In a total shoulder replacement, both the humeral head and the socket, or glenoid, of the shoulder is replaced. There is a risk that the glenoid component will loosen over time for people who are young or very active. The glenoid component is made of polyethylene and is cemented into place. Over time, this can loosen as a result of the forces placed on this component during shoulder motion. Based on your lifestyle, we may determine that a partial shoulder replacement would be better for you. Weightlifters, triathletes, or others with demanding hobbies or occupations may wear out the polyethylene glenoid socket more quickly. Another scenario where hemiarthroplasty may be used is in a condition called vascular necrosis, or AVN. This is a clinical condition that develops when the blood supply to the humeral head is compromised, causing deterioration. The surgeon only needs to replace the ball in this situation since the socket of the joint is still well preserved.