Session 9: Anatomy of the Posterior Forearm Flashcards
Superficial muscles of the posterior forearm.
Brachioradialis Extensor carpi radialis longus Extensor carpi radialis brevis Extensor digitorum Extensor digiti minimi Extensor carpi ulnaris Anconeus
Which muscles originate from the common extensor origin?
Extensor carpi radialis brevis Extensor digitorum Extensor digiti minimi Extensor carpi ulnaris
Origination, insertion, action and innervation of brachioradialis.
Originates from the proximal aspect of the lateral supracondylar ridge of the humerus Inserts onto the distal end of the radius Action is to flex the elbow when the forearm is in mid-prone. In supinated position the brachioradialis only assist in flexion. This is a bit paradoxical as brachioradialis is in the posterior compartment. Innervated by the radial nerve.
Origination, insertion, action and innervation of extensor carpi radialis longus.
Originates from the lateral supracondylar ridge of the humerus (distal to the origination of brachioradialis). Inserts onto the dorsal surface of the base of the second metacarpal bone. Extends and abducts the wrist. Innervated by the radial nerve.
Origination, insertion, action and innervation of extensor carpi radialis brevis.
Originates from the common extensor origin of the lateral epicondyle. Inserts onto the dorsal surface of the base of the third metacarpal bone. Extends and abducts the wrist. Innervated by the deep branch of the radial nerve. This is because the origin of ECRB is distal to the origin of ECRL and the radial nerve has already divided into its superficial and deep branches at this point.
Origin, insertion, action and innervation of extensor digitorum.
Originates from the common extensor origin of the lateral epicondyle. The tendon of extensor digitorum continues into the distal part of the forearm where it splits into four tendons. They insert into the extensor hood of the four fingers. Main extensor of the four fingers. Extends the four fingers at the metacarophalangeal joint (MCPJ) and both interphalangeal joints (DIPJ and PIPJ). Innervated by the posterior interosseous branch of the radial nerve. This is the name given to the deep branch of the radial nerve after it has passed between the two heads of supinator and entered the posterior compartment of the forearm.
What is juncturae tendinum? What is its function?
Fibrous bands on the dorsum of the hand. This connection between the tendons prevents full extension of the middle or ring finger if the other fingers are flexed.
Why can you still extend index and little finger even though juncturae tendinum is there?
Because index finger has a second tendon which is extensor indicis. Little finger also has a second tendon which is extensor digits minimi.
Origin, insertion, action and innervation of extensor digiti minimi.
Originates from the common extensor origin on the lateral epicondyle of the humerus. Inserts on the ulnar side of the extensor digitorum onto the hood of the little finger. Action is to extend the little finger and also assist in extension at the wrist. Innervated by the posterior interosseous branch of the radial nerve.
Origin, insertion, action and innervation of extensor carpi ulnaris.
ECU has two heads. The humeral head originates from the common extensor origin on the lateral epicondyle of the humerus. The ulnar head originates from the olecranon, the posterior surface of the proximal ulna and the deep fascia. Inserts onto the base of the fifth metacarpal. Action is to adduct the wrist and extend the wrist. Innervated by the posterior interosseous branch of the radial nerve.
Origin, insertion, action and innervation of anconeus.
Originates from the common extensor origin on the lateral epicondyle. Inserts onto the radial side of the olecranon and the posterior surface of the proximal ulna. Weak extensor of the elbow. Stabilise the elbow joint. During pronation of the forearm anconeus abducts the ulna and prevents the joint capsule from impingement within the olecranon fossa.
Deep muscles of the posterior forearm.
Supinator Abductor pollicis longus Extensor pollicis brevis Extensor pollicis longus Extensor indicis
Origin, insertion, action and innervation of supinator.
Two heads of origin. Humeral head originates from the common extensor origin on the lateral epicondyle of the humerus. The ulnar head originates from the supinator crest on the radial border of the proximal shaft of the ulna. Inserts together onto the proximal radial border of the radius. Action is to supinate the forearm when there is an absence of resistance. Innervated by the deep branch of the radial nerve.
Origin, insertion, action and innervation of abductor pollicis longus.
Originates from the interosseous membrane and the adjacent posterior surfaces of the radius and ulna. Inserts onto the radial side of the base of the first metacarpal. Radially abducts the thumb and assists in extension of the carpometacarpal joint. Innervated by the posterior interosseous branch of the radial nerve.
Origin, insertion, action and innervation of extensor pollicis longus.
Originates from the middle third of the posterior surface of the ulna and interosseous. Inserts onto the distal phalanx of the thumb (longus). EPL extends all of the joints of the thumb, carpometacarpal, MCPJ and interphalangeal joint. Innervated by the posterior interosseous branch of the radial nerve.
Origin, insertion, action and innervation of extensor pollicis brevis.
Originates from the posterior surface of the radius and interosseous membrane. Inserts onto the of the proximal phalanx of the thumb (brevis). Extends the MCPJ and carpometacarpal joints of the thumb. Innervated by the posterior interosseous branch of radial nerve. All deep muscles except for supinator are innervated by the posterior interosseous branch of radial nerve. Supinator is innervated by the deep branch of the radial nerve.
Origin, insertion, action and innervation of extensor indicis.
Originates from the posterior surface of the interosseous membrane distal to origin of EPL. Inserts onto the extensor hood of the index finger on the ulnar side of the tendon of extensor digitorum. Extends the index finger. Innervated by the posterior interosseous branch of the radial nerve.
What sensory parts does the radial nerve innervate?
Majority of the skin of the posterior arm, the lower lateral arm, the posterior forearm, the dorsal surface of the radial side of the hand. The dorsal surface of the radial three and half digits apart from the skin over the dorsum of the distal phalanges.
What does the radial nerve innervate?
Triceps brachii and the extensor muscles in the forearm + brachioradialis.
Route of the radial nerve in the arm.
The radial nerve is a direct continuation of the posterior cord of the brachial plexus. It exits the axilla inferiorly and enters the posterior compartment of the arm. Here it will give off branches to the long and lateral heads of the triceps brachii and the posterior cutaneous nerve of the arm. It then enters the radial groove of the humerus and travels between the origins of the lateral and medial heads of triceps. Within the radial groove it gives off a branch to the medial head of triceps as well. Here it also gives off two additional cutaneous branches which are lower lateral cutaneous nerve of the arm and posterior cutaneous nerve of the forearm. The radial nerve the emerges from the radial groove and gives off a branch to brachioradialis and extensor carp radialis longus. It then travels anterior to the lateral epicondyle of the humerus through the cubital fossa.
What does the posterior cutaneous nerve of the arm innervate?
The posterior surface of the arm.
What does the lower lateral cutaneous nerve of the arm innervate?
The lateral aspect of the arm, inferior to the insertion of the deltoid muscle.
What does the posterior cutaneous nerve of the forearm innervate?
A strip of skin down the middle of the posterior forearm.
Route of the radial nerve in the cubital fossa and down into the forearm.
In the cubital fossa the radial nerve will terminate by dividing into two branches: the deep branch of the radial nerve which is a motor nerve and also a superficial branch which is a sensory nerve. The deep branch will supply extensor carpi radialis brevis, after this it will exit the cubital fossa by passing posteriorly between the two heads of supinator and also innervate it. Now the deep branch changes name into the posterior interosseous nerve and it will supply the remaining superficial and deep muscles of the posterior forearm.
What does the wrist joint consist of?
The radius, the lunate, the scaphoid and the triangular fibrocartilage complex.
What type of joint is the wrist joint?
An ellipsoid synovial joint.
What movements does the wrist joint allow?
Moves in two planes. Flexion Extension Adduction Abduction and circumduction which is a result of the four movements.
What ligaments stabilise the wrist joint?
Dorsal and palmar radiocarpal ligament as well as ulnar and radial collateral ligaments. The radiocarpal ligaments play an important role in ensuring that the hand follows the radius during pronation and supination of the forearm.
Major muscles responsible for flexion of the the wrist.
Flexor carpi ulnaris Flexor carpi radialis Palmaris longus (very weak flexor)
Major muscles responsible for extension of the wrist.
Extensor carpi radialis longus Extensor carpi radialis brevis Extensor carpi ulnaris
Adduction of the wrist.
Extensor carpi ulnaris Flexor carpi ulnaris
Abduction of the wrist.
Flexor carpi radialis Extensor carpi radialis longus Extensor carpi radialis brevis
The carpal bones in the proximal row. Radial to ulnar.
Scaphoid Lunate Triquetrum Pisiform
The carpal bones in the distal row. Radial to ulnar.
Trapezium Trapezoid Capitate Hamate
What is the hook of hamate?
A projection on the palmar surface of hamate.
Function of hook of hamate.
Forms the ulnar border of the carpal tunnel. Forms the radial border of the Guyon’s canal. Numerous structures attach onto the hook of hamate like the flexor retinaculum and the tendon of flexor carpi ulnaris.
What is important clinically to know about the scaphoid bone?
That it has retrograde blood supply from a dorsal carpal branch of the radial artery. Enters the schapoid distally and supplies the proximal 80% of the scaphoid by retrograde flow. If the scaphoid fractures it is important to treat it as it has a high rate of non-union.
How are the metacarpal bones numbered?
Radial to ulnar. I - V
Proximal articulation of metacarpal I.
Trapezium
Proximal articulation of II.
Trapezoid.
Proximal articulation of III.
Capitate.
Movements of the thumb.
Extension Flexion Palmar abduction Radial abduction Opposition and retropulsion Palmar adduction and radial adduction + circumduction
Movements of the fingers.
Extension and flexion.
Hyperextension.
Abduction and adduction.
Circumduction.
What passes through guyon’s canal?
Ulnar nerve and ulnar artery.
