Scapular notching results when the medial aspect of the humeral cup contacts the lateral scapular margin.
An example is shown here in the area marked by the dark line. Note that the scapular bone in this area has been completely reabsorbed, leaving the glenoid component relatively unsupported. Notching has been associated with damage to the polyethylene of the humeral cup, with instability and with inferior clinical outcomes.
The authors hypothesized that inferiorly tilting the glenosphere (as shown below) would decrease the grade of notching. It is of interest that notching was present in 70% of their 71 cases at a minimum of 12 months after surgery. There was no statistically significant different in the notching rate or severity between those shoulders with inferior tilt and those with neutral tilt.
The shoulders in this study were not randomized and were not controlled for the different types of prostheses used. The clinical outcomes are not presented.
Many factors can affect notching, including the design of the component (especially with respect to the offset of the glenosphere from the scapula) and the superior-inferior position of the glenoid.
Inferior tilt would appear to have the disadvantage of moving the center of rotation and, therefore, the humeral component medially - in closer proximity to the scapula - as suggested by the diagrams above from this article. Inferior tilt also has the disadvantage of require sacrifice of bone at the inferior glenoid - glenoid bone stock is precious in the elderly individuals requiring this procedure.
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