Humerus
Humerus | |
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Details | |
Identifiers | |
Latin | humerus |
MeSH | D006811 |
TA98 | A02.4.04.001 |
TA2 | 1180 |
FMA | 13303 |
Anatomical terms of bone |
The humerus (
Etymology
The word "humerus" is derived from
Structure
Upper extremity
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.
Head
The head (caput humeri), is nearly hemispherical in form. It is directed upward, medialward, and a little backward, and articulates with the
Anatomical neck
The anatomical neck (collum anatomicum) is obliquely directed, forming an obtuse angle with the body. 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 from the tubercles. The line separating the head from the rest of the upper end is called the anatomical neck. It affords attachment to the articular capsule of the shoulder-joint, and is perforated by numerous vascular foramens. Fracture of the anatomical neck rarely occurs.[2]
The anatomical neck of the humerus is an indentation distal to the head of the humerus on which the articular capsule attaches.
Surgical neck
The surgical neck is a narrow area distal to the tubercles that is a common site of fracture. It makes contact with the axillary nerve and the posterior humeral circumflex artery.
Greater tubercle
The greater tubercle (tuberculum majus; greater tuberosity) is a large, posteriorly placed projection that is placed laterally. The greater tubercle is where supraspinatus, infraspinatus and teres minor muscles are attached. The crest of the greater tubercle forms the lateral lip of the bicipital groove and is the site for insertion of pectoralis major.
The greater tubercle is just lateral to the anatomical neck. Its upper surface is rounded and marked by three flat impressions: the highest of these gives insertion to the supraspinatus muscle; the middle to the infraspinatus muscle; the lowest one, and the body of the bone for about 2.5 cm. below it, to the teres minor muscle. The lateral surface of the greater tubercle is convex, rough, and continuous with the lateral surface of the body.[2]
Lesser tubercle
The lesser tubercle (tuberculum minus; lesser tuberosity) is smaller, anterolaterally placed to the head of the humerus. The lesser tubercle provides insertion to subscapularis muscle. Both these tubercles are found in the proximal part of the shaft. The crest of the lesser tubercle forms the medial lip of the bicipital groove and is the site for insertion of teres major and latissimus dorsi muscles.
The lesser tuberosity, is more prominent than the greater: it is situated in front, and is directed medialward and forward. Above and in front it presents an impression for the insertion of the tendon of the subscapularis muscle.[2]
Bicipital groove
The tubercles are separated from each other by a deep groove, the
Shaft
Body of humerus | |
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Details | |
Identifiers | |
Latin | corpus humeri |
MeSH | D006811 |
TA98 | A02.4.04.001 |
TA2 | 1180 |
FMA | 13303 |
Anatomical terms of bone |
The body or shaft of the humerus is triangular to cylindrical in cut section and is compressed anteroposteriorly. It has 3 surfaces, namely:
- Anterolateral surface: the area between the lateral border of the humerus to the line drawn as a continuation of the crest of the greater tubercle. The antero-lateral surface is directed lateralward above, where it is smooth, rounded, and covered by the radial sulcus, directed obliquely from behind, forward, and downward, and transmitting the radial nerve and profunda artery.
- Anteromedial surface: the area between the medial border of the humerus to the line drawn as a continuation of the crest of the greater tubercle. The antero-medial surface, less extensive than the antero-lateral, is directed medialward above, forward and medialward below; its upper part is narrow, and forms the floor of the intertubercular groove which gives insertion to the tendon of the latissimus dorsi muscle; its middle part is slightly rough for the attachment of some of the fibers of the tendon of insertion of the coracobrachialis muscle; its lower part is smooth, concave from above downward, and gives origin to the brachialis muscle.
- Posterior surface: the area between the medial and lateral borders. The posterior surface appears somewhat twisted, so that its upper part is directed a little medialward, its lower part backward and a little lateralward. Nearly the whole of this surface is covered by the lateral and medial heads of the Triceps brachii, the former arising above, the latter below the radial sulcus.
Its three borders are:
- Anterior: the anterior border runs from the front of the greater tubercle above to the pectoralis major muscle. About its center it forms the anterior boundary of the deltoid tuberosity, on which the deltoid muscle attaches; below, it is smooth and rounded, affording attachment to the brachialis muscle.
- Lateral: the lateral border runs from the back part of the greater tubercle to the lateral lateral intermuscular septum.
- Medial: the medial border extends from the lesser tubercle to the medial intermuscular septum.
The deltoid tuberosity is a roughened surface on the lateral surface of the shaft of the humerus and acts as the site of insertion of deltoideus muscle. The posterorsuperior part of the shaft has a crest, beginning just below the surgical neck of the humerus and extends till the superior tip of the deltoid tuberosity. This is where the lateral head of triceps brachii is attached.
The radial sulcus, also known as the spiral groove is found on the posterior surface of the shaft and is a shallow oblique groove through which the radial nerve passes along with deep vessels. This is located posteroinferior to the deltoid tuberosity. The inferior boundary of the spiral groove is continuous distally with the lateral border of the shaft.
The nutrient foramen of the humerus is located in the anteromedial surface of the humerus. The nutrient arteries enter the humerus through this foramen.
Distal humerus
Lower extremity of humerus | |
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Details | |
Identifiers | |
Latin | extremitas distalis humeri |
MeSH | D006811 |
TA98 | A02.4.04.001 |
TA2 | 1180 |
FMA | 13303 |
Anatomical terms of bone |
The distal or lower extremity of the humerus is flattened from before backward, and curved slightly forward; it ends below in a broad, articular surface, which is divided into two parts by a slight ridge. Projecting on either side are the lateral and medial epicondyles.
Articular surface
The articular surface extends a little lower than the epicondyles, and is curved slightly forward; its medial extremity occupies a lower level than the lateral. The lateral portion of this surface consists of a smooth, rounded eminence, named the capitulum of the humerus; it articulates with the cup-shaped depression on the head of the radius, and is limited to the front and lower part of the bone.
Fossae
Above the front part of the trochlea is a small depression, the
Above the back part of the trochlea is a deep triangular depression, the
The coronoid fossa is the medial hollow part on the anterior surface of the distal humerus. The coronoid fossa is smaller than the olecranon fossa and receives the coronoid process of the ulna during maximum flexion of the elbow.
Above the front part of the capitulum is a slight depression, the radial fossa, which receives the anterior border of the head of the radius, when the forearm is flexed.
These fossæ are separated from one another by a thin, transparent lamina of bone, which is sometimes perforated by a
The Capitulum is a rounded eminence forming the lateral part of the distal humerus. The head of the radius articulates with the capitulum.
The trochlea is spool-shaped medial portion of the distal humerus and articulates with the ulna.
Epicondyles
The epicondyles are continuous above with the supracondylar ridges.
- The supinatorand some of the extensor muscles.
- The pronator teres, and to a common tendon of origin of some of the flexor muscles of the forearm; the ulnar nerveruns in a groove on the back of this epicondyle.
The medial supracondylar crest forms the sharp medial border of the distal humerus continuing superiorly from the medial epicondyle. The lateral supracondylar crest forms the sharp lateral border of the distal humerus continuing superiorly from the lateral epicondyle.[3]
Borders
The medial portion of the articular surface is named the trochlea, and presents a deep depression between two well-marked borders; it is convex from before backward, concave from side to side, and occupies the anterior, lower, and posterior parts of the extremity.
- The lateral border separates it from the groove which articulates with the margin of the head of the radius.
- The medial border is thicker, of greater length, and consequently more prominent, than the lateral.
The grooved portion of the articular surface fits accurately within the
Articulations
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.
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Diagram of the humanshoulder joint, front view
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Diagram of the human shoulder joint, back view
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The left shoulder and acromioclavicular joints, and the proper ligaments of the scapula.
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Head of humerus
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The supinator.
Nerves
The
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'.[4] It lies posterior to the medial epicondyle, and is easily damaged in elbow injuries.[citation needed]
Function
Muscular attachment
The
The
The
The
The four muscles of supraspinatus, infraspinatus, teres minor and subscapularis form a musculo-ligamentous girdle called the
Other animals
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. In many reptiles and some mammals (where it is the primitive state), the lower extremity includes a large opening called the entepicondylar foramen to allow the passage of nerves and blood vessels.[5]
Additional images
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Position of humerus (shown in red). Animation.
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Left humerus. Animation.
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3D image
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Human arm bones diagram.
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Humerus - inferior epiphysis. Anterior view.
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Trochlea. Posterior view.
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Humerus - inferior epiphysis. Posterior view.
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Humerus - superior epiphysis. Anterior view.
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Humerus - superior epiphysis. Posterior view.
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Elbow joint. Deep dissection. Anterior view.
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Elbow joint. Deep dissection. Posterior view.
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Elbow joint. Deep dissection. Posterior view.
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The left shoulder and acromioclavicular joints, and the proper ligaments of the scapula
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Left humerus. Anterior view.
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Left humerus. Posterior view.
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Left humerus. Anteriolateral view.
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Left humerus. Medial view.
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Fracture of the proximal humerus
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Left elbow-joint, showing anterior and ulnar collateral ligaments.
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Capsule of elbow-joint (distended). Posterior aspect.
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Humerus anatomy
Ossification
During embryonic development, the humerus is one of the first structures to ossify, beginning with the first ossification center in the shaft of the bone. Ossification of the humerus occurs predictably in the embryo and fetus, and is therefore used as a fetal biometric measurement when determining gestational age of a fetus. At birth, the neonatal humerus is only ossified in the shaft. The epiphyses are cartilaginous at birth.[6] The medial humeral head develops an ossification center around 4 months of age and the greater tuberosity around 10 months of age. These ossification centers begin to fuse at 3 years of age. The process of ossification is complete by 13 years of age, though the epiphyseal plate (growth plate) persists until skeletal maturity, usually around 17 years of age.[7]
See also
References
- ^ Harper, Douglas. "Humerus". Online Etymology Dictionary. Retrieved 6 November 2014.
- ^ a b c d e Gray's Anatomy, see infobox
- ^ "Humerus Anatomy at DocJana.com". docjana.com. 2 March 2019.
- ^ "Funny Bone". Word Detective.
- ISBN 0-03-910284-X.
- PMID 28357556.
- PMID 24450686.
- This article incorporates text in the public domain from page 209 of the 20th edition of Gray's Anatomy (1918)
External links
- New International Encyclopedia. 1905.
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- Humerus[permanent dead link] - BlueLink Anatomy, University of Michigan Medical School