The optimal placement of components in reverse total shoulder arthritis is a subject of much debate. The authors of Challenges for Optimization of Reverse Shoulder Arthroplasty Part II: Subacromial Space, Scapular Posture, Moment Arms and Muscle Tensioning provide an in-depth analysis of some of these factors.
The following summarizes their key findings:
(A) Hierachical order of the most important factors to optimize abduction and adduction ranges of motion.
(1) Lingualizing the gleosphere’s center of rotation
(2) distalizing glenosphere (e.g. By placing the baseplate lower, or using a smaller baseplate, and/or using an inferiorly eccentric baseplate),
(3) Tilting the glenosphere inferiorly
(4) Increasing the angle of the neck-shaft.
Below are the effects of offset and superior/inferior positions. The green zone represents the impingement-free area of adduction/abduction.
(B) Patients suffering from severe kyphosis may experience reduced adduction/absduction, external rotation, extension, and/or external rotation. A higher retrotorsion and lower neck-shaft angle may be considered.
(C) An abduction moment arm with a medial centre of rotation and a tuberosity lateralized is maximized.