Elbow

Generality

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

It has the task of shortening and lengthening the upper limb as needed, in order to place the hand in a useful point of the 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 of the arm is called the humerus; the bones of the forearm are instead two, respectively called the radius and the ulna.

Three bones are therefore involved in the "elbow joint:

• the lower end of the humerus;
• the upper end of the radius;
• the upper extremity of the ulna.

Functions of the elbow

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 flexion and extension movements of the forearm on the arm; the movements of:

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

With the forearm flexed, very modest lateral movements are also possible.

The three joints of the elbow

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

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

• The humero-ulnar joint:
  • Biomechanics: only allows the flexion and extension of the forearm on the arm;
  • Anatomy: The trochlea of ​​the humerus is articulated with the trochlear notch of the ulna
• The "articulation of the humerus with the radius:
  • Biomechanics: only allows the flexion and extension of the forearm on the arm;
  • Anatomy: the head of the radius articulates with the capital of the humerus
• The articulation of the radius with the ulna:
  • Biomechanics: allows the movements of pronation (rotation inwards) and supination (rotation outwards).
  • Anatomy: the head of the radius articulates with the radial notch of the ulna forming the "proximal radio-ulnar joint.

Elbow bones

Homer

The distal end of the humerus (distal shaft) has a wide and flat shape (which is why it is also called the humeral “blade”) and is lined with cartilage.

The humeral blade has two articular surfaces:

• the trochlea: located laterally it is a hollow surface, in the shape of a pulley;
• the capital (or head of the humerus): located medially it is a hemispherical surface;

separated by a groove of varying depth.

As shown in the picture:

• the trochlea articulates with the trochlear notch of the ulna
• the capital is articulated with the head of the radius

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

At the level of the epicondyles, numerous muscles are inserted that allow the movements of the forearm, wrist and hand. Particularly:

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

Ulna

The upper extremity of the ulna is made up of a large hook-shaped cavity, called the trochlear notch (or large sigmoid cavity or semilunar notch), bounded 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 delimited 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 the pronator teres muscle originates and the brachial muscle is inserted,

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

Radio

The upper end of the radius consists of:

• capital or head of the radius, which represents the most voluminous and rounded area;
• neck, which is the narrowest part under the head

Elbow muscles

As seen in the previous chapter, the muscles that enter the elbow via their respective tendons are located on the sides of the joint, where they do not interfere with movement.

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

1. The epicondylar muscles (long radial extensor and short radial extensor of the carpus, common extensor of the fingers, ulnar extensor of the carpus, extensor of the little finger, aconeum) originate from the lateral epicondyle and allow the extension movements of the fingers and wrist;
2. The epitrochlear muscles (pronator teres, radial flexor of the carpus, long palmar, ulnar flexor of the carpus) originate from the epitrochlea (or medial epicondyle); allow the movements of pronation (the rotation of the forearm that is performed to unscrew using a screwdriver with the right hand) and flexion of the fingers and wrist (the movement that is made to make a fist or to bring the hand to the mouth when elbow is stationary)
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 (bringing the hand closer to the head) and supination of the forearm (the rotation of the forearm which allows the palm of the hand to turn upwards);
   • the triceps brachialis posteriorly, which allows the elbow extension movement (moving the hand away from the head).

Elbow ligaments

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

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

Another important elbow ligament is the:

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

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

Elbow disorders

The repeated stimulation of the muscles that are inserted into the elbow with their tendons can trigger painful syndromes in this joint complex.

• Epicondylitis (or tennis elbow) involves the lateral epicondyle of the humerus and the tendon structures of the extensor (long and short) of the carpus which are inserted in this area; the patient with epicondylitis has pain on the outside of the elbow;
• Epithrocleitis (or golfer's elbow) involves the epitrochlea (also known as the medial epicondyle) and the tendon structures of the muscles that insert into this area; the patient with epithrocleitis has pain in the inner part of the elbow;
• bursitis of the elbow: Bursae are small balloons filled with liquid, which act as cushions to facilitate sliding in places where a tendon or ligament rubs against another tissue. At the level of the elbow there are several bags and the one most prone to inflammation (bursitis) is the olecranon bursa. In addition to traumatic factors, elbow bags can become inflamed by repetitive gestures or functional overload (manual and sports workers).

The elbow is also prone to traumatic pathologies, such as:

• Dislocation: there is a permanent displacement of the articular surfaces with respect to the original position; in most cases, the ulna moves posterior to the humerus. It is typically caused by a fall on the palm of the defensive hand with the elbow slightly flexed.
• Injury of the medial collateral ligament of the elbow: consequence of acute traumatic injuries due to the application of joint levers in wrestling sports; it can also affect javelinists and other throwers who throw from above the head.