Muscles of the Posterior Forearm Compartment PDF 2024/2025

MUST MSK(101-1) Academic year: 2024/2025 ANATOMY DEPARTMENT Muscles of posterior compartment of the forearm Prof. Dr. Hayam Elsaady Farhoud  Muscles of posterior compartment of the forearm The extensor group, are supplied by the radial nerve and its posterior inter...

MUST MSK(101-1) Academic year: 2024/2025 ANATOMY DEPARTMENT Muscles of posterior compartment of the forearm Prof. Dr. Hayam Elsaady Farhoud  Muscles of posterior compartment of the forearm The extensor group, are supplied by the radial nerve and its posterior interosseous branch. the muscles of the back are arranged functional, Acting on the digits: digitorum. thumb: pollicis. wrist: carpi. A- superficial group 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 muscle B- deep group 8- Supinator muscle 9- Abductor pollicis longus 10- Extensor pollicis brevis 11- Extensor pollicis longus 12- Extensor indicis Brachioradiali sItOrigin: is the most lateral muscle of the group From the upper 2/3 of lateral supracondylar ridge Insertion: Into the lateral surface of the lower end of radius. (just above the styloid process). Nerve supply: radial nerve. (where it lies on the lateral side of the arm). Action:1- Put the forearm in the midpron position (i.e. midway between pronation and supination). 2- Flexion of elbow joint N.B. radial nerve and radial artery are overlapped by the brachioradialis muscle  2- Extensor carpi radialis longus Origin: From the lower 1/3 of lateral supracondylar ridge Insertion: Into the base of the 2nd metacarpal bone. Nerve supply: radial nerve (where it passes on the lateral side of the arm). Action: Extend and abduct the wrist  3- Extensor carpi radialis brevis Origin: From the common extensor, which arises from the front of the lateral epicondyle Insertion: Into the back of the base of the 3rd metacarpal bone Nerve supply: posterior interosseous nerve, while on the front of the elbow joint and before piercing the supinator). Action: Extend and abduct the wrist 4- Extensor digitorum Origin: From the common extensor origin Insertion: Into the base of the middle and distal phalanges of the medial 4 fingers -Each tendon joins the extensor expansion (dorsal digital expansion) which covers the dorsum of the proximal phalanx. -This expansion divides into 3 parts (one median and 2 collaterals): The median part: is inserted into the base of the middle phalanx. The 2 collaterals: are inserted together into the base of the distal phalanx. Nerve supply: posterior interosseous nerve (after emerging on the back of forearm). Action: 1. Extends the metacarpo-pharengeal and interphalangeal joint of the medial 4 fingers. 2. Helps in extension of the wrist joint. 5- Extensor digiti minimi a slender muscle just medial to the extensor digitorum Origin: From the common extensor origin Insertion: Into the extensor expansion of the little finger Nerve supply: posterior interosseous nerve Action: Extends all joints of the little finger 6-Extensor carpi ulnaris Origin: 1-From the common extensor origin 2- the posterior border of the ulna by aponeorosis (this aponeurosis is common to the flexor carpi ulnaris and flexor digitorum profundus). Insertion: Into the back of the base of the 5th metacarpal bone Nerve supply: posterior interosseous nerve Action: Extends and adducts the wrist joint (when it acts with the flexor carpi ulnaris, the result is pure adduction). 7- Anconeus muscle It is the most medial, muscle of the superficial group, triangular in shape and is the shortest of the group. Origin: From the back of the lateral epicondyle by a rounded tendon. Insertion:. Into the lateral surface of olecranon process and upper ¼ of the back of the shaft of the ulna, above the oblique upper part of the posterior border. Nerve supply: radial nerve Action: Extends the elbow N.B. the branch from the radial nerve arises in the spiral groove and descends through the medial head of triceps to reach the anconeus. Muscles of posterior compartment of the forearm B- deep group the deep layer are arranged from above -Supinator:downwards the highest and is attached to both radius and ulna. -Abductor pollicis longus: arises from both radius and ulna just below the supinator. -The 2 extensors of the thumb: The 2 muscles lie side by side. the extensor pollicis longus(from the ulna), and extensor pollicis brevis (from the radius). -Extensor indices: is the lowest and arises from the ulna. 8- Supinator muscle :Origin superficial part from the lateral epicondyle and radial collateral ligament of the elbow joint -1.deep part from supinator crest and fossa (the depression just in front) -2 :Insertion Into the upper 1/3 of the lateral surface of the radius Nerve supply: posterior interosseous nerve (before the nerve pierces the muscle). Action: supinates the forearm Main relations: -It forms a part of the floor of the cubital fossa. -The posterior interosseous nerve pierces the muscle Just above the lower border of the muscle. -The posterior interosseous artery appears Just below the lower border of the muscle. 9- Abductor pollicis longus Origin: 1- from the upper part of the back of the ulna below the anconeus 2- from the middle 1/3 of the back of radius below supinator 3- back of interosseous membrane Insertion: Into the base of the 1st metacarpal bone Nerve supply: posterior interosseous nerve Action: 1- abduct carpo-metacarpal joints of the thumb 2- abduct the wrist The tendon of Abductor pollicis longus is accompanied by the tendon of the extensor pollicis brevis, and both tendons wind round the lateral side of forearm where they cross over the 2 tendons of the extensor carpi radialis longus and extensor carpi radialis brevis 10- Extensor pollicis Origin: 1- brevis from the middle 1/3 of the back of radius below abductor pollicis longus 2- back of interosseous membrane Insertion: Into the base of proximal phalanx of the thumb Nerve supply: posterior interosseous nerve Action:1- extends metacarpophalangeal joint of the thumb 2- help in abduction of the wrist 11- Extensor pollicis longus Origin: 1- from the middle 1/3 of the back of the ulna below the abductor pollices longus 2- back of interosseous membrane , just below the abductor pollicis longus. Insertion: Into the base of the distal phalenx of the thumb (The tendon winds laterally round the dorsal tubercle on the back of the lower end of the radius) Nerve supply:posterior interosseous nerve Action:Extends all the joints of the thumb. Remember the following insertions into the thumb. Base of metacarpal bone: abductor pollicis longus. Base of proximal phalanx: extensor pollicis brevis. Base of distal phalanx : extensor pollicis longus 12- Extensor indicis Origin:1- from the lower part of the back of the ulna below the extensor pollices longus 2- back of interosseous membrane Insertion: Into the extensor expansion of the index finger (in addition to the tendon from the extensor digitorum) (compare with the little finger). Nerve supply: posterior interosseous nerve Action: Extends the index finger Each of the following fingers has 2 extensors: Thumb: extensor pollicis longus and brevis. Index finger: extensor digitorum and extensor indicis.  ANATOMICAL SNUFF-BOX Laterally: tendons of abductor pollicis longus and extensor pollicis brevis. Medially: tendon of extensor pollicis longus. Floor: scaphoid and trapezium (most lateral carpal bones) Radial artery: passes on its floor (the only content). Digital branches of radial nerve: descend in its roof. Cephalic vein: ascends in its roof.  Extensor expansion The extensor expansions (are triangular aponeuroses by which the extensor tendons insert onto the phalanges. (also known as the extensor hood or dorsal digital expansion)​ Muscles attached in extensor expansion extensor digitorum muscle. lumbrical muscles (hand) dorsal interossei muscles (hand) palmar interossei muscles (hand)