This narrative review reconstructs the 20-year intellectual and experimental journey by which Paul Grammont developed the biomechanical rationale for the modern reverse shoulder prosthesis. It traces the path from comparative anatomy observations through failed predecessors to the Delta III design. The paper explains why each prior approach failed and what specific mechanical insight Grammont contributed.
C.S. Neer called cuff tear arthropathy 'limited goals surgery' because every implant before Grammont failed for the same mechanical reason: without a functioning rotator cuff, the unopposed deltoid generates eccentric shear that loosens the glenoid and cannot center the humeral head.
When you evaluate a patient with cuff tear arthropathy, the reverse shoulder prosthesis works because of one deliberate departure from anatomy: the COR is placed at the glenoid face, not in the humeral head. This single change increases the deltoid lever arm and converts destabilizing shear into concentric compression at the baseplate.
Knowing this principle explains the scapular notching you will see on postoperative radiographs. Notching is the geometric consequence of the same medialization that makes the prosthesis mechanically stable — the humeral cup swings into the scapular pillar during adduction because the COR is medial.
Current lateralized-glenosphere designs reduce notching and increase motion, but move away from Grammont's lever-arm principle. The functional trade-off is still debated. For the boards, the key distinction is COR position: prior reverses had a lateralized COR; Grammont moved it to the glenoid face, and that single change is the entire basis of modern reverse shoulder arthroplasty.
This narrative review reconstructs the 20-year intellectual and experimental journey by which Paul Grammont developed the biomechanical rationale for the modern reverse shoulder prosthesis. It traces the path from comparative anatomy observations through failed predecessors to the Delta III design. The paper explains why each prior approach failed and what specific mechanical insight Grammont contributed.
C.S. Neer called cuff tear arthropathy 'limited goals surgery' because every implant before Grammont failed for the same mechanical reason: without a functioning rotator cuff, the unopposed deltoid generates eccentric shear that loosens the glenoid and cannot center the humeral head.
When you evaluate a patient with cuff tear arthropathy, the reverse shoulder prosthesis works because of one deliberate departure from anatomy: the COR is placed at the glenoid face, not in the humeral head. This single change increases the deltoid lever arm and converts destabilizing shear into concentric compression at the baseplate.
Knowing this principle explains the scapular notching you will see on postoperative radiographs. Notching is the geometric consequence of the same medialization that makes the prosthesis mechanically stable — the humeral cup swings into the scapular pillar during adduction because the COR is medial.
Current lateralized-glenosphere designs reduce notching and increase motion, but move away from Grammont's lever-arm principle. The functional trade-off is still debated. For the boards, the key distinction is COR position: prior reverses had a lateralized COR; Grammont moved it to the glenoid face, and that single change is the entire basis of modern reverse shoulder arthroplasty.