Morfología comparada de la escápula de primates humanos y no humanos mediante morfometría geométrica. Estudio preliminar.

Este trabajo estudia la morfología comparada de la escápula de primates humanos y no humanos mediante morfometría geométrica. Se han utilizado 62 omóplatos de individuos adultos de sexo desconocido (22 humanos actuales, 1 Neandertal y 39 primates no humanos), procedentes de las colecciones de las Universidades UAB, UB y del Museo de Ciencias Naturales de Barcelona. Cada escápula se fotografió ortogonalmente y se cuantificó su morfología mediante el uso de puntos anatómicos de referencia (12 para la cara posterior y 13 para la anterior). Después de evaluar la fiabilidad de las mediciones mediante un test de distancias euclídeas, se analizó la diversidad de este hueso en las diferentes especies de primates mediante un Análisis de Componentes Principales (ACP). Los resultados mostraron clara separación morfológica entre primates cuadrúpedos y no cuadrúpedos (suspensores, saltadores y bípedos). En este último conjunto los humanos se separan netamente del resto. En los primates cuadrúpedos predomina la dimensión horizontal (mayor anchura y menor altura), mientras que en los no cuadrúpedos se da la tendencia contraria (menor anchura y mayor altura). La espina escapular queda situada en posición más horizontal enprimates cuadrúpedos respecto a los no cuadrúpedos, aunque en el género Homo, esta inclinación está atenuada. La escápula analizada de Neandertal, si bien es más robusta y con menor inclinación de la espina escapular que la de los humanos actuales, se agrupa bien con éstos. Nuestros resultados muestran el potencial de la metodología utilizada para el estudio de la morfología escapular de Homo y demás géneros de primates

Dynamic acromiohumeral interval changes during scapular plane arm motions

This purpose of this dissertation is to explore changes in the acromiohumeral interval during dynamic motion in the scapular plane. All of the experiments were completed in the Football Operations Athletic Training Room at Louisiana State University. The first experiment which investigated dynamic acromiohumeral interval changes in baseball players during a loaded and unloaded scaption exercise from 0°-75°, has been accepted for publication by the Journal of Shoulder and Elbow Surgery (in press, 2010). The mean acromiohumeral interval (AHI) for unloaded and loaded scaption decreased significantly (p\u3c.001) from the arm at the side until 45° and loaded scaption narrowed AHI at 60° (p=.005) and 75° (p=.003). The second experiment investigates AHI and scapular upward rotation (SUR) changes in baseball and softball players during scaption exercises from 0°-75°. Significant load related narrowing of the AHI at 45°(p=.005), 60°(p=.001), and 75°(p\u3c.001) and a significant load-position interaction (p=.001) at 0° and 75°was observed for all subjects. No gender differences in SUR or AHI were found. AHI and SUR displayed moderate positive correlations at 30° for both the unloaded scaption (r=.648, p=.001) and the loaded scaption (r=.445, p=.038) however, no significant relationships were present at 0°, 45°, 60° or 75°. The third experiment compared dynamic acromiohumeral interval and scapulohumeral rhythm changes in trained and untrained females during scaption exercises from 0°-90°. In general, AHI was maximal with the arm at the side and declined significantly (p\u3c.001) during arm elevation until 60°, but increased significantly (p\u3c.001) between 60° and 90°. Significant load related narrowing of the AHI at all positions (p\u3c.05), a more negative SUR at 0° (p\u3c.001) and a more positive SUR at 90° (p=.009) was observed for all subjects. Female athletes had significantly stronger external rotators (p\u3c.001), larger overall AHI (p=.003) and more SUR (p=.008) than untrained females. Significant positive correlations (p\u3c.05) between AHI and SUR were observed at 0°, 30°, and 60° during both loaded and unloaded scaption

A Closed-Loop EMG-Assisted Shoulder Model

The human shoulder is a complex musculoskeletal system. Knowledge about its kinematics and dynamics can help improve associated treatments. However, to date direct measurements of these quantities can be only granted through invasive investigations or expensive imaging techniques. Musculoskeletal shoulder models provide useful predictions of shoulder kinematics and dynamics. Nevertheless, there remain significant gaps between the model predictions and behaviors of the real system. This thesis aims at extending an existing shoulder musculoskeletal model for patient-specific clinical applications. To this end, number of improvements are considered. The initial model only considered an outstretch arm. Therefore, the elbow and the muscles spanning it are added in the extended model. To this end, the bone morphologies of the ulna and the radius and muscles architectures are obtained from MRI scans. The elbow is modeled using two hinge joints replicating its flexion/extension and pronation/supination motions. The model is developed based on anthropometric data of a single subject. Given anthropometric variabilities among subjects, it cannot predict inter-individual differences. Therefore, scaling routines are developed to scale the model to a specific subject. The model's bone segment inertial properties, skeletal morphologies, and muscles architectures are scaled according to any specific subject. The effects of anthropometric parameters on glenohumeral (GH) joint reaction force predictions are evaluated. Humeral head translations (HHT) play a crucial role in the GH joint functions. Given that the model is developed based on inverse dynamics, it falls short of predicting the HHT. Therefore, a framework is developed allowing forward-dynamics simulation of the model with a six DOF GH joint. A deformable articular contact is included in the framework defining the GH joint contact force in terms of the joint rotations and translations. A videogrammetry systems is used for recording upper extremity motions. It measures trajectories of skin-fixed markers. However, it cannot practically track scapula motions and the GH joint center. Therefore, a method is developed estimating the GH joint center and consequently scapula motions. Multi-segment optimization is used to reconstruct the measured motions in terms of joints angles. A musculotendon model is a key component for muscle-driven applications of the model. A Hill-type musculotendon model is developed. However, the initial state of the Hill-type model is not provided. Therefore, singular perturbation analysis is used to propose a method providing an initial state for the developed Hill-type model. Given that the model is over-actuated, an optimal load-sharing is used to predict muscle forces. It overlooks antagonistic muscle co-contractions. However, muscle co-contractions play crucial roles in the GH joint stability. Therefore, the load-sharing is modified such that measured electromyography (EMG) data can be incorporated. It is hypothesized that inclusions of the measured EMG can improve model predictions of muscle co-contractions. The developed model provides predictions of joints angles, muscles forces, and GH joint force and translations that are in good agreements with in vivo studies. It could be populated with pre/post operative patients of total shoulder arthroplasty to answer clinical questions regarding treatments of GH joint osteoarthritis

Performance Benefits of Customised Seating Interfaces for Elite Wheelchair Racing Athletes

The limited customisation in commercially available wheelchairs does not always appropriately accommodate the anthropometric variations resulting from specific impairment. Wheelchair racing athletes demonstrate up to 3.8% total body mass greater in the upper extremities, and up 9.8% total body mass reductions in their lower extremities, and between-limb asymmetries of 62.4%. As a consequence, athletes may not have the stable base of support required for optimal propulsion. The optimisation of an entire wheelchair to match unique athlete geometry is both time consuming and costly, as wheelchairs cost over $2000 each. The use of assistive technology can provide an efficient transition between the commercially available equipment and the unique athlete anthropometry. Customised seating interfaces offer a time and cost effective solution, facilitating regular modifications to satisfy athlete growth. These solutions have been used extensively in clinical applications for enhanced stress distribution and injury prevention at the seating interface; however, they have not yet been applied to sporting contexts. The goal of this research was to investigate the performance impact of customised seating interfaces on wheelchair racing propulsion technique. Supplementary goals included the development of practically viable instrumentation solutions and a musculoskeletal model representative of the unique wheelchair racing athlete anthropometries and physical capabilities to assess injury risk to analyse performance impact holistically. The research was split into four main themes: 1. Verification of the importance of the seating interface relative to other key performance parameters such as aerodynamics and glove selection. 2. Instrumentation of the hand-pushrim and seating interfaces 3. Development of a musculoskeletal model 4. Computational modelling of performance and injury risk Computational modelling was performed in the OpenSim environment which coupled kinematic inputs from 3D motion capture (VICON Bonita V16; Oxford Metrics, Oxford, United Kingdom), with kinetic inputs from a pressure mat at the seating interface (XSensor LX100; Calgary, Alberta, Canada) and inertial measurement units (IMUs) (I Measure U; New Zealand) to estimate the hand-interface interactions. This was achieved using Newton’s Second Law, incorporating athlete-specific mass data (from the analysis DXA scans), and acceleration measured from the IMU. Customised seating interfaces reduced the undesirable peak translations of the knee by up to 41.8% and lateral translation of the spine by 33.4%. These translated towards enhanced performance, with an average performance time reduction of 29.8 s (3.7% race time) in the eight international competitions following the inclusion of the customised seating interface. Additionally, athletes using cushioned seating interfaces had reduced peak pressures at the seating interface as compared to those without the interface. Instrumentation can be used outside the laboratory environments, and can, therefore, be applied in the daily training environment to optimise performance preparation. This research provided foundation work for the use of computational biomechanical analyses for the holistic assessment of wheelchair racing performance. Whilst this research has demonstrated the potential impact computational modelling approaches can have on the performance preparation of athletes, some areas for further refinement have been identified. Future research into the processing of IMU data and the validation of musculoskeletal models for wheelchair racing athletes are the critical areas for improvement. Once achieved, the computational modelling approaches explored in this research can positively impact performance outcome, particularly when coupled with the optimisation of equipment, such as customised seating interfaces.Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 201

The Scapula in Musculoskeletal Modelling of Extreme Activities

This thesis presents a musculoskeletal model that predicts the muscle and joint forces in the upper limb during an extreme activity. The scapula is an important link in the kinematic and dynamic chain of the upper limb; with its muscles acting as the primary stabilisers to the inherently unstable glenohumeral joint, thus allowing effective transmission of load through the kinematic chain of the shoulder. This bone is poorly represented in musculoskeletal models during these activities. Large soft-­‐tissue artefacts are a key reason for this. The shoulder is particularly prone to injury in overhead activities of the upper limb. Heavily loaded activities in these positions are of interest because they represent a limit, in that few people are capable of performing them. Pull-­‐ups are a common training activity that involve the movement of a large load with the arms overhead. Predicting the forces involved in such an activity allows a testing of current model limits and hypotheses on the function and biomechanics of the scapula. A novel methodology to track the dynamically moving scapula is validated using motion capture technology. This method is shown to improve measurement accuracy when compared to the literature. Kinematics of the scapula and upper limb are thus measured, presented and discussed for three types of pull-­‐up activity. The modelling aspects of the work build on a previous upper limb model, primarily adapting the kinematics representation. This better respects the measured kinematics through a relaxation of the closed-­‐chain mechanism as well as improving the ability to non-­‐homogeneously scale the model. The inverse dynamics description is modified to allow a variable hand load, muscle wrapping parameters and changed to prevent sudden unphysiological changes in moment arms and muscle bounds are increased to allow equilibrium to be reached with the inter-­‐segmental moments. Musculoskeletal loads are thus presented using a model that allows the dynamic analysis of extreme activities. Eccentric loading of the supraspinatus, deltoid and triceps was found to exist in potentially vulnerable positions, coinciding with a high incidence of impingement injury in pull-­‐up type activities. The glenohumeral joint reaction force is seen to be more centralised with a general increase in rotator cuff activation, although teres major and posterior deltoid seem to be key stabilisers. Pectoralis major was detrimental to stability, highlighting the importance of the scapula in positioning muscles during overhead activities. Comparison of model predictions with literature EMG results show good agreement