Lecture 7 - Anterior and Posterior Compartments of the Forearm PDF

Bones of forearm Radius & Ulna Radius & Ulna  Radius The radius is the lateral bone of the forearm. Its proximal end articulates with the humerus at the elbow joint and with the ulna at the proximal radioulnar joint. Its distal end articulates with the...

Bones of forearm Radius & Ulna Radius & Ulna  Radius The radius is the lateral bone of the forearm. Its proximal end articulates with the humerus at the elbow joint and with the ulna at the proximal radioulnar joint. Its distal end articulates with the scaphoid and lunate bones of the hand at the wrist joint and with the ulna at the distal radioulnar joint. At the proximal end of the radius is the small circular head. The upper surface of the head is concave and articulates with the convex capitulum of the humerus. The circumference of the head articulates with the radial notch of the ulna. Below the head the bone is constricted to form the neck. Below the neck is the bicipital tuberosity (radial) for the insertion of the biceps muscle. The shaft of the radius, is wider below than above. It has a sharp interosseous border medially for the attachment of the interosseous membrane that binds the radius and ulna together. The pronator tubercle, for the insertion of the pronator teres muscle, lies halfway down on its lateral side. At the distal end of the radius is the styloid process; this projects distally from its lateral margin. On the medial surface is the ulnar notch, which articulates with the round head of the ulna. The inferior articular surface articulates with the scaphoid and lunate bones. On the posterior aspect of the distal end is a small tubercle, the dorsal tubercle, which is grooved on its medial side by the tendon of the extensor pollicis longus.  Ulna The ulna is the medial bone of the forearm. Its proximal end articulates with the humerus at the elbow joint and with the head of the radius at the proximal radioulnar joint. Its distal end articulates with the radius at the distal radioulnar joint, but it is excluded from the wrist joint by the articular disc. The proximal end of the ulna is large and is known as the olecranon process; this forms the prominence of the elbow. It has a notch on its anterior surface, the trochlear notch, which articulates with the trochlea of the humerus. Below the trochlear notch is the triangular coronoid process, which has on its lateral surface the radial notch for articulation with the head of the radius. The shaft of the ulna tapers from above down. It has a sharp interosseous border laterally for the attachment of the interosseous membrane. The posterior border is rounded and subcutaneous and can be easily palpated throughout its length. Below the radial notch is the supinator crest that gives origin to the supinator muscle. At the distal end of the ulna is the small rounded head, which has projecting from its medial aspect the styloid process Hand bones  Bones of the hand There are eight carpal bones, made up of two rows of four. The proximal row consists of (from lateral to medial) the scaphoid, lunate, triquetral, and pisiform bones. The distal row consists of (from lateral to medial) the trapezium, trapezoid, capitate, and hamate bones. Together, the bones of the carpus present on their anterior surface a concavity, to the lateral and medial edges of which is attached a strong membranous band called the flexor retinaculum. In this manner, an osteofascial tunnel, the carpal tunnel, is formed for the passage of the median nerve and the flexor tendons of the fingers. There are five metacarpal bones, each of which has a base, a shaft, and a head. There are three phalanges for each of the fingers but only two for the thumb.  Fascial Compartments of the Forearm The forearm is enclosed in a sheath of deep fascia, which is attached to the periosteum of the posterior subcutaneous border of the ulna. This fascial sheath, together with the interosseous membrane and fibrous intermuscular septa, divides the forearm into anterior and posterior compartments, each having its own muscles, nerves, and blood supply. Fascial Compartments of the Forearm  Contents of the Anterior Fascial Compartment of the Forearm (flexors) Muscles: A superficial group, consisting of the pronator teres, the flexor carpi radialis, the palmaris longus, flexor digitorum superficialis and the flexor carpi ulnaris;; and A deep group consisting of the flexor pollicis longus, the flexor digitorum profundus, and the pronator quadratus Blood supply to the muscles: Ulnar and radial arteries Nerve supply to the muscles: All the muscles are supplied by the median nerve and its branches, except the flexor carpi ulnaris and the medial part of the flexor digitorum profundus, which are supplied by the ulnar nerve.  Muscles of the front of the Forearm A. superficial group: from lateral to medial: 1- pronator teres, 2- flexor carpi radialis, 3- palmaris longus 4- flexor digitorum superficialis 5- flexor carpi ulnaris B. deep group 1- flexor pollicis longus, 2- flexor digitorum profundus, 3- pronator quadratus Front of the forearm: Superficial group of muscles Front of the forearm: Deep group of muscles A. superficial group There are 5 muscles arise by common tendon; front of medial epicondyle (common flexor origin). 1. Pronator teres Origin: by two heads: a. The humeral head: from the common flexor origin (in front of the medial epicondyle) and medial supracondylar ridge. b. The ulnar head: from the medial side of the coronoid process of the ulna Insertion: to a rough area (pronator tuberosity) at the middle of lateral surface of shaft of radius. Nerve supply: Median nerve Action: Pronation of forearm. N.B.: The median nerve passes between the 2 heads of 2. Flexor carpi radialis Origin: common flexor origin Insertion: base of second and third metacarpal bones Nerve supply: median nerve Action: flexion and abduction of wrist joint 3. Palmaris longus Origin: common flexor origin Insertion: palmar aponeurosis and flexor retinaculum. Nerve supply: median nerve Action: flexion of hand at wrist superficialis Origin: a- Humero-ulnar head: common flexor origin, coronoid process (medial border) of ulna. b- Radial head: anterior oblique line of radius. Insertion: middle phalanx of medial 4 fingers. Nerve supply: median nerve. Action: 1. Flexion of wrist joint. 2. Flexion of proximal & middle phalanges of medial 4 fingers. N.B.: The median nerve lies behind this muscle (between it and Flexor digitorum 5. Flexor carpi ulnaris Origin: humeral head: medial epicondyle of humerus. ulnar head: medial aspect of olecranon process and posterior border of ulna. Insertion: pisiform bone, hook of the hamate and base of fifth metacarpal bone. Nerve supply: ulnar nerve. Action: Flexes and adducts hand at wrist joint. If acting with flexor carpi radialis, it produces only B. Deep group 1. Flexor pollicis longus Origin: upper 2/3 of anterior surface of radius and interosseous membrane. Insertion: Distal phalanx of thumb. Nerve supply: Anterior interosseous branch of median nerve. Action: Flexes the joints of thumb 2. Flexor digitorum profundus Origin: Anteromedial surface of shaft of ulna and interosseous membrane. Insertion: Distal phalanges of medial four fingers (it pierces the corresponding tendon of superficialis muscle. Nerve supply: Ulnar (medial half) and median (lateral half) nerves. Action: Flexes distal phalanx of fingers; then assists in flexion of middle and proximal phalanges and 3. Pronator quadratus Origin: Anterior surface of shaft of ulna (lower part). Insertion: Anterior surface of shaft of radius (lower part). Nerve supply: Anterior interosseous branch of median nerve. Action: Pronates forearm. Muscles of anterior compartment of the forearm  Contents of the Posterior Fascial Compartment of the Forearm (extensors):  Muscles: A. The superficial group: includes the brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, and anconeus. B- The deep group: includes the supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis.  Blood supply: Posterior and anterior interosseous arteries  Nerve supply to the muscles: radial nerve and its deep branch. The superficial group 1. Brachioradialis Origin: from lateral supracondylar ridge of the humerus. Insertion: on the lateral side of the distal end of the radius just proximal to the radial styloid process (at the base of styloid process of radius). Nerve supply: radial nerve.  Action: Flexes forearm at elbow joint; rotates forearm to the midprone position. In the anatomical position, the brachioradialis is part of the muscle mass overlying the anterolateral surface of the forearm and forms the lateral boundary of the cubital fossa. Because the brachioradialis is anterior to the elbow joint, it acts as an accessory flexor of this joint even though it is in the posterior compartment of the forearm. Its action is most efficient when the forearm is midpronated and it forms a prominent bulge as it acts against resistance. The radial nerve & artery are overlapped by this 2. Extensor carpi radialis longus Origin: from the distal part of the lateral supraepicondylar ridge and the lateral epicondyle of the humerus. Insertion: on the dorsal surface of the base of metacarpal II. Nerve supply: radial nerve. Action: The extensor carpi radialis longus 3. Extensor carpi radialis brevis Origin: front of lateral epicondyle of humerus (common extensor origin). Insertion: Posterior surface of base of third metacarpal bone. Nerve supply: Deep branch of radial nerve (posterior interosseous nerve). Action: Extends and abducts hand at wrist 4. Extensor digitorum Origin: front of lateral epicondyle of humerus (common extensor origin). Insertion: Middle and distal phalanges of medial four fingers (through extensor expansion). Nerve supply: Deep branch of radial nerve (posterior interosseous nerve). Action: 1. Extends metacarpophalangeal & interphalangeal joints of medial four fingers. 2. Helps in extension of the wrist. Extensor expansion The dorsal extensor expansion receives : -the tendon of insertion of the corresponding interosseous muscle on each side - the tendon of the lumbrical muscle on the lateral side. 5. Extensor digiti minimi Origin: Common extensor origin. Insertion: Extensor expansion of little finger. Nerve supply: Deep branch of radial nerve (posterior interosseous nerve). Action: Extends the joints of little finger. 6. Extensor carpi ulnaris Origin: Common extensor origin & post. Border of ulna. Insertion: Base of 5th metacarpal bone. Nerve supply: Deep branch of radial nerve (posterior interosseous nerve). Action: Extends and adducts hand at wrist joint 7. Anconeus Origin: Lateral epicondyle of humerus. Insertion: lateral surface of the olecranon process & upper part of post. Surface of ulna. Nerve supply: Radial nerve. Action: helps in elbow extension. The deep group 8. Supinator Origin:Lateral epicondyle of humerus (superficial part), supinator crest and fossa of ulna (deep part). Insertion: upper part of lateral surface of radius (neck and shaft). Nerve supply: : Deep branch of radial nerve (posterior interosseous nerve). Action: Supination of forearm. 9. Abductor pollicis longus Origin: Posterior surface of shafts of radius (below supinator) and ulna (below anconeus) and interosseous membrane. Insertion:Base of first metacarpal bone Nerve supply: : Deep branch of radial nerve (posterior interosseous nerve). Action: Abducts and extends thumb. 10. Extensor pollicis brevis Origin: Posterior surface of shaft of radius (below abductor pollicis longus) & interosseous membrane. Insertion: Base of proximal phalanx of thumb. Nerve supply: Deep branch of radial nerve (posterior interosseous nerve). Action: Extends metacarpophalangeal joints (distal phaanx) of thumb 11. Extensor pollicis longus Origin: Posterior surface of shaft of ulna (middle third) & interosseous membrane. Insertion: Base of distal phalanx of thumb. Nerve supply: Deep branch of radial nerve (posterior interosseous nerve). Action: Extends distal phalanx of thumb. 12. Extensor indices Origin: Posterior surface of shaft of ulna (lower part). Insertion: Extensor expansion of index finger. Nerve supply: Deep branch of radial nerve (posterior interosseous nerve). Action:Extends metacarpophalangeal joint of index finger. Tennis Elbow: Tennis elbow is caused by a partial tearing or degeneration of the origin of the superficial extensor muscles from the lateral epicondyle of the humerus. Tennis Elbow:  It is characterized by pain and tenderness over the lateral epicondyle of the humerus, with pain radiating down the lateral side of the forearm.  It is common in sports which involve using forearm extensors as tennis, swimming and basketball).  Choose the correct answer: 1- The muscle supplied by the ulnar nerve in the forearm: A. Flexor carpi radialis. B. Flexor carpi ulnaris. C. Extensor carpi radialis. D. Extensor carpi ulnaris. 2- The muscle takes origin from lateral epicondyle of humerus: A. Anconeus. B. Palmaris longus. C. Pronator teres. D. Flexor carpi ulnaris. 3- The muscle Inserted into distal end of radius is: A. Extensor carpi ulnaris. B. Flexor digitorum superficialis. C. Flexor digitorum profundus. D. Brachioradialis.  Choose the correct answer: 4- Regarding pronator teres which of the following statement is correct? A. It forms the lateral border of the cubital fossa. B. It arises from the coronoid process and lateral epicondyle. C. The Median nerve passes deep to both heads. D. It is the most lateral of the superficial flexors of the forearm. 5- The following are true about flexor carpi radialis EXCEPT: A. it arises from the common flexor origin at the humerus. B. Palmaris longus lies medially. C. It is supplied by the median nerve. D. It inserts into the base of the 2nd and 3rd metacarpals. 6- Which muscle arises from both the radius and ulna: A. extensor pollicis longus. B. extensor pollicis brevis. C. abductor pollicis longus. D. extensor indicis.