Glenoid osteotomy shoulder surgery, illustration. This operation involves the cutting of the bone (osteotomy) in the shoulder joint (glenoid cavity). Part of the scapula (at left) is being cut and extended, with bone graft material (red) inserted in the gap created. This is typically done to stabilise the joint to prevent dislocations. The rounded area at right is the head of the humerus (upper arm bone).