Nerve Injuries

Question 1

In a mid-shaft humeral fracture why is there no paraesthesia in the posterior arm, forearm and lateral arm?

Answer 1

Because the posterior and lateral cutaneous branches are given off proximal to the lesion.

Question 2

Describe the pathology behind the hand of benediction.

Also describe the sensory deficit.

Answer 2

High median nerve lesion (supracondylar fracture)
Lateral FDP and all of FDS paralysed. 
Thenar muscles paralysed - not deep head of FPB 
Lateral 2 lumbricals paralysed. 
Thumb extended and adducted 
(Opponens pollicis and APB paralysed)
Middle finger and index finger extended 
(FDP lateral + lumbrical paralysis) 
Little and ring finger flexed
(Medial FDP and lumbricals unaffected) 

Palmar and cutaneous branches of the medial nerve lost
No sensory innervation to:
- Lateral palmar surface
- Lateral 3 and a 1/2 digits palmar surface + dorsal nail beds of respective digits.

Question 3

In long lasting high median nerve injury and lower median nerve injury what may present and why?

Answer 3

Ape hand deformity

Externally rotated and adducted thumb

Due to oppenens pollicis being paralysed aswell as abductor pollicis brevis
(Thenar muscle supply paralysis)

Question 4

How can you distinguish between high and low median nerve lesions?

Answer 4

In a high lesion FPL is paralysed
Therefore absent flexion of IPJ of the thumb but adequate flexion of MCPJ of the thumb.

No hand of benediction in low level injury

Question 5

Describe the pathology behind ulnar claw in a injury at the wrist.

Where would the sensory deficit be seen?

Answer 5

Medial 2 lumbricals paralysed 
Hyperextension at MCPJs 
(Unopposed extension by extensor digitorum)
Flexion at PIP and DIPJs 
(Unopposed flexion from FDP and FDS)

Palmar surface of medial 1 and 1/2 fingers + dorsum of the nail beds.

Question 6

How come sensory deficit is only seen in the palmar surfaces of the 1 and 1/2 medial digits plus their respective nail beds in a ulnar nerve injury at the wrist?

Answer 6

Because the palmar and posterior cutaneous branches are given off proximal to the wrist lesion.

Question 7

Give 2 possible causes for a high ulnar nerve lesion.

Answer 7

Medial epicondylar fracture

Cubital tunnel compression

Question 8

What other muscles are also paralysed in a high ulnar nerve lesion that are not paralysed in a low ulnar nerve lesion?

Answer 8

FCU and medial half of FDP

Question 9

What is the ulnar paradox?

Answer 9

The higher the lesion the less obvious the ulnar claw.

This is due to paralysis of the flexor muscles FCU and FDP (medial) which in a low lesions will actively flex the medial 2 digits however when paralysed this will not occur to as great of an extent.

Question 10

Why is there no flexion of DIPJ in high ulnar nerve lesion?

Answer 10

Due to paralysis of FDP