Date of Completion

5-5-2012

Embargo Period

5-15-2012

Open Access

Open Access

Abstract

Representing upper extremity posture has posed a great challenge in the field of analytical biomechanics due to their great freedom of motion, which allows for large rotations in multiple directions. The Euler and quaternion methods, which are two commonly used methods for describing joint angles and body segment postures and movement, have great limitations when dealing with upper extremities. The planar projection method has also been used to represent joint angles and body segment postures and movement. The advantages of this method over other common methods are that it yields rotations with anatomical meaning that make it easy to understand from a clinical standpoint, it is not affected by Gimbal lock phenomenon, and is more accurate at large multi-axis rotations, which make it a good candidate for representing upper extremity posture. The disadvantages of this method are that it has some accuracy limitations when dealing with multi-axis rotations beyond 60 degrees, with complex rotation of the body structures inside of soft tissue, and has error associated with it when projecting onto global planes. This thesis investigated a modified planar projection approach using a simplified opto-electronic marker configuration to improve the accuracy when calculating upper extremity orientations. One modification of the method was that anatomical planes were calculated by defining orthogonal axes at the chest and rotating the axes to account for the slope of the chest. By defining the anatomical axes using anatomical landmarks of the upper torso, the body can move freely without disturbing the anatomical plane calculations. Projecting onto planes that are defined locally for different body segments rather than global segments, eliminated the angle errors previously associated with the planar projection method. This modified method was tested using human and mechanical tests and was applied to data pertaining to laparoscopic surgical hand tool use. The biomechanical risk exposure of the tasks was quantified from the postural results using a threshold technique and a novel approach to the Rapid Upper Limb Assessment.

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