Shoulder hemiarthroplasty is a procedure that replaces half of the shoulder joint. Your shoulder joint is made up of two parts: A ball at the end of the humerus bone in your upper arm is called the humeral head. A socket in your shoulder blade called the glenoid. The humeral head rotates within the glenoid to make the shoulder joint. In shoulder hemiarthroplasty, the humeral head is replaced, and the glenoid is left intact. The surgeon will then repair the rotator cuff tissue to complete the surgery.