The rotator cuff is made up of muscles, tendons and ligaments that surround the bones of the shoulder. The shoulder is a ball and socket type joint that allows for a large range of motion. It is the muscles and ligaments that help stabilize the shoulder and allow for all the motion. All of these muscles attach to the scapula (shoulder blade) and the humerus of the arm. There are four muscles that specifically make up the rotator cuff.
Supraspinatous
The supraspinatous is the only superior muscle of the rotator cuff and it originates from the top medial part of the scapula, which is the side of the scapula closest to the spine. This muscle travels along the top of the scapula and inserts on the greater tubercle of the humerus, near the top of the shoulder. The greater tubercle can be found by touching the humerus just below the clavicle (collar bone) at the shoulder and turning the arm in and out. The tubercle will feel like a large bump rising under the finger tips. The main action of the supraspinatous is to help move the arm up and away from the body. The supraspinatous is also the most commonly injured rotator cuff muscle according to SportsMedicineDr.com.
Infaspinatous
The infraspinatous is one of two muscles of the posterior rotator cuff and originates from the lower medial part of the scapula. The muscle stretches over most of the lower portion of the scapula and inserts on the greater tubercle of the humerus overlaying the supraspinatous. The main action of the infraspinatous is to rotate the arm laterally, or in external rotation.
Teres Minor
The teres minor is the other posterior rotator cuff muscle and it originates from the lowest and most lateral portion of the scapula, or the part of the scapula that is closer to the arm. The teres minor travels along the lateral edge of the scapula and inserts below the infraspinatous on the greater tubercle of the humerus. Its main action is to rotate the arm laterally or in external rotation.
Subscapularis
The subscapularis muscle originates from the anterior side of the scapula or the front or inside of the scapula, closest to the ribs. This muscles spans the whole of the scapula and inserts on the lesser tubercle of the humerus. The lesser tubercle of the humerus can be found the same way the greater tubercle can; it is just a smaller and harder-to-feel bump. The subscapularis is the only anterior muscle of the rotator cuff.
References
- National Institutes of Health: Shoulder Anatomy
- Sports Med Dr.: Shoulder Injuries
- "Selected Topics from Basic Sciences to Clinical Competency;" Nikita Vizniak, BSc, DC; 2003
