Anatomy of the Shoulder

The shoulder is designed to have a great amount of mobility.  Its range of motion is greater than any other joint in the body.  It is used for lifting and for positioning the hand so that it can perform any task.

The shoulder is a large, complex joint comprised of bones, joints, muscles, soft tissues (ligaments, tendons, and cartilage), bursae, nerves, and blood vessels.  All of these work together to provide the stability and the propulsion necessary for normal shoulder function involved in raising, lowering, pushing, pulling, and rotating the arm.

Bones and Joints

Bones and joints make up the deepest layer of the shoulder.  The humerus (upper arm bone) and the scapula (shoulder blade) work together like a ball and socket to form the main shoulder joint, the glenohumeral joint.

A bony extension from the rear of the scapula is the acromion.  It is the “roof” of the shoulder.  The bony extension from the front of the scapula is the coracoid process.  The clavicle (collar bone) and the acromion meet to form the acromioclavicular joint.  The sternal end of the clavicle, the cartilage of the first rib, and the upper part of the breastbone meet to form the sternoclavicular joint.  The point at which the shoulder blade skims against the rib cage is called the scapulothoracic joint even though it is really not a joint at all.

The glenohumeral joint provides a large amount of shoulder movement.  The acromioclavicular joint helps to transmit forces through the upper limb and shoulder to the axial skeleton.  The sternoclavicular joint supports the joining of the arm and shoulder to the main skeleton.  It assists movement of the upper arm, especially when throwing and thrusting.

Muscles

Rotator cuff muscles are located just outside the shoulder joint.  The four short muscles assist with rotating the shoulder, with raising the arm, and in keeping the shoulder joint stable.   The deltoid muscle is the strongest and largest muscle in the shoulder.  Once the arm leaves the side of the body, the deltoid muscle is used to lift the arm.

Soft Tissues

Ligaments attach bones to bones.  Tendons attach muscle to bones.  Ligaments and tendons are both made of collagen fibers that are bundled together.  The bundles come in various sizes and thicknesses to provide different degrees of strength.  Articular cartilage covers the ends of bones at any joint.  It absorbs shock and allows joint surfaces to safely move against each other, making motion easier.

Ligaments work in a variety of ways within the shoulder.  Some ligaments form a joint capsule, or water tight sac, that keeps the shoulder from being dislocated.  Ligaments connect the clavicle to the scapula.  The labrum is a wedge-shaped structure formed by ligaments.  It makes a deeper socket for the humerus.

The biceps tendon attaches to the top of the end of the scapula at the labrum.  It helps stabilize the joint.  Four rotator cuff tendons connect muscles to the humerus.

Articular cartilage covers the end of the humerus and the scapula where they meet.

Bursae

Bursae are located throughout the body.  A bursa is a small sac of lubricating fluid that is found between two moving surfaces.  A bursa cushions and protects the rotator cuff’s tendons.

Nerves and Blood Vessels

The radial nerve, the ulnar nerve, and the median nerve begin at the shoulder, and travel down the arm.  Messages from the brain travel to muscles that move the arm.  Messages about sensations travel back to the brain.  Blood vessels that supply the arm with blood travel with the nerves.  The axillary artery passes through the axilla, or armpit.  Its smaller branches supply blood to the different parts of the shoulder.

If you are feeling any type of shoulder pain or discomfort, please schedule a consultation at Jacksonville Orthopaedic Institute Beaches.  One of our highly-skilled surgeons will be happy to discuss your pain, your lifestyle, and the steps necessary to ensure that you are back to your best self.  Contact us today at 904-241-1204 or online at www.joibeaches.com!

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