The authors of The reverse shoulder arthroplasty angle: a new measurement of glenoid inclination for reverse shoulder arthroplasty, point out that the key to achieving inferior inclination is to recognize that (1) the baseplate should be placed on the inferior aspect of the bony glenoid and
(2) the preoperative inclination of the inferior glenoid (C-D) is different than the inclination of the entire glenoid (A-B).
The supraspinatus fossa line is a useful reference line to measure glenoid inclination because the sclerotic line of the supraspinatus fossa line is visible on both plain radiographs and CT scans.
They defined the preoperative reverse shoulder arthroplasty angle as the angle between a line perpendicular to a line drawn along the floor of the supraspinous fossa and the plane of the inferior glenoid (A-S) (below left).
The postoperative reverse shoulder arthroplasty angle is the angle between a line perpendicular to a line drawn along the floor of the supraspinous fossa and the plane of the baseplate (below right).
They suggest that the ideal inclination of the baseplate is perpendicular to the line drawn along the floor of the supraspinous fossa, i.e. the postoperative reverse shoulder arthroplasty angle is zero.
In 47 shoulders with rotator cuff tear arthropathy the preoperartive reverse shoulder arthroplasty angles measured 25±8 degrees on plain radiographs, 20±6 on reformatted 2D CT scans, and 21±5 on 3D reconstructions: thus, each method gave comparable values.
The Favard classification describes the common patterns of glenoid erosion seen with rotator cuff tear arthropathy: no erosion (E0), varying degrees of concentric central erosion (E1), and eccentric superior erosion (E2 and E3). The blue wedges indicate the amount of correction of inclination necessary to place the baseplate perpendicular to a line drawn along the floor of the supraspinous fossa.
Correction of the inclination can be accomplished by reaming the inferior glenoid, adding bone graft beneath the upper part of the baseplate, or using a superiorly augmented baseplate.
Comment: The preoperative reverse shoulder arthroplasty angle is useful for determining the amount of correction needed while the postoperative reverse shoulder arthroplasty angle is useful for determining whether the desired correction was achieved.
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Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link).
Shoulder rehabilitation exercises (see this link).