These are a few cases of baseplate failures in reverse total shoulder prostheses performed using different modern systems. What are the commonalities between these failures?
Answer: the glenosphere in each of these cases has been shook up more than usual. This is because the major loads on the glenoid component – whether from deltoid contraction, from a fall, or from pushing up from the bed – exert a superiorly directed force on the glenosphere that challenges the base plate’s fixation to bone.
The ability of the glenoid component to resist these major loads depends on (1) secure bony fixation of the inferior screws in bone (green arrows) to resist failure in traction and (2) compression of the superior aspect of the baseplate against glenoid bone (yellow arrow) to prevent its rocking upwards as pointed out in Factors affecting fixation of the glenoid component of a reverse total shoulder prothesis.
If any of these are insecure, upward forces on the glenosphere could cause the baseplates to move away from bone.
The key to good carpentry is: (1) prepare the glenoid so that the superior baseplate has maximum contact with the host bone, and (2) secure the screw.