The shoulder is the most flexible joint in the body enabling 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.
The shoulder is a ball and socket joint made up of three bones, namely the humerus, scapula, and clavicle.
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.
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.
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 are the thick strands of fibers that connect one bone to another. The ligaments of the shoulder joint include
- Coraco-clavicular ligaments: these ligaments connect the collarbone to the shoulder blade at the coracoid process
- Acromio-clavicular ligament: this connects the collarbone to the shoulder blade at the acromion process
- Coraco-acromial 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 water-tight sac around the joint. Glenohumeral ligaments play a very important role in providing stability to the otherwise unstable shoulder joint by preventing dislocation.
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 are strong tissues that join muscle to bone allowing the muscle to control the movement of the bone or joint. Two important group 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 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 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.
Rotator Cuff Tear
Rotator cuff is the group of tendons in the shoulder joint providing support and enabling wider range of motion.Read more
Pain in the shoulder suggests a shoulder injury which is more common in athletes participating in sports...Read more
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Shoulder impingement is the condition of inflammation of the tendons of the shoulder joint.Read more
The shoulder joint is a ball and socket joint. A 'ball' at the top of the upper arm bone (the humerus)...Read more
Arthritis of the Shoulder
The term arthritis literally means inflammation of a joint, but is generally used to describe...Read more
Frozen shoulder, also called adhesive capsulitis is a condition characterized by pain and loss of motion in shoulder joint.Read more
Shoulder instability is a chronic condition that causes frequent dislocations of the shoulder joint.Read more
Shoulder Joint Tear
The shoulder joint is a "ball and socket" joint that enables the smooth gliding and thereby the movements of arms.Read more
Thoracic Outlet Syndrome
The thoracic outlet is a small passageway leading from the base of the neck to the armpit and arm.Read more
Playing more overhead sports activities and repeated use of shoulder at workplace may lead to sliding...Read more
Little League Shoulder
Little league shoulder is an injury to the growth plate of the upper arm bone in the shoulder joint of children.Read more
Bicep Tendon Rupture
The biceps muscle is present on the front side of your upper arm and functions to help you bend and rotate your arm.Read more
Shoulder injuries most commonly occur in athletes participating in sports such as swimming, tennis...Read more
Clavicle fracture, also called broken collarbone is a very common sports injury seen in people...Read more
Fracture of the Shoulder Blade
The scapula (shoulder blade) is a flat, triangular bone providing attachment to the muscles of the back, neck, chest and arm.Read more
The glenoid is the socket that forms the ball and socket joint of the shoulder. Fractures of the glenoid...Read more
Baseball and Shoulder Injuries
Shoulder injuries in baseball players are usually associated with pitching. While this overhand throwing...Read more
Ultrasound is a common imaging technique that employs high frequency sound waves to create images...Read more
Shoulder Joint Replacement
The shoulder is a highly movable body joint that allows various movements of the arm.Read more
Partial Shoulder Replacement
Partial shoulder replacement, also called shoulder hemiarthroplasty is a surgical procedure during...Read more
Reverse Shoulder Replacement
Reverse total shoulder replacement, is an advanced surgical technique specifically designed for...Read more
Revision Shoulder Replacement
Total shoulder replacement is the replacement of the head of the humerus (upper arm bone) and the glenoid cavity...Read more
Hydrodilatation is one of the latest techniques for treatment of frozen shoulder or adhesive capsulitis.Read more
Minimally Invasive Shoulder Joint Replacement
Shoulder joint replacement is a surgical procedure to replace damaged bone surfaces with artificial...Read more
Arthroscopic Bankart Repair
The shoulder joint (glenohumeral joint) is a ball and socket joint, where the head of the upper arm bone...Read more
Shoulder Labrum Reconstruction
The shoulder joint is a ball and socket joint. A 'ball' at the top of the upper arm bone (the humerus) fits...Read more
Arthroscopy is a minimally invasive diagnostic and surgical procedure performed for joint problems.Read more