In addition to the bones and joints, the shoulder contains a network of soft tissues, such as muscles, tendons, and ligaments. These soft tissues are prone to injury.

Muscles and Tendons of the Shoulder

Tendons of the rotator cuff including the subscapularis, infraspinatus, teres minor, and supraspinatus.

The rotator cuff is a group of muscles that move the joints of the shoulder. It includes the subscapularis, infraspinatus, teres minor, and supraspinatus.

The most frequently injured group of muscles and tendons within the shoulder is the rotator cuff. The rotator cuff originates at the scapula (shoulder blade) and attaches to the head of the humerus (arm bone). It stabilizes the glenohumeral joint by hugging the rounded humeral head to the concave glenoid cavity. The rotator cuff consists of 4 muscles and their tendons.

The subscapularis is a large, triangular-shaped muscle located toward the front of the shoulder. It is responsible for rotating the head of the humerus internally (toward the body).
The infraspinatus is a thick, triangular-shaped muscle located on the back of the shoulder blade. It is mainly responsible for providing the force needed for external rotation of the shoulder (away from the body).
The teres minor lies below the infraspinatus at the back of the shoulder. It assists in adduction (movement toward the midline of the body) and extension (movement behind the body) of the shoulder.
The supraspinatus is located directly on top of the shoulder and runs along the back. It is mainly responsible for helping to raise the arm away from the side. It is the smallest of the 4 rotator cuff muscles.

See How Do Rotator Cuff Injuries Occur?

The rotator cuff, particularly the supraspinatus, is most at risk of injury, such as tearing, because the muscles and tendons are used in a wide range of motions and are often responsible for lifting heavy loads.

See Rotator Cuff Injuries: Symptoms

In addition to the rotator cuff there are a number of other shoulder muscles, including:

The deltoid, a triangular-shaped muscle that covers the glenohumeral joint. The deltoid is responsible for a number of things, such as preventing joint dislocation when lifting heavy objects, helping raise the arm, and aiding other muscles in the chest.
The triceps brachii, a muscle that assists in rotating the upper arm.
The pectoralis minor, which begins in the upper ribs and fans out toward the shoulder area.
The biceps brachii, a muscle located on top of the humerus. It rotates the forearm and flexes the elbow.
The latissimus dorsi, a flat and rectangular muscle located on the back. It assists the arm in rotation and movement toward and away from the body.

The biceps brachii tendon, which connects the bicep muscle to bones in the shoulder and elbow, is most susceptible to injury. Generally, a person can recover from a bicep tendon injury without surgical treatment.

Ligaments, Labrum, and Bursae of the Shoulder

Ligaments of the shoulder including subacromial bursa, coracohumeral ligament, transverse humeral ligament, subscapular bursa, glenohumeral ligament

Shoulder ligaments and bursae are soft tissue structures. Ligaments connect the bones of the shoulder. Bursae are fluid-filled sacs that act as buffers between bones and other soft tissues, such as tendons.

The ligaments, labrum, and bursae are fixed structures that reinforce and stabilize the shoulder.

Ligaments of the shoulder
Ligaments are fibrous bands of tissue that connect bone to bone. A network of ligaments stabilizes the shoulder. These ligaments include:

Glenohumeral ligaments, which are 3 ligaments that reinforce the front of the shoulder’s glenohumeral joint. It spans from the edge of the glenoid cavity to the neck of the humerus (arm bone).
Coracohumeral ligament, a strong and broad band that strengthens the upper aspect of the bicep brachii muscle.
Transverse humeral ligament, which attaches to 2 different points at the top of the humerus. It creates an arched tunnel for the bicep tendon to pass under.

When one of these ligaments tears it can lead to shoulder separation or dislocation. When a joint in the shoulder separates or dislocates, a medical professional will usually have to manually return the bones to the correct alignment.

See Treatment for a Dislocated Shoulder

Shoulder labrum
The labrum is a slippery, tough ring of cartilage that rims the glenoid cavity (shoulder socket). The labrum helps:

Keep the head of the humerus in place
Ensure smooth movement of the ball-and-socket joint

See SLAP Tear Shoulder Injury and Treatment

A shoulder’s labrum can be damaged or torn as a result of an acute injury, overuse, or as part of the aging process.

See Labrum Tear Treatments

Shoulder bursae
A bursa is a small, fluid-filled sac that reduces friction between bone and soft tissue. Bursae are located at various points around the body where muscles, tendons, and ligaments rub against bone during movement. The 2 primary bursae in the shoulder are the:

Subscapular bursa, which is located between the glenohumeral joint (ball-and-socket joint) and the subscapularis muscle.
Subacromial bursa, which is located directly under the acromion, a bony projection on top of the scapula (shoulder blade). The subacromial bursa helps the rotator cuff function.

A bursae can become inflamed from unusual pressure or overuse. The subacromial bursa, located above the glenohumeral joint and under the acromion, is the most susceptible to injury and is often the cause of shoulder impingement.

See Nonsurgical Treatments for Shoulder Impingement

Dr. David Novak is an orthopedic surgeon and specializes in orthopedic sports medicine. He performs complex arthroscopic procedures for a range of orthopedic conditions and sports injuries of the shoulder, elbow, knee, and ankle. Dr. Novak is active in academia, participating in clinical research and training fellow orthopedic surgeons in advanced shoulder arthroscopy at national meetings.