Forearm Flashcards
The anterior interosseous is a branch of which nerve?
The anterior interosseous nerve is a branch of the median nerve that provides motor innervation to the deep muscles in the flexor compartment, including flexor pollicis longus, the radial half of flexor digitorum profundus, and pronator quadratus. The other related nerve to think about is the posterior interosseous nerve, which is the terminal branch of the deep radial nerve. It provides sensory innervation to the wrist area.
What muscle is innervated by branches of both the median and ulnar nerves?
The median and ulnar nerve both innervate flexor digitorum profundus. Flexor carpi ulnaris is innervated by the ulnar nerve only. Flexor digitorum superficialis and flexor pollicis longus are innervated by the median nerve. Pronator quadratus is innervated by the anterior interosseus nerve, which is a branch of the median nerve.
What muscle is innervated by branches of both the median and ulnar nerves?
The median and ulnar nerve both innervate flexor digitorum profundus. Flexor carpi ulnaris is innervated by the ulnar nerve only. Flexor digitorum superficialis and flexor pollicis longus are innervated by the median nerve. Pronator quadratus is innervated by the anterior interosseus nerve, which is a branch of the median nerve.
Interruption of the median nerve in the cubital fossa affects what movement(s) of the thumb?
The recurrent branch of the median nerve innervates the thenar compartment of the hand. This nerve innervates opponens pollicis, which opposes the thumb, and flexor pollicis brevis, which helps to flex the thumb. So, disrupting the median nerve would impair both flexion and opposition of the thumb.
Compression of the median nerve in the carpal tunnel affects which hand muscle(s)?
Flexor pollicis brevis
Structures within the carpal tunnel include the:
The radial bursa and ulnar bursa are both found in the carpal tunnel. These bursae are complex synovial coverings that protect the flexor tendons. The carpal tunnel is formed where the flexor retinaculum spans from the scaphoid and trapezium to the hamate and pisiform, deep and slightly distal to the palmar carpal ligament. This creates a canal that covers the flexor digitorum superficialis tendons, the flexor digitorum profundus tendons, the tendon of flexor pollicis longus, and the median nerve. These tendons in the carpal tunnel are covered by the ulnar and radial bursae. The flexor digitorum superficialis and flexor digitorum profundus tendons are covered by the ulnar bursa, and the tendon of flexor pollicis longus is covered by the radial bursa. So, both bursae are in the carpal tunnel.
You suspect a localized tearing of the origin of a muscle producing the equivalent of “tennis elbow.
Tennis elbow is usually caused by inflammation of the common extensor tendon on the lateral side of the forearm, but we know that that’s not what happened here. Instead, the patient tore a muscle at its origin, near the lateral epicondyle of the humerus. Brachioradialis originates from the upper two-thirds of the lateral supracondylar ridge of the humerus, so this is the muscle that she probably tore. This also makes sense given her activities–brachioradialis flexes the elbow and assists in pronation and supination, so she would have been using this muscle while gardening.
The common flexor tendon is associated with the medial epicondyle, not the lateral epicondyle. Extensor carpi radialis brevis and extensor digitorum take origin from the common extensor tendon, which attaches to the lateral epicondyle. This tendon would be inflamed in a classic case of tennis elbow, but the common extensor tendon is not the structure that was injured in this patient’s case. Pronator teres takes origin from the common flexor tendon and the medial side of the ulna.
The injury has avulsed (torn away from the bone) which structure from her distal phalanx to produce this condition?
The extensor expansions are the expanded distal ends of the extensor tendons which wrap around the heads of the metacarpals and the bases of the proximal phalanges and insert on the bases of the middle and distal phalanges. These extensor expansions hold the extensor tendon in the middle of the digit and provide a place for the lumbricals and interossei to attach. If an extensor expansion was torn, the extensor tendon would not be held in place and a lumbrical would be torn from its attachment. This would impair extension at the joint.
Extensor carpi radialis brevis and longus are involved with extending the wrist and abducting the hand. These muscles do not produce extension at the fingers. Extensor digiti minimi and extensor indicis help with extension at the 5th and 2nd finger, but they do not act at the third finger.
The function of the posterior interosseous nerve is
sensory from the wrist joint
Development of “tennis elbow” (lateral epicondylitis) involves the origin of which muscle?
Extensor carpi radialis brevis
When falling on an outstretched hand, the most commonly dislocated carpal bone is the
LUNATEIt is fairly common for the lunate to be dislocated anteriorly–this injury may result from a fall on an extended wrist. The lunate may be pushed out of its place on the floor of the carpal tunnel and move toward the palm of the wrist. This dislocation may compress the median nerve and lead to carpal tunnel syndrome. Also remember: scaphoid, the lateral bone in the proximal row of carpals, is frequently fractured when someone falls on an outstretched wrist! Capitate, hamate, and trapezoid are not commonly injured in these falls.
Colles’ fracture.
The Colles’ fracture is a fracture to the distal end of the radius. It usually occurs when someone tries to catch themselves from falling on an outstretched arm. So, you need to look in the answer choices for a muscle that inserts on the distal end of the radius. Brachioradialis inserts on the lateral side of the base of the styloid process of the radius, so this muscle could pull the broken piece of the radius out of place. This is why a cast over a Colles’ fracture needs to extend up to the elbow–brachioradialis needs to be immobilized!
Extensor carpi ulnaris inserts on the medial side of the base of the 5th metacarpal. Extensor carpi radialis longus inserts on the dorsum of the second metacarpal bone. Pronator quadratus extends between the distal ulna and radius– it serves to pronate the hand. Although this muscle attaches to the broken part of the radius, it is not the most important muscle to stabilize following the injury. Extensor carpi radialis brevis inserts on the dorsum of the third metacarpal bone. So, none of the other muscles would pull on the distal piece of the radius as much as brachioradialis.
If the tendon of palmaris longus were transected, what movement would be affected?
Palmaris longus is a small muscle in the anterior compartment of the arm–it flexes the hand at the wrist and tightens the palmar aponeurosis. If this tendon was cut, it would be more difficult to flex the wrist. Flexor pollicis longus flexes the MP and IP joints of the thumb. Flexor digitorum profundus and superficialis flex the proximal IP joints of digits 2, 3, 4, and 5. Extensor carpi ulnaris, extensor carpi radialis longus and extensor carpi radialis brevis all extend the wrist.
The pulse of the radial artery at the wrist is felt immediately lateral to which tendon?
The radial artery runs on the radial side of the wrist, lateral to the tendon of flexor carpi radialis. So, the radial pulse will be felt immediately lateral to this tendon. Remember–the radial artery enters the wrist on the anterior side. This means that the extensor tendons, which are on the posterior side of the wrist, will not be involved with the radial artery! The tendons for flexor digitorum profundus and superficialis are found more towards the center of the wrist, not on the wrist’s lateral side. These tendons cross under the flexor retinaculum to reach the hand.
If the medial epicondyle of the humerus is fractured and the nerve passing dorsal to it is injured, which muscle would be most affected?
The nerve passing dorsal to the medial epicondyle of the humerus is the ulnar nerve. In the forearm, the ulnar nerve innervates flexor carpi ulnaris and the ulnar side of flexor digitorum profundus. So, flexor carpi ulnaris would be most affected if the ulnar nerve was disrupted. What other symptoms might you see? Paralysis of hand muscles (except for the thenar compartment and the first two lumbricals) and numbness over the ulnar 1.5 digits in the hand!
The extensor muscles (extensor digitorum and extensor carpi ulnaris) are in the posterior compartment of the forearm–they are innervated by the radial nerve. Flexor digitorum superficialis is innervated by the median nerve only. Although the ulnar side of flexor digitorum profundus would be impaired following the injury, the radial side of flexor digitorum profundus would still be innervated by the median nerve.
