Elbow and Radioulnar Joints: Structure and Function

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The Elbow and Radioulnar Joints: Learning Outcomes

• Orientate and identify key bony points on the distal end of the humerus, radius, and ulna
• Describe the structure, function, and classification of the elbow and radioulnar joints and surrounding inert, soft tissue structure
• Describe the structure and function of the interosseous membrane of the upper limb
• Describe the course and structure of the nerve and blood supply to these joints

The Humerus

• The distal end of the humerus is expanded laterally, flattened anteroposteriorly, and bent slightly forwards
• The capitulum is located laterally
• The trochlea is located medially, note the shallow groove for the ulna nerve
• The humerus also includes medial and lateral epicondyles
• As well as medial and lateral supracondylar ridges
• Has an olecranon fossa
• Has a radial fossa (laterally)
• As well as a coronoid fossa (medially)

Radius and Ulna

• Radius includes head of the radius, radial tuberosity, radial styloid process, and lister's tubercle (dorsal tubercle)
• The ulna has a trochlear notch, olecranon, coronoid process, radial notch, supinator crest and ulnar styloid process

The Elbow Joint (Cubital Joint)

• Joint Classification: Synovial hinge joint (with two articulations)
• Axis of movement: One degree of freedom available (about a transverse axis)

Articular Surfaces

• Humero-ulnar joint (medially): Trochlea of the humerus, and the trochlear notch of ulna
• Humero-radial joint (laterally): Capitulum of the humerus, and superior concave surface head of radius
• All surfaces are covered with hyaline cartilage

Humero-ulnar Joint Details

• Trochlea of Humerus is an almost circular pulley-shaped trochlea with an oblique groove and tilted inferiorly on the medial side which creates the carrying angle
• The trochlea of humerus is concave in the frontal plane, and convex in the sagittal plane
• The Trochlear notch of the ulna has a deep trochlear notch with ridge running from the tip of olecranon to the tip of coronoid process
• It also has a congruent fit to groove on trochlea

Humeroradial Joint Details

• The capitulum of the humerus has an incomplete hemispherical shape with variable radius of curvature and is covered in hyaline cartilage, thickest centrally
• The head of the radius has a superior concave surface for articulation with the capitulum and a raised edge for capitulo-trochlear groove

Elbow Joint Features

• The trochlea (distal end humerus) and the trochlear notch of the ulna, bulge anteriorly from the anterior surface of the humerus
• This facilitates greater range of flexion by delaying the contact of the two bones
• The trochlea tilted inferiorly on the medial side leads to a lateral deviation of ulna & radius from the humerus ('carrying angle')
• Men = 10-15°, women = 20-25°

Joint Capsule

• Single fibrous capsule, lined with synovial membrane, shared with the superior radioulnar joint
• There is no direct attachment to the radius
• Blends with collateral ligaments, increasing its strength
• Weaker anteriorly and posteriorly

Ligaments

• Two sets of strong triangular bands on each side of the joint, blending with the joint capsule
• Ulnar Collateral and Radial Collateral

Ulnar Collateral Ligaments

• Anterior band: From the medial epicondyle (anteriorly) to the coronoid process
• Posterior band: From the medial epicondyle (posteriorly) to the olecranon
• Transverse band: From the coronoid process to the olecranon
• Intermediate band: From the medial epicondyle to the transverse band
• Action = Limits abduction, the anterior band also helps limit extension

Radial Collateral Ligament

• Strong triangular band (not as strong as the ulnar collateral ligament)
• From: Lateral epicondyle (deep to common extensor tendon)
• To: Blends with the annular ligament of the radius and margins of the radial notch of the ulna
• Action: Limits adduction

Elbow Movements

• Includes Flexion and Extension

Elbow Flexion Details

• ROM is approximately 145 degrees (active) and 160 degrees (passive)
• Created by: Brachialis, Biceps brachii, Brachioradialis
• Limited by: Soft tissue apposition, tension in the triceps, and posterior joint capsule

Elbow Extension

• Range of motion is 0 degrees
• Created by the Triceps and anconeus (Actively)
• Limited by: Tension in the flexor muscles, anterior joint capsule, and possibly bony apposition (olecranon in olecranon fossa)

Elbow Stability

• Medial more stable than lateral due to articular surfaces having a greater surface area medially and greater reciprocity medially
• Also the capsule has no lateral bony attachment
• And the radial collateral ligament is not as strong
• Flexion is more stable than extension due to greater contact between the articular surfaces of trochlea and trochlear notch
• And the head of the radius moves closer to capitulum
• Greatest stability is at a 90-degree midpoint of pronation and supination, the position you assume for delicate dextrous movements and power movements

Radioulnar Joint Articulations

• Superior radioulnar joint, and Inferior radioulnar joint
• As well as the Interosseous membrane

Superior Radioulnar Joint

• Joint classification: Synovial pivot joint
• Axis of movement: Vertical
• Articular Surfaces: head of the radius is oval-shaped, lined with hyaline cartilage, radial notch on ulna creates 1/5 of ring, lined with hyaline cartilage, annular ligament creates 4/5 of fibro-osseous ring, lined with fibrocartilage
• Joint Capsule: Extensive, shared with elbow
• Synovial membrane: hangs as fold below the annular ligament, allows for rotation of the radius

Ligaments of The Superior Radioulnar Joint

• Annular Ligament: Creates 4/5 of ring. Strong and flexible, allowing the oval head to rotate freely, attached to the anterior and posterior margins of the radial notch
• Superior support is provided by the radial collateral ligament (ligament blends with the annular ligament & margins of the radial notch)
• The upper part is lined with fibrocartilage continuous with hyaline cartilage of the radial notch
• The lower part is lined with synovial membrane
• Action: Prevents displacement of radial head and stabilizes joint Quadrate Ligament
• From: Lower border of radial notch of the ulna
• To: Adjacent medial surface of the neck of radius proximal to the radial tuberosity
• Fibers run in a criss-cross orientation meaning that in any position of pronation or supination some fibers are under tension
• There is an overall constant tension in the ligament in all positions
• Action: Limits both pronation and supination Inferior Radioulnar Joint
• Joint classification: Synovial pivot joint
• Axis of movement: Vertical
• Articular Surfaces - Distal ulna with crescent shape lined with hyaline cartilage
• Distal radius has biconcave ulnar notch, lined with hyaline cartilage
• Articular disk: Triangular fibrocartilage, apex at root of ulnar styloid and base at inferior edge ulnar notch on radius
• Joint Capsule: Loose to allow movement to occur
• Articular disk:
  • Triangular fibrocartilaginous disc, thicker on the peripherally
  • From (apex) lateral side of the base of the styloid process of ulna
  • To: (Base) sharp inferior edge of ulna notch on radius
• Principle structure is uniting the radius and ulna
• Increases stability at joint

Interosseous Membrane

• Strong fibrous sheet between interosseous borders of the radius and ulna
• Direction of fibers: downwards and medially in an oblique fashion
• Transmits forces from the hand to the radius, ulna, and humerus
• Oblique cord superiorly and opening distally for vessels to pass
• Tightest in mid-position
• Functions: Divides forearm into anterior and posterior compartments, shock absorption and dissipation, and attachment site for deep muscles

Movements of the Radioulnar Joints

• Pronation: involves rotation of the radius around the ulna so that the two bones cross in space, in the anatomical position the palm of the hand is facing backward
• Supination: The reverse action brings the bones back to parallel and the palm of the hand faces forwards in the anatomical position
• Range of motion approximately 180 degrees, full pronation to supination
• Movement involves the rotation of the lower end of the radius around the head of the ulna
• Superior radioulnar joint: Movement involves rotation of the head of the radius within the fibro-osseous ring, which is limited by tension in the quadrate ligament
• Inferior radioulnar joint: Movement involves the rotation of the lower end of the radius around the head of the ulna
• Very stable joint (due to articular disk, interosseus membrane and pronator quadratus)

Nerve Supply

• Includes the median, ulnar, musculocutaneous, and radial nerves

Musculocutaneous Nerve

• Arises from the ventral rami of C5, 6 and 7, the superior and middle trunks (anterior divisions) and the lateral cord
• In axilla lies lateral to the axillary artery,
• Descends into the arm by piercing coracobrachialis (which it also innervates)
• Runs distally between biceps and brachialis into the lateral side of the arm.
• Becomes the lateral cutaneous nerve of the forearm emerges laterally from underneath biceps
• Motor supply: Biceps brachii, medial part of brachialis and coracobrachialis
• Sensory supply: Skin on the lateral half of the forearm down to the base of the thumb (via the lateral cutaneous nerve of the forearm)

Median Nerve

• Arises from C5, 6, 7, 8, T1, the superior, middle and inferior trunks (anterior divisions) and the lateral and medial cords
• Enters the arm from the axilla at the inferior margin of teres major and passes down the medial side of the arm under cover of biceps brachii
• Lies on brachialis in the lower part of the arm and enters cubital fossa.
• Motor supply: Pronator teres, Pronator quadratus and muscles of the forearm
• Sensory supply: Articular branches to elbow joint

Ulnar Nerve

• Arises from ventral rami of C8 and T1 (and occasionally C7), inferior trunk (anterior division) and the medial cord
• Runs medial to axillary artery and descends down medial to brachial artery and anterior to triceps.
• Halfway down in the arm, the ulnar nerve pierces the intermuscular septum to enter the posterior compartment of arm
• Runs down to Medial epicondyle of humerus, and lies to the medial epicondyle of humerus lies in the ulnar groove behind medial epicondyle (funny bone), before entering forearm
• Motor supply is to muscles of the forearm
• Sensory supply: Articular branches to elbow joint

Radial Nerve

• Arises from C5, 6, 7, 8, T1, the superior, middle and inferior trunks (posterior divisions) and the posterior cord
• Lies behind the axillary artery in the axilla and passes anterior to subscapularis, latissimus dorsi and teres major tendons
• Enters the posterior aspect of the arm via the triangular space (formed by the humerus laterally and the long head of triceps medially and teres major superiorly)
• Along the radial groove of the humerus (medial to lateral) and runs between the lateral and the medial heads of the triceps
• Pierces intermuscular septum to enter anteiror compartment
• Divides into superficial and deep branches anterior to lateral epicondyle
• Motor Supply: to the Triceps, anconeus, brachialis (lateral 1/3), brachioradialis, supinator, and muscles of the forearm
• Sensory Supply: Skin on back of arm and forearm (via the posterior cutaneous nerve of the arm, the lower lateral cutaneous nerve of arm and posterior cutaneous nerve of forearm) articular branches to the elbow

Blood Supply: Brachial Artery

• A continuation of the axillary artery, rising inferior to the teres major to the cubital fossa
• Travels across the front crease of elbow and splits into two branches just below the elbow: ulnar artery and radial artery
• These branches continue into the hand. Damage to the brachial artery can be very serious as it is the only blood supply to the hand