l., Milano, Italy 1. Summary/conclusions A single gait cycle from a volunteer was analysed simul- taneously by using four different protocols among the most commonly utilised in clinical gait analysis laboratories. The marker-set was designed to integrate those of the four relevant instructions. One volunteer was analysed, with marker place- ment and necessary measurements performed by relevant experts. Except biases associated to the different definitions of anatomical reference systems, the consistency among the four data set obtained was considerable. 2. Introduction The large number of gait analysis laboratories all over the world routinely utilise data collection and reduction pro- cedures embraced in a few well-known protocols [1–5]. These differ considerably for the marker-set utilised, addi- tional measurements taken at data collection, definition of the anatomical landmarks and references, joint axis conventions, etc. Single cases or general studies are discussed with their clinical implications and shared at meetings and in journals indifferently coming from these disparate protocols without full consciousness of these methodological differences. In the present study, a comparison is made between four of these protocols by looking at exactly the same single gait cycle. 3. Statement of clinical significance Gait analysis results are interpreted routinely within the process of clinical decision making, but it is still unknown to what extent the different protocols utilised worldwide com- pare to each other. This knowledge would make gait analyser more conscious about the reliability and the limits of his own clinical gait variables. 4. Methods The plug-in-gait (Vicon Motion Systems Ltd., Oxford, UK) [1,2], Saflo [3], CAST [4] and T3Dg [5] protocols were