Elbow Joint Anatomy and Function

• These notes are for MBBS, BDS, and Physiotherapy students.

Cubital Fossa

• Triangular shaped hollow area/depression located on the anterior side of the upper limb between the arm and forearm.
• It lies anterior to the elbow joint when in standard anatomical position.

Boundaries of the Cubital Fossa

• Superior (proximal) border is an imaginary horizontal line connecting the medial and lateral epicondyles of the humerus.
• Medial (ulnar) border is defined by the lateral border of the pronator teres muscle.
• Lateral (radial) border is defined by the medial border of the brachioradialis muscle.
• Apex is directed inferiorly and formed by the meeting point of the lateral and medial boundaries.
• Roof (superficial boundary) consists of skin and superficial fascia, which contains the median cubital vein, lateral cutaneous nerve of the forearm, and medial cutaneous nerve of the forearm. The deep fascia of the forearm is reinforced on the medial side by the Bicipital aponeurosis.
• Floor (deep boundary) is formed by the brachialis muscle of the arm and the supinator muscle of the forearm.

Contents of the Cubital Fossa

• Contains four main vertical structures (from medial to lateral):
  • Median nerve
  • Terminal part of the brachial artery
  • Biceps brachii tendon
  • Radial nerve and its branches, including the posterior interosseous branch and terminal superficial branch
• Brachial artery typically terminates near the apex of the fossa, bifurcating into the radial (superficial) and ulnar (deeper) arteries at the level of the neck of the radius.

Clinical Relevance of the Cubital Fossa

• Measurement of blood pressure involves palpating the brachial artery in the cubital fossa. Medial to the biceps brachii tendon is used to determine stethoscope placement.
• Phlebotomy uses the superficial area to access veins like the median cubital, preferred for its stability and less sensitive overlying skin.
• Supracondylar fracture is a distal humerus break, commonly transverse/oblique from falls on an outstretched hand, especially in children
• This fracture can damage cubital fossa contents and potentially cause Volkmann's ischemic contracture if the brachial artery is affected. Damage to anterior interosseous, ulnar, or radial nerves may also occur.

Elbow Joint

• Synovial hinge joint between the lower end of the humerus and the upper ends of the radius and ulna. Communicates with the proximal radioulnar joint.

Articulations of the Elbow Joint

• Humeroulnar articulation
  • Trochlear notch of ulna and the trochlea of humerus
  • Trochlea (medial) has a grooved surface extending to the posterior humerus surface and articulating with the deep trochlear notch on the ulna.
• Humeroradial articulation
  • Head of the radius and capitulum of the humerus
  • Cylindrical head of the radius is spherically concave and articulates with the capitulum, a spherical part on the humerus's lower end.
• Head of the radius and radial notch of the ulna (proximal radioulnar joint)
  • Shares the joint capsule with the elbow joint but has no functional role at the elbow.
• The head of the radius and the coronoid process of the ulna are received by the fossa above the capitulum and trochlea in full flexion, respectively. The olecranon of the Ulna goes into the deep fossa posteriorly in full extension.

Capsule of the Elbow Joint

• The capsule is strong and fibrous, helping to strengthen the joint.
• It is thickened medially and laterally as collateral ligaments stabilize flexing and extending motion
• Ligaments strengthen the capsule at the sides, but it remains weak in the front and behind.
• Capsule attachment sites:
  • Humerus: medial and lateral margins of the trochlea and capitulum
  • Front: above the coronoid and radial fossae
  • Back: above the olecranon fossa
  • Distally: margins of the trochlear notch of the ulna and the annular ligament of the proximal radioulnar joint (not attached to the radius)

Synovial Membrane

• Synovial membrane lines the fibrous capsule and reflects onto the humerus, lining coronoid and radial anterior fossae, along with the posterior olecranon fossa.

Bursae in the Elbow

• Bursae are membranous sacs filled with synovial fluid that reduces friction between moving parts.
  • Intratendinous olecranon bursa: Located within the triceps brachii tendon.
  • Subtendinous olecranon bursa: Located between the olecranon and the triceps brachii tendon, it reduces friction during extension and flexion.
  • Subcutaneous olecranon bursa: Located between the olecranon and the overlying connective tissue and is implicated in olecranon bursitis..

Ligaments of the Elbow Joint

• Ulnar collateral (medial) ligament:
  • A triangular band consisting of anterior, middle, and posterior bands.
  • Anterior band (strongest): medial epicondyle of the humerus to a small tubercle on the medial border of the coronoid process.
  • Posterior band joins the tubercle and the medial border of the olecranon.
  • Middle band connects these two, with a grooved surface lodging the ulnar nerve.
• Radial collateral (lateral) ligament:
  • A triangular band.
  • Apex: lateral epicondyle.
  • Base: fuses with the annular ligament of the head of the radius.
• Annular ligament:
  • Attached to the anterior and posterior margins of the radial notch of the ulna.
  • Clasps the head and neck of the radius in the proximal radioulnar joint.
  • Has no attachment to the radius, which allows it to rotate freely within the annular ligament.

Movements of the Elbow Joint

• The orientation leads to simple hinge movements- flexion and extension.
• Flexion: 140° range from the straight (extended) position
  • Full flexion: the three bony points (medial and lateral epicondyles of the humerus and the olecranon process of the ulna makes an equilateral triangle.
  • Muscles: Brachialis, Biceps brachii, and Brachioradialis provide flexion
  • Biceps brachii: chief flexor of the elbow joint.
• Extension: the ulna makes an angle of about 170° with the humerus, diverging laterally.
  • The angle "carrying angle" fits elbow to waist when the arm is at side and increases in women.
  • The tip of the olecranon aligns with the humeral epicondyles when extended.
  • Muscles of extension: Triceps brachii and Anconeus.

Nerve Supply

• Supplied by Musculocutaneous, Median, Ulnar, and Radial nerves.

Blood Supply

• Supplied by arteries derived from the elbow anastomosis formed by collateral branches of the brachial and recurrent branches of the radial and ulnar arteries.

Stability

• Quite stable due to the radial and ulnar collateral ligaments

Surgical Approach

• Common approaches come from the sides.
• Medially, the ulnar nerve is displaced backwards, and the common flexor origin is detached to expose the capsule.
• Laterally, the common extensor origin is detached, keeping the incision above the radius head to protect the posterior interosseous nerve as it winds around the shaft within supinator.
• For aspiration/injection, the needle is on the posterolateral with the elbow at the right angle. Keep the medial side clear to protect the ulnar nerve.

Clinical Relevance

• Bursitis:
  • Inflammation from friction and pressure.
  • Subcutaneous bursitis: Infection can occur from skin laceration.
  • Subtendinous bursitis: Caused by repeated flexion/extension, common in assembly line workers. Flexion is more painful.
• Dislocation:
  • Elbow dislocation: From a fall with the elbow flexed; more common in children
  • The distal end of the humerus: driven through the weakest part of the joint capsule (anterior side)
  • Ulnar collateral ligament typically tears, and there may be ulnar nerve involvement. Dislocations are primarily posterior.
• Epicondylitis (Tennis Elbow/Golfer's Elbow):
  • Overuse strain of the common tendon origin (flexor or extensor origin), leading to pain and inflammation.
  • Tennis players: pain in the lateral epicondyle (common extensor origin)
  • Golfers: pain in the medial epicondyle (common flexor origin)
• Supracondylar Fracture:
  • A fall on outstretched hand, common in children
  • Direct damage/swelling: interferes blood supply in the forearm via the brachial artery. Ischemia can cause Volkmann's ischemic contracture
  • Also results in damage to nerves (medial, ulnar, or radial).

Proximal Radioulnar Joint

• A uniaxial synovial pivot joint located between the circumference of the head of the radius and the fibro-osseous ring formed by the annular ligament and the radial notch of the ulna.

Articulation

• Head of the radius and radial notch of the ulna.

Capsule and Synovial Membrane

• The articular inner aspect of the annular ligament is lined by hyaline cartilage.
• The capsule and lateral elbow joint ligament are attached to the annular ligament. Both proximal radioulnar and elbow joints share the same synovial membrane.
• Lies the intracapsular part of the radial neck, supported below by the quadrate ligament.

Movement

• Primary movements: pronation and supination.
• Movement causes the head of the radius to rotate within the annular ligament
• Pronation: pronator quadratus and pronator teres
• Supination is by Supinator and Biceps brachii, of which the Biceps brachii is the chief supinator

Stability

• Stabilized by the interosseous membrane in the forearm and the annular ligament.

Nerve Supply

• Innervation: Median, Musculocutaneous, Ulnar, and the Radial nerve.

Blood supply

• Similar to that of the elbow joint (cubital anastomosis).

Clinical Relevance

• Monteggia Fracture:
  • Fracture of the proximal third of the ulna
  • Dislocation of the radial head at the proximal radioulnar joint.
  • Named after Giovanni Battista Monteggia.
  • Caused by a fall on an outstretched hand with the forearm in excessive pronation (hyper-pronation injury).

Anastomosis Around the Elbow

• This forms from an extensive circulatory arterial network between the brachial artery and its terminal branches.
• Superior and inferior ulnar collateral branches of the brachial artery and the radial and middle collateral branches of the profunda brachii artery descend from above to reconnect on the joint capsule. They connect with the anterior and posterior ulnar recurrent branches of the ulnar artery, the radial recurrent branch of the radial artery, and the interosseous recurrent branch of the common interosseous artery.

Vessels Involved in Cubital Anastomosis Include

• Terminal branches of the brachial artery (radial and ulnar arteries).
• Branches of the profunda brachii artery (middle and radial collateral arteries).
• Other branches of the brachial artery
• Superior ulnar collateral artery
• Inferior ulnar collateral artery (with anterior and posterior branches)
• Branches of the ulnar artery (anterior and posterior recurrent ulnar artery and common interosseous artery).
• Branches of the radial artery (recurrent radial artery).
• Branches of the common interosseous artery (posterior and anterior interosseous arteries).