Session 4 Anatomy Flashcards
Describe the ulnar artery in the forearm
Origin: larger terminal branch of brachial artery in the cubital fossa
Course: descends inferomedially and then directly inferiorly, deep to superficial and intermediate layers of flexor muscles to reach medial side of forearm; passes superficial to flexor retinaculum at wrist and passes ulnar canal to enter hand
Pulsations of the ulnar artery can be palpated on the lateral side of the flexi carpi ulnaris tendon where it lies anterior to the ulnar head. The ulnar nerve is on the medial side of the ulnar artery.
Describe the radial artery in the forearm
Origin: small terminal branch of brachial artery in the distal part of the cubital fossa.
Runs Inferolaterally under cover of the brachioradialis –> lies lateral to flexor carpi radialis tendon in distal forearm –> winds around lateral aspect of radius and crosses the floor of the anatomical snuffbox to pierce first dorsal interosseous muscle.
Palpation site: where the radial artery lies on the anterior surface of the distal end of the radius lateral to the tendon of the flexi carpi radicalis. Here the artery is covered only by fascia and skin.
Describe the Median Nerve in the forearm
Major branch in the forearm is the anterior interosseous nerve.
Course: enters cubital fossa medial to brachial artery, exits by passing between the heads of the pronator teres, descends in fascial plane between flexor digitorum Superficialis and profundus, runs deep as it approaches flexor retinaculum to traverse carpal tunnel.
What happens when the median nerve is severed in the elbow region?
Flexion of the proximal interphalangeal joints of the 1st-3rd digits is lost and flexion of the 4th and 5th digits is weakened.
Flexion of the DIPs of the 4th and 5th digits is not affected because the medial (ulnar) part of the flexor digitorum profundus is innervated by the ulnar nerve.
The ability to flex the MCP joints of the 2nd and 3rd lumbricals is affected because the median nerve supplies the 1st and 2nd lumbricals so when a person tries to make a fist, the 2nd and 3rd fingers remain partially extended.
Thenar muscle function is also lost
Hand of Benediction - only apparaent when patient is asked to try to make a fist
What happens when the anterior interosseous branch of the median nerve is injured?
Thenar muscle function is unaffected but there is paresis (partial paralysis) of the flexor digitorum and flexor pollicis longus occurs.
When the person attempts to the make the “okay” sign, a pinch posture of the hand results instead owing to the absence of flexion of the IP joint of the thumb and DIP of the index finger.
Describe the Ulnar Nerve in the forearm
Course: enters forearm by passing between heads of flexor carpi ulnaris after passing POSTERIOR to the medial epicondyle of humerus; descends forearm between flexor carpi ulnaris and flexor digitorum Profundus, becomes along with ulnar artery just proximal to the wrist.
Then pass superficial to the flexor retinaculum and enter the hand by passing through a groove between the pisiform and hook of the hamate.
What are the effects of the injury resulting when the medial part of the elbow hits a hard surface, fracturing the medial epicondyle?
Compression of the ulnar nerve at the elbow (cubital tunnel syndrome)
Any lesion superior to the medial epicondyle will produce paraesthesia of the median part of the dorsum of the hand.
Ulnar nerve injury usually produces numbness and tingling (paraesthesia) in the medial part of the palm and the medial one and a half fingers.
Severe compression may also produce elbow pain that radiates distally.
Ulnar nerve injury can result in extensive motor and sensory loss of the hand.
An injury to the nerve in the distal part of the forearm denervates most intrinsic hand muscles. Power of wrist adduction is impaired.
What are the four places ulnar nerve injuries usually occur in?
Posterior to the medial epicondyle of the humerus
In the cubital tunnel formed by the tendinous arch connecting the humeral and ulnar heads of the flexi carpi ulnaris
At the wrist
In the hand
After ulnar nerve injury, the person has difficulty making a fist…why?
In the absence of opposition, the MCP joints become hyper-extended and the patient cannot flex the 4th and 5th digits at the DIPs - ulnar nerve palsy.
How does a clawed hand result from ulnar nerve injury?
The person cannot extend the interphalangeal joints when trying to straighten the fingers.
The deformity results from atrophy of the interosseous muscles of the hand supplied by the ulnar nerve.
The claw is produced by the unopposed action of the extensors and flexor digitorum profundus.
- The MCP joints are hyperextended due to unopposed extension from the long extensor muscles in the posterior compartment of the forearm.*
- The IP joints are flexed due to unopposed flexion from the long flexor muscles in the anterior compartment of the arm. The extensor muscles cannot extend at the IP joints as their energy is dissipated in hyperextending the MCP joints.*
- The ulnar claw only occurs in the little and ring fingers, as the lateral two lumbricals are innervated by the median nerve.*
Describe the course of the radial nerve in the forearm
Enters cubital fossa between the brachioradialis and brachialis; ANTERIOR to lateral epicondyle.
Divides into terminal superficial and deep branches.
Describe how the radial nerve is usually injured?
Usually injured in the arm by a fracture of the humeral shaft.
The injury is proximal to the motor branches to the long and short extensors of the wrist and so wrist drop is the primary clinical manifestation.
Injury to the deep branch of the radial nerve may occur when wounds of the posterior forearm are deep (penetrating)
What happens if the deep branch of the radial nerve is injured?
Results in an inability to extend the thumb and the metacarpophalangeal joints of the other digits
Thus the integrity of the deep branch may be tested by asking the person to extend the MCP joints while the examiner provides resistance.
Loss of sensation does not occur because the deep branch of the radial nerve is entirely muscular and articular in distribution.
What happens when the superficial branch of the radial nerve, a cutaneous nerve, is severed?
Sensory loss is usually minimal.
Commonly a coin-shaped area of anaesthesia occurs distal to the bases of the 1st and 2nd metacarpals,
The reason the area of sensory loss is less than expected is the result of the considerable overlap from cutaneous branches of the median and ulnar nerves.
What is a Colles Fracture?
A complete transverse fracture of the distal 2cm of the radius - most common fracture of the forearm.
The distal fragment is displaced posteriorly and is often comminuted (broken into pieces).
The fracture results from forced extension of the hand, usually as a result of trying to ease a fall by out stretching the upper limb.
Because of the rich blood supply to the distal end of the radius, bony union is good.
Dinner fork deformity
What is the Hand of Benediction?
When the median nerve is damaged, ability to flex the MCP joints of the 2nd and 3rd digits is affected because the digital branches of the median nerve supply the 1st and 2nd lumbricals.
If the patient is asked to make a fist, they will be able to flex the little and ring fingers. This action is performed by the medial half of the flexor digitorum profundus and the medial two lumbricals.
The patient will not be able to flex the index and middle fingers. Thus, the patient displays a claw shape, where the little and ring fingers and flexed, the index and middle fingers extended.
