UPPER EXTREMITY KINEMATIC MODEL FOR WALKER ASSISTED GAIT Kelly M.B. Strifling 1 , Mei Wang 2 , Kevin Cao 1 , Jeffrey Ackman 3 , Jeffrey Schwab 2 , and Gerald F. Harris 1,2 1 Orthopaedic and Rehabilitation Engineering Center (OREC), Marquette University, Milwaukee, WI, USA 2 Department of Orthopaedic Surgery, Medical College of Wisconsin, Milwaukee, WI, USA 3 Motion Analysis Laboratory, Shriners Hospital for Children, Chicago, IL, USA E-mail: kelly.strifling@mu.edu INTRODUCTION Recent literature has begun to explore the value of upper extremity (UE) modeling. Existing UE models vary according to task being performed (Newsam 1999, Petuskey 2007). The International Society of Biomechanics (ISB) has played a leading role in standardizing UE motion through joint recommendations (Wu, 2005). However, UE joint motion is very complex, so there is considerable difficulty in developing a standard model for all applications. The focus of this study is to design and evaluate an upper extremity model to be used with children with cerebral palsy using walkers. Our group previously developed and validated an UE model to be used with normal adults (Bachschmidt, 2001). The adult model aided in the development of the current pediatric model. METHODS The design of the pediatric model separates the UEs into seven segments: the torso, humeri, forearms, and hands. During data collection, all segments were represented by a minimum of three markers, with the torso having six, for a total of eighteen anatomical markers. When recorded in space the markers described the positions of the seven defining segments and create coordinate systems for each segment. Each adjacent segments coordinate systems are related to one another through joints. The torso and humerus are connected by a three degree of freedom shoulder (glenohumeral) joint, with motion described as ab/adduction, flexion/extension, and internal/external rotation. The humerus is connected to the forearm by a two degree of freedom elbow joint, with motion of flexion/extension and pronation/supination. The forearm joins the hand through a two degree of freedom wrist joint, with motion in ulnar/radial deviation, and flexion/extension. The torso orientation is described with respect to the lab coordinate system. All segments are defined by local coordinate systems (Fig. 1). Figure 1: Segmental Axes The local coordinate systems are related to one another by a series of Euler angle rotations, sequenced flexion/extension  ab/adduction  internal/external rotation. Equations 1-4 give the individual rotation matrices and equation 2 is the rotation matrix. A Vicon 524 motion analysis