Compartments of the forearm + cubital fossa

Interosseous membrane

- Thin Z-shaped fibrous sheet (comprised of collagen fibers) that connects to the medial border of ulna and lateral border of radius - Divides forearm into the anterior + posterior compartments and is the site of attachment for many muscles. - Main function is to transfer forces from the radius, ulna, and humerus and to stabilize the forearm during movement. - Upper margin of membrane is free while inferior aspect has an aperture. - Vessels pass between the anterior + posterior compartments above the free upper margin & through the aperture. - Length changes with movement of the wrist and forearm. - Injury or tear of this membrane poses a challenging surgical intervention as the surgeon needs to know how to reconstruct precisely in an anatomical manner

Cubital fossa

- Triangular depression inside of elbow - Area of transition between arm & forearm - Anterior to elbow joint - Apex has medial borders of PT and BR - Imaginary line through epicondyles is the base

Cubital tunnel syndrome

- Ulnar nerve compression at the elbow - Tingling + numbness over the palmar and dorsal surfaces of pinky/little finger and ulnar/medial half of ring finger. - Ulnar nerve: Funny bone nerve (bumping it = sensation of pins & needles) - Weak grip and clumsiness due to muscle weakness in the affected arm and hand

Nerves in forearm

- Ulnar nerve lies posterior to vessels of arm and inclines backwards away from vessels. - It is easily palpable as it lies in the groove behind medial epicondyle. - Radial nerve arises from posterior cord of brachial plexus. - Near elbow region, it enters anterior compartment of forearm to run between brachioradialis & brachioradialis. - RN divides into superficial & deep branches at level of lateral epicondyle. - Median nerve lies medial to brachial artery.

Veins in the forearm

- Vary in tributary pattern - Phlebotomist collect blood from these veins for lab testing

BP & cubital fossa

- When taking BP reading, clinician places stethoscope over brachial artery in cubital fossa - It is lateral to the median cubital vein or medial to biceps tendon

Deep layer of the anterior compartment

1. Flexor digitorum profundus 2. Flexor pollicis longus 3. Pronator quadratus

Superficial muscles of anterior compartment

1. Pronator teres 2. Flexor carpi radialis 3. Palmaris longus 4. Flexor carpi ulnaris - Originate from medial epicondyle of humerus - All besides PT extend into the hand

Posterior compartment of the forearm

2 LAYERS - Superficial - Deep MUSCLES - Movement of wrist - Extension of fingers and thumb - Supination INNERVATION - Radial nerve for all - Extensor carpi ulnaris is innervated by the Posterior interosseous nerve which is a branch of the RN

Pronator syndrome

- A condition in which the median nerve is entrapped by the two heads of the pronator teres, leading to pain on activities involving pronation. - Median is a mixed nerve but compression only results in motor weakness of muscles innervated by it - Anterior interosseous nerve branch of the MN continues in the forearm to innervate muscles but lacks sensory component - Compression of MN vs AIN can be differentiated, MN has sensory component so patient will also have sensory deficits CAUSES - Underlying metabolic disorder (Diabetes, hypothyroidism) - Swollen & inflammation of structures around elbow.

Cubital tunnel

- A tunnel of muscle, ligament, and bone on the inside of the elbow - Ulnar nerve passes deep to a fascial covering, just behind the medial epicondyle to enter forearm between to heads of flexor carpi ulnaris.

Abductor pollicis longus & extensor pollicis brevis

- APL, EPB, EPL emerge from between ED & ECRB tendons and pass into the thumb - APL & EPB form muscular bulge in distal posterolateral surface of forearm

Blood supply of posterior compartment of forearm

- Blood supply is predominantly through branches of radial, PI and AI arteries

Arteries in anterior compartment

- Brachial artery enters forearm from the arm by passing through the cubital fossa - At apex of CF, it divides into the radial and ulnar arteries - These pass distally to supply hand and give rise to vessels of the posterior compartment - Radial & ulnar are subcutaenous so they're easy to cut into - Due to dual supply, injured artery can be ligated or repaired so no ischemia occurs because of palmar anastomosis

Floor of the cubital fossa

- Brachialis, supinator, biceps tendon

Mobile wad

- Brachioradialis, Extensor carpi radialis longus & Extensor carpi radialis brevis - Flexors at elbow joint

Shaft of ulna

- Broad proximally and narrow distally - Anterior border is smooth - Posterior border is sharp and palpable - Interosseous border is sharp to provides attachment to interosseous membrane

Distal end of ulna

- Characterised by rounded head and styloid process

Anterior compartment of forearm

3 LAYERS 1. Superficial 2. Intermediate 3. Deep MUSCLES ARE FOR - Movement of wrist joint - Flexing fingers and thumb - Pronation INNERVATION - Median nerve for almost all muscles - Ulnar nerve for Flexor carpi ulnaris & medial half of Flexor digitorum profundus

Removing the roof of cubital fossa

Nerves and arteries lie on the floor

Proximal end of ulna

OLECRANON - Large projection - Rough superior area for attachment to triceps - Posterior surface is smooth at the tip of the elbow RADIAL NOTCH - Articulates with head of radius CORONOID PROCESS - Triangular - Forms trochlear notch with olecranon - Marked by radial notch laterally TROCHLEAR NOTCH - Formed by coronoid + olecranon - Articulates with humerus' trochlea

Compartment syndrome

- Condition in which increased tissue pressure within a limited space compromises the circulation and function of the contents of that space. - Happens when pressure is elevated over a certain level for some time sufficient to occlude smaller vessels so they are unable to maintain circulation - Inadequate tissue perfusion leads to inadequate tissue oxygenation to the nerves as well as muscles within the affected compartment - This compromises the function of muscles and causes swelling, pain & palpable pulse

Proximal end of radius

- Consists of disc shaped head - Head articulates with radial notch of ulna - Has a neck and radial tuberosity (blunt projection)

Surface anatomy of posterior forearm

- Creased area behind your elbow joint marks presence of olecranon of ulna. - Just medial/ulnar and inferior to it lies the brachioradialis muscle - You can locate course of radial artery via an imaginary line extending from crux of cubital fossa inferiorly along the length of radius laterally - Medial to it lies the cephalic vein. - At the wrist, prominences can be palpated at radial and ulnar ends marking presence of respective styloid processes.

Causes of cubital tunnel syndrome

- Cubital tunnel syndrome may happen when a person bends the elbows often (when pulling, reaching, or lifting), leans on their elbow a lot, or has an injury to the area. - Unusual repetitive activities that exert pressure - Arthritis, bone spurs, and previous fractures or dislocations of the elbow can also cause cubital tunnel syndrome. - In many cases, the cause is not known.

Distal end of radius

- Diamond-shaped lateral surface becomes styloid process distally - Marked by 2 facets for articulation with scaphoid and lunate

Lateral view of posterior wrist & forearm

- Distal ends of the tendons of the extensor carpi radialis longus and brevis muscles are on the lateral side of the wrist - They can be accentuated by making a tight fist and extending the wrist against resistance.

Tuberosity of ulna

- Extends from coronoid process above - Provides attachment for brachialis

Syndesmosis

- Fibrous joint at which two bones are bound by long collagen fibers

Galeazzi's fracture

- Fracture of distal third of radius, with partial dislocation of the head of the ulna at the wrist joint

Monteggia's fracture

- Fracture of the proximal third of the ulnar shaft, with anterior dislocation of the radial head at the elbow

Arteries in forearm

- Give rise to cubital anastomosis which leads to collateral circulation - Brachial artery divides into 2 terminal branches, radial & ulnar artery - Other branches are profunda brachii & superior ulnar collateral

Ulna

- Inner and longer of the two bones of the forearm - Triangular cross section - Has proximal end, shaft and small distal end

Radius

- Lateral bone of the forearm (THUMB SIDE) - Triangular - Small proximal end, shaft & large distal end

Supinator crest of ulna

- Lateral side inferior to radial notch - Provides attachment to supinator muscle

Nerves in the anterior compartment

- Median, Ulnar & superficial branches of Radial nerve

Shaft of the radius

- Narrow proximally which is continuous with radial tuberosity & neck superiorly - Broad distally - Anterior border begins as continuation of radial tuberosity. It crosses the shaft diagonally as oblique line - Posterior border is only seen in middle-third of bone - Interosseous border is sharp and provides attachment to interosseous membrane

Intermediate later of anterior compartment

- Only has flexor digitorum superficialis - It has two heads - Median nerve & Ulnar artery pass deep to the muscle, between the two heads - FDS forms four tendons in the distal forearm, these pass through the carpal tunnel of the wrist & onto the 4 fingers

Forearm

- Part of the upper limb that extends between the elbow joint & the wrist joint PROXIMAL - Most major structures pass between the arm and forearm through the cubital fossa, which is anterior to the elbow joint. - The exception is the Ulnar nerve, it passes posterior to the medial epicondyle of the humerus. DISTAL - Structures pass between the forearm & the hand through the carpal tunnel. - Exception is the Radial artery that passes posteriorly around the wrist to enter the hand posteriorly. The cubital fossa & carpal tunnel serve as important anatomical landmarks regarding passage of structures into and out of forearm.

Anatomical snuff box

- Revealed when hyperextension and abduction of the thumb is done - Medial margin is tendon of EPL, lateral margin is formed by tendons of EPB and APL - Radial artery passed through AS when travelling laterally around the wrist to reach back of hand - Pulse of RA can be felt in floor of AS when wrist is relaxed - Cephalic vein crosses roof of AS Muscles: Extensor pollicis longus Extensor pollicis brevis Abductor pollicis longus

Roof of cubital fossa

- Skin, superficial fascia - Cephalic & Basilic veins drain into Median cubital vein - Deep fascia, bicipital aponeurosis (broad aponeurosis of the biceps brachii which separates superficial from deep structures)

Surface anatomy of anterior forearm

- Supero-medial lies the cubital fossa. - Metacarpophalangeal joint of 2nd digit (knuckle of index finger) is anterior to medial epicondyle. - Opposition of thumb (thumb makes contact with baby finger) results in flexion of palmaris longus tendon (sometimes absent in individuals/congenital absence) in distal forearm. Note median nerve is lateral/radial to it. - Medial to palmaris longus is flexor carpi ulnaris tendon. - Lateral to palmaris longus is flexor carpi radialis tendon. - Lying between palmaris longus tendon and flexor carpi radialis tendon distally is median nerve.

Fractures of radius & ulna

- They behave as one despite being separate, so when there's injury, both are usually affected - This means both bones get fractured or one gets fractured while one gets dislocated - Mechanism of injury & age of patient determine which kind of fracture occurs - Due to these fracture patterns that cause dislocations too, whenever a fracture of the radius or ulna is demonstrated radiographically, further images of the elbow and wrist should be obtained to exclude dislocations.

Compartments of forearm

Compartments separated by: 1. Lateral IMS that goes from anterior border of the radius to deep fascia surrounding limb 2. Interosseous membrane linking adjacent borders of radius & ulna along their length 3. Deep fascia attachment along posterior border of ulna Anterior - Flexion of the wrist and digits Posterior - Extension of wrist and digits

Deep group of the posterior compartment

Five muscles 1. Supinator 2. Abductor pollicis longus 3. Extensor pollicis brevis 4. Extensor pollicis longus 5. Extensor indicis - Originate from PS of radius, ulna & IM and pass into digits - Exception is Supinator which also arises from supinator crest of ulna/lateral epicondyle of humerus and doesn't pass into hand

Superficial posterior group

Seven muscles: 1. Brachioradialis 2. Extensor carpi radialis longus 3. Extensor carpi radialis brevis 4. Extensor digitorum 5. Extensor digiti minimi 6. Extensor carpi ulnaris 7. Anconeus - All besides BR & AC have common origin from lateral epicondyle & supra epicondylar ridge of humerus - BR & AC extend as tendons into hand