Elbow Joint Anatomy and Radiology

Elbow Joint - Relevant Bony Anatomy

• The elbow joint includes the supracondylar region.
• The lateral epicondyle is part of the epicondyles.
• The medial epicondyle is also an epicondyle.
• The capitulum and trochlea are condyles.

Elbow Joint Bony Features & Radiology

• Lateral and medial supracondylar ridges are visible in the AP view.
• In the AP view, note the olecranon fossa and process.
• The medial epicondyle is a point of reference in the AP view.
• The capitellum and trochlea can be seen in the AP view.
• The humero-radial and humero-ulna joints are visible in the AP view.
• Visualize the radial head and neck, and radial tuberosity in the AP view.
• Note the coronoid process and proximal radio-ulnar joint in the AP view.
• The capitulum and trochlea can be viewed anteriorly.
• The olecranon process and coronoid process are viewable in the posterior view.

Elbow Joint Bony Features & Radiology (Lateral View)

• The coronoid fossa is a key feature in the lateral view.
• You can see the capitellum in the lateral view.
• The radial head is apparent in the lateral view.
• Visualize the coronoid process in the lateral view.
• The trochlea is visible in the lateral view.
• The olecranon fossa is visible in the lateral view.
• The olecranon process can be seen in the lateral view.

Elbow Joint Anatomy

• A complex synovial joint.
• Includes two components: humero-ulnar and humero-radial joints.
• The humero-ulnar joint is between the trochlea and the trochlear notch of the ulna.
• The humero-radial joint is between the capitellum and radial head, enabling flexion and extension.
• The proximal radio-ulnar joint is between the radial head and radial notch of the ulna, facilitating supination/pronation.
• Both joints share a common synovial cavity.

Elbow Synovial Fold Syndrome

• Elbow synovial fold syndrome causes snapping pain and elbow locking during flexion and extension.
• On examination, pain is located posterolaterally, not along the lateral epicondyle or extensor tendon origin.
• Elbow synovial fold syndrome involves a thickened and inflamed plica and chondral fraying of the radial head and capitellum.
• MR arthrography reveals a thickened posterolateral fold.

Ligaments of the Elbow Joint

• The lateral collateral ligament complex has a proximal attachment at the lateral epicondyle of the humerus.
• Its distal attachment includes the annular ligament and proximal ulna.
• It provides lateral stability against varus forces.
• The medial collateral ligament complex has a proximal attachment at the medial epicondyle of the humerus.
• Its distal attachment is at the proximal ulna.
• It provides medial stability against valgus forces.
• The annular ligament holds the head of the radius against the radial notch of the ulna.
• It allows rotatory movement of the radius for supination/pronation of the forearm.

Valgus and Varus Forces

• Valgus and varus forces are defined by the direction of angulation of the distal bone.
• Varus force involves an inward force on the distal bone.
• Valgus force involves an outward force on the distal bone.
• The LCL protects against varus forces; LCL injury results from varus forces.
• The MCL protects against valgus forces; MCL injury results from valgus forces.

Stability of the Elbow Joint

• Bony factors, ligaments, and muscles contribute to stability.
• Stabilizing factors are described as part of a ring of 4 columns.
• Damage to these columns can lead to elbow instability.
• An isolated large coronoid fracture or medial epicondylar fracture may cause instability.
• The anterior column includes the coronoid process, anterior capsule, and brachialis.
• The lateral column is made up of the radial head, capitellum, and LCL complex.
• The medial column consists of the coronoid process, MCL complex, and medial epicondyle.
• The posterior column includes the olecranon process, posterior capsule, and triceps brachii.

Dislocation of Elbow 1: Proximal Radioulnar (Pulled Elbow/Nurse Maid’s Elbow)

• Pulled elbow typically occurs in children younger than 5 years.
• It is due to a radial head not well developed and a relatively loose annular ligament.
• The mechanism involves a sudden, longitudinal traction applied to the forearm with the elbow in extension.
• Presentation includes pain or reluctance to use the affected upper limb.
• The elbow is usually in extension and the forearm in pronation.

Dislocation of Elbow 2: Humero-Radio-Ulnar Joint

• The humero-radio-ulnar joint is the second most common site for joint dislocation.
• Dislocation is commonly posterior.
• The mechanism involves posterior movement of forearm bones due to axial force on a partially flexed elbow.
• The coronoid process normally resists posterior displacement of the ulna.
• Both the radius and ulna dislocate posteriorly.
• Always look for associated injuries.
• The "terrible triad" includes elbow dislocation, radial head fracture due to axial compression, and coronoid fracture. It makes the joint unstable and leads to recurrent dislocations.
• Damage to neurovascular structures may be at risk with associated fractures.
• The ulnar nerve, median nerve, and brachial artery might be damaged.

Dislocation of Elbow 3

• Monteggia fracture dislocation involves an anterior dislocation of the radial head.
• It is associated with a fracture of the proximal 1/3 of the ulna.

Neurovascular Relations of Elbow

• Elbow injuries carry a risk of damage to neurovascular structures.
• The median nerve, radial nerve, and ulnar nerve are at risk.
• The brachial artery/veins are vulnerable.

Volkmann Ischemic Contracture

• Supracondylar humeral fractures carry a risk of damaging the brachial artery, potentially severing or causing compression and spasm.
• Ischemia of forearm muscles leads to muscle necrosis within 4-6 hours, resulting in fibrosis and contractures, ultimately causing deformity.
• Acute symptoms include the 5 Ps: pallor, pulselessness, pain, paraesthesia, and paralysis.

2ry Ossification Centers

• Long bones ossify using primary and secondary ossification centers.
• Primary centers appear during prenatal development in the diaphysis (shaft).
• Secondary centers appear postnatally in the epiphysis region, with multiple centers present.
• Cartilages may appear as translucent gaps in radiographs, potentially mistaken for fractures.

2ry Ossification Centers - Clinical Scenario

• There are six secondary ossification centers in relation to the elbow.
• A 7-year-old with a swollen elbow after a fall may have an ossification center-related injury.
• Ossification center appearance times: capitellum (1 year), radial head (3 years), internal epicondyle (5 years), trochlea (7 years), olecranon (9 years), external epicondyle (11 years).

Supracondylar Fracture (SC #) of Humerus

• Normal elbow anatomy in extension shows a thin bone above the condyles.
• Hyperextension leads to fracture at the narrow supracondylar region.
• Bleeding into the joint space occurs.

Anterior & Posterior Fat Pad Sign

• Fat pad sign indicates a joint effusion or haemarthrosis.
• Joint cavity normally contains two fat pads.
• The posterior fat pad is located inside the olecranon fossa.
• The anterior fat pad projects slightly outside the coronoid fossa, sometimes seen in normal lateral radiographs.
• Intraarticular supracondylar fractures can lead to haemarthrosis and elevation of fat pads.
• If fat pad signs are positive after trauma, always look carefully for fractures.

Clinical Scenario 2

• A 12-year-old presenting with a swollen elbow after a FOOSH requires diagnosis.
• Radiological features are essential for diagnosis.
• Use the anterior humeral line and radiocapitellar line to differentiate subtle supracondylar fractures and radial head dislocations.
• The anterior humeral line should intersect the middle 1/3 of the capitellum on an AP view; if disrupted, suspect an SC fracture.
• The radiocapitellar line should intersect the middle of the capitellum irrespective of projection. Disruption suggests radial head dislocation.

Clinical Scenarios 3-4

• 15 and 12 year old patients presenting with swollen elbows after a fall require diagnosis.
• Radiological features help in diagnosis.

Muscles acting on Proximal and Distal Radio-Ulnar Joint (Anterior Compartment of Forearm)

• Pronators include pronator teres and pronator quadratus.
• Muscles acting on the wrist (joints associated with carpus) include flexors: flexor carpi radialis/ulnaris.
• Muscles acting on the digits (digitorum) include flexors: flexor digitorum superficialis/profundus.
• Muscles acting on thumb (pollicis) include flexors: flexor pollicis longus.
• Muscles are arranged in superficial, intermediate, and deep groups.

Anterior Compartment Muscles of Forearm

• Muscles are categorized as superficial, intermediate, and deep.
• Superficial muscles: pronator teres, flexor carpi ulnaris, palmaris longus, flexor carpi radialis.
• Intermediate muscle: flexor digitorum superficialis.
• Deep muscles: flexor digitorum profundus, flexor pollicis longus, pronator quadratus.
• Most muscles are supplied by the median nerve, except for 2 medial muscles (FCU and medial 2 heads of FDP), which are supplied by ulnar nerve.
• All deep layer, including the flexor pollicis longus, flexor digitorum profundus and pronator quadratus, are supplied by the anterior interosseous branch.
• Medial epicondylitis (golfer's elbow) results from overuse of flexors, leading to inflammation and pain at the medial epicondyle.

Brachioradialis

• The brachioradialis is located between the flexor and extensor compartments of the wrist and elbow.
• Movements include strong flexion of the semi-pronated forearm.
• It supinates the pronated forearm to mid-position and pronates the supinated forearm to mid-position.
• Innervated by the radial nerve

Posterior Compartment Muscles of Forearm

• Muscles include the extensor retinaculum, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, extensor carpi radialis brevis, extensor carpi radialis longus, anconeus, extensor pollicis brevis, abductor pollicis longus, extensor indicis, extensor pollicis longus, supinator.
• Common extensor origin at the lateral epicondyle.
• Innervation: ECRL by the radial nerve; all others by deep radial or posterior interosseous nerve.
• Lateral epicondylitis (tennis elbow) results from overuse of extensors, causing inflammation and pain at the lateral epicondyle.

Anatomical Snuff Box

• It's a triangular depression bounded by tendons.
• The extensor pollicis longus medially and abductor pollicis longus and extensor pollicis brevis laterally.
• The floor is the scaphoid and trapezium.
• It becomes tender when there is a scaphoid or trapezium fracture.
• The radial artery and superficial branch of the radial nerve run inside.

Extensor Expansion

• The lateral bands, median band, and extensor expansion contribute to finger extension.
• Mallet finger results from rupture of the extensor tendon at the DIP joint.

Nerves in the Forearm

• The ulnar nerve passes between the two heads of the flexor carpi ulnaris.
• The median nerve passes between the two heads of the pronator teres.
• The anterior interosseous branch innervates the flexor pollicis longus, FDP lateral ½, and pronator quadratus
• Deep radial nerve passes between the two heads of the supinator.
• Deep radial branch passes as the posterior interosseous N into the posterior compartment compartment.
• The superficial branch courses along the Brachioradialis.

Arteries in the Forearm

• Brachial artery branches into the radial and ulnar arteries.
• The posterior interosseous artery branches off from the ulnar artery.
• The ulnar artery gives off the common interosseous artery.
• The anterior interosseous artery also branches off from the ulnar .
• Terminal branches create the Palmar arches.

Multiple Choice Questions

1. Which structure does NOT articulate at the elbow joint?

• A) Capitulum
• B) Trochlea
• C) Radial Head
• D) Ulna
• E) Radius Notch

2. The “terrible triad” of the elbow includes all EXCEPT which injury?

• A) Elbow Dislocation
• B) Radial Head Fracture
• C) Coronoid Fracture
• D) Olecranon Fracture
• E) Axial Compression

3. Concerning the ligaments of the elbow, which statement is FALSE?

• A) The lateral collateral ligament complex consists of the radial collateral ligament and the ulnar collateral ligament, and the distal attachment is the proximal ulna
• B) The medial collateral ligament complex provides medial stability against valgus forces
• C) The distal attachment of LCL is the Annular ligament and Proximal ulna
• D) Allow rotatory movement of the radius for the supination/pronation of forearm for the Annular ligament
• E) LCL complex, the Proximal attachment is the lateral epicondyle of trhe humerus

4. Which of the following statements concerning the muscles in the anterior compartment is FALSE?

• A) Pronator teres and Pronator quadratus are pronators
• B) Flexor Carpi (wrist) radialis/ulnaris is a flexor
• C) Flexor Digitorum Superficialis/Profundus will cause Digits to flex
• D) the Flexor Pollicis longus is located in both the Anterior and Thumb
• E) The muscles are superficial, intermediate and deep

5. Which nerve does NOT pass around or through the elbow joint?

• A) Median
• B) Axillary
• C) Radial
• D) Anterior Interosseous
• E) Ulnar