| In the 1970's clinicians observed that total shoulder arthroplasty patients with a deficient rotator cuff demonstrated recurrent problems with dislocation and scapular fixation, resulting in failed devices and poor patient outcomes. An alternative design, known as reverse shoulder arthroplasty (RSA), was developed for these patients in which the articulating surfaces are reversed from the anatomic state. This biomechanical modification increases conformity, medializes the center of rotation and increases the deltoid moment arm in an attempt to restore stability and range of motion in rotator cuff deficient patients.;With RSA, native biomechanics are not preserved and therefore, alternative failure mechanisms may present. One common complication observed is scapular impingement, which occurs when the humeral component impinges on the scapula, resulting in bone degradation and polyethylene debris release to the surrounding joint space. Historically, polyethylene debris in large volumes has resulted in osteolysis and ultimately, failure of the implant. The goal of this work is to develop validated methods for analyzing the impingement wear and intended articulation wear of humeral liners of various designs. This work will aim to identify likely risk factors for osteolysis in an attempt to prevent subsequent failures.;As a response to the high prevalence of scapular impingement and scapular notching, manufacturers have altered designs to lateralize and distalize the center of rotation to pull the humeral component away from the scapula. Altering these biomechanics will inherently change the muscle forces required to perform activities of daily living, however, these changes have not previously been quantified. Scapular fracture has been observed to be prevalent in reverse shoulder arthroplasty, with incidences of up to 10% reported in the literature. The goal of this work is to determine how changes in the joint center affect the resulting muscle load and consequently, the strain state of the scapula using a combination of solid modeling, dynamic modeling, and finite element analysis.;Understanding the polyethylene wear mechanisms of RSA as well as potential impacts of altering the RSA design to prevent scapular impingement on scapular biomechanics will allow clinicians to make more informed decisions regarding appropriate device design and surgical technique for a given patient population. |
