Advances in Nerve Repair Patrick M. Kane, MD The Philadelphia Hand Center, P.C. Philadelphia, Pennsylvania

GOALS OF NERVE REPAIR  Provide precise apposition of two sides of a transected nerve.  Use a minimum number of sutures.  Minimize scar tissue.  Avoid tension at the repair site.  Eliminate the incidence of neuromas.  Maximize the number and concentration of axonal fibers that regenerate across the repair site.

PRIMARY REPAIR  Repair within several hours following the original injury.  Best for: o Sharp nerve lacerations, either complete or partial o Clean wound with well-vascularized surrounding tissue

DELAYED PRIMARY REPAIR  Repair within 5-7 days following the original nerve injury.  Recommended for avulsion injuries when the zone of injury is not readily apparent.  A delay as short as 5-7 days may lead to nerve retraction, edema, and loss of compliance, all of which may make direct end-to-end repairs impossible without excessive tension. o Interpositional nerve grafts may be required o Median nerve lacerations at the wrist, for example, are especially susceptible

SECONDARY REPAIR  Repair greater than 7 days following the original nerve injury.

PRINCIPLES OF NERVE REPAIR  Thorough preoperative motor and sensory physical examination.  Magnification with loupes or microscope.  Microsurgical technique utilizing 8-0 or 9-0 nylon sutures.  Nerve repair: o Avoid the temptation to position the adjacent joint into an extreme position simply to relieve tension on the nerve repair, and avoid excessive tension at the repair site with an interpositional nerve graft. o Use a synthetic absorbable nerve conduit if primary end-to-end repair is not possible. o Perform an epineurial repair if fascicles lack clearly defined anatomic borders or if repairing a single small peripheral nerve (e.g. digital nerve). o When group fascicles are well defined, group fascicular repair is recommended to maximize motor/sensory matching. TYPES OF NERVE REPAIR  Epineurial repair: o Appropriate for small nerves containing one or two fascicles, such as digital nerves o Surface vessels are useful in realigning and matching the nerve ends appropriately o Standard microsurgical repair technique to allow appropriate reapproximation of the epineurium on both ends of the nerve. Minimize number of sutures to reduce amount of scar tissue formation at the repair site. o Also appropriate for mixed nerves where separate motor and sensory fascicle identification not possible  Group fascicular repair: o Higher magnification needed o Appropriate alignment of fascicles, based on location and shape of fascicles o In a major nerve, four or five groups may be chosen and are then approximated with sutures in both the internal and external epineurium  Individual fascicular repair: o Not proven to be superior to epineurial or group fascicular repairs o Benefit of improved fascicle alignment may be offset by increased scarring associated with this technique.

FASCICLE MATCHING METHODS  Intraoperative nerve stimulation in the awake (and cooperative) patient to determine location of proximal sensory and distal motor fascicles.  Histochemical staining: o Applicable within the first 7-9 days following the original nerve injury o Acetylcholinesterase – Found in motor axons, not sensory axons o Carbonic anhydrase – Present in sensory axons and myelin of sensory axons

NERVE DEFECTS  Nerve grafts are necessary when neurorrhaphy cannot be performed without excessive tension and act to provide a source of empty endoneurial tubes through which the regenerating axons can be directed.  Donor nerves: o Sural nerve – Within the lateral aspect of the posterior leg compartment; travels with the lesser saphenous vein; and most easily identified posterior to the lateral malleolus at the ankle level o Medial antebrachial cutaneous nerve o Lateral antebrachial cutaneous nerve o Distal end of the posterior interosseous nerve – Within the floor of the fourth dorsal extensor tendon compartment at the level of the distal forearm  Vascularized nerve grafts: o Utilized for large nerve defects in proximal nerve injuries o Helpful if poor recipient tissue bed is present  Nerve conduits: o For defects < 3 cm in length, but best results for defects < 2 cm in length o Vein interposition grafts o Synthetic absorbable nerve conduits o Peripheral nerve allografts o Autogenous vein grafts may be placed in normal configuration or as an “inside out” vein, with largely equivalent results. Main disadvantage is that the vein graft will collapse and possibly retard nerve regeneration across the conduit. o Synthetic absorbable nerve conduits provide a non-collapsible scaffold that theoretically enhances nerve regeneration. Main disadvantages are $500-$1000 cost per conduit and foreign material.

NERVE TRANSFERS  Nerve transfer surgery (neurotization) was first developed in the mid 1800s with the use of animal models.  Following a proximal nerve lesion with a poor prognosis, expendable motor or sensory nerves can be re-directed in proximity of a specific target: muscle or skin territory. Resulting in improved and faster re-innervation.  The field of nerve transfer surgery is rapidly expanding in the treatment of not only the brachial plexus, but also the arm, forearm and hand.  The numerous advantages offered by transposing a functional nerve stump in proximity to a target muscle or skin territory have created new and exciting alternatives for the management of nerve injuries, particularly those occurring far proximal in the arm or the brachial plexus.  Research in the filed is ongoing, blinded randomized studies comparing traditional tendon transfers to nerve transfers are required  In the report by Özkan T, et al., prospective study was conducted to evaluate patient outcomes following sensory nerve transfer;  20 patients with irreparable ulnar or median nerve lesions underwent the procedure;  18 of 20 patients attended a sensory re-education program after surgery;  2-point discrimination of less than 10 mm was achieved in 15 of 25 hands;  18 of 20 patients reported that the function of their hands improved after the procedure;  Good or excellent results were associated with immediate transfer of the nerve, young age, and patients' attendance to the sensory re-education program after surgery; ref: Restoration of sensibility in irreparable ulnar and median nerve lesions with use of sensory nerve transfer: long-term follow-up of 20 cases.