Forearm Muscles Anatomy PDF

Anterior compartment forearm Anterior &posterior compartment forearm Page 1  Anterior (Flexor) Compartment Demarcation Medially: ○ Olecranon...

Anterior compartment forearm Anterior &posterior compartment forearm Page 1  Anterior (Flexor) Compartment Demarcation Medially: ○ Olecranon Process: This is the bony prominence of the ulna at the elbow. It forms the point of the elbow and serves as a key landmark for the medial border. ○ Posterior Border of Ulna: This is the edge of the ulna bone that runs along the back (posterior) side of the forearm. It helps define the medial boundary of the anterior compartment. Floor of the Anterior Compartment Laterally: ○ Anterior Border of Radius: This is the edge of the radius bone that runs along the front (anterior) side of the forearm. It helps define the lateral boundary of the anterior compartment. Anterior Surface of Radius: The front surface of the radius bone. Anterior and Medial Surfaces of Ulna: The front and inner surfaces of the ulna bone. Interosseous Membrane: A fibrous sheet that connects the radius and ulna bones. The fibers of this membrane run downwards and medially, providing additional structural support and separation between the anterior and posterior compartments. Contents of the Anterior (Flexor) Compartment Muscles There are 8 muscles in the anterior compartment, divided into two groups: 1. Superficial Group (5 muscles): ○ Pronator Teres ▪ Origin: □ Humeral (superficial) head: Lower part of medial supracondylar ridge and anterior part of medial epicondyle □ Ulnar (deep) head: Medial border of coronoid process of ulna ▪ Insertion: Middle of the lateral surface of Radius ▪ Course: Two heads join, proceed downward and laterally, forming the medial boundary of cubital fossa; median nerve passes between two heads ▪ Nerve Supply: Median nerve (before it passes between two heads) ▪ Action: Pronation of forearm, weak flexor of elbow ○ Flexor Carpi Radialis ▪ Origin: Medial epicondyle, adjoining deep fascia ▪ Insertion: Palmar surface of base of second and third metacarpal bones ▪ Course: Forms fusiform belly, tendon in the middle of forearm; at the wrist, accompanied by the tendon of brachioradialis laterally; radial artery intervenes between two tendons; perforates flexor retinaculum ▪ Nerve Supply: Median nerve ▪ Action: Flexor of wrist; along with Extensor Carpi Radialis Longus (ECRL) & Extensor Carpi Radialis Brevis (ECRB) - abduction of wrist ○ Palmaris Longus ▪ Origin: Medial epicondyle of humerus ▪ Insertion: Continues as central part of palmar aponeurosis ▪ Course: Long tendon passes in front of flexor retinaculum ▪ Nerve Supply: Median nerve ▪ Action: Weak flexor of wrist ○ Flexor Carpi Ulnaris ▪ Origin: □ Humeral head: Medial epicondyle of humerus □ Ulnar head: Medial margin of olecranon process and 2/3rd of the posterior border of ulna ▪ Insertion: Pisiform bone, through pisohammate and pisometacarpal ligament to hook of hamate and base of fifth metacarpal ▪ Course: Two heads form a tendinous arch; ulnar nerve and posterior ulnar recurrent artery pass below it ▪ Nerve Supply: Ulnar nerve ▪ Action: Flexor of wrist; along with Extensor Carpi Ulnaris (ECU) - adduction of wrist joint ○ Flexor Digitorum Superficialis ▪ Origin: □ Humero-ulnar head: Medial epicondyle of humerus and medial margin of coronoid process □ Radial head: Whole length of anterior oblique line of radius ▪ Insertion: Base of proximal phalanx of each digit; tendon splits into two to allow passage of tendon of Flexor Digitorum Profundus; slips reunite and split again to attach to sides of the shaft of middle phalanx ▪ Course: Forms four tendons above wrist arranged in superficial (mostly radial) and deep group of two each; passes below flexor retinaculum and diverges in palm □ Superficial: for middle and ring finger □ Deep: for index and little finger ▪ Nerve Supply: Median nerve ▪ Action: Flexion of middle phalanx at proximal interphalangeal joint; in prolonged contraction - flexion of metacarpophalangeal joint and wrist joint 2. Deep Group (3 muscles): ○ Flexor Pollicis Longus ▪ Origin: Anterior surface of shaft of radius below anterior oblique line, adjoining interosseous membrane ▪ Insertion: Palmar surface of base of distal phalanx of thumb Anterior &posterior compartment forearm Page 2  Layers of the Muscles in the Posterior Compartment of the Forearm Superficial Layer Deep Layer Functions: Movement of the wrist joint Extension of the fingers and thumb Supination (rotation of the forearm and hand so that the palm faces upward) Nerve Supply: Radial nerve Superficial Layer The superficial layer consists of seven muscles: Brachioradialis Extensor carpi radialis longus Extensor carpi radialis brevis Extensor digitorum Extensor digiti minimi Extensor carpi ulnaris Anconeus All these muscles have a common origin from the supraepicondylar ridge and lateral epicondyle of the humerus. Brachioradialis Origin: Proximal part of the supraepicondylar ridge of the humerus Insertion: Lateral side of the distal end of the radius just proximal to the radial styloid process Action: Flexion of the elbow in midprone position Nerve Supply: Radial nerve Extensor Carpi Radialis Longus (ECRL) Origin: Distal part of the supraepicondylar ridge and the lateral epicondyle of the humerus Insertion: Dorsal surface of the base of metacarpal II Action: Extends and abducts the wrist Nerve Supply: Radial nerve before it divides into superficial and deep branches Extensor Carpi Radialis Brevis (ECRB) Origin: Lateral epicondyle of the humerus Insertion: Dorsal surfaces of the bases of metacarpals II and III Action: Extends and abducts the wrist Nerve Supply: Deep branch of the radial nerve before it passes between the two heads of the supinator muscle Extensor Digitorum Origin: Lateral epicondyle of the humerus Insertion: Forms four tendons, each passing into a finger. Each tendon inserts, via a triangular-shaped connective tissue aponeurosis (the extensor hood), into the base of the dorsal surfaces of the middle and distal phalanges of the medial four fingers. Action: Extension of the digits at the interphalangeal and metacarpophalangeal joints Nerve Supply: Posterior interosseous nerve Extensor Digiti Minimi Origin: Lateral epicondyle of the humerus Insertion: With the tendon of the extensor digitorum, into the extensor hood of the little finger Action: Accessory extensor of the little finger Nerve Supply: Posterior interosseous nerve Extensor Carpi Ulnaris Origin: Lateral epicondyle of the humerus Insertion: Medial side of the base of metacarpal V Action: Extends and adducts the wrist Nerve Supply: Posterior interosseous nerve Anconeus Shape: Triangular Origin: Lateral epicondyle of the humerus Insertion: Posterolateral surface of the olecranon and related posterior surface of the ulna Action: Accessory extensor of the elbow joint Nerve Supply: Branch of the radial nerve that innervates the medial head of the triceps brachii muscle Deep Layer The deep layer of the posterior compartment of the forearm consists of five muscles: Supinator Abductor pollicis longus Extensor pollicis brevis Extensor pollicis longus Extensor indicis Except for the supinator, all these muscles originate from the posterior surfaces of the radius, ulna, and interosseous membr ane and pass into the thumb and index finger. Nerve Supply: Anterior &posterior compartment forearm Page 3 Anterior &posterior compartment forearm Page 4 Anterior &posterior compartment forearm Page 5  ▪ Action: Flexion of middle phalanx at proximal interphalangeal joint; in prolonged contraction - flexion of metacarpophalangeal joint and wrist joint 2. Deep Group (3 muscles): ○ Flexor Pollicis Longus ▪ Origin: Anterior surface of shaft of radius below anterior oblique line, adjoining interosseous membrane ▪ Insertion: Palmar surface of base of distal phalanx of thumb ▪ Course: Passes below flexor retinaculum ▪ Nerve Supply: Anterior interosseous branch of median nerve ▪ Action: Flexor of thumb ○ Flexor Digitorum Profundus ▪ Origin: □ Anterior and medial surface of upper 3/4th of shaft of ulna □ Including medial surface of coronoid and olecranon process □ Adjoining interosseous membrane □ Upper 3/4th of posterior border of ulna ▪ Insertion: Palmar surface of base of terminal (distal) phalanx of medial four fingers ▪ Course: Forms four tendons; remain united except the tendon for index finger; passes deep to flexor retinaculum; diverges in palm; passes between slips of superficialis; gives origin to four lumbricals ▪ Nerve Supply: □ Medial part: Ulnar nerve □ Lateral part: Anterior interosseous branch of median nerve ▪ Action: Flexes terminal phalanx ○ Pronator Quadratus ▪ Origin: Quadrilateral muscle extending anteriorly in front of interosseous membrane to both bones of forearm; bony ridge on antero- medial surface of lower 1/4th of ulna ▪ Insertion: Anterior surface of lower 1/4th of radius, adjoining anterior border of radius ▪ Nerve Supply: Anterior interosseous branch of median nerve ▪ Action: □ Superficial fibers: Principal pronators □ Deep fibers: Prevent separation of two bones on thrust Vessels Radial Artery: Supplies blood to the lateral aspect of the forearm. Ulnar Artery: Supplies blood to the medial aspect of the forearm. Common Interosseous Branch of Ulnar Artery: Divides into anterior and posterior interosseous branches, supplying blood to the interosseous membrane and surrounding structures. Nerves Median Nerve: Innervates most of the muscles in the anterior compartment. Ulnar Nerve: Innervates the flexor carpi ulnaris and the medial part of the flexor digitorum profundus. Anterior Interosseous Branch of Median Nerve: Innervates the deep muscles of the anterior compartment. Anterior &posterior compartment forearm Page 6  Abductor pollicis longus Extensor pollicis brevis Extensor pollicis longus Extensor indicis Except for the supinator, all these muscles originate from the posterior surfaces of the radius, ulna, and interosseous membr ane and pass into the thumb and index finger. Nerve Supply: Posterior interosseous nerve Supinator Origin: Two heads Superficial (humeral) head: Lateral epicondyle of the humerus and the related anular ligament and the radial collateral ligam ent of the elbow joint Deep (ulnar) head: Supinator crest on the posterolateral surface of the ulna Insertion: Lateral surface of the radius superior to the anterior oblique line Action: Supinates the forearm and hand Nerve Supply: Deep branch of the radial nerve Abductor Pollicis Longus Origin: Proximal posterior surfaces of the radius and the ulna and from the related interosseous membrane Insertion: Lateral side of the base of metacarpal I Action: Abducts the thumb at the joint between the metacarpal I and trapezium bones Additional Info: The tendon contributes to the lateral border of the anatomical snuffbox at the wrist Extensor Pollicis Brevis Origin: Distal to the origin of the abductor pollicis longus from the posterior surface of the radius and interosseous membrane Insertion: Dorsal surface of the base of the proximal phalanx Action: Extends the metacarpophalangeal and carpometacarpal joints of the thumb Additional Info: The tendon contributes to the lateral border of the anatomical snuffbox at the wrist Extensor Pollicis Longus Origin: Posterior surface of the ulna and adjacent interosseous membrane Insertion: Dorsal surface of the distal phalanx of the thumb Action: Extends all joints of the thumb Additional Info: The tendon forms the medial margin of the anatomical snuffbox at the wrist Extensor Indicis Origin: Distal to the extensor pollicis longus from the posterior surface of the ulna and adjacent interosseous membrane Insertion: Extensor hood of the index finger with the tendon of the extensor digitorum Action: Accessory extensor of the index finger Anterior &posterior compartment forearm Page 7 Anterior &posterior compartment forearm Page 8 Anterior &posterior compartment forearm Page 9 Anterior &posterior compartment forearm Page 10 Anterior &posterior compartment forearm Page 11 Anterior &posterior compartment forearm Page 12 Anterior &posterior compartment forearm Page 13 Anterior &posterior compartment forearm Page 14 Anterior &posterior compartment forearm Page 15 Anterior &posterior compartment forearm Page 16