Back of Forearm.pptx

Back of Forearm

1. Back of Forearm Dr. Diwakar Kumar Shah Assistant Professor Department of Anatomy Nobel Medical College Teaching Hospital

2. Introduction to the forearm The forearm extends from the elbow to the wrist and contains two bones, which are tied together by the thin strong fibrous membrane—the interosseous membrane. The head of radius is at the proximal end of the forearm whereas the head of ulna is at the distal end of the forearm. The radius and ulna at both their ends articulate with each other to form the superior and inferior radio-ulnar joints. All important movements of supination and pronation of the forearm occur at these joints. The upper ends of radius and ulna articulate with the lower end of humerus to form elbow joint. The main purpose of the movements of the forearm at elbow and radio-ulnar joints is to place the hand at the desired place. The muscles, nerves, and vessels are present both on the front and back of the forearm.

3. FASCIAL COMPARTMENTS OF THE FOREARM The forearm is enclosed in sheath of deep fascia of the forearm (antebrachial fascia). It is attached to the posterior subcutaneous border of the ulna. From the deep surface fascia, septa pass between the muscles and some of these septa reach the bone. This deep fascia, together with interosseous membrane and fibrous intermuscular septa divide the forearm into several compartments, each having its own muscles, nerves, and blood supply. Classically, the forearm is divided into the two compartments: Anterior compartment Posterior compartment The anterior compartment contains the structures on the front of the forearm and the posterior compartment contains the structure on the back of the forearm. Near the wrist, the deep fascia presents two localized thickenings, the flexor and the extensor retinacula, which retain the digital tendons in position during hand movements.

4. Back of Forearm The following structures are to be studied on the back of the forearm: Muscles of the back of the forearm Posterior interosseous nerve Posterior and anterior interosseous arteries

5. Muscles of the back of the forearm Superficial Muscles of the back of forearm Brachioradialis Extensor carpi radialis longus (ECRL) Extensor carpi radialis brevis (ECRB) Extensor digitorum (ED) Extensor digiti minimi (EDM) Extensor carpi ulnaris (ECU) Anconeus Lateral group of superficial extensors Posterior group of superficial extensors

6. Brachioradialis Origin Upper two-third of the lateral supracondylar ridge of the humerus Insertion Lateral surface of the distal end of radius just above the styloid process Nerve supply Radial nerve Action Flexes the elbow joint. Pronates the supinated forearm to midprone position Supinates the pronated forearm to midprone position

7. Extensor carpi radialis longus (ECRL) Origin Lower one-third of the lateral supracondylar ridge of the humerus Insertion Lateral side of the dorsal surface of the base of second metacarpal bone Nerve supply Radial nerve Action Acting with extensor carpi ulnaris extends the wrist Acting with flexor carpi radialis abducts the wrist

8. Extensor carpi radialis brevis (ECRB) Origin By a common tendon from the lateral epicondyle of the humerus and lateral ligament of the elbow joint Insertion Lateral side of the dorsal surface of the base of third metacarpal bone Nerve supply Posterior interosseous nerve before piercing the supinator Action Acting with extensor carpi ulnaris extends the wrist Acting with flexor carpi radialis abducts the wrist

9. Extensor digitorum Origin By a common tendon from the lateral epicondyle Insertion Gives rise to four tendons for medial four digits. By the extensor expansion it is inserted into the dorsum of middle and terminal phalanges Nerve supply Posterior interosseous nerve Action Extends the medial four digits. Can also extend the wrist

10. Extensor digiti minimi Origin By the common tendon from the lateral epicondyle Insertion Lies medial to the extensor digitorum tendon for the little finger. Through the extensor expansion, it is inserted into the dorsum of middle and terminal phalanges of little finger Nerve supply Posterior interosseous nerve Action Extends the little finger Helps in the extension of the wrist

11. Extensor carpi ulnaris (ECU) Origin By the common tendon from the lateral epicondyle and by an aponeurosis from the upper two-third of the posterior border of ulna along with flexor carpi ulnaris and flexor digitorum profundus Insertion Into a tubercle on the medial side of the dorsal surface of the base of the fifth metacarpal Nerve supply Posterior interosseous nerve Action Acting with extensor carpi radialis it extends the wrist Acting with flexor carpi ulnaris it adducts the wrist

12. Anconeus Origin From the back of the lateral epicondyle Insertion Lateral side of the olecranon process and upper one-fourth of the posterior surface of the ulna Nerve supply Nerve to anconeus , which arises from radial nerve in spiral groove and descends through medial head of the triceps brachii Action Weak extensor of the elbow joint

13. Fig. showing the origin of superficial muscles of the back of forearm

14. Fig. Insertion of Superficial Muscles of back of forearm

15. Deep Muscles of the back of forearm There are five deep muscles of the back of forearm, from above downwards they are: Supinator Abductor pollicis longus (APL). Extensor pollicis brevis (EPB). Extensor pollicis longus (EPL). Extensor indicis. The three deep extensors of the forearm, which act on thumb ( abductor pollicis longus, extensor pollicis brevis, and extensor pollicis longus ) lie deep to the superficial extensors and in order to gain insertion on the three short long bones of thumb ‘ crop out ’ (emerge) from the furrow in the lateral part of the forearm between lateral and posterior groups of superficial extensor. These three muscles are therefore termed outcropping muscles .

16. Supinator Origin Lateral epicondyle Lateral ligament of the elbow joint Annular ligament Supinator crest of ulna and from the triangular area in front of it Insertion Upper one-third of the posterior, lateral, and anterior surfaces of the radius Nerve supply Posterior interosseous nerve before piercing the supinator Action Supination of the forearm

17. Abductor pollicis longus (APL) Origin Lateral part of the posterior surface of ulna below the anconeus Middle one-third of the posterior surface of radius (below the posterior oblique line) and intervening posterior surface of interosseous membrane Insertion Lateral side of the base of first metacarpal Nerve supply Posterior interosseous nerve Action Abducts the thumb

18. Extensor pollicis brevis (EPB) Origin From a small area on the posterior surface of radius below the origin of abductor pollicis longus and from adjoining interosseous membrane Insertion Dorsal surface of the base of proximal phalanx of thumb Nerve supply Posterior interosseous nerve Action Extends the thumb at metacarpophalangeal joint and extends the carpometacarpal joint

19. Extensor pollicis longus Origin From lateral part of middle one-third of the posterior surface of ulna and adjoining interosseous membrane Insertion Dorsal surface of the base of distal phalanx of thumb Nerve supply Posterior interosseous nerve Action Extends the joints of thumb Helps in the extension of the wrist

20. Extensor indicis Origin From the posterior surface of ulna below the origin of extensor pollicis longus and also from the adjoining interosseous membrane Insertion The tendon lies medial to the extensor digitorum tendon for the index finger Through the extensor expansion, it is inserted into the dorsum of middle and distal phalanges of the index finger Nerve supply Posterior interosseous nerve Action Extends the index finger Helps in the extension of the wrist

21. Fig. Origin & Insertion of deep muscles of back of forearm

22. EXTENSOR RETINACULUM The deep fascia on the back of the wrist is thickened to form an oblique fibrous band called extensor retinaculum . It is directed downwards and laterally, and about 2 cm broad vertically. Attachments The medial end of extensor retinaculum is attached to the styloid process of ulna, triquetral, and pisiform bones. Its lateral end is attached to the lower part of the anterior border of the radius. Functions It holds the extensor tendon in place on the back of wrist and prevents their bowstrings when the hand is extended at the wrist joint.

23. Compartments The space deep to the extensor retinaculum is divided into six compartments by five septa extending from retinaculum to the dorsal aspects of the lower ends of radius and ulna. The compartments are numbered I to VI from lateral to medial side.

24. POSTERIOR INTEROSSEOUS NERVE Origin and Course The posterior interosseous nerve is the deep terminal branch of the radial nerve. It is motor and chief nerve of the back of the forearm. It begins in the cubital fossa as one of the two terminal branches of radial nerve at the level of lateral epicondyle of humerus. It leaves the cubital fossa by winding around the lateral side of the neck of radius in the substance of supinator. After emerging from supinator, it runs in the fascial plane between superficial and deep extensor muscles. At the lower border of extensor pollicis brevis, it passes deep to the extensor pollicis longus to lie on the posterior surface of interosseous nerve, on which it runs downwards up to the wrist where it ends into a pseudoganglion.

25. Branches Muscular branches Before piercing supinator , it gives branches to the extensor carpi radialis brevis and supinator. While passing through supinator , it gives another branch to the supinator. After emerging from supinator , it gives branches to three superficial extensors (extensor digitorum, extensor digiti minimi , and extensor carpi ulnaris ) and all deep extensors. Articular branches to the wrist joint, distal radio-ulnar joint, and carpal joints. Lesion of posterior interosseous nerve: The posterior interosseous nerve (i.e., deep terminal branch of the radial nerve) may be damaged during surgical exposure of the head of radius in fracture proximal end of radius. Since the extensor carpi radialis longus is spared wrist drop does not occur.

26. POSTERIOR INTEROSSEOUS ARTERY The posterior interosseous artery is a smaller terminal branch of the common interosseous artery from ulnar artery. It begins in the cubital fossa, enters the back of the forearm by passing through the gap between the oblique cord and upper margin of the interosseous membrane. From here, it passes between supinator and abductor pollicis longus to accompany the posterior interosseous nerve. In the lower part of the forearm, it becomes markedly reduced and ends by anastomosing with the anterior interosseous artery. In the lower part of forearm, the anterior interosseous artery enters the back of the forearm by piercing interosseous membrane just above the pronator quadratus and supplies low one-fourth of the back of the forearm. The posterior interosseous artery in the cubital fossa gives interosseous recurrent artery, which takes part in the formation of anastomosis around the elbow joint.