Muscles and Innervation of the Forearm PDF

Department of Radiology and Ultrasound Ibn Khaldun Private University College Muscles and Innervation of the Forearm Dr. Mohanad Mohammed Lec. 6 Ahmed ...

Department of Radiology and Ultrasound Ibn Khaldun Private University College Muscles and Innervation of the Forearm Dr. Mohanad Mohammed Lec. 6 Ahmed  Term of Movement Flexion: Decreasing the angle between two body parts. Extension: Increasing the angle between two body parts. Abduction: Moving a body part away from the midline of the body. Adduction: Moving a body part toward the midline of the body. Pronation: Turning the palm downward. Supination: Turning the palm upward.  Muscles Anatomy of the Forearm, Wrist And Hand 1- Muscles in the Anterior Compartment of the Forearm. The muscles in the anterior compartment of the forearm are organised into three layers: A- Superficial Compartment: flexor carpi ulnaris, palmaris longus, flexor carpi radialis, pronator teres. B- Intermediate Compartment : flexor digitorum superficialis. C- Deep Compartment : flexor pollicis longus, flexor digitorum profundus and pronator quadratus.  A- Superficial Compartment They all originate from a common tendon, which arises from the medial epicondyle of the humerus. 1- Flexor Carpi Ulnaris Attachments: The flexor carpi ulnaris has two origins. The humeral head originates from the medial epicondyle of the humerus with the other superficial flexors, whilst the ulnar head originates from the olecranon of the ulna. The muscle tendon passes into the wrist and attaches to the pisiform bone, hook of hamate, and base of the 5th metacarpal Actions: Flexion and adduction at the wrist. 2- Palmaris Longus This muscle is absent in about 15% of the population. Attachments: Originates from the medial epicondyle, attaches to the flexor retinaculum of the wrist. Actions: Flexion at the wrist. Innervation: Median nerve. 3- Flexor Carpi Radialis Attachments: Originates from the medial epicondyle, attaches to the base of metacarpals II and III. Actions: Flexion and abduction at the wrist. Innervation: Median nerve. 4- Pronator Teres Attachments: It has two origins, one from the medial epicondyle, and the other from the coronoid process of the ulna. It attaches laterally to the mid- shaft of the radius. Actions: Pronation of the forearm. Innervation: Median nerve.  B- Intermediate Compartment The Flexor digitorum superficialis is the only muscle of the intermediate compartment. Attachments: It has two heads – one originates from the medial epicondyle of the humerus, the other from the radius. The muscle splits into four tendons at the wrist, which travel through the carpal tunnel, and attach to the base of the middle phalanx of the four digits. Actions: Flexes the metacarpophalangeal joints and proximal interphalangeal joints at the 4 fingers, and flexes at the wrist. C- Deep Compartment There are three muscles in the deep anterior forearm: 1- flexor digitorum profundus 2- flexor pollicis longus 3- pronator quadratus. 1- Flexor Digitorum Profundus Attachments: Originates from the ulna and associated interosseous membrane. At the wrist, it splits into four tendons, that pass through the carpal tunnel and attach to the distal phalanges of the four fingers. Actions: It is the only muscle that can flex the distal interphalangeal joints of the fingers. It also flexes at metacarpophalangeal joints and at the wrist. Innervation: The medial half (acts on the little and ring fingers) is innervated by the ulnar nerve. The lateral half (acts on the middle and index fingers) is innervated by the 2- Flexor Pollicis Longus This muscle lies laterally to the flexor digitorum profundus Attachments: Originates from the anterior surface of the radius and surrounding interosseous membrane. Attaches to the base of the distal phalanx of the thumb. Actions: Flexes the interphalangeal joint and metacarpophalangeal joint of the thumb. Innervation: Median nerve (anterior interosseous branch). 3- Pronator Quadratus A square shaped muscle found deep to the tendons of the flexor digitorum profundus and flexor pollicis longus. Attachments: Originates from the anterior surface of the ulna and attaches to the anterior surface of the radius. Actions: Pronates the forearm. Innervation: Median nerve (anterior interosseous branch).  2- Muscles in the Posterior Compartment of the Forearm The muscles in the posterior compartment of the forearm are commonly known as the extensor muscles. The general function of these muscles is to produce extension at the wrist and fingers. They are all innervated by the radial nerve. The muscles in this compartment are organised into two layers; deep and superficial. These two layers are separated by a layer of fascia. A- Superficial Muscles The superficial layer of the posterior forearm contains seven muscles. Four of these muscles (extensor carpi radialis brevis, extensor digitorum, extensor carpi ulnaris and extensor digiti minimi) share a common tendinous origin at the lateral epicondyle 1- Brachioradiali s Attachments: Originates from the proximal aspect of the lateral supracondylar ridge of humerus, and attaches to the distal end of the radius, just before the radial styloid process. Actions: Flexes at the elbow. Contributes to supination at the proximal radioulnar joint.  2- Extensor Carpi Radialis Longus and Brevis The extensor carpi radialis muscles are situated on the lateral aspect of the posterior forearm. Due to their position, they are able to produce abduction as well as extension at the wrist. Attachments: The ECRL originates from the lateral supracondylar ridge of the humerus, while the ECRB originates from the lateral epicondyle. Their tendons attach to metacarpal bones II and III. Actions: Extends and abducts the wrist. 3- Extensor Digitorum Communis The extensor digitorum is the main extensor of the fingers. To test the function of the muscle, the forearm is pronated, and the fingers extended against resistance. Attachments: Originates from the lateral epicondyle. The tendon continues into in the distal part of the forearm, where it splits into four, and inserts into the extensor hood of each finger. Actions: Extension of the digits at the interphalangeal and 4- Extensor Digiti Minimi The extensor digiti minimi is thought to originate from the extensor digitorum muscle. In some people, these two muscles are fused together. Anatomically, the extensor digiti minimi lies medially to the extensor digitorum. Attachments: Originates from the lateral epicondyle of the humerus. It attaches, with the extensor digitorum tendon, into the extensor hood of the little finger. Actions: Extends the little finger, and contributes to extension at the wrist. 5- Extensor Carpi Ulnaris The extensor carpi ulnaris is located on the medial aspect of the posterior forearm. Due to its position, it is able to produce adduction as well as extension at the wrist. Attachments: Originates from the lateral epicondyle of the humerus, and attaches to the base of metacarpal V. Actions: Extension and adduction of wrist. 6- Anconeus The anconeus is situated medially and proximally in the extensor compartment of the forearm. It is blended with the fibres of the triceps brachii, and the two muscles can be indistinguishable. Attachments: Originates from the lateral epicondyle, and attaches to the posterior and lateral part of the olecranon. Actions: Extends and stabilises the elbow joint. Abducts the ulna during pronation of the forearm. Cross section of the muscles of the distal forearm. Some extensor muscles, such as the anconeus, are not visible as they are situated proximally in the forearm. Dissection of the Superficial Muscles of the Posterior Forearm B- Deep Muscles There are five muscles in the deep compartment of the posterior forearm: 1- Supinator 2- Abductor pollicis longus 3- Extensor pollicis brevis 4- Extensor pollicis longus 5- Extensor indicis. With the exception of the supinator, these muscles act on the thumb and the 1- Supinator The supinator lies in the floor of the cubital fossa. It has two heads, which the deep branch of the radial nerve passes between. Attachments: It has two heads of origin. One originates from the lateral epicondyle of the humerus, the other from the posterior surface of the ulna. They insert together into the posterior surface of the radius.  2- Abductor Pollicis Longus The abductor pollicis longus is situated immediately distal to the supinator muscle. In the hand, its tendon contributes to the lateral border of the anatomical snuffbox. Attachments: Originates from the interosseous membrane and the adjacent posterior surfaces of the radius and ulna. It attaches to the lateral side of the base of metacarpal I. Actions: Abducts the thumb. Innervation: Radial nerve (posterior interosseous branch). 3- Extensor Pollicis Brevis The extensor pollicis brevis can be found medially and deep to the abductor pollicis longus. In the hand, its tendon contributes to the lateral border of the anatomical snuffbox. Attachments: Originates from the posterior surface of the radius and interosseous membrane. It attaches to the base of the proximal phalanx of the thumb. Actions: Extends at the metacarpophalangeal and carpometacarpal joints of the thumb. 4- Extensor Pollicis Longus The extensor pollicis longus muscle has a larger muscle belly than the EPB. Its tendon travels medially to the dorsal tubercle at the wrist, using the tubercle as a ‘pulley’ to increase the force exerted. The tendon of the extensor pollicis longus forms the medial border of the anatomical snuffbox in the hand. Attachments: Originates from the posterior surface of the ulna and interosseous membrane. It attaches to the distal phalanx of the thumb. Actions: Extends all joints of the thumb: carpometacarpal, metacarpophalangeal and interphalangeal. 5- Extensor Indicis This muscle allows the index finger to be independent of the other fingers during extension. Attachments: Originates from the posterior surface of the ulna and interosseous membrane, distal to the extensor pollicis longus. Attaches to the extensor hood of the index finger. Actions: Extends the index finger. Innervation: Radial nerve (posterior THANK YOU