2. Fracture of Which Bone May Cause Paralysis of the Flexor Digiti Minimi and Opponens Digiti Minimi Muscles? (See Im- Age Below)

Lab 4—Forearm & Hand Skeletal—Questions 1 of 2

1. Which bone articulates with the radius and triquetrum? (See image below).

2. Fracture of which bone may cause paralysis of the flexor digiti minimi and opponens digiti minimi muscles? (See image below).

3. Which is the site of attachment of the muscles that form the thenar eminence? (See image below).

4. Which is the site of tendinous attachment of the flexor digitorum superficialis? (See image below).

5. Fracture of which bone may cause a deep tenderness in the anatomic snuffbox? (See image below).

1 Lab 4—Forearm & Hand Skeletal—Questions

1. Answer B. (1) The Innate bone articulates with the radius and triquetrum.

2. Answer C. (1) The hook of the hamate provides attachment for the flexor digiti minimi brevis and opponens digiti minimi muscles. Therefore, its fracture may cause paralysis of these muscles.

3. Answer E. (1) The base of the proximal phalanx of the thumb is the site of attachment for the flexor pollicis brevis, which, along with the opponens pollicis, form the thenar eminence. It is also the site of attachment for the adductor pollicis brevis.

4. Answer D. (1) The middle phalanx of the ring finger is the site of attachment for the flexor digitorum superficialis.

5. Answer A. (1) The scaphoid bone forms the floor of the anatomic snuff box and its fracture may cause a deep tenderness. When fractured, the proximal fragment may undergo avascular necrosis because the blood supply is inter- rupted.

2 Lab 4—Forearm & Hand Skeletal—Questions 2 of 2

6. A 24-year-old male slips on a banana peel and falls 9. If the floor of the anatomic snuffbox and origin of the onto his outstretched hand. Which of the following struc- abductor pollicis brevis are damaged, which of the follow- tures transmits the force from the radius to the ulna? ing bones is most likely to be involved? A. Triangular fibrocartilage B. Interosseous membrane A. A C. Scaphoid bone B. B D. Ulnar collateral ligament C. C E. Radial collateral ligament D. D E. E

7. Destruction of the structure indicated by the letter E 10. A man pushes a piano across the floor. At the wrist, most likely causes weakness of which of the following the force is transmitted from the carpal bones to the radi- muscles? (See image below). us. At the elbow, the force is transmitted from the ulna to A. Flexor carpi radialis the humerus. Which of the following structures transmits B. Palmaris longus the force from the radius to the ulna? C. Flexor carpi ulnaris A. Annular ligament D. Brachioradialis B. Bicipital aponeurosis E. Flexor digitorum superficialis C. Flexor retinaculum D. Intermuscular septum E. Interosseous membrane

7. 11. When examining muscle function at the metacarpophalangeal (MP), proximal interphalangeal (PIP), and distal interphalangeal (DIP) joints, what findings do you expect in the presence of radial nerve palsy? A. Inability to abduct the digits at the MP joint B. Inability to adduct the digits at the MP joint C. Inability to extend the MP joint only D. Inability to extend the MP, PIP, and DIP joints E. Inability to extend the PIP and DIP joints

8. The victim of an automobile accident has a destructive injury of the proximal row of carpal bones. Which of the following bones is most likely damaged? A. Capitate B. Hamate C. Trapezium D. Triquetrum E. Trapezoid

3 Lab 4—Forearm & Hand Skeletal—Questions

6. Answer B. (11) The interosseous membrane con- 9. Answer B. (1) The scaphoid forms the floor of the ducts force from the radius to the ulna when the force anatomic snuffbox and provides a site for origin of the originates from the wrist. abductor pollicis brevis.

7. Answer C. (1) The hook of hamate and the pisiform 10. Answer E. (3) The interosseous membrane (E) is a provide insertion for the flexor carpi ulnaris. fibrous sheet between the radius and ulna, forming the radio-ulnar syndesmosis. It divides the forearm into anterior and posterior compartments, and transmits force from the radius to the ulna.

11. Answer C. (7) Radial nerve palsy produces an inability to extend the metacarpophalangeal joints, owing to paralysis of the extensor digitorum communis muscle. However, the lumbrical and interossei muscles, which are served by the median and ulnar nerves and insert into the dorsal expansions (extensor hoods) of the proximal phalanges, are able simultaneously to flex the metacarpophalangeal joints and to extend the interphalangeal joints [thus not (answers d and e)]. Also, abduction of the digits, a function of the dorsal interossei, and adduction, a function of the palmar interossei, are both mediated by the ulnar nerve and, therefore, unaffected [thus not (answers a and b)].

8. Answer D. (1) The proximal row of carpal bones consists of the scaphoid, lunate, triquetrum, and pisiform bones, whereas the distal row consists of the trapezium, trapezoid, capitate, and hamate bones.

4 Lab 4—Forearm & Hand Muscles; Tendons — Questions 1 of 3

1. A 23-year-old woman who receives a deep cut to her 5. A 21-year-old man injures his right arm in an automo- ring finger by a kitchen knife is unable to move the meta- bile accident. Radiographic examination reveals a fracture carpophalangeal joint. Which of the following pairs of of the medial epicondyle of the humerus. nerves was damaged? After this injury, the patient is unable to do which of the A. Median and ulnar following? B. Radial and median C. Musculocutaneous and ulnar A. Flex the proximal interphalangeal joint of his ring finger D. Ulnar and radial B. Flex the DIP joint of his index finger E. Radial and axillary C. Feel sensation on his middle finger D. Abduct his thumb E. Adduct his index finger

2. A 16-year-old patient has weakness flexing the meta- 6. A 22-year-old man fell off his bicycle and fractured the carpophalangeal joint of the ring finger and is unable to medial epicondyle of the humerus. The physician must adduct the same finger. Which of the following muscles is determine the integrity of the ulnar nerve. Which pair of most likely paralyzed? muscles would allow the patient to hold a dollar bill be- A. Flexor digitorum profundus tween the fingers against resistance? B. Extensor digitorum A. Abductor digiti minimi–dorsal interossei C. Lumbrical B. Adductor pollicis–lumbricals D. Dorsal interosseous C. Dorsal interossei–palmar interossei E. Palmar interosseous D. Lumbricals–palmar interossei

3. A patient comes in complaining that she cannot flex her 7. A patient develops a significant clawing of the fourth proximal interphalangeal joints. Which of the following and fifth digits secondary to nerve injury. Which muscle muscles appear(s) to be paralyzed on further examination has been weakened and therefore results in the clawing? of her finger? A. Extensor digitorum A. Palmar interossei B. Lumbrical B. Dorsal interossei C. Flexor digitorum superficialis C. Flexor digitorum profundus D. Dorsal interosseous D. Flexor digitorum superficialis E. Flex or digiti minimi E. Lumbricals

4. A patient with Bennett’s fracture (a fracture of the base 8. A man who uses hand tools for a living begins to devel- of the first metacarpal bone) experiences an impaired op pain and paresthesia in his right hand at night. The thumb movement. Which of the following intrinsic muscles altered sensation is most evident on the palmar aspects of the thumb is most likely injured? of the index and middle fingers. What else are you most A. Abductor pollicis brevis likely to see in this patient? B. Flexor pollicis brevis (superficial head) A. Atrophy of the thenar eminence C. Opponens pollicis B. Weakness in extension of the thumb D. Adductor pollicis C. Radial deviation of the hand at the wrist during wrist E. Flexor pollicis brevis (deep head) flexion D. Altered sensation in skin over the anatomic snuffbox E. Inability to spread the fingers

5 Lab 4—Forearm & Hand Muscles; Tendons — Answers

1. Answer D. (1) The metacarpophalangeal joint of the 5. Answer E. (1) The fingers are adducted by the pal- ring finger is flexed by the lumbrical, palmar, and dorsal mar interosseous muscles; abduction is performed by the interosseous muscles, which are innervated by the ulnar dorsal interosseous muscles. The palmar and dorsal in- nerve. The extensor digitorum, which is innervated by the terosseous muscles are innervated by the ulnar nerve. radial nerve, extends this joint. The musculocutaneous The proximal interphalangeal joints are flexed by the flex- and axillary nerves do not supply muscles of the hand. or digitorum superficialis, which is innervated by the medi- The median nerve supplies the lateral two lumbricals, an nerve. However, the DIP joints of the index and middle which can flex metacarpophalangeal joints of the index fingers are flexed by the flexor digitorum profundus, which and middle fingers. is innervated by the median nerve (except the medial half of the muscle, which is innervated by the ulnar nerve). The median nerve supplies sensory innervation on the palmar aspect of the middle finger. The abductor pollicis brevis is innervated by the median nerve; the abductor pollicis longus is innervated by the radial nerve.

2. Answer E. (1) The dorsal and palmar interosseous 6. Answer C. (8) To hold a dollar bill between any two and lumbrical muscles can flex the metacarpophalangeal adjacent digits (2 and 5), one digit must abduct, while the joints and extend the interphalangeal joints. The palmar adjacent digit must adduct to press against its neighbor. interosseous muscles adduct the fingers, while the dorsal The palmar interossei, which insert into the proximal pha- interosseous muscles abduct the fingers. The flexor digi- langes on the ulnar side of the index finger and the radial torum profundus flexes the distal interphalangeal (DIP) sides of the ring and little fingers, adduct digits 2, 4, and 5 joints. (PAD = palmar adduct). The dorsal interossei, which insert into the proximal phalanges on the radial side of the index finger, on both sides of the middle finger, and on the ulnar side of the ring finger, abduct digits 2 and 4 (DAB = dorsal abduct). The thumb and the fifth digit each has its own abductor. The ulnar nerve innervates all interossei via its deep branch.

3. Answer D. (1) The flexor digitorum superficialis 7. Answer B. (9) Loss of the medial two lumbrical muscle flexes the proximal interphalangeal joints. The muscles innervated by the ulnar nerve is the main reason flexor digitorum profundus muscle flexes the DIP joints. for the clawing of digits 4 and 5. Lumbricals produce flex- The palmar and dorsal interossei and lumbricals can flex ion at the metacarpophalangeal joints and extension at metacarpophalangeal joints and extend the interphalan- the interphalangeal joints; clawing results in extension at geal joints. The palmar interossei adduct the fingers, and the metacarpophalangeal joints and flexion at the inter- the dorsal interossei abduct the fingers. phalangeal joints.

4. Answer C. (1) The opponens pollicis inserts on the 8. Answer A. (6) The man most likely has carpal tun- first metacarpal. All other intrinsic muscles of the thumb, nel syndrome affecting the median nerve. In addition to including the abductor pollicis brevis, the flexor pollicis altered sensation over the palmar aspects of the lateral brevis, and the adductor pollicis muscles, insert on the digits, median nerve compression may result in a loss of proximal phalanges. opposition due to atrophy of muscles in the thenar eminence.

6 Lab 4—Forearm & Hand Muscles; Tendons — Questions 2 of 3

9. A 19-year-old construction worker sustains a superficial 13. A 27-year-old man with cubital tunnel syndrome com- laceration of the anterior wrist just proximal to the thenar plains of numbness and tingling in the ring and little finger and hypothenar eminences. Sensation is intact. Which and back and sides of his hand because of damage to a of these tendons has most likely been severed? nerve in the tunnel at the elbow. Which of the following A. Extensor carpi ulnaris muscles is most likely to be paralyzed? B. Flexor digitorum profundus A. Flexor digitorum superficialis C. Flexor digitorum superficialis B. Opponens pollicis D. Flexor pollicis longus C. Two medial lumbricals E. Palmaris longus D. Pronator teres E. Supinator

10. A 55-year-old history professor had been experiencing 14. Wrist-drop results in a very weak hand grasp. This is why self increasing pain in his right hand over the last few months. -defense classes teach you to flex the wrist of an attacker hold- Additionally, he noticed that he was losing strength in his ing an object to loosen their grip on an object. The strength of the thumb. Finally, convinced by his wife to see a doctor, he grasp is greatest with the wrist in the extended position for which asked the physician if his pain might have anything to do of the following reasons? with extensive typing on his computer. The doctor ordered x A. Flexor digitorum superficialis and profundus muscles are stretched when the wrist and metacarpophalangeal joints are -rays and an MRI-scan. After careful analysis of the radio- extended logical results, his doctor referred the man to an orthopedic B. Lever arms of the interossei are longer when the metacar- specialist. The patient MOST likely suffers from which of the pophalangeal joints are extended following conditions? C. Lever arms of the lumbrical muscles are longer when the met- A. Dupuytren contracture acarpophalangeal joints are extended B. carpal tunnel syndrome D. Line of action of the extensor digitorum muscle is most direct C. Erb palsy in full extension D. pronator syndrome E. Radial half of the flexor digitorum profundus muscle is para- E. wrist drop lyzed because it is innervated by the radial nerve

11. A 45-year-old plumber presented in the clinic com- 15. A 45-year-old plumber presented in the clinic complaining of longstanding pain in the elbow. Subsequent plaining of longstanding pain in the elbow. Subsequent examination revealed normal flexion/ extension at both examination revealed normal flexion/ extension at both the elbow and the wrist, but weakened abduction of the the elbow and the wrist but weakened abduction of the thumb and extension at the metacarpophalangeal joints of thumb and extension at the metacarpophalangeal joints of the fingers. Those symptoms were found to be caused by the fingers. These symptoms were found to be caused by entrapment of the posterior interosseus nerve. Which of entrapment of the posterior interosseus nerve. Which of the following muscles could itself cause entrapment of the the following muscles could be expected to demonstrate posterior interosseus nerve? normal contraction? A. Extensor carpi ulnaris A. Extensor indices B. Extensor indices B. Extensor digitorum C. Anconeus C. Extensor carpi radialis longus D. Extensor digitorum D. Abductor pollicis longus E. Supinator E. Extensor digit minimi

12. A 27-year-old pianist with a known carpal tunnel syn- 16. A 16-year-old girl is brought to the emergency depart- drome experiences difficulty in finger movements. Which ment after attempting suicide by cutting her wrist. The of the following intrinsic muscles of her hand is para- deepest part of the wound is between the tendons of the lyzed? flexor carpi radialis and the flexor digitorum superficialis. A. Palmar interossei and adductor pollicis This patient is most likely to have a deficit of which of the B. Dorsal interossei and lateral two lumbricals following? C. Lateral two lumbricals and opponens Pollicis A. Adduction and abduction of the fingers D. Abductor pollicis brevis and palmar interossei B. Extension of the index finger E. Medial two and lateral two lumbricals C. Flexion of the ring and small fingers D. Sensation over the base of the small finger E. Opposition of the thumb and other fingers

7 Lab 4—Forearm & Hand Muscles; Tendons — Answers

9. Answer E. (3) The most superficial of the above 13. Answer C. (1) The ulnar nerve innervates the two tendons is the palmaris longus (E). The extensor carpi medial lumbricals. However, the median nerve innervates ulnaris A. is not on the anterior wrist. The flexor digitorum the two lateral lumbricals, the flexor digitorum superficial- profundus B., flexor digitorum superficialis (C), and flexor is, the opponens pollicis, and the pronator teres muscles. pollicis longus (D) tendons are all in the carpal tunnel, and are thus covered by the flexor retinaculum, whereas the palmaris longus is not.

10. Answer B. (2) This patient likely suffers from car- 14. Answer A. (7) Muscles are most powerful (disregarding pal tunnel syndrome, in which repetitive stresses placed leverage factors) when stretched by extension of the joint(s) on the tendons crossing the wrist can produce inflamma- over which they pass, because this places the sarcomeres at tion in the carpal tunnel, leading to compression of the the optimum tension-producing length in the length-tension rela- tionship. Thus, hand grasp is strongest when the wrist joint and median nerve. Because the median nerve supplies the metacarpophalangeal joints are extended, which stretches the muscles of the thenar eminence, carpal tunnel syndrome digitorum superficialis and profundus flexors to their optimum is characterized by atrophy of these muscles. In particu- position [thus not (answer d)]. Paralysis of the radial nerve with lar, atrophy of flexor pollicis brevis will result in weakened subsequent wrist-drop will weaken hand grasp because the ex- flexion of the thumb. trinsic flexor muscles are compelled to operate in a nonoptimum region. The lever arms of the lumbricals (answer c) and interossei (answer b) are greatest when the metacarpophalangeal joints are flexed, a consideration that does not apply to the patient presented in the question. The median nerve innervates the radial side of the flexor digitorum profundus [the (answer e) is irrelevant to the question].

11. Answer E. (7) Each of the muscles listed (answers 15. Answer C. (9) All of the muscles listed are inner- a, b, c, and d) above is innervated by the deep branch of vated by the posterior interosseus branch of the radial the radial nerve or its terminal portion, the posterior inter- nerve (the terminal part of the deep radial nerve). Exten- osseus nerve. The deep radial nerve passes between the sor carpi radialis longus, however, is innervated by a deep and superficial layers of the supinator muscle and muscular branch of the radial nerve proximal to the origin lies on a bare area of the radius where it may be com- of the deep branch. Its function would, therefore, be pre- pressed by action of the supinator or damaged by a frac- served in entrapment of the posterior interosseus nerve. ture of the radius.

12. Answer C. (1) The median nerve innervates the abductor 16. Answer E. (3) Opposition of the thumb and other pollicis brevis, opponens pollicis, and two lateral lumbricals. The fingers involves flexion of the flexor carpi radialis (FCR) ulnar nerve innervates all interossei (palmar and dorsal), the and flexor digitorum superficialis (FDS), both innervated adductor pollicis, and the two medial lumbricals. by the median nerve.

The FDS muscle in the forearm gives rise to 4 tendons that pass through the flexor retinaculum of the carpal tunnel and insert at the proximal interphalangeal joints. (So, it's an extrinsic muscle of the hand.) The FCR muscle passes a tendon just lateral to the FC- ulnaris tendon, and inserts at the base of the 2nd metacarpal.

8 Lab 4—Forearm & Hand Muscles; Tendons —Questions 3 of 3

17. An automobile body shop worker has his middle finger crushed while working on a transmission. Which of the following muscles is most likely to retain function? A. Extensor digitorum B. Flexor digitorum profundus C. Palmar interosseous D. Dorsal interosseous E. Lumbrical

18. A 27-year-old baseball player is hit on his forearm by a high-speed ball during the World Series, and the muscles that form the floor of the cubital fossa appear to be torn. Which of the following groups of muscles have lost their functions? A. Brachioradialis and supinator B. Brachialis and supinator C. Pronator teres and supinator D. Supinator and pronator quadratus E. Brachialis and pronator teres

19. A 24-year-old carpenter suffers a crush injury of his entire little finger. Which of the following muscles is most likely to be spared? A. Flexor digitorum profundus B. Extensor digitorum C. Palmar interossei D. Dorsal interossei E. Lumbricals

20. A 31-year-old roofer walks in with tenosynovitis resulting from a deep penetrated wound in the palm by a big nail. Examination indicates that he has an infection in the ulnar bursa. This infection most likely resulted in necrosis of which of the following tendons? A. Tendon of the flexor carpi ulnaris B. Tendon of the flexor pollicis longus C. Tendon of the flexor digitorum profundus D. Tendon of the flexor carpi radialis E. Tendon of the palmaris longus

9 Lab 4—Forearm & Hand Muscles; Tendons —Answers

17. Answer C. (1) The extensor digitorum, flexor digitorum profundus, dorsal interosseous, and lumbrical muscles are attached to the middle digit, but no palmar interosseous muscle is attached to the middle digit.

18. Answer B. (1) The brachialis and supinator muscles form the floor of the cubital fossa. The brachioradialis and pronator teres muscles form the lateral and medial boundaries, respectively. The pronator quadratus is attached to the distal ends of the radius and the ulna.

19. Answer D. (1) The dorsal interossei are abductors of the fingers. The little finger has no attachment for the dorsal interosseous muscle because it has its own abductor. Therefore, the dorsal interosseous muscle is not affected. Other muscles are attached to the little finger, thus they are injured.

20.Answer C. (1) The ulnar bursa, or common synovi- al flexor sheath, contains the tendons of both the flexor digitorum superficialis and profundus muscles. The radial bursa envelops the tendon of the flexor pollicis longus. The tendons of the flexor carpi ulnaris and the palmaris longus are not contained in the ulnar bursa.

10 Lab 4—Forearm & Hand Multi —Questions 1 of 1

1. The patient is unable to abduct her middle finger because of 3, The patient is unable to adduct her little finger because paralysis of this structure. (See image below). of paralysis of this structure. (See image below).

2. A lesion of the median nerve causes paralysis of this struc- 4. Atrophy of this structure impairs extension of both the ture. (See image below). metacarpophalangeal and interphalangeal joints. (See image below).

11 Lab 4—Forearm & Hand Multi —Answers

1. Answer D. (1) This is the second dorsal interosseous 3. Answer G. (1) This is the third palmar interosseous muscle, which abducts the middle finger. muscle, which adducts the little finger.

2. Answer A. (1) This is the flexor pollicis longus, which is 4. Answer E. (1) The extensor digitorum extends both the innervated by the median nerve. metacarpophalangeal and interphalangeal joints.

12 Lab 4—Forearm & Hand Nerves — Questions 1 of 6

1. A 57-year-old woman presents with increasing numb- 5. A 25-year-old medical student had been experiencing ness of the fourth and fifth digits on her right hand. On numbness and tingling on the medial aspect of his right examination, it is noticed that she has a wasted hypothe- hand. When questioned by his physician he mentioned nar eminence, inability to abduct the thumb, and a char- that he often studies for long stretches of time with his acteristic claw hand. Which of the following nerves has elbows resting on the desk, supporting the weight of his most likely been injured? head. Which of the following nerves is MOST likely com- A. Axillary nerve promised in this patient? B. Anterior interosseous nerve A. radial C. Radial nerve B. ulnar D. Ulnar nerve C. median E. Median nerve D. musculocutaneous E. axillary

2. Referring to the figure, 6. The secretary of a rather verbose academic physician extension of the inter- in internal medicine complains of numbness and tingling phalangeal joints of the in her hands and fingers. She is constantly typing long digit indicated by "E" is patient visit dictations and now has carpal tunnel syn- controlled by the drome, which is due to compression of which one of the following structures? A. ulnar nerve A. Ulnar artery B. radial nerve B. Ulnar nerve C. median nerve C. Median nerve D. axillary nerve D. Flexor carpi radialis tendon E. musculocutaneous E. Palmaris longus tendon nerve

3. A 45-year-old computer programmer with an unremark- 7. A workman accidentally able medical history has been experiencing sharp pains in lacerated his wrist as shown in the accompanying dia- his hand over the last few months. This pain frequently gram. On exploration of the radiates proximally to his elbow. His physician observed wound, a vessel and nerve weakness and incoordination of the thumb, with atrophy are found to have been of the thenar eminence. Cutaneous sensation to the the- severed, but no muscle tendons were damaged. nar eminence was normal. Which of the following nerves From the indicated location is MOST likely affected? of the laceration and loss of A. ulnar sensation, the involved B. radial nerve is which of the following? C. lateral cutaneous nerve of the forearm D. median A. Median nerve E. musculocutaneous B. Recurrent branch of the median nerve C. Superficial branch of the radial nerve D. Ulnar nerve

4. A 31-year-old patient complains of sensory loss over 8. The ulnar nerve arises from what spinal nerves? the anterior and posterior surfaces of the medial third of A. C5-C7 the hand and the medial one and one-half fingers. He is B. C7-T1 diagnosed by a physician as having “funny bone” symp- C. C8-T1 toms. Which of the following nerves is injured? D. C3-C5 A. Axillary B. Radial C. Median D. Ulnar E. Musculocutaneous

13 Lab 4—Forearm & Hand Nerves — Answers

1. Answer D. (5) The ulnar nerve supplies sensation to the 5. Answer B. (2) This man was likely experiencing numb- fourth and fifth digits and innervates the hypothenar muscles, ness and pain from compression of the ulnar nerve as it travels the dorsal interosseus muscles that abduct the fingers, and the behind the medial epicondyle of the humerus. The ulnar nerve is medial half of the flexor digitorum profundus (to the ring and little subcutaneous at this point and vulnerable to injury. This is easily fingers or fourth and fifth digits) that flexes the distal interphalan- demonstrated by pinching behind one’s medial epicondyle, geal joints. The claw hand is a condition in which the ring and which may cause pain and produce a tingling sensation in the little fingers are hyperextended at the metacarpophalangeal hand due to compression of the ulnar nerve. With severe ulnar joints and flexed at the interphalangeal joints. The axillary and nerve palsy, a condition known as clawhand may develop. anterior interosseous nerve do not supply the hand. Injury to the Clawhand occurs as a result of paralysis of the medial two lum- radial nerve results in wrist drop. Injury to the median nerve bricals, resulting in flexion of the interphalangeal joints of the 4th causes an ape hand (flattening of the thenar eminence). and 5th digits due to the now unopposed actions of flexor digitorum superficialis. Weakened adduction of the hand would also be seen as a result of paralysis of flexor carpi ulnaris.

2. Answer A. (6) The ulnar nerve innervates two lumbricals 6. Answer C. (5) In carpal tunnel syndrome, structures en- and interosseous muscles, which extend at the interphalangeal tering the palm deep to the flexor retinaculum are compressed; joints. these include the median nerve and the tendons of the flexor pollicis longus, flexor digitorum profundus, and flexor digitorum superficialis muscles. The flexor carpi radialis runs lateral to the carpal tunnel and inserts on the bases of the second and third metacarpals. Structures entering the palm superficial to the flex- or retinaculum include the ulnar nerve, ulnar artery, and palmaris longus tendon (which inserts on the palmar aponeurosis).

3. Answer D. (2) Compression of the median nerve as it 7. Answer D. (7) The ulnar nerve descends along the post- passes through the carpal tunnel results in carpal tunnel syn- axial (ulnar) side of the forearm. It passes lateral to the pisiform drome. Inflammation of the carpal tunnel frequently occurs in bone and under the carpal volar ligament, but superficial to the people who perform manual tasks with their wrists extended for transverse carpal ligament. In the hand it divides into superficial long periods of time (e.g., typing). This position of the wrist can and deep branches. The median nerve (answer a) lies deep to put pressure on the median nerve. For this reason, proper ergo- the transverse carpal ligament where it is protected from superfi- nomics can be very important. Cutaneous sensation to the the- cial lacerations. Emerging from the carpal tunnel, it gives off the nar eminence is spared because the branch of the median vulnerable recurrent branch (answer b) to the thenar eminence. nerve that supplies the skin of the thenar eminence is given off The superficial branch of the radial nerve (answer c) supplies prior to the carpal tunnel and travels superficially with respect to the dorsolateral aspects of the wrist and hand. the flexor retinaculum. In severe cases of carpal tunnel syndrome, wasting of the thenar muscles occurs, resulting in a flattened appearance (simian hand). Treatment of carpal tunnel syndrome includes local injection with corticosteroids and/or surgical sectioning of the flexor retinaculum to alleviate pressure on the median nerve.

4. Answer D. (1) The ulnar nerve supplies sensory fibers to 8. Answer C. (2) The ulnar arises from C8-T1. The me- the skin over the palmar and dorsal surfaces of the medial third dian nerve arises from C6-C8 and radial arise from C5- of the hand and the medial one and one-half fingers. The medi- T1. The musculocutaneous arises from C5-C7. There is an nerve innervates the skin of the lateral side of the palm; the no nerve that arises from C3-C5. palmar side of the lateral three and one-half fingers; and the dorsal side of the index finger, the middle finger, and one-half of the ring finger. The radial nerve innervates the skin of the radial side of the hand and the radial two and one-half digits over the proximal phalanx.

14 Lab 4—Forearm & Hand Nerves —Questions 2 of 6

9. If the musculocutaneous nerve were to become dam- 13. A 17-year-old boy is injured in an automobile acci- aged, what function would be lost? dent. He has a fracture of the shaft of the humerus. Fol- A. Forearm flexion lowing this accident, the patient has no cutaneous sensa- B. Forearm extension tion in which of the following areas? C. Wrist flexion A. Medial aspect of the arm D. Wrist extension B. Lateral aspect of the forearm E. Pronation C. Palmar aspect of the second and third digits D. Area of the anatomic snuffbox E. Medial one and one-half fingers

10. There are only 30 minutes left before the concert 14. A 29-year-old carpenter receives a crush injury of his starts. The pianist, who incidentally has a cut over the metacarpophalangeal joint of the fourth digit (ring finger) palmar surface of her wrist, noticed that she is unable to while remodeling his neighbor's porch. Which of the fol- pick up a piece of music between her index and middle lowing pairs of nerves innervates the muscle that moves fingers. Which of the following nerves is most likely dam- the injured joint? aged? A. Median and ulnar nerves A. Radial nerve B. Radial and median nerves B. Axillary nerve C. Musculocutaneous and ulnar nerves C. Ulnar nerve D. Ulnar and radial nerves D. Median nerve E. Radial and axillary nerves E. Anterior interosseous nerve

11. A man injures his wrist on broken glass. Which of the 15. A young man suffers a transverse cut across the ante- following structures entering the palm superficial to the rior surface of the wrist that severs the major nerve which flexor retinaculum may be damaged? lies superficial to the flexor retinaculum. Which of the fol- A. Ulnar nerve and median nerve lowing actions will be LOST as a result of the severing of B. Median nerve and flexor digitorum profundus this major nerve? C. Median nerve and flexor pollicis longus A. extending the fingers at their interphalangeal joints D. Ulnar artery and ulnar nerve B. spreading apart the fingers (abducting the fingers) E. Ulnar nerve and flexor digitorum superficialis C. flexing the fingers at their interphalangeal joints D. abducting the hand at the wrist E. adducting the hand at the wrist

12. A 22-year-old female Macarena dancer fell from the 16. A 45-year-old woman, who has worked typing on the stage and complains of elbow pain and inability to supi- computer 8 hours a day for the last 5 years, comes to her nate her forearm. Which of the following nerves are most primary care physician complaining of a few months of likely injured from this accident? progressive numbness in the 2nd and 3rd digit of the right A. Median and ulnar nerves hand and weaknesses and numbness of the 1st digit. B. Axillary and radial nerves Phalen and Tinel signs are positive. What is the most like- C. Radial and musculocutaneous nerves ly injury? D. Ulnar and axillary nerves A. Median nerve at the elbow E. Musculocutaneous and median nerves B. Radial nerve at the axilla C. Median nerve at the wrist D. Ulnar nerve at the elbow E. Ulnar nerve at the wrist

15 Lab 4—Forearm & Hand Nerves — Answers

9. Answer A. (2) The major muscles innervated by the 13. Answer D. (1) The superficial branch of the radial musculocutaneous nerve are the brachialis and biceps nerve runs distally to the dorsum of the hand to innervate brachii. Therefore, forearm flexion would be lost. Forearm the radial side of the hand, including the area of the ana- extension is controlled by the triceps brachii which is in- tomic snuffbox and the radial two and one-half digits over nervated by the radial nerve. The wrist flexors are inner- the proximal phalanx. The medial aspect of the arm is vated mostly by the median and ulnar nerves. Wrist ex- innervated by the medial brachial cutaneous nerve; the tensors are innervated by the radial nerve. The pronators lateral aspect of the forearm is innervated by the lateral (pronator quadratus and pronator teres) are innervated by antebrachial cutaneous nerve of the musculocutaneous the anterior interosseous and median nerves.. nerve; the palmar aspect of the second and third digits is innervated by the median nerve; and the medial one and one-half fi ngers are innervated by the ulnar nerve.

10. Answer C. (5) This pianist is unable to pick up a 14. Answer D. (5) The metacarpophalangeal joint of music piece between the index and middle fingers, be- the ring finger is extended by the extensor digitorum, cause she cannot adduct her index finger and abduct the which is innervated by the radial nerve. This joint is flexed middle finger. Adductor of the index finger is a palmar by the lumbrical and interossei muscles, abducted by the interosseous muscle, which is innervated by the ulnar dorsal interosseous, and adducted by the palmar interos- nerve. Abductors of the middle finger are dorsal interosseous. The medial two lumbricals and both the dorsal and seous muscles, which are innervated by the ulnar nerve. palmar interossei are innervated by the ulnar nerve. The The other nerves do not innervate adductors or abductors median, musculocutaneous, and axillary nerves are not of the fingers. involved in movement of the metacarpophalangeal joint of the ring finger.

11. Answer D. (1) Structures entering the palm super- 15. Answer B. (2) The median and ulnar nerves are ficial to the flexor retinaculum include the ulnar nerve, ul- the major nerves that extend across the wrist into the nar artery, palmaris longus tendon, and palmar cutaneous hand. Upon entering the hand, the nerves give rise to mo- branch of the median nerve. The median nerve, the flexor tor branches that innervate the hand muscles and cutane- pollicis longus, and the flexor digitorum superficialis and ous sensory branches that innervate the skin of the thumb profundus run deep to the flexor retinaculum. and fingers. One of the major motor deficits that may oc- cur from injury to the ulnar nerve at any site along its course through the upper limb is weakness or inability to abduct and adduct the fingers. The ulnar nerve (UN) and ulnar artery (UA) cross the wrist by extending anterior to the flexor retinaculum . Upon entering the hand, the ulnar nerve divides into a superficial branch and a deep branch. The deep branch of the ulnar nerve innervates 13 hand muscles.

12. Answer C. (1) The supinator and biceps brachii 16. Answer C. (2) The lesion of the median nerve at muscles supinate the forearm. The supinator is innervat- the wrist level is very common in people who type for long ed by the radial nerve, and the biceps brachii is innervat- periods. It is known as the carpal tunnel syndrome. Pa- ed by the musculocutaneous nerve. tient may have Phalen sign and Tinel sign.

16 Lab 4—Forearm & Hand Nerve —Questions 3 of 6

17. A 35-year-old female clerk presents with occasional 21. A 53-year-old African American man involved in a mo- left wrist pain and a burning sensation in her palm and tor vehicle accident sustains a severe mid-shaft fracture thumb, index, and middle fingers of her left hand. She of the right humerus. Vitals are Temp-100.0F, BP- states that the burning sensation is especially notable 120/88mm/Hg, pulse- 118/min, and RR- 14/min. Exami- when she wakes up in the morning. Vital signs are PR: nation reveals wrist drop and no ulnar or radial pulses in 80/min; BP: 115/70mm Hg; RR: 14/min; Temperature: the right arm. Examination reveals decreased sensation 100.5F. Physical examination demonstrates mild sensory over the dorsal aspect of the lateral 3½ digits. The rest of loss in the first and second fingers, as well as a positive the physical exam is otherwise unremarkable. What nerve Tinel sign. What nerve is most likely compressed? is most likely injured given the findings in this patient? A. Axillary nerve A. Musculocutaneous nerve B. Radial nerve B. Axillary nerve C. Ulnar nerve C. Median nerve D. Median nerve D. Ulnar nerve E. Musculocutaneous nerve E. Radial nerve

18. A 25-year-old man comes to the emergency room 22. A humeral fracture results in wrist drop in your patient. (ER) 2 hours after a motorcycle accident. At physical ex- Which letter in the figure below identifies the injured neu- am (PE), patient has difficulty adducting and abducting ral structure? the digits, weakness for on flexing of the wrist, and Fro- ment's sign. What is the most likely injury? A. A B. B A. Median nerve at the elbow C. C B. Radial nerve at the axilla D. D C. Median nerve at the wrist E. E D. Ulnar nerve at the elbow F. F E. Ulnar nerve at the wrist G. G H. H

19. A secretary comes in to your office complaining of 22. pain in her wrists from typing all day. You determine that she likely has carpal tunnel syndrome. Which of the following conditions would help you determine the diagno- sis? A. Inability to adduct the little finger B. Inability to flex the DIP joint of the ring finger C. Flattened thenar eminence D. Loss of skin sensation of the medial oneand one-half fingers E. Atrophied adductor pollicis muscle

20. A man is unable to hold typing paper between his in- 23. After winning a boxing match, a 24-year old man is dex and middle fingers. Which of the following nerves was unable to abduct his fingers. Which of the following likely injured? nerves is injured? A. Radial nerve A. Ulnar nerve B. Median nerve B. Median nerve C. Ulnar nerve C. Radial nerve D. Musculocutaneous nerve D. Musculocutaneous nerve E. Axillary nerve E. Axillary nerve

17 Lab 4—Forearm & Hand Nerve — Answers

17. Answer D. (2) She is likely to have carpal tunnel 21. Answer E. (2) This patient has a mid-shaft fracture of the syndrome. The symptoms of median nerve compression humerus. The most likely nerve injured, given the constellation at the carpal tunnel include sensory loss in the first, sec- of findings, is the radial nerve. The presentation of wrist drop is ond, third, and part of the ring finger of the patient. Tinel highly suggestive of radial nerve injury. There is also numbness and a reduction of sensation on the back surface of the forearm sign is a physical diagnostic test in which the physician and hand. will tap over the median nerve at the wrist. If the patient The musculocutaneous nerve provides mainly sensation to the experiences shooting pain from the wrist to the hand, then upper arm. These patients have elbow flexion weakness. the Tinel's sign is positive. Ulnar nerve injury usually causes loss of sensation of the little finger and usually the ulnar side of the ring finger will be impaired. Median nerve injury leads to weak pronation of the forearm, weak flexion, & radial deviation of wrist. It also leads to atrophy of the thenar eminence, as well as an inability to oppose or flex the thumb. In addition, sensory loss involves the thumb and radial 2½ fingers.

18. Answer D. (2) The lesion of the ulnar nerve at the 22. Answer B. (6) The injured structure is the radial elbow causes the loss of adduction (palmar interosseous) nerve indicated by the letter B. and abduction (dorsal interosseous) of the fingers and difficulty of the flexion the wrist (flexor carpi ulnaris), clawing of ulnar two fingers is not seen, because extrinsic muscles producing IP joint flexion are also denervated. Froment's sign can be seen.

19. Answer C. (1) The carpal tunnel contains the median nerve and the tendons of flexor pollicis longus, flexor digitorum profundus, and flexor digitorum superficialis muscles. Carpal tunnel syndrome results from injury to the median nerve, which supplies the thenar muscle. Thus, injury to this nerve causes the flattened thenar eminence. The middle finger has no attachment for the adductors. The ulnar nerve innervates the medial half of the flexor digitorum profundus muscle, which allows flexion of the DIP joints of the ring and little fingers. The ulnar nerve supplies the skin over the medial one and one-half fingers and adductor pollicis muscle.

20. Answer C. (1) To hold a typing paper, the index 23. Answer A. (5) The ulnar nerve innervates the dor- finger is adducted by the palmar interosseous muscle, sal interossei, which arc the only abductors of the fingers. and the middle finger is abducted by the dorsal interosse- The little finger is abducted by the abductor digiti minimi, ous muscle. Both muscles are innervated by the ulnar which is innervated by the ulnar nerve. The thumb is ab- nerve. ducted by the abductor pollicis brevis and longus, which are innervated by the median and radial nerves, respectively. The musculocutaneous and axillary nerves do not supply the hand muscles.

18 Lab 4—Forearm & Hand Nerve —Questions 4 of 6

24. A 42-year-old woman present(s) to an outpatient clinic 28. A 39-year-old man has suffered for many years from pains in with a 6-month history of numbness and tingling on the his right arm. Recently, after moving to a new job that requires car- palmar aspect of her lateral three and one-half fingers, rying heavy parcels, the pain has worsened, and occasional tingling and numbness is felt in the little finger and ring finger of the loss of pronalion, and flattening of the thenar eminence. right hand. The area of pain in the limb is localized to the medial Injury to which of the following nerves could cause such a side of the arm and forearm and the ulnar side of the hand. Gen- condition? eral muscle strength in the right extremity is less than in the left, A. Axillary nerve and there is particular weakness of opposition and adduction of the B. Musculocutaneous nerve right thumb. Wasting of the right hypothenar and thenar eminence C. Median nerve is evident, and the patient cannot hold a piece of paper between his index and middle fingers. The most likely site of the injury is D. Radial nerve A. lower trunk of the brachial plexus E. Ulnar nerve B. upper trunk of the brachial plexus C. posterior cord of the brachial plexus D. ulnar nerve E. median nerve

25. A patient has a tiny (0.2 cm) but exquisitely painful 29. Your patient has fallen on his outstretched hand and tumor under the nail of her index finger. Local anesthetic has dislocated a carpal bone. The patient does not seek block to a branch of which of the following nerves would treatment, and several weeks later he begins to exhibit be most likely to provide adequate anesthesia for the sur- signs of nerve compression. The patient is most likely to gical removal of the mass? present with which of the following conditions? A. Axillary A. Wrist drop B. Median B. Clawing of ring and index fingers C. Musculocutaneous C. Inability to spread and oppose the fingers D. Radial D. Weakness in the ability to oppose the thumb E. Ulnar E. Pain on the palmar aspects of the ring and little fingers

26. A 60-year-old man presents for evaluation of weak- 30. A 16-year-old girl is brought to the emergency depart- ness in his left wrist and pain in his left middle finger. He ment after attempting suicide by cutting her wrist. The is otherwise in good health. Physical evaluation reveals deepest part of the wound is between the tendons of the diminished triceps reflex and weakness with extension of flexor carpi radialis and the flexor digitorum superficialis. the forearm. Compression of which spinal nerve most This patient is most likely to have a deficit of which of the likely contributes to this patients symptoms? following? A. C5 A. Adduction and abduction of the fingers B. C6 B. Extension of the index finger C. C7 C. Flexion of the ring and small fingers D. C8 D. Sensation over the base of the small finger E. T1 C5 E. Opposition of the thumb and other fingers

27. After a night of fraternity parties, a 21-year-old college 31. The police bring in a murder suspect who has been in junior came to the ER the following morning complaining a gunfight with a police officer. The suspect was struck by that she could not raise her wrist. There was no history of a bullet in the arm; his median nerve has been damaged. trauma. On examination, the patient could not extend her Which of the following symptoms is likely produced by this fingers or wrist but could flex them. She could also both nerve damage? flex and extend her elbow normally. There were no other A. Waiter’s tip hand motor deficits. The symptoms suggest damage to which B. Claw hand of the following? C. Wrist drop A. Median nerve D. Ape hand B. Ulnar nerve E. Flattening of the hypothenar eminence C. Radial nerve D. Axillary nerve E. Musculocutaneous nerve

19 Lab 4—Forearm & Hand Nerve —Answers

24. Answer C. The median nerve supplies the skin on the 28. Answer A. (6) The patient has a combination of signs palmar aspect of the lateral three and one-half fingers and the that can be attributed to an ulnar nerve lesion and a median dorsal side of the index finger, middle finger, and one half of the nerve lesion. The lower trunk of the brachial plexus contains CS ring finger. The median nerve innervates the pronator teres and and T1 fibers, which are found in both the median and ulnar pronator quadratus muscles and the thenar muscles. The axil- nerves and is the likely site of a single lesion affecting fibers in lary and musculocutaneous nerves do not supply I he skin or both nerves. muscles of the hand. The radial nerve does not innervate muscles of the hand but innervates the skin of the radial side of the hand and the radial two and one-half digits over the proximal phalanx. The ulnar nerve innervates not only the palmaris brevis, hypothenar muscles, adductor pollicis, dorsal and palmar interosseus, and medial two lumbrical muscles but also the skin over the palmar and dorsal surfaces of the medial one third of the hand and the skin of the little finger and the medial side of the ring finger.

25. Answer B. (4) The tumor in question is probably a be- 29. Answer D. (6) The most commonly dislocated carpal nign glomus tumor, which is notorious for producing pain far out bone is the lunate. The lunate typically dislocates anteriorly and of proportion to its small size. The question is a little tricky (but compresses the median nerve, leading to altered sensation over important clinically for obvious reasons) because the most distal the palmar aspects of the lateral digits and to a weakness in aspect of the dorsal sk.in of the fingers, including the nail beds, thumb opposition. is innervated by the palmar digital nerves rather than the dorsal digital nerves. Specifically, the median nerve, through its palmar digital nerves, supplies the nail beds of the thumb, index finger, middle finger, and half the ring finger. The axillary nerve (choice A), musculocutaneous nerve (choice C), and radial nerve (choice D) do not supply the nail beds. The radial nerve does supply the more proximal skin of the back of the index finger. The ulnar nerve (choice E) supplies the nail beds of the small finger and half the ring finger.

26. Answer C. (10) A herniated disk at the cervical lev- 30. Answer E (3) The structure between the two tendons el most commonly occurs at the disk between C6 and C7 mentioned is the median nerve. Loss of the median nerve at the vertebrae, which causes the compression of the C7 spinal wrist results in loss of thenar muscle innervation, resulting in an nerve. Compression of the C7 spinal nerve unique causes inability to oppose the thumb. Opposition of the thumb and other fingers involves flexion of the flexor carpi radialis (FCR) and pain and paresthesia of the middle finger and can also flexor digitorum superficialis (FDS), both innervated by the medi- cause diminished triceps reflex and weakness in forearm an nerve. The FDS muscle in the forearm gives rise to 4 ten- extension. Answer A: The C5 spinal nerve fibers are dons that pass through the flexor retinaculum of the carpal tun- found in the axillary nerve. Patients with a neuropathy of nel and insert at the proximal interphalangeal joints. (So, it's an C5 have difficulties with shoulder abduction. The biceps extrinsic muscle of the hand.) The FCR muscle passes a ten- brachii and brachioradialis deep tendon reflexes can be don just lateral to the FC-ulnaris tendon, and inserts at the base diminished with compression of this nerve fibers. C5 of the 2nd metacarpal. radiculopathy does not lead to loss of sensation in the hands. Answer B: C6 compression can lead to weakness of flexion of the arm at the elbow, not of extension. Like

27. Answer C. (7) The radial nerve innervates extensors of 31. Answer D. (1) Injury to the median nerve produces the the upper extremity. Damage to the radial nerve in the radial ape hand (a hand with the thumb permanently extended). Injury groove is frequently caused by supporting the arm in an out- to the radial nerve results in loss of wrist extension, leading to stretched position as may be encountered when an inebriated wrist drop. Damage to the upper trunk of the brachial plexus college student passes out on her friend’s sofa. This is some- produces waiter’s tip hand. A claw hand and flattening of the times referred to as “Saturday night palsy.” The median nerve hypothenar eminence or atrophy of the (answer a) supplies the pronators (teres and quadratus) and the hypothenar muscles result from damage to the ulnar nerve. flexors of the fingers, thumb, and wrist. The ulnar nerve (answer b) supplies the flexor carpi ulnaris and a portion of flexor digitorum profundus. The axillary nerve (answer d) innervates the deltoid and teres minor and is thus involved in abduction of the arm. The musculocutaneous nerve (answer e) innervates flexors of the elbow joint (e.g., biceps brachii).

20 Lab 4—Forearm & Hand Nerve — Questions 5 of 6

32. A patient presents in her fifth pregnancy with a history of numb- 35. A 36-year-old plumber slips and breaks a porcelain ness and tingling in her right thumb and index finger during each of sink, cutting an anterior aspect of his wrist deeply on a her previous four pregnancies. Currently, the same symptoms are sharp edge. On arrival to the emergency department, he constant, although generally worse in the early morning. Symptoms could be somewhat relieved by vigorous shaking of the wrist. Neuro- can adduct his thumb but not oppose it. Which of the fol- logic examination revealed atrophy and weakness of the abductor lowing structures has been severed? pollicis brevis, the opponens pollicis, and the first two lumbrical mus- A. Radial nerve cles. Sensation was decreased over the lateral palm and the volar B. Median nerve aspect of the first three digits. Numbness and tingling were marked- C. Ulnar nerve ly increased over the first three digits and the lateral palm when the wrist was held in flexion for 30 seconds. The symptoms suggest D. Anterior interosseous nerve damage to which of the following? E. Posterior interosseous nerve A. The radial artery B. The median nerve C. The ulnar nerve D. Proper digital nerves E. The radial nerve

33. A 62-year-old man is diagnosed with a Pancoast's 36. An indoor soccer player runs into another player while tumor that invades the inferior trunk of the brachial plex- running after the ball. She falls to the ground and frac- us. Which of the following muscle actions most likely re- tures the medial epicondyle of the humerus. Which of the sulted from injury to the brachial plexus? following symptoms might she present with when seeing A. Lateral rotation of the arm a physician in the emergency room? B. Extension of the ring finger A. Impaired abduction of the hand C. Abduction of the index finger B. Carpal tunnel syndrome D. Flexion of the forearm C. Wrist drop E. Pronation of the forearm D. Thenar atrophy E. Inability to sweat on the medial part of the hand

34. In the cross-section below, a lesion of a nerve at 'A' 37. A 29-year-old patient comes in; he cannot flex the would result in distal interphalangeal (DIP) joint of the index finger. His A. paresthesia of the lateral aspect of the palm physician determines that he has nerve damage from a B. wrist drop supracondylar fracture. Which of the following conditions C. paresthesia in skin over the anatomic snuffbox is also a symptom of this nerve damage? D. inability to press the pulp of the thumb against the pulp A. Inability to flex the DIP joint of the ring finger of the index finger B. Atrophy of the hypothenar eminence E. inability to spread the fingers C. Loss of sensation over the distal part of the second digit D. Paralysis of all the thumb muscles E. Loss of supination

34.

21 Lab 4—Forearm & Hand Nerve — Answers

32. Answer B. (7) The patient has a classic case of carpal 35. Answer B. (5) The median nerve enters the palm tunnel syndrome, in which the median nerve is compressed as it of the hand through the carpal tunnel deep to the flexor passes through the carpal tunnel formed by the flexor retinacu- retinaculum, giving off a muscular branch (recurrent lum in the wrist. Evidence for involvement of the median nerve is branch) to the thenar muscles including the abductor polli- weakness and atrophy of the thenar muscles (abductor pollicis cis brevis, flexor pollicis brevis, and opponens pollicis. brevis, opponens pollicis) and lumbricals 1 to 3. Sensory deficits also follow the distribution of the median nerve. The median The ulnar nerve enters the hand superficial to the flexor nerve enters the hand, along with the tendons of the superficial retinaculum and lateral to the pisiform bone, supplying the and deep digital flexors, through a tunnel framed by the carpal hypothenar muscles and adductor pollicis. The patient bones and the overlying flexor retinaculum. Symptoms are can adduct his thumb but not oppose it. Therefore, the worse in the early morning and in pregnancy because of fluid median nerve is injured. The radial nerve and the anterior retention, resulting in swelling that entraps the median nerve. and posterior interosseous nerves do not supply the mus- Flexing the wrist for an extended period exaggerates the pares- cle that opposes the thumb. thesia (“Phelan’s” sign) by increasing pressure on the median nerve.

33. Answer C. (5) The ulnar nerve arises from the lower 36. Answer E. (5) Fracture of the medial epicondyle of the trunk of the brachial plexus, which is formed by ventral primary humerus might injure the ulnar nerve, which supplies the skin of rami of C8 and Tl. Abduction of the index finger is done by the the medial side of the hand; thus, a lesion of the ulnar nerve palmar interosseus muscle, which is innervated by the ulnar would cause no cutaneous sensation and lack of sweating in nerve. Lateral rotation of the arm is performed by the deltoid and that area. The muscles involved in abduction of the hand are the teres minor muscles, which are innervated by the axillary nerve. flexor carpi radialis and the extensor carpi radialis longus and The ring finger is extended by the extensor digitorum, which is brevis, which are innervated by the median and radial nerves, innervated by the radial nerve. The forearm is flexed by the bi- respectively. Carpal tunnel syndrome and thenar atrophy result ceps brachii and brachialis muscles, which are innervated by the from a lesion of the median nerve, whereas wrist drop results musculocutaneous nerve. Pronator teres and pronator quad- from a lesion of the radial nerve. ratus muscles, which pronate the forearm, are innervated by the median nerve.

34. Answer E. (6) A lesion of the ulnar nerve at the 37. Answer C. (1) The flexor digitorum profundus muscle wrist may result in an inability to spread and oppose the flexes the DIP joints of the index and middle fingers and is fingers. innervated by the median nerve, which also supplies sensation over the distal part of the second digit. The same muscle flexes the DIP joints of the ring and little fingers but receives innervation from the ulnar nerve, which also innervates the hypothenar muscles. The median nerve innervates the thenar muscles. The radial nerve innervates the supinator, abductor pollicis longus, and extensor pollicis longus and brevis muscles. The ulnar nerve innervates the adductor pollicis. The musculocutaneous nerve supplies the biceps brachii that can supinate the arm.

22 Lab 4—Forearm & Hand Vessels — Questions 1 of 1

1. A construction worker suffers a destructive injury of the 4. A patient complains of having pain with repeated move- structures related to the anatomic snuffbox. Which of the ments of his thumb (claudication). His physician performs following structures would most likely be damaged? the Allen test and finds an insufficiency of the radial ar- A. Triquetral bone tery. Which of the following conditions would be a result of B. Trapezoid bone the radial artery stenosis? C. Extensor indicis tendon A. A marked decrease in the blood flow in the superficial D. Abductor pollicis brevis tendon palmar arterial arch E. Radial artery B. Decreased pulsation in the artery passing superficial to the flexor retinaculum C. Ischemia of the entire extensor muscles of the forearm D. A marked decrease in the blood flow in the princeps pollicis artery E. A low blood pressure in the anterior interosseous artery

2. A patient presents to the emergency department after sustaining a laceration of the first web space of his hand in a rock-climbing accident. Which of the following structures is also likely to be injured? A. Deep branch of radial nerve B. Opponens pollicis C. Radial artery D. Recurrent branch of median nerve E. Superficial palmar arch

3.A 17-year-old boy presents to emergency room with severe bleeding from his right hand. He was involved in a gang fight an hour ago, where he received a stab wound by the penetrated sharp knife in the region of the anatomical snuff box (see image below). He was successfully re- suscitated. Damage to which artery is responsible for this excessive bleeding? A. Brachial artery B. Princeps pollicis artery C. Radial artery D. Anterior carpal arch E. Ulnar artery

23 Lab 4—Forearm & Hand Vessels — Answers

1. Answer E. (1) The radial artery lies on the floor of the 4. Answer D. (1) The radial artery divides into the prin- anatomic snuffbox. Other structures are not related to the ceps pollicis artery and the deep palmar arterial arch. snuffbox. The tendons of the extensor pollicis longus, ex- Thus, stenosis of the radial artery results in a decreased tensor pollicis brevis, and abductor pollicis longus mus- blood flow in the princeps pollicis artery. The superficial cles form the boundaries of the anatomic snuffbox. The palmar arterial arch is formed primarily by the ulnar artery, scaphoid and trapezium bones form its floor. which passes superficial to the flexor retinaculum. The extensor compartment of the forearm receives blood from the posterior interosseous artery, which arises from the common interosseous branch of the ulnar artery. Howev- er, the radial and radial recurrent arteries supply the brachioradialis and the extensor carpi radialis longus and brevis.

2. Answer C. (4) After crossing the floor of the anatomic snuff box, the radial artery passes deep to the tendon of extensor pollicis longus to enter the palm deeply in the space between the first and second metacarpals (first web space). Within this space, it contributes to the for- mation of the deep palmar arterial arch.

3. Answer C. The radial artery runs through the anatomic snuffbox. It would be causing the excessive bleeding in this case due to dame by penetrating injury. The anatomical snuff box is a triangular depression on the dorsal lateral aspect of the hand. The carpal bones, scaphoid and trapezium, forms its floor. The boundaries of the anatomic snuff box are as follows: - It is bounded medially by the tendon of extensor pollicius longus. - It is bounded laterally by the tendons of abductor pollicius longus and extensor pollicius brevis. - It is bounded proximally by sty- loid process of radius bone. The radial artery is present on the lateral side of the arm and travels through the anatomic snuff box. It enters the palm by passing between the two heads of the first dorsal interosseous muscle. It terminates into the princeps pollicis artery and the deep palmar arch.