physiology

Elbow

Generality

The elbow is the joint at the junction of the arm and forearm.

Its task is to shorten and lengthen the upper limb according to need, to place the hand in a useful point of space (for example to bring a piece of food to the mouth).

  • The arm is the portion of the upper limb between the shoulder joint and the elbow.
  • The forearm is the portion of the upper limb between the elbow and the wrist.

The only bone in the arm is called the humerus ; the bones of the forearm are instead two, respectively called radios and ulna .

Three bones are therefore involved in the elbow joint:

  • the lower end of the humerus;
  • the upper end of the radio;
  • the upper end of the ulna.

Elbow functions

The elbow joint belongs to the class of hinged joints (hinge or ginglimo) and as such has two degrees of freedom, with which it allows ample movements of flexion and extension of the forearm on the arm ; the movements of:

  • pronation : rotation towards the inside of the forearm, which allows the palm of the hand to face downwards;
  • supination : rotation towards the outside of the forearm, which allows the palm of the hand to face upwards.

Very slight lateral movements are also possible with a flexed forearm.

The three joints of the elbow

That of the elbow is a complex articulation that includes three independent joints, enclosed in a single joint capsule, with a single synovium and a common ligamentous apparatus.

Specifically, in addition to the aforementioned articulation between the humerus and ulna (humerus), the elbow also includes the joints between the humerus and radius (humeroradial) and between radius and ulna (radioulnar).

  • The humerus-ulnar joint:
    • Biomechanics: allows only flexion and extension of the forearm on the arm;
    • Anatomy: The trochlea of ​​the humerus is articulated with the trochlear groove of the ulna
  • The articulation of the humerus with the radium:
    • Biomechanics: allows only flexion and extension of the forearm on the arm;
    • Anatomy: the head of the radius is articulated with the capital of the humerus
  • The articulation of the radius with the ulna:
    • Biomechanics: allows pronation (inward rotation) and supination (outward rotation) movements.
    • Anatomy: the head of the radius is articulated with the radial incision of the ulna forming the proximal radio-ulnar joint.

Bones of the elbow

Homer

The distal end of the humerus ( distal diaphysis ) has a broad and flat shape (for this reason it is also called the humeral "paletta") and is covered by cartilage.

The humeral palette has two articular surfaces:

  • the trochlea : situated laterally is a hollow surface, shaped like a pulley;
  • the capital (or head of the humerus): located medially is a hemispherical surface;

separated by a groove of variable depth.

As shown in the figure:

  • the trochlea is articulated with the trochlear incisura of the ulna
  • the capital is articulated with the head of the radium

On both sides of the distal shaft of the humerus there is a bony protuberance, called an epicondyle, situated immediately above the trochlea on one side and the capital on the other.

At the epicondyle level, numerous muscles are inserted to allow forearm, wrist and hand movements. In particular:

  • in the lateral epicondyle the muscles of the posterior compartment of the forearm are inserted (forearm extensor muscles)
  • in the medial epicondyle (or epitrocleus ) the muscles of the anterior compartment of the forearm (flexor muscles of the forearm) are inserted.

Ulna

The upper extremity of the ulna is constituted by a large cavity in the form of a hook, called trochlear incisura (or large sigmoid cavity or semilunar incisura), delimited by two bony protrusions, anteriorly the coronoid (or coronoid process) and posteriorly the olecranon .

As shown in the figure, the trochlear notch of the ulna is therefore bounded by:

  • olecranon : a large bony protrusion into which the common tendon of the brachial triceps is inserted;
  • coronoid process : in the lower part, from which originates the pronator round muscle and inserts the brachial muscle,

Laterally between the coronoid and olecranon there is a small incisura, called radial incisura, which allows the ulna to articulate with the radial capital.

Radio

The upper end of the radio consists of:

  • capital or head of the radio, which represents the largest and most rounded area;
  • neck, which is the narrowest part below the head

Elbow muscles

As seen in the previous chapter, the muscles that insert into the elbow through their respective tendons are located at the sides of the joint, where they do not interfere with movement.

The muscles that originate or are inserted at the level of the elbow are numerous and are divided into the following groups:

  1. The epicondyloid muscles (long radial extensor and short radial extensor of the carpus, common extensor of the fingers, ulnar extensor of the carpus, extender proper to the little finger, aconus) originate from the lateral epicondyle and allow the extension movements of the fingers and the wrist;
  2. Epitrochlear muscles (round pronator, radial flexor of the carpus, long palmar, ulnar flexor of the carpus) originate from the epitrochlea (or medial epicondyle); allow pronation movements (the rotation of the forearm performed to unscrew using a screwdriver with the right hand) and flexion of the fingers and wrist (the movement that is performed to make the fist or to bring the hand to the mouth when the elbow is still
  3. Other important muscles that fit on the elbow are
    • the biceps brachialis and the brachialis anteriorly, which allow the movement of flexion of the elbow (to bring the hand to the head) and of supination of the forearm (the rotation of the forearm that allows the palm of the hand to face upwards);
    • the brachial triceps posteriorly, which allows the extension movement of the elbow (remove the hand from the head).

Elbow ligaments

The three joints of the elbow (humerus-radial, humero-ulnar and proximal radio-ulnar) are kept in contact with each other by a fibrous sleeve, called joint capsule, stabilized by robust collateral ligaments; these can be distinguished in a medial ligamentous complex and in a lateral complex:

  • medial or ulnar collateral ligament : fixed superiorly on the humerus and inferiorly on the ulna;
  • lateral or radial collateral ligament : fixed above the humerus and inferiorly on the radius;

Another important elbow ligament is:

  • annular radium ligament : it surrounds the radial capital like a ring and is inserted on the ulna; its presence is fundamental to keep the radium firmly close to the ulna during the movements, allowing it only to rotate on its own axis during the prono-supination

It is recalled that radio and ulna are kept close, for their entire length, by a robust connective structure: the interosseous membrane.

Elbow disorders

The repeated stress of the muscles that insert into the elbow with their tendons can trigger pain syndromes on this joint complex.

  • Epicondylitis (or tennis elbow) involves the lateral epicondyle of the humerus and the tendon structures of the extensors (long and short) of the carpus that are inserted in this area; the patient with epicondylitis has pain on the outside of the elbow;
  • Epitrocleite (or golfer's elbow) involves the? Epitroclea (also called the medial epicondyle) and the tendinous structures of the muscles that are inserted in this area; the patient with epitrocleitis has pain in the inside of the elbow;
  • bursitis of the elbow : the bags are small balloons filled with liquid, which act as bearings to facilitate sliding in the seats where a tendon or a ligament rubs against another fabric. At the elbow level there are several bags and the one most subject to inflammation (bursitis) is the olecranon bag. In addition to traumatic factors, elbow bags can become inflamed due to repetitive gestures or functional overload (manual and sports workers).

The elbow is also subject to traumatic diseases, such as:

  • Luxation : there is a permanent displacement of the articular surfaces with respect to the original position; in most cases, the ulna moves posteriorly to the humerus. It is typically caused by a falling defense palm with the elbow slightly flexed on the palm of the hand.
  • Injury of the medial collateral ligament of the elbow : consequence of acute traumatic lesions due to the application of joint levers in the fight sports; it may also be of interest to javelins and other pitchers who throw their heads overhead.