Electronic Thesis and Dissertation Repository

Thesis Format



Master of Engineering Science


Mechanical and Materials Engineering


Ferreira, Louis


The fundamental mechanism of aseptic glenoid component loosening, the rocking horse phenomenon, is a reaction to glenohumeral articular forces that are not centered on the component. While glenoid component loosening remains a problem, the underlying mechanisms that lead to fixation failure at the bone-component contact remain controversial. Several studies employing the ASTM F2028 technique have successfully recreated the rocking horse effect. However, no obvious strategy to decrease component loosening has been presented. This thesis investigates the behavior of forces that lead to component loosening on cyclically loaded components using three different protocols and testing apparatuses—a Stewart Platform, a cyclic loading experimental rig, and an ASTM F2028-17-compliant version of the experimental rig. The experimental assessment of response forces acting on the glenoid implant is a desired outcome since it can be used to compare implant designs and allows for controlled testing of alternative materials for prosthesis advancement to lessen the stresses that produce the rocking horse phenomena.

Summary for Lay Audience

A variety of disorders can cause shoulder discomfort and impairment, prompting patients to seek partial or complete shoulder joint replacement surgery. The shoulder is classified as a nonconforming ball-and-socket joint. The ball, which is the spherical head of the upper arm bone, is inserted into the glenoid, a shallow socket in the shoulder. To restore the shoulder's function, total shoulder arthroplasty (TSA), the gold standard for surgical treatment of severe shoulder osteoarthritis, involves replacing both the ball and socket with artificial components that closely resemble the natural shape of the bones. TSA results in decreased pain and greater mobility; nevertheless, glenoid loosening, a serious side effect that can develop years after surgery and cause postoperative discomfort, function limitations, and occasionally the need for revision surgery, is still a major concern. The mechanism behind glenoid loosening is called the rocking horse phenomenon, or edge loading. It develops from the ball prosthesis' repetitive motion on the glenoid implant's surface. During edge loading, the glenoid component is compressed against its bone fixation on one side, while experiencing lift on the opposite side. Ultimately, this repetitive movement causes the implant to become detached from its bone fixation. An indispensable factor in determining the incidence of wear and loosening as well as the recommended activity levels for patients following TSA is the amount of load that the prosthetic glenoid component is subjected to during edge loading. This thesis focuses on the design and implementation of a testing apparatus designed to simulate edge loading to evaluate the behavior of the forces acting on aseptic glenoid implants. The testing device's performance was evaluated, and its capacity to reproduce the rocking horse phenomena was validated. Further testing of the device compares various implant types and assesses their response to cyclic stresses. The findings in this body of work support the theory that glenoid prosthetic design has an impact on response forces under cyclic loading, with increased stress loading being detected when the humeral head travels further from the component's center.