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.
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.
Little league shoulder is an injury to the growth plate of the upper arm bone at the shoulder joint of children. It is an overuse injury caused by repeated pitching or throwing, especially in children between the ages of 10 to 15 years. This condition is mostly seen in baseball pitchers, but children in other sports who use improper throwing action are also at risk.
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.
The shoulder is a highly mobile ball and socket joint. The ball of the upper arm bone (humerus) is held in place at the socket (glenoid) of the shoulder blade (scapula) by a group of ligaments. A partial dislocation of the shoulder joint is termed as a subluxation. This means the ball has partially moved out of the glenoid as opposed to a dislocation, where the ball completely moves out of the glenoid.
Sports that involve overhead movements and repeated use of the shoulder at your workplace may lead to sliding of the upper arm bone from the glenoid. The dislocation might be a partial dislocation (subluxation) or a complete dislocation causing pain and shoulder joint instability. The shoulder joint often dislocates in the forward direction (anterior instability), and sometimes in the backward or downward direction.
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. A direct blow over the shoulder that may occur during a fall on an outstretched arm or a motor vehicle accident may cause the clavicle bone to break.
Shoulder injuries in baseball players are usually associated with pitching. While this overhand throwing activity can produce great speed and distance for the ball, when performed repeatedly, can place a lot of stress on the shoulder. While pitching, the arm is thrown outward and backward to generate speed.
Throwing injuries of the shoulder are injuries sustained as a result of trauma by athletes during sports activities that involve repetitive overhand motions of the arm as in baseball, American football, volleyball, rugby, tennis, track and field events, etc.
The acromioclavicular joint is part of the shoulder joint. It is formed by the union of the acromion, a bony process of the shoulder blade, and the outer end of the collar bone or clavicle. The joint is lined by cartilage that gradually wears with age as well as with repeated overhead or shoulder level activities such as basketball.
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.
Conventional surgical methods such as total shoulder joint replacement have been shown to be significantly ineffective 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 rotator cuff is a group of 4 muscles in the shoulder joint including the supraspinatus, infraspinatus, teres minor, and subscapularis. These muscles originate in the scapula and attach to the head of the humerus through tendons. The rotator cuff forms a sleeve around the humeral head and glenoid cavity...
Total shoulder replacement surgery is performed to relieve these symptoms. 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.
The acromioclavicular (AC) joint is one of the joints present within your shoulder. It is formed between a bony projection at the top of the shoulder blade (acromion) and the outer end of the clavicle (collarbone). The joint is enclosed by a capsule and supported by ligaments.
Overuse and injury can cause fraying of the biceps tendon and eventual rupture. A biceps tendon rupture can either be partial, where it does not completely tear the tendon or complete, where the tendon completely splits in two and is torn away from the bone.
Acromioplasty is the surgical removal of a small part of the surface of the acromion (bony process on your shoulder blade). The shoulder joint is made up of a ball and socket joint, where the head of the humerus (upper arm bone) articulates with the socket of the scapula (shoulder blade), which is called the glenoid.
Shoulder instability is a chronic condition that causes the frequent dislocation 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. A partial dislocation is referred to as a subluxation while a complete separation is referred to as a dislocation.
Subacromial decompression is a surgical procedure performed for the treatment of a condition called shoulder impingement. In shoulder impingement, the degree of space between the rotator cuff tendon and shoulder blade is decreased due to irritation and swelling of the bursa or due to development of bone spurs.
A break in the bone that makes up the shoulder joint is called a shoulder fracture. The clavicle (collarbone) and end of the humerus (upper arm bone) closest to the shoulder are the bones that usually are fractured. The scapula, or shoulder blade, is not easily fractured because of its protective cover of surrounding muscles and chest tissue.
Triceps repair is a surgical procedure that involves the repair of a ruptured (torn) triceps tendon. A tendon is a tough band of fibrous tissue which connects muscle to bone and works together with muscles in moving your arms, fingers, legs, and toes. The triceps tendons connect the triceps muscles to the shoulder blade and elbow in your arm.