The humerus (/ˈhjuːmərəs/, plural: humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a rounded head, a narrow neck, and two short processes (tubercles, sometimes called tuberosities). The body is cylindrical in its upper portion, and more prismatic below. The lower extremity consists of 2 epicondyles, 2 processes (trochlea & capitulum), and 3 fossae (radial fossa, coronoid fossa, and olecranon fossa). As well as its true anatomical neck, the constriction below the greater and lesser tubercles of the humerus is referred to as its surgical neck due to its tendency to fracture, thus often becoming the focus of surgeons.
Position of humerus (shown in red)
from an anterior viewpoint
|Anatomical terms of bone|
At the shoulder, the head of the humerus articulates with the glenoid fossa of the scapula. More distally, at the elbow, the capitulum of the humerus articulates with the head of the radius, and the trochlea of the humerus articulates with the trochlear notch of the ulna.
The axillary nerve is located at the proximal end, against the shoulder girdle. Dislocation of the humerus's glenohumeral joint has the potential to injure the axillary nerve or the axillary artery. Signs and symptoms of this dislocation include a loss of the normal shoulder contour and a palpable depression under the acromion.
The radial nerve follows the humerus closely. At the midshaft of the humerus, the radial nerve travels from the posterior to the anterior aspect of the bone in the spiral groove. A fracture of the humerus in this region can result in radial nerve injury.
The ulnar nerve lies at the distal end of the humerus near the elbow. When struck, it can cause a distinct tingling sensation, and sometimes a significant amount of pain. It is sometimes popularly referred to as 'the funny bone', possibly due to this sensation (a "funny" feeling), as well as the fact that the bone's name is a homophone of 'humorous'. It lies posterior to the medial epicondyle, and is easily damaged in elbow injuries.
The deltoid originates on the lateral third of the clavicle, acromion and the crest of the spine of the scapula. It is inserted on the deltoid tuberosity of the humerus and has several actions including abduction, extension, and circumduction of the shoulder. The supraspinatus also originates on the spine of the scapula. It inserts on the greater tubercle of the humerus, and assists in abduction of the shoulder.
The infraspinatus and teres minor insert on the greater tubercle, and work to laterally, or externally, rotate the humerus. In contrast, the subscapularis muscle inserts onto the lesser tubercle and works to medially, or internally, rotate the humerus.
The biceps brachii, brachialis, and brachioradialis (which attaches distally) act to flex the elbow. (The biceps do not attach to the humerus.) The triceps brachii and anconeus extend the elbow, and attach to the posterior side of the humerus.
The four muscles of supraspinatus, infraspinatus, teres minor and subscapularis form a musculo-ligamentous girdle called the rotator cuff. This cuff stabilizes the very mobile but inherently unstable glenohumeral joint. The other muscles are used as counterbalances for the actions of lifting/pulling and pressing/pushing.
Primitive fossils of amphibians had little, if any, shaft connecting the upper and lower extremities, making their limbs very short. In most living tetrapods, however, the humerus has a similar form to that of humans; connecting their extremities. In many reptiles and some primitive mammals, the lower extremity includes a large foramen, or opening, which allows nerves and blood vessels pass through.
Left humerus. Animation.
Upper end Accompanies shaft in 20th year. The parts which form upper end - Head Starts from 1st year, Greater tubercle Starts from 3rd year, Lesser tubercle Starts from the fifth year.
Lower end Accompanies shaft in 16th to 17th year. The parts which form lower end are - Capitulum and the lateral flange of trochlea Sarts from 2nd year, Medial part of trochlea starts from 10th year, Lateral epicondyle starts from 12th year and Medial epicondyle starts from the sixth year.
The anatomical neck of the humerus is obliquely directed, forming an obtuse angle with the body of the humerus. It represents the fused epiphyseal plate.It gives attachment to the capsular ligament of the shoulder joint except at the upper inferior-medial aspects
It is best marked in the lower half of its circumference; in the upper half it is represented by a narrow groove separating the head of the humerus from the two tubercles, the greater tubercle and the lesser tubercle.
It affords attachment to the articular capsule of the shoulder-joint, and is perforated by numerous vascular foramina.Body of humerus
The body or shaft of the humerus is almost cylindrical in the upper half of its extent, prismatic and flattened below, and has three borders and three surfaces.Capitulum of the humerus
In human anatomy of the arm, the capitulum of the humerus is a smooth, rounded eminence on the lateral portion of the distal articular surface of the humerus. It articulates with the cupshaped depression on the head of the radius, and is limited to the front and lower part of the bone.
In non-human tetrapods, the name capitellum is generally used, with "capitulum" limited to the anteroventral articular facet of the rib (in archosauromorphs).Coronoid fossa of the humerus
Superior to the anterior portion of the trochlea is a small depression, the coronoid fossa, which receives the coronoid process of the ulna during flexion of the forearm. It is directly adjacent to the radial fossa of the humerus.Deltoid tuberosity
In human anatomy, the deltoid tuberosity is a rough, triangular area on the anterolateral (front-side) surface of the middle of the humerus to which the deltoid muscle attaches.Glenoid cavity
The glenoid cavity or glenoid fossa of scapula is a part of the shoulder. It is a shallow, pyriform articular surface, which is located on the lateral angle of the scapula. It is directed laterally and forward and articulates with the head of the humerus; it is broader below than above and its vertical diameter is the longest.
This cavity forms the glenohumeral joint along with the humerus. This type of joint is classified as a synovial, ball and socket joint. The humerus is held in place within the glenoid cavity by means of the long head of the biceps tendon. This tendon originates on the superior margin of the glenoid cavity and loops over the shoulder, bracing humerus against the cavity. The rotator cuff also reinforces this joint more specifically with the supraspinatus tendon to hold the head of the humerus in the glenoid cavity.
The cavity surface is covered with cartilage in the fresh state, and its margins, slightly raised, give attachment to a fibrocartilaginous structure, the glenoid labrum, which deepens the cavity. This cartilage is very susceptible to tearing. When torn, it is most commonly known as a SLAP lesion which is generally caused by repetitive shoulder movements.
Compared to the acetabulum (at the hip-joint) the glenoid cavity is relatively shallow. This makes the shoulder joint prone to dislocation (luxation). Strong glenohumeral ligaments and muscles prevents dislocation in most cases.
By being so shallow the glenoid cavity allows the shoulder joint to have the greatest mobility of all joints in the body, allowing 120 degrees of unassisted flexion. Additional range of motion in shoulder flexion (typically up to 180 degrees in humans) is also accomplished by the great mobility of the scapula (shoulder blade) through a process known as scapulohumeral rhythm.Greater tubercle
The greater tubercle of the humerus is situated lateral to the head of the humerus and posterolateral to the lesser tubercle.
Its upper surface is rounded and marked by three flat impressions.
the highest of these gives ("superior facet") insertion to the supraspinatus
the middle ("middle facet") to the infraspinatus.
the lowest one ("inferior facet"), and the body of the bone for about 2.5 cm; below it, to the teres minor.The lateral surface of the greater tubercle is convex, rough, and continuous with the lateral surface of the body.
Between the greater tubercle and the lesser tubercle is the bicipital groove (intertubercular sulcus).
All three of the muscles that attach to the greater tubercle are part of the rotator cuff, a muscle group that stabilizes the shoulder joint. The fourth muscle of the rotator cuff (the subscapularis) does not attach to the greater tubercle, but instead attaches to the lesser tubercle.Humerus fracture
A humerus fracture is a break of the humerus bone in the upper arm. Symptoms are pain, swelling, and discoloration of the skin at the site of the fracture. Bruising appears a few days after the fracture. The neurovascular bundle of the arm may be affected in severe cases, which will cause loss of nerve function and diminished blood supply beneath the fracture. Proximal and distal fractures will often cause a loss of shoulder or elbow function. Displaced shaft and distal fractures may cause deformity, and such shaft fractures will often shorten the length of the upper arm.
Humerus fractures usually occur after physical trauma, falls, excess physical stress, or pathological conditions such as tumors. Falls are the most common cause of proximal and shaft fractures, and those who experience a fracture from a fall usually have an underlying risk factor for bone fracture. Distal fractures occur most frequently in children who attempt to break a fall with an outstretched hand. Fractures of the humerus may be classified by the location into proximal region, which is near the shoulder, the middle region or shaft, and the distal region, which is near the elbow. These locations can further be divided based on the extent of the fracture and the specific areas of each of the three regions affected.
Most humerus fractures are nondisplaced and will heal within a few weeks if the arm is immobilized. Severe displaced humerus fractures and complications often require surgical intervention. In most cases, normal function to the arm returns after the fracture is healed. In severe cases, however, function of the arm may be diminished after recovery.Lateral epicondyle of the humerus
The lateral epicondyle of the humerus is a small, tuberculated eminence, curved a little forward, and giving attachment to the radial collateral ligament of the elbow joint, and to a tendon common to the origin of the supinator and some of the extensor muscles. Specifically, these extensor muscles include the anconeus muscle, the supinator, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris. In birds, where the arm is somewhat rotated compared to other tetrapods, it is termed dorsal epicondyle of the humerus. In comparative anatomy, the term ectepicondyle is sometimes used.A common injury associated with the lateral epicondyle of the humerus is lateral epicondylitis also known as tennis elbow. Repetitive overuse of the forearm, as seen in tennis or other sports, can result in inflammation of "the tendons that join the forearm muscles on the outside of the elbow. The forearm muscles and tendons become damaged from overuse. This leads to pain and tenderness on the outside of the elbow."Lateral supracondylar ridge
The lower part of the lateral border of the body of the humerus forms a prominent, rough margin, a little curved from behind forward, the lateral supracondylar ridge (or line), which presents an anterior lip for the origin of the Brachioradialis above, and Extensor carpi radialis longus below, a posterior lip for the Triceps brachii, and an intermediate ridge for the attachment of the lateral intermuscular septum.Lesser tubercle
The lesser tubercle of the humerus, although smaller, is more prominent than the greater tubercle: it is situated in front, and is directed medially and anteriorly.
Above and in front it presents an impression for the insertion of the tendon of the subscapularis.Medial epicondyle of the humerus
The medial epicondyle of the humerus is an epicondyle of the humerus bone of the upper arm in humans. It is larger and more prominent than the lateral epicondyle and is directed slightly more posteriorly in the anatomical position. In birds, where the arm is somewhat rotated compared to other tetrapods, it is called the ventral epicondyle of the humerus. In comparative anatomy, the more neutral term entepicondyle is used.
The medial epicondyle gives attachment to the ulnar collateral ligament of elbow joint, to the pronator teres, and to a common tendon of origin (the common flexor tendon) of some of the flexor muscles of the forearm: the flexor carpi radialis, the flexor carpi ulnaris, the flexor digitorum superficialis, and the palmaris longus.
The ulnar nerve runs in a groove on the back of this epicondyle. The medial epicondyle protects the ulnar nerve. The ulnar nerve is vulnerable because it passes close to the surface along the back of the bone. Striking the medial epicondyle causes a tingling sensation in the ulnar nerve. This response is known as striking the “funny bone”. The name funny bone could be from a play on the words humorous and humerus, the bone on which the medial epicondyle is located. The medial epicondyle is located on the distal end of the humerus. Additionally, the medial epicondyle is inferior to the medial supracondylar ridge. It is also proximal to the olecranon fossa.Pectoralis major
The pectoralis major (from Latin pectus, meaning 'breast') is a thick, fan-shaped muscle, situated at the chest (anterior) of the human body. It makes up the bulk of the chest muscles and lies under the breast. Below (deep to) the pectoralis major is the pectoralis minor, a thin, triangular muscle. In sports as well as bodybuilding, the pectoral muscles may colloquially be referred to as "pecs", "pectoral muscle" or "chest muscle" due to its being the larger and most superficial muscle in the chest area.Shoulder
The human shoulder is made up of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone) as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder make up the shoulder joints. The shoulder joint, also known as the glenohumeral joint, is the major joint of the shoulder, but can more broadly include the acromioclavicular joint. In human anatomy, the shoulder joint comprises the part of the body where the humerus attaches to the scapula, and the head sits in the glenoid cavity. The shoulder is the group of structures in the region of the joint.The shoulder joint is the main joint of the shoulder. It is a ball and socket joint that allows the arm to rotate in a circular fashion or to hinge out and up away from the body. The joint capsule is a soft tissue envelope that encircles the glenohumeral joint and attaches to the scapula, humerus, and head of the biceps. It is lined by a thin, smooth synovial membrane. The rotator cuff is a group of four muscles that surround the shoulder joint and contribute to the shoulder's stability. The muscles of the rotator cuff are supraspinatus, subscapularis, infraspinatus, and teres minor. The cuff adheres to the glenohumeral capsule and attaches to the humeral head.
The shoulder must be mobile enough for the wide range actions of the arms and hands, but stable enough to allow for actions such as lifting, pushing, and pulling.Shoulder joint
The shoulder joint (or glenohumeral joint from Greek glene, eyeball, + -oid, 'form of', + Latin humerus, shoulder) is structurally classified as a synovial ball and socket joint and functionally as a diarthrosis and multiaxial joint. It involves articulation between the glenoid cavity of the scapula (shoulder blade) and the head of the humerus (upper arm bone).
Due to the very loose joint capsule that gives a limited interface of the humerus and scapula, it is the most mobile joint of the human body.Supracondylar humerus fracture
A supracondylar humerus fracture is a fracture of the distal humerus just above the elbow joint. The fracture is usually transverse or oblique and above the medial and lateral condyles and epicondyles. This fracture pattern is relatively rare in adults, but is the most common type of elbow fracture in children. In children, many of these fractures are non-displaced and can be treated with casting. Some are angulated or displaced and are best treated with surgery. In children, most of these fractures can be treated effectively with expectation for full recovery. Some of these injuries can be complicated by poor healing or by associated blood vessel or nerve injuries with serious complications.Surgical neck of the humerus
The surgical neck of the humerus is a constriction below the tubercles of the greater tubercle and lesser tubercle, and above the Deltoid Tuberosity.
It is much more frequently fractured than the anatomical neck of the humerus. A fracture in this area is most likely to cause damage to the axillary nerve and posterior circumflex humeral artery. Damage to the axillary nerve affects function of the teres minor and deltoid muscles, resulting in loss of abduction of arm (from 15-90 degrees), weak flexion, extension, and rotation of shoulder as well as loss of sensation of the skin over a small part of the lateral shoulder.Upper extremity of humerus
The upper or proximal extremity of the humerus consists of the bone's large rounded head joined to the body by a constricted portion called the neck, and two eminences, the greater and lesser tubercles.Zhuchengtitan
Zhuchengtitan (meaning "Zhucheng titan") is a genus of titanosaurian sauropod dinosaur from the Late Cretaceous of Shandong, China. It contains a single species, Z. zangjiazhuangensis, named by Mo Jinyou and colleagues in 2017 from a single humerus. Zhuchengtitan can be identified by the extreme width of the top end of its humerus, as well as the expansion of the deltopectoral crest on its humerus; both of these characteristics indicate that it was likely closely related to Opisthocoelicaudia. However, it differs from the latter by the flatter bottom articulating surface of its humerus. Zhuchengtitan lived in a floodplain environment alongside Shantungosaurus, Zhuchengtyrannus, and Sinoceratops.