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.
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.
The shoulder joint is a ball and socket joint. A ball at the top of the upper arm bone (humerus) fits neatly into a socket, called the glenoid, which is part of the shoulder blade (scapula). The glenoid is surrounded by a ring of fibrous cartilage called the labrum for stabilization of the shoulder joint. The biceps tendon attaches inside the shoulder joint at the superior labrum of the shoulder joint.
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.
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. A partial dislocation is referred to as a subluxation whereas a complete separation is referred to as a dislocation.
The shoulder joint is a ball and socket joint. A ball at the top of the upper arm bone (humerus) fits neatly into a socket, called the glenoid, which is part of the shoulder blade (scapula). The glenoid is surrounded by a ring of fibrous cartilage called the labrum for stabilization of the shoulder joint.
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. The scapula, on the other hand, is not easily fractured because of its protective cover by the surrounding muscles and chest tissue.
The humerus is the bone that forms the upper arm. It articulates with the glenoid cavity of the scapula (shoulder blade) to form the shoulder joint and with the lower arm bones – the ulna and radius – to form the elbow joint. The proximal humerus is the upper end of the arm bone that forms the shoulder joint.
The shoulder is a ball and socket joint, formed by the bone of the upper arm (humerus), which articulates with the shoulder blade in a cavity called the glenoid fossa.
The joint relies a great deal on surrounding soft-tissue structures such as tendons, ligaments, and muscles (rotator cuff muscles) to maintain smooth motion and stability.
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. Throwing injuries are mostly seen in the shoulder and elbow and can occur due to improper techniques, training errors, muscle imbalance, and overuse of muscles.
The shoulder consists of a ball-and-socket joint formed by the upper end of the humerus (upper arm bone) and a cavity in the shoulder blade called the glenoid. The glenoid cavity is surrounded by a rim of cartilage called the labrum. The labrum adds depth to the cavity making the joint more stable and positions the ball within the socket.
The biceps muscle is the muscle of the upper arm which is necessary for the movement of the shoulder and elbow. It is made of a ‘short head’ and a ‘long head’ which function together. These are connected to the shoulder joint by two tendons called the proximal biceps tendons and to the elbow joint by a single distal biceps tendon.
Your biceps muscle has two heads, a long head, and a short head, which are both attached to the shoulder. The long head of the biceps tendon is a tough band of connective fibrous tissue that attaches the long head of the biceps to the top of the shoulder socket.
The shoulder consists of a ball and socket joint where the rounded end of the humerus (upper arm bone) fits into a socket (glenoid cavity) formed by the shoulder blade. The joint is stabilized by the surrounding capsule, ligaments, and tendons of the rotator cuff muscles. Shoulder instability results when the humerus is not held firmly within the socket and moves away from the glenoid cavity.
Your shoulder consists of a ‘ball-and-socket joint’. The humerus (upper arm bone) has a rounded head (ball) that is attached to the glenoid cavity (socket) in the shoulder blade. Certain injuries can cause dislocation of the joint and damage to the humeral head. Damage to the back and outer portion of the humeral head can result in a defect called a Hill-Sachs lesion.
Failed shoulder surgery is a surgery that did not meet expectations and resulted in recurring pain or other unwanted symptoms. All surgeries are associated with risks, some have a higher risk than others. The most commonly reported failed shoulder surgeries include rotator cuff repairs and shoulder stabilization for shoulder instability.
The biceps muscle is present on the front 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.
Frozen shoulder, also called adhesive capsulitis, is a condition characterized by pain and loss of motion in the shoulder joint. Frozen shoulder is caused by inflammation of the shoulder capsule. The shoulder capsule becomes thick, tight, and the stiff bands of tissue called adhesions may develop.
The scapula (shoulder blade) is a flat, triangular bone providing attachment to the muscles of the back, neck, chest, and arm. The scapula consists of a body, neck and spine portion.
Scapular fractures are uncommon and require a large amount of force to fracture.
A superior labrum anterior and posterior tear or SLAP tear is an injury to the labrum. This injury may also involve the biceps tendon, which is attached to the top part of the labrum. The injury occurs from repeated use of the shoulder while throwing or a fall onto the shoulder.
The shoulder joint (glenohumeral joint) is a ball and socket joint, where the head of the upper arm bone (humerus) attaches to the shoulder socket (glenoid cavity). The shoulder socket is extremely shallow and therefore needs additional support to keep the shoulder bones from dislocating.
The shoulder joint is a ball and socket joint. A ball at the top of the upper arm bone (the humerus) fits neatly into a socket, called the glenoid, which is part of the shoulder blade (scapula). The labrum is a ring of fibrous cartilage surrounding the glenoid, which helps in stabilizing the shoulder joint. The biceps tendon is attached inside the shoulder joint at the superior labrum of the joint.
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.
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 pectoralis muscle is a large fan-shaped muscle comprised of the pectoralis major and pectoralis minor muscles that stretch from the armpit to the collarbone and down across the lower chest region on both sides of the chest. The two sides of the chest connect at the breastbone or sternum. The pectoralis major is a powerful muscle that aids in rotating the arm inward and move it closer to the body.
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.
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.
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.