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Shoulder Anatomy

Shoulder Anatomy

The shoulder is the most flexible joint in the body that enables a wide range of movements including forward flexion, abduction, adduction, external rotation, internal rotation, and 360-degree circumduction. Thus, the shoulder joint is considered the most insecure joint of the body, but the support of ligaments, muscles, and tendons function to provide the required stability.

Bones of the Shoulder

The shoulder joint is a ball and socket joint made up of three bones, namely the humerus, scapula, and clavicle.

Humerus

The end of the humerus or upper arm bone forms the ball of the shoulder joint. An irregular shallow cavity in the scapula called the glenoid cavity forms the socket for the head of the humerus to fit in. The two bones together form the glenohumeral joint, which is the main joint of the shoulder.

Scapula and Clavicle

  • The scapula is a flat triangular-shaped bone that forms the shoulder blade. It serves as the site of attachment for most of the muscles that provide movement and stability to the joint. The scapula has four bony processes - acromion, spine, coracoid and glenoid cavity. The acromion and coracoid process serve as places for attachment of the ligaments and tendons.
  • The clavicle bone or collarbone is an S-shaped bone that connects the scapula to the sternum or breastbone. It forms two joints: the acromioclavicular joint, where it articulates with the acromion process of the scapula and the sternoclavicular joint where it articulates with the sternum or breast bone. The clavicle also forms a protective covering for important nerves and blood vessels that pass under it from the spine to the arms.

Soft Tissues of the Shoulder

The ends of all articulating bones are covered by smooth tissue called articular cartilage, which allows the bones to slide over each other without friction, enabling smooth movement. Articular cartilage reduces pressure and acts as a shock absorber during movement of the shoulder bones. Extra stability to the glenohumeral joint is provided by the glenoid labrum, a ring of fibrous cartilage that surrounds the glenoid cavity. The glenoid labrum increases the depth and surface area of the glenoid cavity to provide a more secure fit for the half-spherical head of the humerus.

Ligaments of the Shoulder

Ligaments are thick strands of fibers that connect one bone to another. The ligaments of the shoulder joint include:

  • Coracoclavicular ligaments: These ligaments connect the collarbone to the shoulder blade at the coracoid process.
  • Acromioclavicular ligament: This connects the collarbone to the shoulder blade at the acromion process.
  • Coracoacromial ligament: It connects the acromion process to the coracoid process.
  • Glenohumeral ligaments: A group of 3 ligaments that form a capsule around the shoulder joint and connect the head of the arm bone to the glenoid cavity of the shoulder blade. The capsule forms a watertight sac around the joint. Glenohumeral ligaments play a very important role in providing stability to the otherwise unstable shoulder joint by preventing dislocation.

Muscles of the Shoulder

The rotator cuff is the main group of muscles in the shoulder joint and is comprised of 4 muscles. The rotator cuff forms a sleeve around the humeral head and glenoid cavity, providing additional stability to the shoulder joint while enabling a wide range of mobility. The deltoid muscle forms the outer layer of the rotator cuff and is the largest and strongest muscle of the shoulder joint.

Tendons of the Shoulder

Tendons are strong tissues that join muscle to bone allowing the muscle to control the movement of the bone or joint. Two important groups of tendons in the shoulder joint are the biceps tendons and rotator cuff tendons.

  • Bicep tendons are the two tendons that join the bicep muscle of the upper arm to the shoulder. They are referred to as the long head and short head of the bicep.
  • Rotator cuff tendons are a group of four tendons that join the head of the humerus to the deeper muscles of the rotator cuff. These tendons provide more stability and mobility to the shoulder joint.

Nerves of the Shoulder

Nerves carry messages from the brain to muscles to direct movement (motor nerves) and send information about different sensations such as touch, temperature, and pain from the muscles back to the brain (sensory nerves). The nerves of the arm pass through the shoulder joint from the neck. These nerves form a bundle at the region of the shoulder called the brachial plexus. The main nerves of the brachial plexus are the musculocutaneous, axillary, radial, ulnar and median nerves.

Blood vessels of the Shoulder

Blood vessels travel along with the nerves to supply blood to the arms. Oxygenated blood is supplied to the shoulder region by the subclavian artery that runs below the collarbone. As it enters the region of the armpit, it is called the axillary artery and further down the arm, it is called the brachial artery.

The main veins carrying de-oxygenated blood back to the heart for purification include:

  • Axillary vein: This vein drains into the subclavian vein.
  • Cephalic vein: This vein is found in the upper arm and branches at the elbow into the forearm region. It drains into the axillary vein.
  • Basilic vein: This vein runs opposite the cephalic vein, near the triceps muscle. It drains into the axillary vein.

Shoulder Conditions

Arthritis of the Shoulder

Arthritis of the Shoulder

The term arthritis literally means inflammation of a joint but is generally used to describe any condition in which there is damage to the cartilage.

Shoulder Pain

Shoulder Pain

Pain in the shoulder may suggest an injury, which is more common in athletes participating in sports such as swimming, tennis, pitching, and weightlifting.

Shoulder Fracture

Shoulder Fracture

A break in a bone that makes up the shoulder joint is called a shoulder fracture. The clavicle and end of the humerus closest to the shoulder are the bones that usually get fractured.

Clavicle Fracture

Clavicle Fracture

The break or fracture of the clavicle (collarbone) is a common sports injury associated with contact sports such as football and martial arts, as well as impact sports such as motor racing.

SLAP Tears

SLAP Tears

The term SLAP (superior –labrum anterior-posterior) lesion or SLAP tear refers to an injury of the superior labrum of the shoulder.

Shoulder Instability

Shoulder Instability

Shoulder instability is a chronic condition that causes frequent dislocation of the shoulder joint. A dislocation occurs when the end of the humerus (ball portion) partially or completely dislocates from the glenoid (socket portion) of the shoulder.

Shoulder Procedures

Shoulder Joint Replacement

Shoulder Joint Replacement

Total shoulder replacement surgery is performed to relieve symptoms of severe shoulder pain and disability due to arthritis. In this surgery, the damaged articulating parts of the shoulder joint are removed and replaced with artificial prostheses.

Shoulder Arthroscopy

Shoulder Arthroscopy

Arthroscopy is a minimally invasive diagnostic and surgical procedure performed for joint problems. Shoulder arthroscopy is performed using a pencil-sized instrument called an arthroscope.

Rotator Cuff Repair

Rotator Cuff Repair

Rotator cuff repair is a surgery to repair an injured or torn rotator cuff. It is usually performed arthroscopically on an outpatient basis. An arthroscope, a small, fiber-optic instrument consisting of a lens, light source, and video camera.

Shoulder Stabilization

Shoulder Stabilization

Shoulder stabilization surgery is performed to improve stability and function to the shoulder joint and prevent recurrent dislocations. It can be performed arthroscopically, depending on your particular condition, with much smaller incisions.

SLAP repair

SLAP repair

A SLAP repair is an arthroscopic shoulder procedure to treat a specific type of injury to the labrum called a SLAP tear.

Minimally Invasive Shoulder Joint Replacement

Minimally Invasive Shoulder Joint Replacement

Shoulder joint replacement is a surgical procedure that replaces damaged bone surfaces with artificial humeral and glenoid components to relieve pain and improve functional ability in the shoulder joint.

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