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.
Bones of the Shoulder
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 breastbone. 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 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.
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 arthritis causes pain and stiffness in the shoulder and typically occurs in people over the age of 50. The hallmark is pain and reduced range of motion. Arthritis can result in painful which may be constant or increase with activity. The diagnosis is typically obvious on X-rays which show reduced joint space and bone spurs.
Rotator cuff tears are one of the most common causes of shoulder pain. Pain typically occurs in the front or side of the shoulder. The pain may radiate to the elbow. Symptoms are worse with overhead activity and often cause difficulty sleeping which can significantly affect quality of life.
Frozen shoulder, also called adhesive capsulitis, causes pain and stiffness in the shoulder. The condition affects the glenohumeral joint (ball and socket joint) and occurs in about 2% of the population and most commonly affects mid-aged people. The hallmark is a normal joint with inability move the shoulder due to adhesions.
The rotator cuff consists of a group of tendons and muscles that surround and stabilize the shoulder. A tear that is larger than 5 cm and involves the infraspinatus and supraspinatus muscles which are part of the rotator cuff may be characterized as a massive rotator cuff tear.
The biceps muscle is present on the front side of your upper arm and functions to help you bend and rotate your arm.
The biceps tendon is a tough band of connective fibrous tissue that attaches your biceps muscle to the bones in your shoulder on one side and the elbow on the other side.
The rotator cuff is a group of tendons in the shoulder that provide support and enable a wide range of motion of the shoulder joint. Major injuries can cause rotator cuff tears. A rotator cuff tear is one of the most common causes of shoulder pain in middle-aged adults and older individuals.
Reverse Total Shoulder Arthroplasty is a type of Shoulder Joint Replacement surgery which addresses not only glenohumeral arthritis, but also shoulder instability. With a traditional Total Shoulder Replacement or arthroplasty, the arthritic surfaces of the glenohumeral joint are smoothed and a prosthetic cup is placed in the glenoid or shoulder socket and a prosthetic ball is inserted into the end of the humerus or arm bone to replace the “ball and socket” joint.
The rotator cuff consists of muscles and tendons that connect the arm to the shoulder blade. Tears in this network of muscles and tendons are usually repaired by suturing the tendon back to its original position. However, tears can occur even after surgery. In such cases a revision rotator cuff repair may be performed.
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. The arthroscope consists of a light system and camera that projects images of the surgical site onto a computer screen for your surgeon to clearly view.
The shoulder joint is stabilized by the joint capsule and rotator cuff. Tears to the rotator cuff can cause severe pain and impairment. When defects in the underlying upper joint capsule add to the instability caused by rotator cuff tears, it cannot be repaired with conventional treatments.
The shoulder is the most flexible joint in the body, enabling a wide range of movements. It is a ball-and-socket joint made up of three bones, namely the humerus, scapula and clavicle. A break in any of these bones making up the shoulder joint is called a shoulder fracture.
Shoulder instability is a chronic condition that causes frequent dislocations of the shoulder joint. A dislocation occurs when the end of the humerus (the ball portion) partially or completely dislocates from the glenoid (the socket portion) of the shoulder.