Lecture 9 - SQ

Question 1

1. What is the relationship of the distal wrist crease to the carpal bones?

Answer 1

. The distal wrist crease lines up approximately with the proximal row of carpal bones. Where
the thenar crease meets the distal wrist crease is a good landmark for the tubercle of the
scaphoid.

Question 2

2. In what position would you ask a patient to hold their hand if you wanted to determine
   whether their lumbrical muscles were functioning normally?

Answer 2

2. The metacarpophalangeal joints should be actively flexed while the interphalangeal joints are
   actively extended. That posture can only be achieved when the lumbricals are functional.

Question 3

3. What is the common distribution pattern for the sensory fields of the radial, median and ulnar
   nerves on the palmar side of the hand?

Answer 3

3. Sensory information from the thumb, most of the palm, the index finger, middle finger and
   the radial half of the ring finger is transmitted via median nerve. The remaining one and half
   fingers, plus the ulnar side of the palm, is innervated by the ulnar nerve. The radial nerve
   does not participate in cutaneous innervation to the palmar side of the hand.

Question 4

4. What are the sources of arterial blood to the hand?

Answer 4

4. The radial and ulnar arteries provide blood to the hand via the superficial and deep palmar
   arches respectively.

Question 5

5. A patient can pick up a suitcase, but can’t pick up a dime. Speculate on the underlying
   mechanical problem.

Answer 5

5. In order to pick up a suitcase one must be able to flex the fingers, but one does not need to use
   the thumb. Picking up a dime, however, requires opposition of the thumb. Thus it is most
   likely that the patient has lost thumb opposition. The problem could lie with the muscles of
   opposition, the joints on which those muscles act, or the innervation to those muscles

Question 6

6. What is a clawed hand deformity?

Answer 6

6. A clawed hand deformity (also known as main en griffe) is a deformity that occurs due to the
   imbalance of the lumbricals, the extensor digitorum and the long digital flexors (FDS/FDP).
   Possible causes are median and/or ulnar nerve lacerations that result in loss of function of the
   muscles which they innervate. The result is hyperextension of the metacarpophalangeal
   joints and flexion of the interphalangeal joints.

Question 7

7. Why is it difficult to fully flex the wrist and fingers at the same time?

Answer 7

7. The extrinsic extensor tendons to the digits are stretched to their limit when one tries to
   simultaneously flex both the wrist and the fingers. This end range limit of the extensor
   tendons creates a biomechanical disadvantage in the flexor system to effectively contract to
   their maximum.

Question 8

8. What position is a patient likely to hold their wrist and hand if the superior trunk of the
   brachial plexus is injured? What position might they hold their wrist and hand if the inferior
   trunk of the brachial plexus is injured?

Answer 8

8. Superior trunk (C5 and C6) injury classically presents itself with the arm and forearm hanging
   limply by the side. The arm is medially rotated and the forearm pronated. This is also called
   the waiter’s tip position. An inferior trunk injury (C8 and T1) presents itself as loss of ulnar
   and median nerve function in the hand. There is no grip. Without C8 and T1 innervation to
   the intrinsic muscles of the hand a claw hand deformity develops.

Question 9

9. Why only dorsal interossei insert on the middle finger?

Answer 9

9. Finger abduction and adduction are defined in relation to the middle finger. The middle finger
   only needs one set of interossei since the muscles on one side of that finger can oppose the
   muscle on the other—abduction to one side is, by definition, adduction to the other

Question 10

10. What areas of sensory loss in the hand might one expect following lesions of the C6, C7 and
    C8 spinal nerve roots?

Answer 10

10. The thumb is in the C6 dermatome field. The two fingers on the thumb side of the hand are in
    the C7 dermatome field. The remaining two fingers, on the ulnar side of the hand, are in the
    C8 dermatome field.

Question 11

11. If the radial nerve is severed at the wrist what would be the motor deficit?

Answer 11

11. Since there are no muscles in the hand innervated by the radial nerve there will be no motor
    loss if this nerve is cut at the wrist.

Question 12

12. What is a “wrist drop”?

Answer 12

12. Loss of radial nerve innervation to the extensor muscles in the forearm results in an inability
    to extend the wrist. Thus the unopposed wrist flexors cause the wrist to fall into flexion
    when the elbow is flexed as a result of the imbalance. That is classic presentation of “wrist
    drop.”