Motor or sensory loss with open wound
Crush or stretch injury without progressive motor or sensory recovery after 3 to 6 months.
Irreparable nerve damage
Acute primary nerve repair without tension to achieve best outcomes
Nerve graft with more than 10% loss of nerve substance
Conversion of open dirty wounds to clean closed wounds before repair
Electrical fascicle identification useful for median/ulnar nerve repairs in the forearm
Acceptable to substitute conduits for nerve grafts with sensory nerve gaps less than 3 cm
Nerve transfers within 6 months following high median/ulnar nerve lesions or upper trunk plexus injury
Healing Times and Progression of Therapy
Volar/dorsal block orthosis with short arc motion for 3 weeks following primary nerve repair
Immobilization of limb in extension for 8 days after nerve graft, followed by unrestricted motion
Sensory reeducation crucial for good outcomes after sensory nerve reconstruction or transfer
Motor reeducation with emphasis on co-contraction of donor muscle following nerve transfer
Nerve repair under tension should be avoided
Nerve graft through a poorly vascularized bed should not be attempted
Communication with surgeon regarding optimum position for limb immobilization essential
Timelines for Return to Work and Activities of Daily Living
Activities of daily living to commence after 3 to 4 weeks in most cases
Because motor and sensory recovery continue past 2 years, long-term job modification may be necessary
Although the techniques of nerve repair have been refined to a considerable degree, they remain relatively crude from the nerve’s perspective. There have been few advances in the practical aspects of a basic nerve repair over the past 20 years, but there have been exciting discoveries that harness the nerve’s regenerative capacities following injury and these have led to new methods for nerve reconstruction. Techniques that have been commonplace for brachial plexus surgery are now migrating into the arm, including end-to-side repairs, nerve conduits, and nerve transfers.
The science and rationale behind nerve reconstruction is built upon an understanding of nerve anatomy, physiology, and the basic science of nerve injury and healing. The reader is referred to Chapter 42 for a detailed discussion of this topic.
A normal nerve has a longitudinal excursion that subjects it to a certain amount of stress and strain in situ. A peripheral nerve is initially easily extensible. Elasticity decreases by as much as 50% in the delayed repair of nerves in which Wallerian degeneration has occurred. Experimentally, blood flow is reduced by 50% when the nerve is stretched 8% beyond its in vivo length. Complete ischemia occurs at 15%. Suture pull-out does not occur until a 17% increase in length has occurred. This suggests that ischemia and not disruption of the anastomosis is the limiting factor in acute nerve repairs. Nerve is a viscoelastic tissue, meaning that when low loading in tension is applied over time the nerve elongates without a deterioration in nerve conduction velocity. Intriguing experimental work has been done with gradual nerve elongation to overcome nerve gaps using tissue expansion and external fixation, but this cannot as yet be considered an accepted standard of treatment.
The Nerve Gap
There is a difference between a nerve gap and a nerve defect. A nerve gap refers to the distance between the nerve ends, whereas a nerve defect refers to the actual amount of nerve tissue that is lost. With simple nerve retraction following division, the fascicular arrangement is similar. With increasing nerve defects between the proximal and distal stumps there is a greater fascicular mismatch between the stumps, which leads to poorer outcomes, especially if the gap exceeds 5 cm.
The location of fascicles varies somewhat within a nerve, and there are cross-connections between them as fibers migrate from one fascicle to another. The use of intraoperative motor and sensory nerve differentiation can diminish the risk of fascicular mismatch when repairing or grafting a nerve.
Electrical Fascicle Identification
Motor and sensory fascicles can be differentiated by direct stimulation up to 72 hours. The median and ulnar nerves in the distal forearm are most amenable to this technique. A low-amperage stimulator is applied to the major fascicles of the proximal nerve end in a systematic manner with the patient under local anesthesia. Sensory fascicles will elicit pain and may be localized to a specific digit. Motor fascicles elicit no response at lower intensities and poorly localized pain at higher intensities. A cross-sectional sketch of the proximal stump is made. The sensory fascicles are tagged with 10-0 nylon and the patient is placed under general anesthesia. The distal stump is then stimulated in a similar fashion. The reverse picture will be seen, with motor fascicles eliciting a muscle twitch and sensory fascicles being silent. A cross-sectional map is again made and used to match the proximal and distal motor and sensory fascicles.
Alternatively, this author has used nerve action potentials (NAPs) in place of the muscle twitch to map the distal stump. The compound motor action potential (CMAP) disappears at 7 to 9 days, whereas the sensory nerve action potential (SNAP) disappears at day 10 to 11. In chronic injuries the NAPs are no longer present; hence, it is necessary to dissect the distal motor branch, and then follow the motor fascicles proximally to the nerve stump ( Fig. 44-1 ).
The principal indication for surgery is a patient who presents with a laceration and a nerve deficit that does not recover within 1 week. A tension-free repair is the goal for any nerve anastomosis. When there is a clean transection of the nerve and the gap is caused by elastic retraction, an acute primary repair is indicated.
Nerve repair cannot be performed in an infected wound. If the degree of the longitudinal injury cannot be determined, nerve repair should be delayed.
Types of Repair
External Epineurial Suture
This technique is appropriate for small nerves containing only one or two fascicles, such as digital nerves. Since they only contain sensory fibers, matching is not a problem. Epineurial repairs are also indicated for mixed nerves where separate motor and sensory fascicle identification is not possible.
Group Fascicular Suture
The motor and sensory groups of fascicles are identified as described. In a major nerve such as the median or ulnar, four or five groups may be chosen for suture. These are then matched appropriately with the opposite end and approximated with sutures in both the internal and external epineurium.
External Epineurial Splint
Jabaley has employed the external epineurium as a splinting device. The external epineurium is incised longitudinally on its superficial surface and dissected away from the underlying fascicles. The epineurium is left attached on the deep surface, several millimeters from each nerve end. A few interrupted sutures with 8-0 nylon are used to join the ends of the external epineurial strips on the deep surface only, completing the construction of the splint. This maneuver provides for a coaptation of individual fascicles or groups of fascicles with little or no tension ( Fig. 44-2 ).
After nerve repair the rehabilitation focuses on three areas: initial immobilization to protect the repair; joint mobilization to promote longitudinal excursion of the nerve; and motor and sensory reeducation. Before wound closure, the adjacent joints are placed in various degrees of flexion and extension so as to determine the optimum limb position that unloads the repair site. This position is maintained with a blocking orthosis for 3 weeks but a protected short arc of motion may be instituted to provide some nerve gliding. The reader is referred to Chapter 44 for a detailed discussion of postoperative management and rehabilitation.
When treatment of a nerve laceration is delayed, fibrosis of the nerve ends prevents approximation; hence, nerve grafting is required, even though there is no loss of nerve tissue. Nerve grafting to repair a defect is indicated when the length of the gap to be bridged would require more than a 10% elongation of the nerve. This is a better indication for grafting than the nerve gap per se, although 4 cm is often used as a critical defect threshold.
Since the graft is vascularized from the tissue bed, nerve grafting cannot be performed in burned or irradiated tissue.
Role of the Nerve Graft
The nerve graft provides a source of empty endoneurial tubes through which the regenerating axons can be directed. A normal nerve can compensate for the change in length with limb flexion and extension because it is surrounded by gliding tissue that permits longitudinal movement. A nerve graft becomes welded to its recipient bed by the adhesions through which it becomes vascularized. As a consequence the nerve graft is exquisitely sensitive to tension because it has no longitudinal excursion. The harvested length of the graft must be long enough to span the nerve gap without tension while the adjacent joints are extended. This is also the position of temporary immobilization. If the limb or digit is immobilized with joint flexion, the graft will become fixed in this position. When the limb is then mobilized at 8 days, the proximal and distal stumps will be subject to tension even though the graft was initially long enough. Early attempts at lengthening the graft will lead to disruption of the anastomosis.
Considerations for Donor Nerve Grafts
Small-diameter grafts spontaneously revascularize, but thick grafts undergo central necrosis with subsequent endoneurial fibrosis that ultimately impedes the advancement of any ingrowing axon sprouts. The donor-site defect must also be acceptable for the patient. For these reasons most of the available grafts are cutaneous nerves. Typical donor nerves include the medial and lateral antebrachial cutaneous nerves and the sural nerve. The distal terminations of the anterior and posterior interosseous nerves are suitable for digital nerve grafts at the distal interphalangeal joint level.
Millesi has written extensively on this subject. If the recipient nerve is the approximate diameter of the graft, the two stumps are transected until normal-appearing tissue without fibrosis is seen; the graft is then inserted by an epineurial repair. Multiple nerve grafts are used to completely cover the cross-sectional area of each fascicle in a 1 to 2 or 1 to 3 ratio ( Fig. 44-4 ). If there is no group fascicular arrangement, interfascicular dissection is not performed. Graft insertion is then guided by the intraneural topography of the nerve for that specific level of injury.