Forearm Anatomy PDF

Dr. Mahir R. Ibrahim Orthopaedic surgeon  Forearm It is the distal unit of articulated upper limb. It extends from the elbow to the wrist and contains two bones, the radius and ulna which are joined by an interosseous membrane. Facial Compartments of Forearm As in...

Dr. Mahir R. Ibrahim Orthopaedic surgeon  Forearm It is the distal unit of articulated upper limb. It extends from the elbow to the wrist and contains two bones, the radius and ulna which are joined by an interosseous membrane. Facial Compartments of Forearm As in the arm, the forearm is divided into anterior and posterior compartment. In the forearm, these compartments are separated by: 1) Lateral intermuscular septum, which passes from the anterior border of the radius to deep fascia surrounding the limb, 2) Interosseous membrane, which links adjacent borders of the radius and ulna along most of their length; 3) The attachment of deep fascia along the posterior border of the ulna.  Anterior Compartment Muscles: Flexors and Pronators Blood vessels: Ulnar and Radial arteries Nerves: Median and Ulnar nerves Muscles of the anterior compartment They are associated with: 1. movements of the wrist joint; 2. flexion of the fingers including the thumb 3. pronation. They are arranged in three layers: 1. Superficial layer 2. Intermediate layer 3. Deep layer Superficial layer Four muscles: 1) Pronator teres 2) flexor carpi radialis 3) palmaris longus 4) flexor carpi ulnaris {PT, FCR, PL, FCU}  Superficial Muscles Origin layerInsertion Innervation Action medial epicondyle of Flexes and Pisiform bone, Flexor carpi humerus; - Ulnar nerve olecranon and hamate and base adducts the ulnaris of metacarpal V [C7,C8, T1] posterior border wrist joint of ulna Medial Palmar Palmaris Median nerve Flexes wrist epicondyle of aponeurosis of longus humerus hand [C7,C8] joint Medial Base of Flexes and Flexor carpi Median nerve epicondyle of metacarpals II abducts the radialis humerus and III [C6,C7] wrist medial epicondyle and adjacent lateral surface pronation Pronator Median nerve supraepicondylar of mid-shaft of teres ridge; -medial side radius [C6,C7] of coronoid process Intermediate layer It consists of one muscle flexor digitorum superficialis {FDS}  Intermediate layer Muscle Origin Insertion Innervation Action Humero-ulnar Four tendons, head-medial which attach to Flexes proximal epicondyle of the palmar interphalangeal Flexor humerus and surfaces of the joints of the Median nerve digitorum adjacent margin middle index, middle, of coronoid phalanges of the [C8,T1] ring, and little superficialis process; radial index, middle, fingers; and the head- oblique ring, and little wrist joint line of radius fingers Deep layer There are three deep muscles in the anterior compartment of the forearm: 1) Flexor digitorum profundus 2) Flexor pollicis longus 3) Pronator quadratus {FDP, FPL, PQ} Deep layer Muscle Origin Insertion Innervation Action Anterior and medial surfaces Four tendons, to Lateral half by Flexes distal Flexor of ulna and the palmar Median nerve; interphalangeal digitorum anterior medial surfaces of the medial half by joints of the profundus half of distal phalanges Ulnar nerve fingers and the interosseous of fingers [C8,T1] wrist joint membrane Anterior surface Flexor Median nerve Flexes of radius and Palmar surface of (anterior interphalangeal pollicis radial half of base of distal interosseous joint of the longus inter-osseous phalanx of thumb nerve) [C7,C8] thumb membrane Median nerve Linear ridge on Pronator Distal anterior (anterior distal anterior Pronation quadratus surface of radius interosseous surface of ulna nerve) [C7,C8]  Blood vessels  The largest arteries in the forearm are in the anterior compartment, pass distally to supply the hand, and give rise to vessels that supply the posterior compartment.  The terminal branches of brachial artery enter forearm through the cubital fossa which are: 1) Ulnar artery 2) Radial artery  Ulnar Artery It is the larger terminal branch of the brachial artery. the artery initially lies on brachialis and deep to pronator teres, flexor carpi radialis, palmaris longus and flexor digitorum superficialis. A It crosses the flexor retinaculum lateral to the ulnar nerve and pisiform bone to enter the hand.  Branches of Ulnar artery 1) Anterior and posterior ulnar recurrent arteries 2) Common interosseous artery 3) Cutaneous branches 4) Muscular branches 5) Dorsal carpal branch and Palmar carpal branch, which supply the wrist.  Radial Artery The radial artery is smaller than the ulnar artery It is:  Just deep to the brachioradialis muscle in the proximal half of the forearm  Medial to the superficial branch of the radial nerve in the middle third of the forearm  Medial to the tendon of the brachioradialis muscle and covered only by deep fascia, superficial fascia, and skin in the distal forearm. Branches of Radial artery 1) Radial recurrent artery 2) Cutaneous branches 3) Muscular branches 4) Palmar carpal branch 5) Superficial palmar branch  Veins of the Forearm Superficial Veins 1) Basilic Vein 2) Cephalic Vein 3) Median Vein Deep Veins Deep venous arch in the hand form vena comitantes 1) Ulnar Vein 2) Radial Vein  Median Nerve The median nerve is the principal nerve of the anterior compartment of the forearm. It supplies all muscles except FCU and medial half of FDP. It has a straight linear course in the fascia on the deep surface of the flexor digitorum superficialis muscle.  Median Nerve Branches: 1) anterior interosseous nerve 2) Articular branch 3) Muscular branches 4) Palmar cutaneous branch  Ulnar Nerve It enters the anterior compartment by passing posteriorly around the medial epicondyle of the humerus and between the humeral and ulnar heads of the flexor carpi ulnaris muscle. it supplies only one and a half muscles, FCU and the ulnar part of the FDP. The ulnar nerve and artery emerge from beneath the FCU tendon and become superficial just proximal to the wrist, superficial to the flexor retinaculum  Ulnar Nerve Branches 1) Muscular branches 2) Two cutaneous branches to the hand; palmar and dorsal 3) Articular branch to elbow  Posterior Compartment Muscles: Extensors of wrist joint + Supinator of forearm Blood Vessels: Branches from 1. Radial artery 2. Anterior interosseous artery 3. Posterior interosseous artery Nerves: Radial nerve  Muscles Arranged in two layers: a) Superficial b) Deep  Superficial layer: 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 Origin Insertion Innervation Action Relatively week flexion of Proximal two thirds of Lateral surface of distal Radial nerve (C5, forearm, maximal when Brachioradialis supraepicondylar ridge end of radius proximal to C6, C7) forearm is in midpronated of humerus styloid process position Lateral Extensor carpi radialis Dorsal aspect of base of Radial nerve (C6, supraepicondylar ridge longus (ECRL) 2nd metacarpal C7) of humerus Extend and abduct hand at the wrist joint; ECRL active during fist clenching Deep branch of Extensor carpi radialis Doral aspect of base of radial nerve (C7, brevis (ECRB) 3rd metacarpal C8) Lateral epicondyle of Extends medial four fingers humerus (common primarily at Extensor expansions of Extensor digitorum extensor origin) metacarpophalangeal joints, medial four fingers secondarily at interphalangeal Posterior joints interosseous Extends 5th finger primarily at Extensor digiti minimi Extensor expansion of 5th nerve (C7, C8), metacarpophalangeal joint, (EDM) finger continuation of secondarily at interphalangeal deep branch of joint radial nerve Lateral epicondyle of Extends and adducts hand at Extensor carpi ulnaris humerus; posterior Dorsal aspect of base of wrist joint (also active during (ECU) border of ulna via a 5th metacarpal fist clenching) shared aponeurosis  Deep Layer 1) Supinator 2) abductor pollicis longus 3) extensor pollicis brevis 4) extensor pollicis longus 5) extensor indicis  Muscle Origin Insertion Innervation Action Lateral epicondyle of Deep branch Supinates forearm; rotates humerus; radial Lateral posterior, and radius to turn palm Supinator collateral and anular anterior surfaces of of radial nerve anteriorlyor superiorly (if ligaments; supinator proximal third of radius (C7, C8) elbow is flexed) fossa; crest of ulna Posterior surface of Extends 2nd finger (enabling Extensor expansion of 2nd Extensor indicis distal third of ulna and finger its independent extension); interosseous membrane helps extend hand at wrist Posterior surface of Abductor pollicis proximal halves of ulna, Abducts thumb and extends it longus (APL) radius, and interosseous Base of 1st metacarpal at carpometacarpal joint membrane Posterior Extends distal phalanx of Posterior surface of Extensor pollicis Dorsal aspect of base of interosseous thumb at interphalangeal joint; middle third of ulna and longus (EPL) interosseous membrane distal phalanx of thumb nerve (C7, C8) extends metacarpophalangeal and carpometacarpal joints Extends proximal phalanx of Extensor pollicis Posterior surface of Dorsal aspect of base of thumb at metacarpophalangeal distal third of radius and brevis (EPB) interosseous membrane proximal phalanx of thumb joint; extends carpometacarpal joint  Blood vessels 1. Posterior interosseous artery: enters post. comp. over proximal margin of interosseous memb. And give recurrent interosseous artery. It terminates by joining the dorsal carpal arch of the wrist. 2. Anterior interosseous artery: has numerous perforating branches, which pass directly through the interosseous membrane to supply deep muscles of the posterior compartment. 3. Radial Artery: has muscular branches, which contribute to the supply of the extensor muscles on the radial side of the forearm.  Radial Nerve It bifurcates into deep and superficial branches under the margin of the brachioradialis muscle in the lateral border of the cubital fossa The deep branch is predominantly motor and passes between the two heads of the supinator muscle. It terminates as Posterior interosseous nerve. The superficial branch is sensory. It passes down deep to the brachioradialis muscle and in association with the radial artery. The nerve continues into the hand where it innervates skin on the dorsolateral surface. Thank you