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Humerus

German: Humerus

1 Definition

The humerus is the longest bone of the upper limb. It consists of an almost cylindrical body (corpus humeri), each having a proximal and distal end section (extremitas proximalis et distalis).

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2 Proximal end section (extremitas proximalis)

At the proximal end 4 important anatomical structures are able to be distinguished: the head (caput humeri), the neck (collum humeri) and two humps, the greater tuberosity (humerus) and the lesser tuberosity (humeri).

2.1 Caput humeri

The nearly hemispherical head of the humerus is angled when in the upper arm is in resting position cranially and medially and lightly towards dorsal. It articulates with the glenoid cavity of the scapula.

2.2 Collum humeri

Immediately below the humeral head is the attachment of the neck of the humerus. It is lightly withdrawn in relation to the joint surface and is also referred to as "collum anatomicum". It serves as a fixture point for the joint capsule of the shoulder joints. Delimited from this is the "collum chirurgicum", a surgically important "breaking point" of the humerus, which lies below the tubercles in the transition to the torso.

2.3 Tuberculum majus (humeri)

The greater tuberosity (tuberculum majus) is located laterally to the humeral head. Its cranial surface is rounded and exhibits three flat impressions that serve from top to bottom as a fixture to the following muscles:

The lateral surface of the tubercle majus is rough and convex and merges without visible margins into the corpus humeri.

2.4 Tuberculum minus (humeri)

The lesser tubercle (tuberculum minus) serves as a muscle attachment, specifically for the musculus subscapularis. Although it is indeed smaller than the greater tuberosity (tuberculum majus), it protudes more prominently frontally. This shows in the pull direction of the tendon of the subscapularis muscle medially.

2.5 Sulcus intertubercularis

A depression runs between the tubercles: the biceps groove (sulcus intertubercularis). Through this runs the long tendon of the caput longum of the musculus biceps brachii and a branch of the arteria circumflexa humeri anterior. The sulcus moves distally until about the beginning of the middle bone third, there losing more and more characteristic form. On both sides of the sulcus there are two bone crests that take their origin from the tubercles, the crista tuberculi majoris and crista tuberculi minoris.

3 Body or shank (corpus humeri)

3.1 Surfaces

3.1.1 Facies anterior lateralis

The facies anterior lateralis is in its proximal part smooth and rounded. It is obscured by the musculus deltoideus. Approximately in the middle of the surface there is a rough bump, the tuberositas deltoidea that marks the insertion point of the muscle of the same name. Beneath it is the sulcus radialis which comes from the facies posterior, in which the nervus radialis and arteria profunda brachii pivot obliquely from behind and above frontally. In the distal part the facies anterior lateralis serves as the origin of the musculus brachialis.

3.1.2 Facies anterior medialis

The facies anterior medialis has a lesser extention than the facies anterior lateralis. Its upper portion is narrow, forming the bottom of the bicipital groove (sulcus intertubercularis) and serves as a fixture surface of the musculus latissimus dorsi. A rough spot in the middle section forms the fixture point of the musculus coracobrachialis. The distal portion serves as the origin of the musculus brachialis.

3.1.3 Facies posterior

The facies posterior is almost entirely covered by the lateral and medial head of the musculus triceps brachii. The origin surface of both muscle heads is intersected by the sulcus radialis.

3.2 Edges

3.2.1 Margo anterior

The anterior border (margo anterior) runs from the front of the greater tuberosity (tuberculum majus) distally up to the fossa coronoidea, thereby dissecting the facies anterior medialis from the facies anterior lateralis. In the upper part is a prominent bony prominence, the crista tuberculi majoris, which serves as an attachment point to the tendon of the musculus pectoralis major. In the middle it takes up the front edge of the tuberositas deltoideae. Distally it appears smooth and rounded and serves as the origin of the musculus brachialis.

3.2.2 Margo lateralis

The lateral margin extends from the rear of the greater tuberosity (tuberculum majus) to the lateral epicondyle and thereby separates the facies anterior lateralis from the facies posterior. The upper half is rounded and difficult to distinguish. It serves as attachment point for the teres minor and distally from there as the origin of the lateral head of the musculus triceps brachii In the center the flat lateral margin (margo lateralis) is crossed by the flat bone impression of the sulcus radialis. It ends in a distal direction in a pronounced bone crest, the crista supracondylaris lateralis, which serves as the origin of the [[musculus brachioradialis].

3.2.3 Margo medialis

The medial border extends from the tuberculum minus to the epicondylus medialis. In the upper third, it appears as a prominent bony prominence, which is called crista tuberculi minoris. This is where the tendon of the musculus teres major is fixed. In the centre it has a slight depression for the tendon of the musculus coracobrachialis. The lower third rises to - with increasing proximity to the epicondylus - a bony prominence, the crista supracondylaris medialis.

4 Distal end (extremitas distalis)

The distal end of the humerus is flattened in an anterior-posterior direction, ends laterally and medially in distinct bony curves (epicondyles) and exhibits as its most important anatomical feature the condyle of the humerus (condylus humeri), which with its joint surfaces (facies articulares) forms the proximal part of the elbow.

4.1 Capitulum humeri

The lateral aspect of the articular surface is composed of a button-like rounded and clearly protruding cartilage surface, which is called capitellum (capitulum humeri) . It articulates with the concave articulation surface of the radius condyle.

4.2 Fossa radialis

Directly proximally to the capitellum one sees a depression in the bone, called the "fossa radialis. It takes up the leading edge of the radial head when the forearm is brought into a strongly bent (flexion) position.

4.3 Trochlea

The medial portion of the joint surface is called the trochlea humeri. It pulls from the front to the back of the humerus as a transverse cylinder and thereby forms an extended tapered cartilage roll. In a mediolateral direction the condyle is concave.

The trochlea articulates flush with the corresponding crescent-formed articular surface of the olecranons of the proximal ulna. The lateral boundary separates the trochlea in a ridge form from the adjacent cartilage surface which is connected to the edge of the radial head. The medial margin is more pronounced and marks the transition to the medial epicondyle (epicondylus medialis).

4.4 Fossa coronoidea

Proximal to the trochlea one sees in the anterior view a small depression, the "fossa coronoidea". It takes up - analogous to the fossa radialis - the processus coronoideus of the ulna in a flexed forearm position.

4.5 Fossa olecrani

On the back of the humerus proximal to the trochlea is another, prominent triangular depression, the fossa olecrani. It takes up the olecranon of the ulna of the forearm in the extension position.

4.6 Epicondylus lateralis

The epicondylus lateralis is a small protrusion furnished with numerous tubercles on the lateral side of the humerus. It is the common origin of the following muscles:

In addition, it serves as an attachment surface for the fibrous bands of ligamentum collaterale radiale. In a proximal direction it continues on to the crista supracondylaris lateralis.

4.7 Epicondylus medialis

The medial epicondyle is more strongly pronounced than the lateral. In a proximal direction it continues on to the crista supracondylaris medialis. It serves as the attachment surface for the ligamentum collaterale ulnare. The medial epicondyle (epicondylis medialis) is the common origin point of the superficial flexor muscles of the forearm:

The nervus ulnaris runs in a bone groove on the posterior side of the epicondylis medialis.

5 Development

The perichondral bone system in the shaft first appears in the 2nd-3rd fetal month. The endochondral ossification centres appear in the epiphyses between the 2nd week of life and 12 years of age. Proximally one observs soon after birth 3 ossification, from where distally 4 ossifications emerge. The distal physis closes, whereas the proximal joint only does this at the end of puberty.

The bone core formation and the epiphyseal gap fusion takes place with females a little earlier than in males.

6 Clinic Observations

Humerus fractures are relatively frequent on account of the exposed position of the upper arm and make up about 4-5% of all fractures. Subcategorisation includes:

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