Clinical Anatomy: Elbow and Forearm

Clinical Anatomy of Upper Limb 2: Elbow and Forearm

• Covers the clinical anatomy of the upper limb, focusing on the elbow and forearm.

Elbow Joint: Relevant Bony Anatomy

• The elbow joint involves bony landmarks in the supracondylar region.
• Key bony features include the epicondyles (lateral and medial), condyles, capitulum, and trochlea.

Elbow Joint Bony Features & Radiology

• Anterior view shows the relationship between the capitulum, trochlea, medial and lateral epicondyles.
• Posterior view presents the olecranon fossa, trochlea.
• Lateral view radiographs highlight the coronoid fossa, capitellum, radial head, olecranon fossa and process, plus the trochlea.

Elbow Joint

• It's a complex synovial joint with two main components.
• The humero-ulnar joint connects the trochlea of the humerus with the trochlear notch of the ulna.
• Humero-radial joints link the capitellum of the humerus to the radial head, facilitating flexion and extension.
• Proximal radio-ulnar joint is between the radial head and radial notch of ulna.
• Both joints share a common synovial cavity allowing supination and pronation.

Elbow Synovial Fold Syndrome

• A 20-year-old female presents with snapping pain and elbow locking during elbow flexion and extension.
• During examination, pain is usually located posterolaterally.
• Elbow synovial fold syndrome involves a thickened and inflamed plica, plus chondral fraying of the radial head and capitellum.
• MR arthrography images reveal the thickened posterolateral fold indicative of the syndrome.

Ligaments of the Elbow Joint

• Lateral collateral ligament complex's proximal attachment is at lateral epicondyle of humerus, and its distal attachment is annular ligament and proximal ulna.
• Medial collateral ligament complex's proximal attachment is at medial epicondyle of humerus, and its distal attachment is at proximal ulna.
• Annular ligament holds the head of the radius against radial notch of ulna allowing rotatory movement.

Valgus and Varus Forces

• Varus force refers to an inward force on the distal bone, and valgus force refers to an outward force on the distal bone.
• The lateral collateral ligament (LCL) protects against varus forces.
• The medial collateral ligament (MCL) protects against valgus forces.

Stability of the Elbow Joint

• Elbow joint stability relies on bony factors, ligaments, and muscles.
• Damage to these columns may lead to elbow instability.
• The stabilizing factors are described as part of a ring of 4 columns.
• Isolated large coronoid or medial epicondylar fractures may cause instability.

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

• Typically occurs in children under 5 years old due to not well developed radial head.
• Mechanism involves sudden, longitudinal traction applied to the forearm with elbow extension.
• Presentation includes pain with reluctance and the elbow in extension with the forearm in pronation.

Dislocation of Elbow 2: Humero-radio-ulnar Joint

• Second most common joint dislocation, generally posterior.
• Posterior movement of forearm bones in relation to the humerus typically from a FOOSH injury.
• Both the radius and ulna dislocate posteriorly.
• Coronoid process resists posterior displacement of ulna.
• Can result in joint instability and recurrent dislocations.
• The "terrible triad" includes elbow dislocation + radial head fracture (Axial compression) + coronoid fracture.
• Damage to neurovascular structures is a risk and associated fractures increase this risk.
• Ulnar nerve, median nerve, and the brachial artery may be damaged.

Dislocation of Elbow 3: Monteggia Fracture Dislocation

• Anterior dislocation of radial head with a fracture of the proximal one third of the ulna.

Neurovascular Relations of Elbow

• Elbow injuries such as supracondylar fractures pose a risk to neurovascular structures.
• Median, radial, and ulnar nerves are vulnerable.
• Brachial artery and veins can also be affected.

Volkmann Ischemic Contracture

• Supracondylar humeral fractures may damage the brachial artery causing contraction.
• Acute symptoms are the 5 "P"s: Pallor, Pulselessness, Pain, Paraesthesia, and Paralysis.
• Ischemia of forearm muscles results in muscle necrosis, fibrosis, contractures and ultimately deformity.

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 on radiographs.

2ry Ossification Centers - Clinical Scenario

• There are six 2ry ossification centers in relation to elbow.
• Times of appearance of 2ry ossification centres in elbow:
  • Capitellum: 1 year
  • Radial head: 3 years
  • Int. epicondyle: 5 years
  • Trochlear: 7 years
  • Olecranon: 9 years
  • Ext. epicondyle: 11 years
• A 7 year-old boy presenting with swollen elbow after a fall on the elbow.

Supracondylar Fracture (SC #) of Humerus

• Note the thin bone above the condyles.
• Hyperextension causes fracture at the narrow SC region.
• Can cause bleeding into the joint space.

Anterior & Posterior Fat Pad Sign

• The posterior fat pad resides inside the olecranon fossa in normal conditions.
• The anterior fat pad slightly projects outside the coronoid fossa, visible on lateral radiographs.
• Elevating fat pads indicates intraarticular fractures and the presence of hemarthrosis.
• The fat pad signs aid in detecting subtle elbow joint effusion or haemarthrosis.
• If positive for fat pad signs after trauma you should look carefully for fractures.

Clinical Scenario 2

• A 12 year old boy is presenting with swollen elbow after a FOOSH.
• Anterior humeral line (AHL) and radiocapitellar line (RCL) helps identify/differentiate subtle supracondylar fractures and radial head dislocation.
• AHL should intersect the middle 1/3 of the capitellum on an AP view – if disrupted in SC.
• RCL should intersect the middle of the capitellum regardless projection - if disrupted when there is radial head dislocation.

Radial Head Dislocation

• Normal radiocapitellar line intersect the mid-capitellum.
• Abnormal radiocapitellar line does not intersect the capitellum indicating radial head dislocation.

Clinical Scenarios 3 – 4

• Triangle is maintained in Supra condylar.
• Triangle is disrupted in elbow dislocation.

Anterior Compartment Muscles of the Forearm

• Muscles act on both the proximal and distal radio-ulnar joints.
• Pronators include the pronator teres and pronator quadratus.
• Flexors include the flexor carpi radialis and ulnaris.
• Flexors act on the digits (digitorum) and thumb (pollicis).
• Are arranged in three groups: superficial, intermediate, and deep.

Anterior Compartment Muscles of the Forearm Details

• Innervation: all muscles are supplied by the median nerve, deep layer by anterior interosseous branch.
• All muscles are supplied by Median N – Deep layer by Anterior interosseous Br. Of Median N, EXCEPT 2 medial (FCU and Medial 2 heads of FDP)
• Medial Epicondylitis (Golfer's elbow): Overuse of flexors inflammation and pain @medial epicondyle.

Brachioradialis

• Positioned between the flexor and extensor compartments of the wrist and elbow.
• Strong flexor of the semi-pronated forearm.
• Supinates the pronated forearm and pronates the supinated forearm to mid-position.
• Innervated by the radial nerve.

Posterior Compartment Muscles of the Forearm

• Muscles include extensor digitorum, extensor digiti minimi, extensor carpi ulnaris.
• Others include the extensor pollicis brevis and longus.
• Also, the abductor pollicis longus, extensor indicis, and anconeus.
• Common extensor origin occurs at the lateral epicondyle.
• ECRL is innervated by the radial nerve; all others are innervated by the deep radial or posterior interosseous nerve.
• Lateral Epicondylitis (Tennis elbow) Overuse of extensors Inflammation & Pain @ lateral epicondyle.

Anatomical Snuff Box

• Triangular depression is bounded by the tendons of the extensor pollicis longus, and extensor pollicis brevis laterally.
• The floor is the scaphoid and trapezium.
• In floor Radial artery and Superficial branch of the radial nerve runs inside.
• Tender when scaphoid # or rarely trapezium #.

Extensor Expansion

• Includes lateral bands, medial band, and extensor expansion.
• Mallet finger is the result of the rupture of extensor tendon at the DIP joint.

Nerves in the Forearm

• Ulnar nerve passes between the ulnar nerve and the flexor carpi ulnaris.
• Median nerve passes between the 2 heads of the pronator teres.
• Anterior interosseous Br. innervates the Flexor pollicis longus, FDP lateral ½ and Pronator quadratus.
• Deep Radial nerve passes between 2 heads of the supinator.
• Superficial branch continues under the brachioradialis.
• Deep radial branch passes into the posterior compartment as the posterior interosseous N.
• Both Ulnar & Median nerves stay anterior and run on the FDP.

Arteries in the Forearm

• The principal arteries are the brachial, radial, and ulnar arteries.
• The common interosseous artery and anterior/posterior interosseous arteries are also present.
• The deep and superficial palmer arches are located in the hand.