As the idea of the ream and run procedure progressed towards clinical application, shoulder fellows Weldon and Boorman carried out some important laboratory research on Optimizing the Glenoid Contribution to the Stability of a Humeral Hemiarthroplasty. In this study on cadaver shoulders they found that the glenoid contribution to shoulder stability (as measured by the balance stability angle) was decreased by the removal of cartilage and labrum and was restored by spherical reaming to a level similar to resurfacing the glenoid with a polyethylene component. They studied the stability of four different glenoid states:
Interestingly, they found that removal of the cartilage from the glenoid surface dramatically diminished the stability provided by the glenoid socket - especially in the posterior inferior direction (compare 'native' to 'denuded' on the figure below - the 225 degree direction is posterior inferior). This helps understand why the humeral head often starts to slip posteriorly in arthritis as shown in previous posts.
When the face of the glenoid is spherically reamed, as we do in performing a ream and run, the stability is restored - even beyond that of the normal glenoid (see 'reamed 22.5' and 'reamed 25.0' on the figure above. As the table below shows, the stability of the reamed glenoid is comparable to that of a polyethylene glenoid component.
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