Forearm
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| Fig1. Ulnar Nerve Compression |
Fig1a. Position of Styloid Processes |
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Fig1b. Colle's Fracture |
Feel the ulna along its entire length from the olecranon to the distal styloid process
The styloid process of the ulna should be proximal to the styloid process of the radius
Most of the radius is covered by muscle but you can palpate the styloid process at the wrist
You can feel the head of the radius by extending the forearm, identify the dimple on the posterior lateral surface of the elbow, press three fingers in the dimple, rotate your free hand as if you were turning a knob - the head should rotate
Recall the position of the ulnar nerve around the medial epicondyle
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| Fig2. Muscles of Forearm |
Fig2a. Flexor Tendons at the Wrist |
Next feel the major muscle groups of the forearm arising from the medial and lateral epicondyles
On the lateral side of the forearm not the bulge of muscle as you flex your elbow against resistance with the thumb up (ie. Slight pronation) - this is the brachioradialis
Pronator your forearm against resistance and feel the pronator teres contract
Flex your hand and fingers against resistance and feel the flexor compartment contract - extend your hand and wrist and feel the extensor muscles contract
Clench your fist and observe the tendons of the flexor muscles - not the flexor carpi radialis, palmaris longus (if present), flexor digitorum superficialis
The radial artery lies just lateral to (thumb side of) the flexor carpi radialis tendon
Take an arterial pulse from this artery
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| Fig2b. Carpal Tunnel |
Where do the median and ulnar nerve lie with respect to the structures just observed at the wrist?
Answer
What is carpal tunnel syndrome?
Answer
Just distal and anterior to the styloid process of the ulna palpate the small pisiform bone of the carpal bones
The styloid process lies at the level of the proximal crease of the wrist
The pisiform lies at the level of the distal crease of the wrist
Extending your thumb and pointing it posteriorly (as in hitch-hiking) you will form a triangular depression at the base of your thumb
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| Fig3. Extensor Tendons Forming Anatomical Snuff Box |
Fig3a. Scaphoid in Snuffbox |
This is the anatomical snuffbox
The two elevated borders are formed by the tendons of the extensor pollicis brevis and extensor pollicis longus
The radial artery runs through the base of the snuff box and provides another place for taking an arterial pulse
The main bone on the floor of the box is the scaphoid and styloid of the radius
Pain in the floor of the snuff box is usually a good indication of an injury to the scaphoid
Displacement of the radial styloid process (due to a fall/fracture) will be felt outside the snuff box instead of in the box
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| Fig4. Bones in Floor of Snuffbox |
Fig4a. Nerve Damage to Hand |
Why is it important to deal with a scaphoid injury immediately?
Answer
The radial nerve supplies the posterior arm and forearm. If the radial nerve were completely severed in the arm (due to a compound fracture of the shaft of the humerus) what paralysis would be observed?
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What position would the arm and wrist take?
Answer
Hand
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| Fig5. Dorsal Venous Arch |
On the dorsum of the hand observe the thinness of the skin and the superficial dorsal venous network ( a common site for inserting intravenous catheters)
Extending your wrist and fingers note the tendons of the extensor muscles
The metacarpal and phalanges can be palpated on the dorsal surface
On the dorsum of the hand, between the thumb and index finger, the first dorsal interosseus can be palpated just under the skin when the index finger is abducted away from the thumb
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| Fig6. Palm of Hand |
Fig6a. Sensory Distribution of Palm |
The palmar surface has a thicker muscle mass, thicker skin, deeper vessels and creases
Identify the hypothenar and thenar muscle masses
Injury to what nerve would result in weakness of the hypothenar muscle group?
Answer