Median Nerve Flashcards
How does the clinical presentation of carpal tunnel syndrome differ from a complete low median nerve palsy?
Carpal tunnel syndrome typically presents with progressive sensory symptoms (numbness, paresthesias) before motor deficits, while complete low median nerve palsy presents with immediate combined sensory and motor deficits affecting thenar muscles due to the sudden loss of nerve function.
What is the primary distinction between high and low median nerve palsy?
High median nerve palsy (injury at/above elbow) affects pronator teres, FDS, and AIN-innervated muscles (FPL, FDP to index/middle fingers, PQ), while low median nerve palsy (injury at wrist) spares these muscles and primarily affects thenar muscles and sensation to the palmar aspect of the lateral 3.5 digits.
Is flexor pollicis longus (FPL) weakness commonly observed in low median nerve palsy?
No, FPL weakness is not common in low median nerve palsy. The FPL is innervated by the anterior interosseous nerve, a branch of the median nerve arising in the proximal forearm; thus, distal lesions typically spare FPL function.
What clinical test would distinguish anterior interosseous nerve syndrome from low median nerve palsy?
The ‘OK sign’ test. Patients with AIN syndrome cannot form an ‘OK’ sign due to weakness of FPL and FDP to the index finger, while patients with isolated low median nerve palsy can perform this sign as FPL function is preserved by the AIN.
Does low median nerve palsy affect sensation on the dorsal aspect of the thumb?
No, sensation on the dorsal aspect of the thumb remains unaffected. This area is primarily innervated by the radial nerve, not the median nerve.
Which areas experience sensory loss in a complete low median nerve palsy?
Sensory loss occurs in the palmar aspect of the radial 3.5 digits (thumb, index, middle, and radial half of ring finger) and the thenar eminence, which are innervated by the digital branches and palmar cutaneous branch of the median nerve.
Is the flexor pollicis brevis (FPB) muscle completely denervated in low median nerve palsy?
No, the FPB muscle is not completely denervated.
It has two heads:
* the superficial head, innervated by the median nerve
* the deep head, innervated by the ulnar nerve;
thus, partial function is preserved.
What percentage of thumb abduction strength is typically lost in median nerve palsy?
Approximately 70% of thumb abduction strength is lost, though the deficit may be less severe in some patients due to retained function of the deep head of FPB through ulnar innervation.
What are the key thenar muscles affected in low median nerve palsy?
- Abductor pollicis brevis,
- opponens pollicis, and the
- superficial head of flexor pollicis brevis
are affected, as they receive innervation from the recurrent branch of the median nerve.
What is the primary functional deficit of the thumb in low median nerve palsy?
Loss of thumb opposition (combined movement of abduction, flexion, and pronation of the first metacarpal), which significantly impairs precision grip and overall hand function.
Can opponensplasty be utilized to restore thumb opposition in cases of low median nerve palsy?
Yes, opponensplasty is a surgical option to restore thumb opposition.
Which tendon transfer options are commonly used for opponensplasty in low median nerve palsy?
Common options include
* extensor indicis proprius (EIP),
* flexor digitorum superficialis from the ring finger,
* palmaris longus tendon transfers.
Which opponensplasty technique has been reported to provide excellent functional results without weakening hand grip?
The extensor indicis proprius (EIP) opponensplasty has been reported to provide consistent excellent functional results without weakening hand grip or causing significant functional deficit.
What is the ‘recurrent branch’ of the median nerve and why is it clinically significant in hand surgery?
The recurrent branch is a motor branch of the median nerve that curves around the distal edge of the flexor retinaculum to innervate the thenar muscles. It is clinically significant because it is susceptible to injury during carpal tunnel release.
Can a patient with low median nerve palsy still flex the thumb at the interphalangeal joint? Why?
Yes. Thumb flexion at the interphalangeal joint is controlled by the FPL, which is innervated by the anterior interosseous nerve proximal to the wrist, making this function preserved in low median nerve palsy.
Why is anatomical knowledge of dual innervation of the FPB important in clinical assessment of median nerve injuries?
Knowledge of FPB’s dual innervation explains the variable presentation of thumb weakness in median nerve palsy and helps clinicians accurately assess residual function, which influences both prognosis and surgical decision-making.
In a patient with low median nerve palsy, what specific movement would be most impaired during a pinch grip?
The opposition component of pinch grip would be most impaired, as this requires the coordinated action of the opponens pollicis and abductor pollicis brevis, both exclusively innervated by the median nerve.
What is the timing controversy regarding opponensplasty in low median nerve palsy?
The controversy involves whether to perform opponensplasty early to prevent contractures and maintain function while awaiting potential nerve regeneration, or to wait for potential nerve recovery before proceeding with tendon transfer.
