Radial Nerve Flashcards
What is the characteristic recovery sequence in radial nerve palsy, and why does it follow this pattern?
The recovery sequence is proximal-to-distal: Brachioradialis → ECRL/ECRB → finger extensors → EIP (last).
This reflects nerve regeneration, where proximally innervated muscles recover first. EIP, with a 30cm reinnervation distance, recovers last.
(Shao et al., 2005; Ochi et al., 2011)
Which nerve innervates the extensor carpi radialis longus (ECRL), and why is this important in diagnosing PIN palsy?
The radial nerve proper innervates ECRL, not the PIN.
In PIN palsy, preserved ECRL function leads to radial-deviated wrist extension, a key diagnostic feature.
(Sigamoney et al., 2017)
Which nerve provides sensory innervation to the first web space, and how does this help differentiate nerve injuries?
The superficial radial nerve provides sensory innervation to the first web space. In PIN palsy, sensation is preserved because the PIN is a pure motor nerve, unlike radial nerve injuries affecting the superficial branch.
(Baklaci et al., 2010)
What are the typical motor deficits in posterior interosseous nerve (PIN) palsy, and why is ECRL function preserved?
Deficits include weakness in finger extension, thumb extension, and ECRB-mediated wrist extension. ECRL function is preserved because it’s innervated by the radial nerve proper, not the PIN.
In a spontaneously resolving radial nerve palsy, which muscle is typically the last to recover, and what is the expected time frame?
Extensor indicis proprius (EIP) is the last to recover, often taking up to 10 months due to its distal innervation and the 1mm/day nerve regeneration rate over a 30cm distance.
(Ochi et al., 2011)
What is the preferred route for pronator teres transfer in wrist extension restoration, and why is ulnar routing avoided?
The preferred route is through the interosseous membrane to ECRB, optimizing biomechanical efficiency. Ulnar routing creates an inefficient vector and is less physiological.
(Kozin, 2005; Bumbasirevic et al., 2016)
When performing a palmaris longus (PL) to extensor pollicis longus (EPL) tendon transfer, how should the tension be set, and what is the intraoperative confirmation of proper tension?
Tension should be set with the wrist in neutral and the thumb in full extension. Proper tension allows full thumb extension with wrist neutral and passive thumb flexion with wrist flexion.
(Moberg’s technique; Brown et al., 2009)
What is a key principle when selecting a donor muscle for tendon transfer?
The donor muscle should have adequate strength, excursion, and a similar line of pull to the recipient tendon to ensure effective functional restoration.
Which muscle’s paralysis creates ‘finger drop’ without wrist extension loss, and why?
Posterior interosseous nerve (PIN) palsy causes finger drop while preserving wrist extension due to intact ECRL function.
(Tubiana’s Examination)
How does ECRB involvement differ in radial nerve palsy compared to PIN palsy?
In radial nerve palsy, ECRB is paralyzed; in PIN palsy, ECRB may have partial function due to dual innervation.
(Sigamoney et al., 2017 cadaveric studies)
Which nerve injury pattern spares brachioradialis function, and why?
Posterior interosseous nerve (PIN) lesions spare brachioradialis because it’s innervated proximally by the radial nerve proper.
(Shao’s recovery sequence)
What are the key components of the physical exam for suspected radial nerve injury?
Inspection for muscle wasting/scars, motor testing (MRC scale), sensory testing (2-point discrimination or Semmes-Weinstein), active/passive ROM, advancing Tinel’s sign.
When are electrodiagnostic studies indicated for radial nerve injuries, and why?
At 6 weeks post-injury to assess Wallerian degeneration and subclinical reinnervation when exam findings are unclear.
Compare nonsurgical vs. surgical options for radial nerve palsy?
Nonsurgical: observation, splinting, therapy for closed/low-grade injuries; Surgical: exploration, repair, grafting, transfers for no recovery after 3 months or open injuries.
What are the advantages and disadvantages of nerve transfers vs. tendon transfers for radial nerve palsy?
Nerve transfers: near-normal biomechanics, preserves donors, slow recovery (9-12 months); Tendon transfers: fast recovery (6-12 weeks), reliable, sacrifices donor muscle.
List common donor-to-recipient tendon transfers for radial nerve palsy?
Pronator teres → ECRB (wrist extension), FCR (or FCU) → EDC (finger extension), Palmaris longus → EPL (thumb extension).
What are indications for early surgical exploration in radial nerve injuries?
Open injuries, high-velocity trauma, suspected nerve transection, associated fractures/vascular injuries.
What outcome metrics evaluate tendon transfer success in radial nerve palsy?
ROM (degrees), grip strength (% contralateral), MRC grades, sensory recovery (2PD), DASH score, patient satisfaction, return to work.
What are potential complications of tendon transfers in radial nerve palsy?
Donor site morbidity, loss of donor function, altered biomechanics, scar restriction, no independent finger extension.
How do nerve allografts compare to autografts in peripheral nerve reconstruction?
Allografts: no donor morbidity, similar outcomes for <15-30 mm gaps (80-85% recovery); Autografts: gold standard but require harvest.
What factors affect nerve regeneration after repair?
Rate ~1 mm/day, influenced by age, injury type/extent, distance to target muscle.
Why maintain full passive ROM in nonsurgical radial nerve palsy management?
Prevents joint contractures and soft-tissue shortening, aiding recovery.
What’s the rationale for the modified Merle d’Aubigné tendon transfer method?
Uses
PT → ECRB,
FCR → EDC,
PL → EPL
to minimize radial deviation and optimize finger/thumb extension.
How does targeted reinnervation differ from traditional nerve transfers, and its advantage?
Transfers nerves to alternative muscles for EMG signals; improves myoelectric prosthetic control.
How does time to functional return differ between tendon and nerve transfers?
Tendon: 6-12 weeks; Nerve: 9-12 months.
Why is donor muscle strength grading key in tendon transfers?
Must be ≥M4 preop, as transfer drops strength by one grade.
How does wrist extension restoration affect grip strength in radial nerve palsy?
Stabilizes finger flexors, significantly improving grip.
What determines FCU vs. FCR choice for finger extension transfers?
FCU: traditional, may cause radial deviation; FCR: longer excursion, better wrist balance.
What MRC motor recovery is typical after tendon transfers for radial nerve palsy?
91-93% achieve ≥M3, ~91% reach M4-M5.
What donor site morbidities occur after tendon transfers for radial nerve palsy?
Loss of donor function, reduced wrist flexion strength, biomechanical imbalance.
How does an advancing Tinel’s sign monitor nerve recovery?
Indicates axonal regeneration along nerve course, guides intervention timing.
Why match tendon excursion in transfers?
Ensures coordinated movement and proper tension, avoiding over/under-correction.
How are high vs. low radial nerve injuries differentiated clinically?
High: proximal to PIN, affects triceps; Low: spares elbow extension, impairs wrist/finger extension.
What diagnostic techniques assess radial nerve injuries?
EMG/NCS at 6 weeks, ultrasound/MRI for anatomy.
What is “internal splinting” in early tendon transfers?
Transfers provide temporary function during nerve regeneration, permanent if regeneration fails.
What factors influence nerve regeneration rate after repair?
~1 mm/day, affected by age, injury extent, distance to muscle.
What criteria guide donor nerve selection in nerve transfers for radial nerve palsy?
Expendable, strong, synergistic, near target muscle.
What advantages do nerve transfers have over grafting in radial nerve injuries?
Avoid grafts, reduce morbidity, shorten regeneration distance.
How is patient satisfaction measured after tendon transfers?
Subjective scales, DASH scores, return-to-work, functional improvement.
