Shoulder Joint replacement is either partial or complete
Complete Shoulder Joint Replacement may be anatomical or reverse, where in anatomical, the soft tissue including the muscles and tendons are intact.
In reverse shoulder joint replacements, the muscles and tendons are weak or injured.
In partial shoulder joint replacements, the cup/glenoid is intact but the ball/head of humerus is damaged.
In this case only the head/ball of humorous has arthritis