Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article


Master of Engineering Science


Mechanical and Materials Engineering


Johnson, James A.


Replacement of the human shoulder with implants is a commonly employed procedure in orthopedics to alleviate patient discomfort and pain. The alignment of the implant relative to bone is an important parameter when considering the stability and long-term fixation of the implant. This thesis explored the effect of the selection of the cut plain by 4 different surgeons in a series of glenoid models, and subsequently evaluated the variation of the cut planes on load transfer from implant to bone using finite element modeling. The findings indicated that there is a wide variation in the selection of the cut plane amongst the surgeons based on a target alignment established via preoperative planning software. Using the variation that was determined in this study, it was shown that the stresses and implant stability or micromotion were highly variable for these various different combinations of cut planes. It is concluded that with current approaches to the selection of cut planes, there is a wide variation in the load transfer mechanics, even for the same bone model. This has implications with regard to surgical outcomes and biomechanical modelling predictions.

Summary for Lay Audience

Shoulder replacement surgery is becoming a more popular procedure in North America. A key component of shoulder implant performance is alignment of the implant. As such, this thesis examined the link between surgeon performance at inserting the glenoid implant and the expected implant performance. Using observed surgeon variability in implant insertion, the impact of glenoid implant misalignment was simulated using three-dimensional computer models. The results of these studies indicated that typical surgeon performance can lead to drastically different implant performance. These results stress the importance of considering surgeon performance when performing biomechanical predictions for new implant designs.