Shoulder arthroplasty

Inclination of the inferior portion of the native glenoid may be reliably measured with the reverse shoulder arthroplasty angle; in patients with rotator cuff tear arthropathy, according to published results. Superior inclination of the baseplate increases the stresses at the implant bone interface while leading to impingement; between the inferior humeral polyethylene insert and scapula pillar; 13 causing medial polyethylene wear, scapular notching, and eventual glenoid implant loosening.

But avoiding superior inclination of the glenoid component; in reverse shoulder arthroplasty (RSA) is crucial. However, they hypothesized that superior inclination underestimated in RSA. But the purpose was to describe and assess a new measurement of inclination; for the inferior portion of the glenoid (where the baseplate rests).

Inferior part of the glenoid fossa

However, researchers compared the reverse shoulder arthroplasty angle; with the global glenoid inclination (total shoulder arthroplasty angle) among 47 shoulders with rotator cuff tear arthropathy. Researchers defined the reverse shoulder arthroplasty angle as the angle between the inferior part of the glenoid fossa; and the perpendicular to the floor of the supraspinatus. However, three independent observers made measurements on plain anteroposterior radiographs and reformatted 2-D CT scans; and compared these measurements with 3-D software measurements.

But results showed a mean reverse shoulder arthroplasty angle of approximately 25° on plain radiographs; 20° on reformatted 2-D CT scans and 21° on 3-D reconstruction software. However, on average, researchers found the mean total shoulder arthroplasty (TSA) angle was approximately 10° less than the mean reverse shoulder arthroplasty angle. Researchers observed this difference on radiographs, 2-D CT or 3-D CT; and regardless of type of glenoid erosion according to Favard.

Reverse shoulder arthroplasty angle

But the difference between TSA angle and reverse arthroplasty angle; was approximately 12° in Favard type E1 glenoids with central concentric erosion. “Preoperative planning is essential for proper assessment of glenoid erosion; and placement of the reverse baseplate tilt,” the authors wrote. “From a surgical standpoint, the [reverse shoulder arthroplasty] RSA angle; is useful to ensure a neutral tilt of the glenoid component. However, by use of 2-D or 3-D planning, this allows measurement of the thickness and the angle of the bone graft or augmented baseplate needed.”

But the same angle not used to measure glenoid inclination in anatomic; and reverse prostheses. The TSA (or β) angle underestimates the superior orientation of the reverse baseplate in RSA. The RSA angle (20° ± 5°) needs to corrected to achieve neutral inclination of the baseplate (RSA angle = 0°). Surgeons should be aware that E1 glenoids (with central erosion) are at risk for baseplate superior tilt; if the RSA angle is not corrected.