Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Science

Program

Surgery

Supervisor

Johnson, James A.

Affiliation

Roth McFarlane Hand and Upper Limb Clinic

2nd Supervisor

Athwal, George S.

Affiliation

Roth McFarlane Hand and Upper Limb Clinic

Joint Supervisor

Abstract

Improving the success of modern reverse shoulder replacements is dependent on optimal initial baseplate fixation. A cadaveric biomechanical investigation examined how peripheral screw position and orientation affect baseplate fixation in normal glenoids. The results show no statistically significant difference between screw position (p=.60) or orientation (p=.20) regarding baseplate micromotion in the non-eroded glenoid. In a subsequent study to determine best management in pathologic baseplate fixation, a computer-model was employed to quantify the erosion in the E2 type glenoid. In the E2 type glenoid, erosion was found to be oriented postero-superiorly and covering an average of 66% of the surface area of the glenoid, requiring a full augmented baseplate for best seating. Overall, these findings support aiming peripheral screws into best quality bone. In the eroded E2 type glenoid, this is located postero-superiorly encompassing two-thirds of the glenoid’s surface and can be managed by dialing a full wedge augmented baseplate postero-superiorly.

Summary for Lay Audience

Improving the success of modern reverse shoulder replacements depends on proper attachment of the baseplate, a component of the shoulder replacement system that is in direct contact with bone. A biomechanical investigation using human cadavers examined how peripheral screw position and orientation affect baseplate fixation in normal glenoids that contain no bone loss. The results show no statistically significant difference between screw position (p=.60) or orientation (p=.20). In a subsequent study to determine best management in baseplate fixation when using a glenoid with bone erosion, a computer-model was used to assess the erosion in the so called E2 type glenoid. In the E2 type glenoid, erosion was found to be oriented upper left corner (in a right shoulder) and covering an average of 66% of the surface area of the glenoid. Overall, these findings suggest that surgeons may aim peripheral screws into the best quality bone. In the eroded E2 type glenoid, this is located in the upper left corner, encompassing the majority of the glenoid’s surface.

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