Bones of the Arm of A.Griguolo

Generality

The bones of the arm are the humerus, the radius and the ulna, provided, however, that the word "arm" indicates the anatomical tract between the shoulder and the wrist.

The bones of the arm are extremely relevant from the anatomical point of view: all three participate in the elbow joint; in addition, the humerus takes part in the shoulder joint and inserts muscles in the proximal portion of the upper limb, while the radius and ulna constitute the wrist joint and insert the distal section of the upper limb into muscles .

Like all bones in the human body, the bones of the arm can also be subject to fracture.

What are the Bones of the Arm?

The bones of the arm are the humerus, the radius and the ulna, in the sense in which however the term "arm" includes the anatomical tract between the shoulder and the wrist, and not, as in reality it would be more correct, the portion anatomical between the shoulder and the elbow .

Therefore, according to the more extended (and less precise from the anatomical point of view) of the word "arm", the bones of the arm are the bone of the so-called anatomical arm (humerus) and the bones of the forearm (radius and ulna).

Anatomy

Equal and longitudinal, the bones of the humerus, radius and ulna arm fall into the three category of so-called long bones ; in human anatomy, long bones are bones developed in length, characterized by a narrow central portion (called body or diaphysis ) and two bulky ends (called proximal epiphysis and distal epiphysis ).

Brief review of the proximal-distal terms

" Proximal " means "closer to the center of the body" or "closer to the point of origin"; " distal ", instead, means "farther from the center of the body" or "farther from the point of origin".

Examples:

The femur is proximal to the tibia, which is distal to the femur.
In the femur, the extremity bordering the trunk is the proximal end, while the extremity bordering the knee is the distal end.

Homer

Of the three bones of the arm, the humerus is the most proximal component; in fact, it runs from the shoulder to the elbow.

If the word "arm" is given its strictly anatomical meaning, the humerus is the only true bone element that can be classified as an arm bone.

PROXIMAL EPIXIS OF THE HUMERUS

The proximal epiphysis of the humerus is the end of the humerus closest to the trunk.

It is anatomically important, because, joining the scapula, it constitutes the so - called glenohumeral articulation (in the common language, the articulation of the shoulder ).

To characterize the morphology of the proximal epiphysis of the humerus are:

The " head ". Projected in the medial direction, it is a semi-spherical bony protuberance, which has a smooth cartilaginous surface.
It is the protagonist of the union between the distal end of the humerus and the glenoid cavity of the scapula, a combination that leads to the formation of the aforementioned shoulder joint.
The " greater tubercle ". It is a fairly large bone process that develops in a lateral direction. Equipped with a front face and a posterior face, its function is to anchor the terminal ends of 3 of the 4 muscles constituting the so-called rotator cuff: the supraspinatus muscle, the sub-spinal muscle (or infraspinatus) and the small round muscle.
The " minor tubercle ". Medial and smaller than the large tubercle, it is the bone process that serves as a point of attachment for the terminal head of the 4th muscle of the rotator cuff; the subscapularis muscle.
The " intertubercular groove ". It is a deep depression located between the two aforementioned tubercles. Traversed internally by the long head of the brachial muscle, it has ridges on the surface that serve to anchor important muscles such as: the large pectoralis, the large round and the large dorsal.

Brief review of the medial-lateral terms

Recalling that the sagittal plane is the anteroposterior division of the human body from which two equal and symmetrical halves are derived, " medial " means "near" or "closer" to the sagittal plane, while " lateral " means "distant or farther" from the sagittal plane ".

Examples:

The second toe is lateral to the big toe, but is medial to the third toe.
The tibia is medial to the fibula, which is lateral to the tibia.

BODY OF THE HERO

The body of the humerus is the portion of humerus between the proximal epiphysis and the distal epiphysis.

Cylindrical superiorly and prismatic inferiorly, the body of the humerus presents 3 anatomically relevant elements, which are:

The " deltoid tuberosity ". It is the bony prominence that houses the terminal head of the deltoid muscle.
The " nutritious hole ". It is the channel that allows the entry, in the humerus, of the blood vessels necessary for the oxygenation and nutrition of the humerus itself.
The " radial groove ". It is a mild depression with lateral orientation, in which the radial nerve and the deep brachial artery flow.

The body of the humerus tightens relationships with different muscles of the upper limb; in particular with: the brachialis muscle, the brachioradialis muscle, the coracobrachialis muscle and the triceps brachialis muscle.

Did you know that ...

Of the three bones of the arm, the humerus corresponds to the femur along the lower limb.

Among the three bones of the arm, the humerus is the largest one.

DISTAL EPIPHIST OF THE HUMER

The distal epiphysis of the humerus is the extremity of the humerus furthest from the trunk.

Its anatomical importance depends above all on its participation in the articulation of the elbow .

Above all, the morphology of the distal epiphysis of the humerus are:

The " medial supracondylar ridge " and the " lateral supracondylar ridge ". They are, respectively, the inner edge and the outer edge of the distal end of the humerus.
On the medial supracondylar crest the initial end of the large round muscle is inserted.
The so-called medial epicondyle and lateral epicondyle . They are two bony prominences perceptible to the touch; on the medial epicondyle resides the tendon of the flexor muscles, while on the lateral epicondyle the tendon of the extensor muscles and the initial head of the anconeus muscle take place.

Anatomy of the elbow

The " fossa coronoidea ", the " radial fossa " and the " fossa olecranica ". They are three depressions; the first two take place on the front of the humerus, while the third is located posteriorly. The coronoid fossa and the radial fossa are used during the flexion movements of the upper limb, to better accommodate radius and ulna; the olecranon fossa, on the other hand, is used during the movements of extension of the upper limb, in order to receive in the best way only the ulna (during these movements the radium does not come into contact with the humerus).
The " troclea " and the " capitulum ". Located on the lower surface of the distal epiphysis of the humerus, the cartilaginous portions of the latter are used to form, through the interaction with radius and ulna, the important articulation of the elbow; specifically, the trochlea interacts with the ulna, while the capitulum interacts with the radium.

Radio

Of the three bones of the arm, the radius is the lateral bone of the anatomical tract between the elbow and the wrist (assuming that the upper limb is extended along the body and the palm of the hand is facing the observer).

For its entire course, the radio runs parallel to the ulna.

PROXIMAL EPIXIS OF THE RADIO

Similar to a cylinder, the proximal radius epiphysis is the end of the radius closest to the humerus.

Its anatomical importance is related to its participation in the elbow joint.

To characterize the morphology of the proximal radium epiphysis are:

The " head ". Representing the upper apex of the radius, it is the smooth bone portion which, through the interaction with the capitulum of the distal end of the humerus, forms the articulation of the elbow.
In addition, it is important to note that, on the medial border of the radium head, there is a particular bone area, which serves to connect the radius with the ulna.
The " radial tuberosity ". Facing the ulna, it is a bone process that serves to accommodate the terminal head of the biceps brachial muscle.

Did you know that ...

Of the three bones in the arm, the radius corresponds to the tibia along the lower argon.

BODY OF THE RADIO

The body of the radium is the portion of radium located between the proximal epiphysis and the distal epiphysis.

With the tendency to widen in a distal direction, the body of the radium stands out for the following anatomical elements:

The " fly surface ". It is the area from which the hand muscle known as the long flexor of the thumb originates; which houses the terminal head of the pronator squared muscle; which inserts into the radio-carpal ligament fly; on which, finally, the nutritious hole takes place (ie the channel that allows the entry of blood vessels destined to oxygenate and nourish the bone tissue of the radium).
The " dorsal surface ". It is the area from which the thumb muscles called the long abductor of the thumb and the extensor of the thumb originate.
The " side surface ". It is the area on which the muscles of the forearm called supinator and pronator round are inserted.
The " bordino interosseo " (or " interossea crest "). It is the region in charge of hooking the so-called radio-ulnar interosseous membrane. The radio-ulnar interosseous membrane is a thin sheet of fibrous tissue which, interposed between radius and ulna, serves to indirectly join the aforementioned bones.

DISTAL EPIFYTS OF THE RADIO

The distal radius epiphysis is the end of the radius closest to the wrist and furthest from the humerus.

It is anatomically important because, by making contact with the bones of the carpus, it actively participates in the formation of the wrist joint .

To distinguish the morphology of the distal epiphysis of the radius are above all:

The " styloid process ". It is a bone projection located in the lateral position, on which the terminal head of the brachioradial muscle and one of the two ends of the collateral radial ligament of the wrist find insertion.
The so-called ulnar hollow . It is the concavity in which the lateral surface of the ulna's head lodges perfectly. This radio-ulna contact in the distal area is added to the radio-ulna union in the proximal area, described above, and to the radio-ulna interaction deriving from the radio-ulnar interosseous membrane.
The " lateral articular facet " and the " medial articular facet ". They are the areas of connection with the carpus of the hand, for the purpose of the articulation of the wrist. More specifically, the first is the junction point with the carpal bone called scaphoid, while the second is the junction point with the carpal bone called semilunar.

Ulna

Of the three bones of the arm, the ulna is the medial bone of the anatomical tract between the elbow and the wrist (assuming that the upper limb is extended along the body and the palm of the hand is facing the observer).

PROXIMAL EPIXIS OF THE ULNA

The proximal epiphysis of the ulna is the end of the ulna closest to the humerus.

Like the proximal epiphysis of the radius, it is important from the anatomical point of view by virtue of its active participation in the elbow joint.

To mark the morphology of the proximal epiphysis of the ulna are:

The so-called olecranon . Representing the most proximal part of the ulna, it is the hook-shaped bone projection that contributes to the formation of the trochlear recess (which will be discussed later).
The olecranon is also a seat for the initial head of the flexor carpi ulnar muscle and a coupling seat for the terminal heads of the anconeus muscles (a part) and brachial triceps.
The " coronoid process ". Located on the anterior surface of the ulna and projected forward, it is the bony crest that contributes, with the olecranon, to the formation of the aforementioned trochlear recess.
The ulnar collateral ligament and the pronator round muscle originate from the coronoid process.
The so-called trochlear recess (or semi-lunar incisura ). It is the wrench-shaped depression with a smooth surface, used to house the humerus trochlea and generate the elbow joint.
The so-called radial recess . Located laterally to the trochlear recess, it is the small depression that serves to house the head of the radium and to form the already discussed union between the ulna and the radio in the proximal site.
The " tuberosity of the ulna ". Located below the coronoid process, it is the bony prominence that houses the terminal head of the brachial muscle.

BODY OF THE ULNA

The body of the ulna is the portion of ulna interposed between the proximal epiphysis and the distal epiphysis.

On the body of the ulna, the following anatomical elements stand out:

The " front surface " (or fly ) and the " back surface " (or dorsal ). They are areas of departure and arrival for different muscles of the forearm and of the hand (eg: anconeus, deep flexor of the fingers, supinator, long abductor of the thumb, extensor of the thumb, extensor of the index, etc.).
Furthermore, exclusively on the front surface, it locates the nutritive hole.
The " interosseo border ". It is equivalent to the interosseous border of the radius, therefore it serves to hook the other end of the interosseous radio-ulnar membrane.

Did you know that ...

Of the three bones of the arm, the ulna corresponds to the fibula in the lower limb.

DISTAL EPIPHIST OF THE ULNA

The distal epiphysis of the ulna is the end of the ulna closest to the wrist and furthest from the humerus.

Its anatomical importance depends above all on its indirect contribution to the wrist joint.

To distinguish the morphology of the distal epiphysis of the ulna are in particular:

The " head of the ulna ". Of rounded shape, it is the small protuberance destined to fit into the already mentioned ulnar recess of the radium
The " styloid process ". Located on the inferior margin of the tibia, in medial position, it is the bony projection on which one of the two ends of the collateral ulnar carpal ligament finds insertion; the ulnar collateral ligament of the carpus is an important ligament of the wrist joint, which basically serves to stabilize the latter.

Function

A first function of the bones of the arm is to allow, thanks to their involvement in important joints such as the shoulder, the elbow and the wrist, the execution of all the movements of the upper limb, from the movements required for complex gestures (eg: throwing a javelin) to the movements required during the simplest gestures (ex: writing, lifting an object, using cutlery, etc.).

A second function of the arm bones is to receive the muscles and ligaments necessary to support the aforementioned joint movements; for example, the humerus hosts fundamental muscles for shoulder and elbow mobility, while ulna and radium give insertion to muscles essential to elbow and wrist mobility.

Finally, a third function of the arm bones is to support the very young human being in four-legged locomotion.