Musculoskeletal biomechanics of the shoulder in functional activities

Abstract

The aim of this thesis is to determine shoulder function, during specific functional tasks and relate this to key parameters associated with pathology. The long-term aim is that the results of this work will influence rehabilitating the shoulder after surgery, improving clinical assessment or preventing specific upper limb injuries. For this, initial studies are required to design and build a simulator to quantify upper limb function during a set of functional tasks, and to quantify upper limb anthropometrics and combine these with a musculoskeletal model. The first part of the thesis focuses on anthropometry. Three different methods are studied for defining anthropometrics. First, a modified regression equation data set is introduced; this can be used for calculating body segment parameters considering a subject’s body mass, height, race, gender and age. The new regressions are compared to cadaveric data from the literature and found to improve the moment of inertia calculations. Two different geometrical modelling approaches are also introduced. This found that the geometrical solid shape representing the body segments can lead to noticeable differences in the body segment parameter results. Finally a laser scanner device is developed and applied to measuring these parameters. A mannequin’s upper arm is scanned and its volume found from the 3D image is compared to the actual one giving an average difference of 3.1%.; in addition, a standard-sized object was scanned allowing the validation of the scanning method for calculating body segment parameters. Finally, these different approaches are analysed and applied to a large set of subjects. This then provides key information for the second part of the thesis. The second part then focuses on the muscle forces in functional activities. Six functional daily activities are used in this study. In addition, a driving simulator is designed in order to quantify kinematics, kinetics and external forces during steering at different conditions and postures. At the same time, a computational musculoskeletal model of upper limb is used for measuring the muscle forces during the six functional tasks. The methodology used and the results of muscle forces in functional activities are presented and analysed; from the literature it is found that the failure strengths for repairs of supraspinatus are close to the muscle forces predicted in this study (224 ± 148 N). Finally, the results of this study could help to improve ergonomics for cars, such as driving wheel and car-sits, and inform return to activity recommendations after upper limb surgery to specific muscles. Keywords: Musculoskeletal biomechanics, upper limb, musculoskeletal modelling, anthropometry, body segment parameters, geometrical modelling, regression analysis, 3D laser surface scanner, functional activities, activities of daily living, driving simulator for steering, shoulder functionality on driving, joint forces, joint stability, muscle forces.