A
To anatomicalize the glenohumeral joint center of rotation
B
To increase the tension on the remaining rotator cuff muscles
C
To lateralize the center of rotation to improve stability
D
To medialize and inferiorize the center of rotation, increasing the deltoid lever arm
Explanation:The correct option is 'd'. The reverse total shoulder arthroplasty (Grammont design) biomechanically medializes and distalizes (inferiorizes) the center of rotation. This recruits more deltoid muscle fibers and significantly increases its moment arm, allowing the deltoid to elevate the arm in the absence of a functioning supraspinatus.
Reference: Boileau P, et al. Grammont reverse prosthesis: design, rationale, and biomechanics. J Shoulder Elbow Surg. 2005;14(1 Suppl S):147S-151S.