Review Question - QID 217907

Rotator cuff arthropathy with superomedial migration may result in superior glenoid bone loss. This may lead to inadvertent placement of the glenosphere too far superior, with superior tilt, or both resulting in increased risk for scapular notching.

Scapular notching is a well-described complication of reverse total shoulder arthroplasty (rTSA) in which the humeral implant polyethylene abuts the inferior glenoid during shoulder adduction movement. Over time, this can result in inferior scapular bone loss, osteolysis, declining function, and implant loosening. While scapular notching was originally believed to be inconsequential, it has been established that patients with scapular notching have lower outcome scores as compared to patients without scapular notching. Therefore, it is imperative to recognize patients at risk for scapular notching and take the appropriate steps intraoperatively to avoid this complication.

Friedman et al. reviewed scapular notching in rTSA. They discuss some techniques that can avoid scapular notching including using lateralizing glenosphere implants, placing the glenosphere with inferior tilt, using an inferior-offset glenosphere with some inferior overhang, using a lateralized humeral implant, and utilizing the deltopectoral approach. They conclude by emphasizing the importance of the surgeon’s understanding of implant biomechanics and design to minimize scapular notching in each patient.

Boileau et al. investigated a novel way to measure the glenoid inclination when planning for rTSA implants. They found that the standard glenoid inclination angle used for templating anatomic total shoulder arthroplasties can result in glenosphere superiorization and/or superior tilted malpositioning. They conclude that their novel rTSA angle accounts for the inferior placement of the glenosphere baseplate on the native glenoid resulting in more reliable and appropriate implant placement.

Figure A shows the Grashey AP view of a right-sided rTSA. There is appreciable inferior scapular notching secondary to the abutment of the inferior glenoid polyethylene against the inferior glenoid.

Incorrect Answers:
Answers 1: Lateralization of the humerus implant decreases the risk of scapular notching. Lateralization is achieved by utilizing an implant with a more acute, lower neck shaft angle (132.5°) as compared to the more obtuse, standard 155 ° used by the Grammont style rTSA implants.
Answer 3: Placing the glenosphere with 10 degrees of inferior tilt decreases the risk of scapular notching. Many of the modern rTSA implant sets include a guide specifically purposed for ensuring placement of some glenosphere inferior tilt.
Answer 4: Using inferior offset glenosphere implants and those used with slight inferior overhang (3mm) appear to confer the greatest reduction in scapular notching.
Answer 5: While the surgical approach is surgeon- and training- dependent, it is generally accepted the risk of superior placement or superior tilt of the glenosphere (and thus the risk for scapular notching) is greater with anterosuperior (i.e deltoid splitting approach) than the deltopectoral approach.