Towards a Classification System for the Shape, Location, and Orientation of Hill-Sachs Lesions

A Hill-Sachs lesion (HSL) is a compression fracture on the humeral head created when the soft humeral head impacts the edge of the glenoid during shoulder dislocation. HSL incidence is reported in 47% of acute anterior glenohumeral dislocations and in 40-80% of patients with chronic instability. A Bankart lesion, the avulsion of the anterior/inferior labrum and inferior glenohumeral ligament from the glenoid rim, is often accompanied by a HSL. Soft tissue repairs are often unsuccessful when a significant bony defect is left untreated; it is our long-term goal to determine which bony defects should be treated to prevent failure of soft tissue repair. Surgeons have proposed the presence of "large" HSLs or the position and orientation of the HSL as causes for recurrent dislocation following Bankart repair. Unfortunately, in the orthopedic literature there is no system for classifying HSLs, or even for quantifying their size, position, and/or orientation which precludes the objective comparison of the work of various authors. The development of such a system is the necessary precursor to the production of any meaningful conclusions about the significance of the HSL. An inexpensive medical image segmentation process using active contours was implemented to build 3D reconstructions of the humeral head. Each of the active contour parameters was optimized for the clinical data set. Literature studies were conducted to come to a consensus on critical lesion traits and methods for computationally quantifying the lesion's traits. The long-term goal of this study is to compare clinical outcomes to the quantitative measures determined using this method.Digitized from a paper copy provided by the Physiological Sciences Graduate Interdisciplinary Program

Generic template based 3D object reconstruction using regional partitioning.

Tong Kai Man.Thesis (M.Phil.)--Chinese University of Hong Kong, 2006.Includes bibliographical references (leaves 76-80).Abstracts in English and Chinese.Chapter 1. --- Introduction --- p.1Chapter 1.1 --- Background --- p.1Chapter 1.2 --- Previous and related works --- p.2Chapter 1.3 --- The Proposed Method --- p.4Chapter 1.4 --- Thesis outline --- p.6Chapter 2. --- Global deformation --- p.8Chapter 2.1 --- Feature points --- p.8Chapter 2.2 --- The deformation --- p.9Chapter 2.2.1 --- Deformation using affine transformation --- p.9Chapter 2.2.2 --- Elastic warping using Radial Basis Functions --- p.12Chapter 2.2.3 --- Biharmonic and triharmonic basic functions --- p.16Chapter 3. --- Local iterative surface fitting --- p.19Chapter 3.1 --- Basic closest point method --- p.19Chapter 3.2 --- Regional partitioning method --- p.27Chapter 3.2.1 --- Defining the regions --- p.29Chapter 3.2.2 --- Propagating from the seeds --- p.31Chapter 3.2.3 --- Handling the distortions --- p.36Chapter 3.3 --- Combined methods for surface fitting --- p.41Chapter 3.3.1 --- Summary of the surface fitting methods --- p.41Chapter 3.3.2 --- Combining the methods --- p.43Chapter 3.3.3 --- Fine-level fitting results --- p.47Chapter 4. --- Enhanced template based 3D Object reconstruction --- p.53Chapter 4.1 --- Compactly supported radial basis functions --- p.53Chapter 4.2 --- Reconstruction using two templates --- p.55Chapter 5. --- Implementations and Results --- p.60Chapter 5.1 --- Creation of 3D objects --- p.60Chapter 5.2 --- Feature points selection --- p.61Chapter 5.3 --- Experiment platform --- p.62Chapter 5.4 --- Results --- p.63Chapter 6. --- Conclusions --- p.71Chapter 6.1 --- Contributions --- p.72Chapter 6.2 --- Future developments --- p.72Appendix A --- p.73Voxel based closest point evaluation --- p.73References --- p.7

The polyhedral Gauss map and discrete curvature measures in geometric modelling.

The Work in this thesis is concentrated on the study of discrete curvature as an important geometric property of objects, useful in describing their shape. The main focus is on the study of the methods to measure the discrete curvature on polyhedral surfaces. The curvatures associated with a polyhedral surface are concentrated around its vertices and along its edges. An existing method to evaluate the curvature at a vertex is the Angle Deficit, which also characterises vertices into flat, convex or saddle. In discrete surfaces other kinds of vertices are possible which this method cannot identify. The concept of Total Absolute Curvature (TAC) has been established to overcome this limitation, as a measure of curvature independent of the orientation of local geometry. However no correct implementation of the TAC exists for polyhedral surfaces, besides very simple cases.For two-dimensional discrete surfaces in space, represented as polygonal meshes, the TAC is measured by means of the Polyhedral Gauss Map (PGM) of vertices. This is a representation of the curvature of a vertex as an area on the surface of a sphere. Positive and negative components of the curvature of a vertex are distinguished as spherical polygons on the PGM. Core contributions of this thesis are the methods to identify these polygons and give a sign to them. The PGM provides a correct characterisation of vertices of any type, from basic convex and saddle types to complex mixed vertices, which have both positive and negative curvature in them.Another contribution is a visualisation program developed to show the PGM using 3D computer graphics. This program helps in the understanding and analysis of the results provided by the numerical computations of curvature. It also provides interactive tools to show the detailed information about the curvature of vertices.Finally a polygon simplification application is used to compare the curvature measures provided by the Angle Deficit and PGM methods. Various sample meshes are decimated using both methods and the simplified results compared with the original meshes. These experiments show how the TAC can be used to more effectively preserve the shape of an object. Several other applications that benefit in a similar way with the use of the TAC as a curvature measure are also proposed