Saturday, July 25, 2015

Shoulder arthroplasty - B2 glenoid - how big of a deal is it really?

Quantification of B2 glenoid morphology in total shoulder arthroplasty.

These authors examined 106 shoulders having total shoulder arthroplasty. They classified glenoids by direct visualization and noted lines of biconcavity demarcation and erosion in B2s. They measured the amount of glenoid bone loss as the maximal distance between a glenoid sizer disk applied to the normal (uneroded) part of the glenoid anteriorly and the edge of the eroded glenoid posteriorly. They then calculated the "angle of erosion" as that between the back side of the unsupported, smooth-backed glenoid sizer disk and the eroded glenoid.

They classified 43 of 106 glenoids (41%) as B2. A biconcavity demarcation line between the paleoglenoid and the neoglenoid was present, on average, from the 1-o'clock to the 7-o'clock position for a left shoulder. Mean depth of erosion was 4.4 mm, occurring at 114° on a Cartesian coordinate system for a left shoulder. The mean angle of erosion was 18° (range, 8°-43°). Despite reaming, 20 of 43 B2 glenoids (47%) had incompletely supported components at final seating.

They documented that  maximal glenoid erosion is usually posteroinferior, not directly posterior.

Their conclusion is that "Use of standard glenoid components to reconstruct them may require significant subchondral bone removal to achieve complete bone support. Alternatively, as a compromise, maintenance of subchondral bone in these cases requires implanting components with incomplete bony support".

Comment: The importance of this paper lies in its documentation (1) biconcave glenoids are common in glenohumeral arthritis and (2) that the glenoid erosion is usually posterior-inferior so that a component with straight posterior augmentation, such as that below

cannot be inserted without substantial sacrifice of precious glenoid bone stock, as shown in the diagram below by our colleague Steve Lippitt

Our approach to the B2 glenoid does not require either "significant subchondral bone removal" or "implanting components with incomplete bony support". Rather we orient the glenoid reamer so that it creates a single bony glenoid concavity with minimal bone removal, accepting some glenoid retroversion as shown in the Lippitt figure below.

Extensive experience has shown us that the humeral head can be durably centered on a retroverted glenoid, using an anteriorly eccentric humeral head component and / or rotator interval plication if necessary as described in prior posts. This same approach - reaming only enough to create a single glenoid concavity - is what we routine use in the ream and run - see this post.

Our technique of glenoid arthroplasty is described in this link.


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You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and runreverse total shoulderCTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'