MEDICAL ANIMATION TRANSCRIPT: The shoulder joint is a highly mobile ball-and-socket joint made up of three bones: the humerus, or upper arm, the clavicle, or collar bone, and the scapula, or shoulder blade. The humeral head is the ball-like structure at the top of the humerus. The clavicle runs between the breastbone and the top of the scapula. The scapula is a flat, triangle-shaped bone that forms the back and top of the shoulder. The glenoid cavity, or socket, is a shallow depression in the part of the scapula closest to the arm. The ball of the humeral head fits into this socket. Articular cartilage is a tissue that covers the humeral head and lines the glenoid cavity. It allows the joint to glide smoothly. Four muscles start at the scapula and run toward the shoulder joint. These muscles are attached to the humerus with tendons, which are strong cords of tissue that connect muscles to bone. These tendons form the rotator cuff, which is a capsule that supports the bones of the shoulder joint and holds the humeral head within the glenoid cavity. The rotator cuff gives the shoulder joint stability, keeping the ball and socket in proper position. The rotator cuff also gives the shoulder joint its wide range of motion. Sometimes, the shoulder joint can become severely damaged from disease or injury. For example, arthritis can erode the articular cartilage in the joint, causing pain and less mobility. Injuries to the rotator cuff, such as a tear, can also cause pain and decrease shoulder joint mobility. Over time, a shoulder with a damaged rotator cuff may develop cuff tear arthropathy, a condition where the shoulder joint develops arthritis due to abnormal motion and instability from the tear. Severe disease or injury of the shoulder joint may need to be treated with a joint replacement. A standard shoulder replacement uses manufactured materials to create a new ball for the head of the humerus and a new socket for the scapula. However, when disease or injury of the shoulder joint is complicated by a severely weakened or injured rotator cuff, a reverse shoulder replacement may be necessary. A reverse shoulder replacement allows the deltoid muscle in the arm to take over movement of the shoulder joint from the weak and injured rotator cuff. In this repair, the position of the ball and the socket are reversed. The socket implant is attached to the top of the humerus, where the ball or head used to be. And, the ball implant is attached to the scapula, where the socket used to be. In a reverse total shoulder replacement, the procedure will begin with an incision over the shoulder joint. The surgeon will separate the head of the humerus from the shoulder joint …and remove it. The humerus will be hollowed out in preparation for placement of the socket implant. Next, the inside of the glenoid cavity will be reshaped to prepare it for placement of the ball implant. A metal base will be attached to the scapula with screws. The ball will be screwed onto the metal base. The socket implant is on a metal stem. It will be inserted into the humerus. Finally, the surgeon will put the new joint together by inserting the ball implant into the socket implant. At the end of the procedure, the incision will be closed with stitches.

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