Generality
The humerus is the equal bone of the human body that constitutes the skeleton of each arm.
Located between the scapula (main shoulder bone) and forearm bones (radius and ulna), it participates in the formation of two important joints of the upper limb: the shoulder joint and the elbow joint.
The proximal end is the portion closest to the scapula and with which it articulates, through a section called the head.
The body is the portion between the two epiphyses and in which different arm muscles are inserted.
Finally, the distal end is the portion adjacent to ulna and radius, the bones with which it forms the elbow joint.
What is the humerus
The humerus is the equal bone of the human body that constitutes the skeleton of each arm .
The arm is the anatomical region of the lower limb lying between the shoulder, above, and the forearm, below.
Belonging to the category of long bones, the humerus forms two joints: one on the side of the shoulder, called the glenohumeral joint (or more simply, the articulation of the shoulder), and one on the side of the forearm, called the elbow joint .
IN THE LOWER ARTS IT CORRESPONDS TO ...
In the lower limb, the bone corresponding to the humerus is the femur . The femur is the even bone that, on its own, makes up the skeleton of each thigh .
Anatomy
Anatomy experts identify three main bone regions (or portions) in the humerus: the proximal end (or proximal epiphysis), the body (or diaphysis) and the distal end (or distal epiphysis).
Figure: the plans with which the anatomists dissect the human body. In the image, in particular, the sagittal plane is highlighted.
Anatomical meaning of proximal and distal
Proximal and distal are two terms with opposite meaning.Proximal means "closer to the center of the body" or "closer to the point of origin". Referring to the femur, for example, it indicates the portion of this bone closest to the trunk.
Distal, on the other hand, means "farther from the center of the body" or "farther from the point of origin". Referred (always to the femur), for example, it indicates the portion of this bone furthest from the trunk (and closer to the knee joint).
End? PROXIMAL OF THE HERO
The proximal end of the humerus is the bone portion closest to the shoulder and which, joining a bone of the latter (in this case the scapula), forms the aforementioned glenohumeral joint.
The relevant anatomical elements of the proximal end are:
- The head . It is the most proximal part of the humerus. Projected in the medial direction, it is a bony protuberance that has the shape of a semi-sphere. It has a smooth surface of cartilaginous nature and covers the important function of articulating with the glenoid cavity (or glenoid fossa) of the scapula and forming the shoulder joint.
- The anatomical neck . It is a border region between the head and other structures of the proximal epiphysis. It is short and narrower than the head.
- The greater tubercle . It is a bone process of moderate size, which develops laterally, immediately after the anatomical neck. It has two faces, one front and one rear.
Its function is to anchor the terminal heads of three total 4 muscles that form the so-called rotator cuff: the supraspinatus muscle, the sub-spinal muscle (or infraspinatus) and the small round muscle (or minor teres).
- The lesser tubercle . It is a small bone process, in a medial position with respect to the large tubercle. It has only one face, the front one, and acts as an insertion point for the terminal head of the 4th muscle of the rotator cuff: the subscapularis muscle.
- The intertubercular sulcus . It is a deep depression, located between the two tubercles and crossed by the tendon of the long head of the brachial muscle. On the superficial margin, the intertubercular groove has ridges, which take the name of lips. The tendons of three important muscles are anchored to the lips: the major pectoral muscle, the large round muscle and the large dorsal muscle.
- The surgical neck . It is the border region, which separates the tubercles (located above) from the body of the humerus (inferiorly).
Brief review of the sagittal plane and of medial and lateral concepts
Medial and lateral are two terms with the opposite meaning. However, to fully understand what they mean, it is necessary to take a step back and review the concept of the sagittal plan.
The sagittal plane, or median plane of symmetry, is the antero-posterior division of the body, a division from which two equal and symmetrical halves are derived: the right half and the left half. For example, from a sagittal plane of the head derive a half, which includes the right eye, the right ear, the right nasal nostril and so on, and a half, which includes the left eye, the left ear, the left nasal nostril etc.
Returning to the medial-lateral concepts, the word media indicates a relationship of proximity to the sagittal plane; while the word side indicates a relationship of distance from the sagittal plane.
All anatomical organs can be medial or lateral with respect to a reference point. A couple of examples clarify this statement:
First example. If the reference point is the eye, it is lateral to the nasal nostril of the same side, but medial to the ear.
Second example. If the reference point is the second toe, this element is lateral to the first toe (toe), but medial to all the others.
BODY OF THE HERO
The body is the central portion of the humerus, between the proximal end and the distal end.
Place of insertion of different muscles, it has a cylindrical aspect, superiorly, and a prismatic form, inferiorly.
The relevant anatomical structures of the humerus body are, in fact, three: the deltoid tuberosity, the nutritive hole and the radial groove.
The deltoid tuberosity is a bony prominence, located a little higher than half, in anterolateral position. Its function is to accommodate the terminal head of the deltoid muscle .
The nutritive hole is the channel that allows the entry, in the humerus, of the blood vessels responsible for the oxygenation and nutrition of the humerus itself.
Finally, the radial groove is a slight depression, which runs diagonally and laterally in the posterior section of the body. Inside, it houses the radial nerve and the deep brachial artery . Laterally, it ends at the deltoid tuberosity.
As far as the muscles that relate to the humerus body are concerned, these are: the coracobrachial muscle, the brachialis muscle and the brachioradialis muscle, on the anterior bone section, and the medial head and lateral head of the brachial triceps, on the bone section rear.
The surfaces of the humerus body
In the body of the humerus, the anatomists recognize three surfaces: antero-medial, antero-lateral and posterior. The nutritive hole is located on the antero-medial surface; the deltoid tuberosity takes place on the anterolateral surface; finally, on the back surface, the radial groove resides.End? DISTAL OF THE HERO
The distal end of the humerus is the bone portion closest to the forearm and whose bones form the elbow joint. The bones of the forearm are two: ulna and radio .
The distal epiphysis of the humerus has several important anatomical structures, which, proceeding from top to bottom, are:
- The medial supracondylar crest and the lateral supracondylar ridge;
- The medial epicondyle and the lateral epicondyle;
- The coronoid fossa (or coronoid dimple), the radial fossa and the olecranon fossa;
- The trochlea and the capitulum .
The medial supracondylar crest and the lateral supracondylar crest are, respectively, the inner edge and the outer edge of the distal end of the humerus. The first of these two ridges is particularly interesting because it houses the initial head of the pronator round muscle; the pronator round muscle is a muscular element that ends in the forearm (anterior region) and allows certain movements of the elbow.
The epicondyls originate from the two supracondyloid crests: clearly, the medial epicondyle derives from the medial crest, while the lateral epicondyle is derived from the lateral crest.
The epicondyles are two bony projections perceptible to the touch, from which different muscles of the forearm are born: on the medial epicondyle, the tendon of the flexor muscles takes place (common flexor tendon); on the lateral epicondyle, the tendon of the extensor muscles (common extensor tendon) and the initial head of the anconeus muscle (on the posterior face) reside.
The coronoid fossa and the radial fossa are two depressions that locate on the anterior surface of the distal end of the humerus, with the first in a medial position with respect to the second.
In fact, they are located in the anterior bone area, interposed between the two epicondyles. During flexion of the forearm, the coronoid fossa receives the so-called coronoid process of the ulna, while the radial fossa receives the so-called radium head.
The olecranon fossa is a depression similar to the previous ones, which, however, is located on the posterior surface of the distal end of the humerus. In a central position, exactly between the two epicondyles, it hosts the eminence of the ulna known as the olecranon, during the extension movements of the forearm.
Troclea and capitulum take place, respectively, below the coronoid fossa and the radial fossa (so the trochlea is medial with respect to the capitulum ). Occupying the lower margin of the distal epiphysis, they have a smooth cartilaginous surface, which allows them to articulate with the bones of the forearm and form the elbow joint.
The trochlea is articulated with the trochlear hollow of the ulna, while the capitulum with a recess characteristic of the head of the radium.
BLOOD SPRAYING
Internally, long bones, such as the humerus (but also the femur, tibia, etc.), have a very specific network of arteries and veins, which serves to guarantee them the right supply of oxygen and nutrients.
Arteries - that is, in vessels that carry oxygen-rich blood - are the so-called nutritive artery and periosteum arteries ; the veins - that is, the vessels that drain the oxygen-poor blood - are the so-called nutritive vein and the periosteum veins .
In the case of the humerus, the aforementioned arteries derive from the brachial artery, while the aforesaid veins from the brachial vein .
The nutritive artery and the nutritive vein deserve a particular note, as they penetrate the body of the humerus, through a previously named structure: the nutritive hole (also known as nutritious channel).
OBSIFICATION OF THE HOMER
Figure: The nutritious vessels and the nourishing hole in the long bones.
Figure: the brachial artery is the main arterial vessel of the upper limb, the one from which the vessels deriving from the forearm, the hand etc. are derived. It runs parallel to the brachial plexus (a reticular formation of spinal nerves) and separates, at the level of the elbow (and before giving rise to many small branches), in the radial artery and the ulnar artery.
The humerus derives from the activity of eight ossification centers, which reside in correspondence with: body, head of the humerus, greater tubercle, lesser tubercle, capitulum, trochlea, medial epicondyle and lateral epicondyle.
The ossification proceeds according to very specific stages, which can be summarized in these brief points:
- To start the process is the center located on the body: this is activated around the 8th week of fetal life and determines the formation of bone in the direction of the body.
At birth, only the ends of the humerus are not yet ossified.
- Proximal end. During the first year of life, the center is activated on the head of the humerus; starting from the third year of life, the center present on the greater tubercle; finally, at the beginning of the fifth year, the center of the minor tubercle.
Generally, at the sixth year of life, the ossification centers of the humeral head and the two tubercles merge their bone formations, generating the proximal epiphysis described above.
The union between the proximal epiphysis and the body occurs around age 20 years.
- Distal end. At the end of the second year of life, the ossification center of the capitulum enters into action, whose bone formation has a medial orientation.
At the age of 5, he begins to ossify the medial epicondyle; at 12, the trochlea; finally at 13-14 years, the medial epicondyle.
At around 16-17 years, the lateral epicondyle, trochlea and capitulum merge with each other and with the body; at the age of 18, the medial epicondyle joins the lateral epicondyle, the trochlea, etc.
Functions
The humerus covers various functions.
First of all, it forms the aforementioned shoulder and elbow joints; these are fundamental for all arm movements, not only during the execution of complex gestures (for example the throwing of a javelin) but also during simpler activities (the so-called activities of daily life such as writing, lifting an object, use cutlery, etc.).
Secondly, it welcomes the muscles that support the movements of these joints: at the top it houses the terminal heads of the muscles that originate from the shoulder (deltoid and rotator cuff muscles); inferiorly it gives rise to the muscular elements that end in the forearm, or in the ulna or in the radium.
Finally, in young children, it is important for locomotion: when walking on all fours, subjects of very young age make use of the support of the upper limbs, and therefore also of the humerus.
| List of the main muscle elements that originate and end at the humerus | ||
Muscle | Head end or initial leader | Contact site on the tibia |
| Supraspinatus muscle | Head end | Greater tubercle |
| Infraspinatus muscle (or inborn) | Head end | Greater tubercle |
| Small round muscle | Head end | Greater tubercle |
| Subscapularis muscle | Head end | Tubercle minor |
| Pectoralis major muscle | Head end | Intertubercular groove |
| Large dorsal muscle | Head end | Intertubercular groove |
| Big round muscle | Head end | Intertubercular groove |
| Deltoid muscle | Head end | Deltoid tuberosity |
| Coracobrachial muscle | Head end | Anteromedial surface of the humerus |
| Brachialis muscle | Initial leader | Anterolateral surface of the body of the humerus, near the deltoid tuberosity |
| Brachioradial muscle | Initial leader | Anterolateral surface of the body of the humerus, above the lateral supracondylar ridge |
| Broad medial muscle of the brachial triceps | Initial leader | Back surfaces of the humerus body |
| Lateral muscle vessel of the brachial triceps | Initial leader | Posterior surface of the body of the humerus |
| Pronator round muscle | Initial leader | Medial supracondylar ridge |
Flexor tendon:
| Initial leader | Medial epicondyle |
Extensor muscle tendon:
| Initial leader | Lateral epicondyle |
| Anconeus muscle | Initial leader | Posterior surface of the lateral epicondyle |
Associated diseases
The humerus can fracture, like virtually any other bone in the human body.
Fruit in general of traumas to the arm, fractures of the humerus can involve all three portions of the aforesaid bone, therefore the proximal end (fractures of the proximal humerus), the body (fractures of the body of the humerus) and the distal end (fractures of the distal humerus).
FRACTURES OF THE PROXIMAL HERO
Fractures of the proximal humerus generally occur after direct hits to the arm or following falls in which the victim of the traumatic event held the extended hand.
Since the so-called axillary nerve and the so-called posterior circumflex artery of the humerus run near the proximal end, a trauma to this bone portion can damage the above anatomical structures, causing respectively a nerve damage and / or vascular damage.
In this case, damage to the axillary nerve can have two consequences:
- Provoke paralysis of the deltoid and small round muscles, effectively interfering with the motor function of the axillary nerve;
- Induce a problem of sensitive origin, at the level of the skin that covers the lower part of the deltoid muscle. The most severe cases involve the complete loss of the sensory innervation.
FRACTURES OF THE BODY OF THE HUMAN
The fractures of the body of the humerus are successive, very often, to direct blows in the median area of the arm.
These types of injuries can be associated, in some specific cases, with damage to the radial nerve and / or the deep brachial artery, ie the two anatomical elements that run inside the radial groove.
In particular, damage to the radial nerve can result in paralysis of the extrinsic extensor muscles of the hand and / or a loss of skin sensitivity at the level of the dorsal surface of the hand and of some of its fingers.
FRACTURES OF THE DISTAL HERO
Fractures of the distal humerus usually involve the area of the two supracondyloid ridges or the medial epicondyle. To cause it to appear, very often, falls on the bent elbow.
Among the most serious complications of the distal end ruptures, a particular mention deserves:
- The interruption of blood flow, within the brachial artery, and the consequent ischemia phenomenon. Caused by bone damage or edema that the fracture determines, this complicated situation is responsible for a phenomenon that is called Volkmann's ischemic contracture .
The ischemic contracture of Volkmann (or Volkmann's syndrome) induces a permanent flexion of the hand and an intense painful sensation during the act of extension of the fingers (of the hand).
It is a typical complication of fractures involving the supracondylar crests of the humerus.
- Median nerve damage . The median nerve is a branch of the brachial plexus, which innervates certain muscles of the hand and some of its cutaneous areas.
It is a complication that most frequently characterizes fractures of the medial epicondyle of the humerus.
