Nerve injury Flashcards
Riche Cannieu anastomosis
Ulnar motor nerve to median nerve communication in the hand
77% in cadaver
Marinacci communication
Reverse Martin Gruber communication or Marinacci communication in which ulnar nerve fibers cross over to median nerve
5-17% patients
Sources of nerve graft
- Sural nerve graft
- Medial and lateral antebrachial cutaneous nerve
- Distal sensory end of posterior interosseous nerve
- Dorsal radial sensory nerve
Sensory versus motor versus mixed nerve grafts which achieves better regeneration?
Motor or mixed nerve grafts achieve better regeneration across the repair.
Martin Gruber anastomosis
Crossover of median nerve or anterior interosseous nerve fibers to the ulnar nerve in proximal forearm
Incidence - 5-34% cadaveric studies and high as 57% in electrophysiologic studies.
Importance of Martin Gruber anastomosis
Intrinsic muscles that are normally innervated by the ulnar nerve may be innervated by median nerve.
Or intrinsic muscles normally supplied by median nerve may still receive median nerve innervation but via the median to ulnar nerve cross over.
This variant requires additional crossover in the palm from ulnar nerve to thenar muscles.
High ulnar nerve injury if it occurs above Martin Gruber anastomosis may present with numbness in ulnar nerve distribution of hand but intact function of hand intrinsic muscles.
Clinical tests for radial nerve function
- Extrinsic motor - Wrist extension
- Intrinsic motor - None
- Sensory - Dorsal first web space
Clinical tests for Median nerve function
- Extrinsic motor - Profundus index finger
- Intrinsic motor - Abductor pollicis brevis
- Sensory - Pulp of index finger
Clinical tests for Ulnar nerve function
- Extrinsic motor -Profundus small finger
- Intrinsic motor - First Dorsal interosseous
- Sensory - Pulp of small finger
Quick intraoperative landmarks used to match fascicles during end to end neurorrhaphy
- Vascular markings within the epineurium
- Size and grouping of fascicles especially at a more distal location
Types of nerve repair
- Primary nerve repair - Sharp, limited crush mechanism, clean wound bed, two ends are easily juxtaposed.
- Nerve graft - Large gap needs to be repaired. 4 - 5 cm gap in upper arm, 1 cm gap in a digital nerve.
- Vascularised nerve graft - ensure survival of graft, hasten regeneration in burns or irradiated tissue with poor vascularity.
- Conduits indicated in patients in whom a small nerve gap is present but no autologous nerve is available or donor defect not warranted.
- Nerve transfer - Ends will not approximate, no vascularised bed, graft not possible, proximal portion of nerve not intact, distal portion of nerve intact.
Classification of nerve repairs
- Primary repair - Nerve repair within first few days
- Delayed primary repair - Nerve repair between 2-7 days
- Secondary repair - Repair after 7 days
Is primary repair better than secondary repair ?
Yes.
Delayed repair or secondary repair preferred until wound is clean
1. Significant crush injury,
2. Highly contaminated wound bed,
3. Questionable viability of nerve because of vascular supply,
4. Infection
Best method for surgical nerve repair
Simple epineurial repair with several interrupted 9-0 or 10-0 nylon sutures through epineurium under microscope control.
No advantage of fascicular or grouped fascicular repair over simple epineurial repair.
What cases of nerve injury will you explore immediately?
Nerve injury with open wounds
eg. Sharp laceration exception gunshot wound which is associated with indirect heat and shock effects.
How to manage a closed nerve injury?
Closed nerve injury includes direct blow, traction injuries, clinical course is followed closely.
Wait till 6-8 weeks, if clinical recovery does not occur, nerve conduction and electromyographic studies are obtained for baseline evaluation. Follow up till 12 weeks and repeat electrical studies.
If improvement in clinical course is seen by 12 weeks, continue conservative management. If no sign of recovery either clinically or electrodiagnostic testing, operative intervention is warranted. Type of surgical procedure varies from neurolysis to nerve grafting or nerve transfer depending on the grade of injury and distance of injury from end organ.
What is the best way to treat peripheral nerve injuries resulting in segmental loss of continuity?
Motor nerve gap that cannot be primarily repaired, autogenous nerve grafts harvested from appropriate donor sites is gold standard.
Cadaveric nerve grafts have been recently commercially available.
1. Limits upto 7 cm in length - cadaveric nerve graft used
2. More than 7 cm in length defect - Autogenous nerve graft used
3. Upto 6 cm defect in motor nerve defect - Vein or conduits have been used in experimental studies.
4. For long nerve gaps - Nerve transfer is better alternative.
5. Maximum length of nerve grafts used successfully > 15 cm
Sensory nerve gaps upto 3 cm length can be repaired with vein grafts and artificial conduits.
Massive loss of nerve segments - transplanted nerves can be used for grafting, especially in whom limited amount of autogenous nerve available such as children and amputees.
Donor nerves can be preserved in cold University of Wisconsin solution for 7 days to reduce antigenicity before transplant. Recipient and donors must be blood type compatible, HLA compatibility not necessary.
Immunosuppression is required until there is evidence of regeneration across the graft into native distal nerve.
When to use motor nerve transfer instead of nerve graft?
- Brachial plexus injuries in which only very proximal or no nerve is available for grafting
- High proximal injuries that require a long distance for regeneration
- To avoid scarred areas where there is high likelihood that critical structures may be injured.
- Major limb trauma with segmental loss of nerve tissue
- As alternative to nerve grafting when time from injury to reconstruction is prolonged
- Partial nerve injuries with a defined functional loss
- Spinal cord root avulsion injuries
- Nerve injuries where level of injury is uncertain such as radiation trauma and multiple level nerve injury
Is motor nerve transfer better than tendon transfer?
Not always.
Nerve injuries that occur more than 12 months earlier or that need to regenerate over long distances will have poor results and should be treated with tendon transfers. The advantage of tendon transfers is the immediate results seen soon after surgery.
Injuries that are amenable to nerve transfers do better because -
1. Nerve transfer can restore motor and sensory function
2. Multiple muscle groups can be restored with a single nerve transfer
3. Insertion and attachments of the muscle are not disrupted, so original muscle function and tension is maintained.
What are nerve transfers?
Nerve transfer uses uninjured proximal nerve to power an injured distal nerve and may restore motor function or sensory function. Motor nerve transfers are designed by selecting donor nerves that supply nonessential muscles or muscles with redundant fibre innervation and that are synergistic with recipient motor nerve.
Example - Transfer of redundant flexor carpi radialis fascicles of the medial nerve and redundant flexor carpi ulnaris fascicles of ulnar nerve to the biceps brachii and brachial branches of musculocutaneous nerve for elbow flexion recovery.
Do all proximal motor nerve injuries result in permanent loss of function?
No. Excellent recovery is possible across long distances under certain circumstances. Early primary repair of sharp transections that maintain motor and sensory topography by excellent coaptation along anatomic landmarks on the epineurium results in good recovery of function.
Nerve repairs in children tend to have good outcomes even with nerve grafts because of enhanced nerve regeneration capacity, shorter distances and possibly greater central plasticity.
Protective sensibility and improved muscle function are possible after long nerve grafts when meticulous micro technique is used and sensory/motor topography is correct.
Describe the functional anatomy of peripheral nerves
4 components -
- Neurons - primary functional units of peripheral nerve are composed of cell bodies and axons. Cell bodies of motor axons are found in the anterior horn area of spinal cord and sensory cell bodies are found in the dorsal root ganglia of the spinal cord.
- Connective tissues of the nerve - 3 layers
a. Endoneurium connective tissue - found around individual axons.
b. Perineurium connective tissue which surround fascicles.
c. Epineurium connective tissue which runs between fascicles and around the outside of the nerve. - Schwann cells - Supply myelin for efficient electrical nerve conduction, appears to influence maturation and resting metabolism of axons.
- End organs - Including motor endplates, sensory receptors, autonomic receptors transduce electrical activity into function.
When does motor recovery appear to become refractory to reinnervation ?
Motor recovery becomes refractory to rein nervation after approximately 15-18 months of denervation.
When does sensory recovery appear to become refractory to reinnervation ?
Sensory recovery has been described up to 20 years after initial denervation.
