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.
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.
Pain in the shoulder may suggest an injury, which is more common in athletes participating in sports such as swimming, tennis, pitching, and weightlifting. The injuries are caused due to the over usage or repetitive motion of the arms.
The shoulder is the most flexible joint in the body that enables a wide range of movements. Ageing, trauma or sports activities can cause injuries and disorders that can range from minor sprains or strains to severe shoulder trauma.
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. Damage of the cartilage in the shoulder joint causes shoulder arthritis. Inflammation is the body's natural response to injury. The warning signs that inflammation presents are redness, swelling, heat, and pain.
A rotator cuff is a group of tendons in the shoulder joint that provides support and enables a wide range of motion. A major injury to these tendons may result in rotator cuff tears. It is one of the most common causes of shoulder pain in middle-aged and older individuals.
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 impingement is the inflammation of the tendons of the shoulder joint. It is one of the most common causes of pain in the shoulder. Shoulder impingement is also called swimmer’s shoulder, tennis shoulder or rotator cuff tendinitis.
Frozen shoulder, also called adhesive capsulitis, is a condition in which you experience pain and stiffness in your shoulder. The symptoms appear slowly, worsen gradually and usually take one to three years to resolve on their own.
MRI is a computer-based imaging technique that creates a magnetic field inside your body to obtain images. The images of nerves or soft tissue inside your body are obtained.
Physical therapy (PT) is an exercise program that helps you improve movement, relieve pain, encourage blood flow for faster healing, and restore your physical function and fitness level.
Cortisone is a corticosteroid released by the adrenal gland in response to stress and is a potent anti-inflammatory agent. Cortisone injections are recommended for injuries that cause pain and inflammation, and those that don’t require surgical treatment.
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, fibre-optic instrument consisting of a lens, light source, and video camera. The camera projects images of the inside of the joint onto a large monitor, allowing your doctor to look for any damage, assess the type of injury and repair it. Large rotator cuff tears may require open surgery.
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.
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. Replacement of both the humeral head and the socket is called a total shoulder replacement.
Traumatic injury to the shoulder, overuse of the shoulder associated with excessive throwing or weightlifting can cause a labral tear. It may also result from a weakened labrum due to aging.
Conventional surgical methods such as total shoulder joint replacement are not very effective in the treatment of rotator cuff arthropathy. Reverse total shoulder replacement is an advanced surgical technique specifically designed for rotator cuff tear arthropathy, a condition where you suffer from both shoulder arthritis and a rotator cuff tear.
The shoulder joint provides a wide range of movement to the upper extremity, but overuse or trauma can cause instability to the joint. The Latarjet procedure is a surgical procedure performed to treat shoulder instability by relocating a piece of bone with an attached tendon to the shoulder joint.