The Influence of Different Rotator Cuff Deficiencies on Shoulder Stability Following Reverse Shoulder Arthroplasty.

Background: The primary indication for reverse shoulder arthroplasty (RSA) is rotator cuff arthropathy caused by a deficient rotator cuff. Cuff deficiency in patients is highly variable in its distribution and extent, with mechanical implications that may significantly affect post-operative recovery. This study investigated the effects of variable cuff deficiency on the propensity for impingement between the scapula and humeral component and resulting subluxation, the source of two common complications (scapular notching and instability).

The effect of glenoid component version and humeral polyethylene liner rotation on subluxation and impingement in reverse shoulder arthroplasty.

Background: A previously validated finite element modeling approach was used to determine how changes in glenoid component version and polyethylene liner rotation within the humeral component affect the arm abduction angle at which impingement between the inferior glenoid and the polyethylene liner occurs as well as the amount of subluxation generated by that impingement.

Materials And Methods: Five glenoid component versions (5° anteversion; neutral; 5°, 10°, and 20° retroversion) and 7 polyethylene liner rotations (20° and 10° anterior; neutral; 10°, 20°, 30°, and 40° posterior) were considered, resulting in 35 different clinically representative models. The humerus was internally and externally rotated and extended and flexed, and the resulting impingement and subluxation were measured.

Cadaveric validation of a finite element modeling approach for studying scapular notching in reverse shoulder arthroplasty.

Cadaveric experiments were undertaken to validate a finite element (FE) modeling approach for studying impingement-related scapular notching in reverse shoulder arthroplasty (RSA). The specific focus of the validation was contact at the site of impingement between the humeral polyethylene component and the inferior aspect of the scapula during an adduction motion. Lateralization of the RSA center of rotation was varied because it has been advocated clinically to reduce impingement and presumably decrease the risk of scapular notching.

Mechanical tradeoffs associated with glenosphere lateralization in reverse shoulder arthroplasty.

Background: Scapular notching in reverse shoulder arthroplasty occurs in up to 97% of patients. Notching is associated with decreased strength and reduced motion and may lead to long-term failure due to polyethylene wear. Many implant systems lateralize the glenosphere to address scapular notching, but the mechanical tradeoffs of lateralization have not been rigorously evaluated.