David J. Slutsky


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3475 Torrance Blvd., Ste F
Torrance, CA 90503


Appointments: 310.792.1809
Fax: 310.792.1811

Office hours: M-F, 9am – 5 pm

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In September 2008, we will be moving to a beautiful new 4,400 sq ft, state of the art dedicated hand center located at 2808 Columbia Ave in Torrance, CA., which will feature onsite nerve conduction studies, occupational hand therapy and digital x-ray.
 


PROCEDURES

NEW ADVANCES IN NERVE REPAIR

I. Introduction
Although the techniques of nerve repair have been refined to an eloquent 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 2 decades. There has however been exciting discoveries which harness the nerve’s regenerative capacities following injury that has led to nouvelle methods for nerve reconstruction. Techniques which have been commonplace for brachial plexus surgery are now migrating into arm, including end-to-side repairs, nerve conduits and nerve transfers. The science and rationale behind nerve reconstruction is built upon the understanding of nerve physiology and biomechanics in addition to an intimate knowledge of nerve anatomy.

Axon Regeneration
Nerve regeneration does not involve mitosis and multiplication of nerve cells. Instead, the cell body restores nerve continuity by growing a new axon. Axon sprouting has been demonstrated as early as 24 hours following nerve transection. One axon sends out multiple unmyelinated axon sprouts from the tip of the remaining axon or collateral sprouts from a nearby proximal node of Ranvier. The distal sprout contains the growth cone. This sends out filopodia which adhere to sticky glycoprotein molecules in the basil lamina of Schwann cells, such as laminin and fibronectin (neurite - promoting factors). The filopodia contain actin, which aid in pulling the growth cone distally. The basil lamina of two abutting Schwann cells form a potential endoneurial tube into which the regenerating axon grows. These axons will deteriorate if a connection with a target organ is not reached. There are up to 50 advancing sprouts from 1 single axon. Initially there are many more nerve fibers crossing a nerve repair than in the parent nerve.24 Although more than 1 axon may enter the same endoneurial tube, there is eventual resorption of the multiple sprouts leaving one dominant axon.
Axons grow between 1-2 mm/day. In general, axons grow approx: 1-2 mm/day. Motor end plates degrade at approximately 1%/wk.41 There is irreversible muscle fibrosis by 24 months. For practical purposes the maximum length that a nerve can grow to restore motor function is approximately 35 cm. This in part accounts for the poor motor recovery when repairing nerve defects proximal to the elbow in adults. Sensory end organs remain viable since there is no end plate and they retain the potential for reinnervation. 36 Reconstruction of a sensory nerve defect by comparison may provide protective sensation even after many years.

Role of the Schwann Cell
Following nerve transection, the Schwann cell removes the axonal and myelin debris in both the severed nerve ends. Schwann cells produce an immediate source of nerve growth factor (NGF) which helps to support the proximal stump. The Schwann cell expresses NGF receptors which aid in directing the advancing growth cone. It also increases it’s production of other neurotrophic factors including, ciliary neurotrophic factor, brain-derived neurotrophic factor and fibroblast growth factor which promote axonal growth. The laminin and fibronectin in the Schwann cell basil lamina act as a rail for the advancing axon sprouts to grow down. The Schwann cell produces a myelin sheath for the immature axon sprout. Cell biologists have attempted to mimic these functions by incorporating Schwann cells, laminin, fibronectin and nerve growth factors into synthetically engineered nerve conduits.

Nerve Biomechanics
A normal nerve has longitudinal excursion which subjects it to a certain amount of stress and strain in situ. A peripheral nerve is initially easily extensible but this rapidly diminishes with further elongation due to the stretching of the connective tissue within the nerve. Chronically injured nerves become even stiffer. Elasticity decreases by as much as 50% in the delayed repair of nerves in which Wallerian degeneration has occurred.38 Experimentally, blood flow is reduced by 50% when the nerve is stretched 8% beyond it’s in vivo length. Complete ischemia occurs at 15%. Suture pullout does not occur until a 17% increase in length. This suggests that ischemia and not disruption of the anastomosis is the limiting factor in acute nerve repairs.8 This observation is also applicable to nerve grafting. Nerve is a viscoelastic tissue in that when low loading in tension is applied over time the nerve elongates, without a deterioration in nerve conduction velocities. At 8% elongation stress relaxation results in the recovery of blood flow within 30 minutes,. Intriguing experimental work has been done with gradual nerve elongation to overcome nerve gaps using tissue expansion and external fixation 29 but this cannot be considered an accepted standard of treatment as yet.

The Nerve Gap
There is a difference between the 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. As the defect between the proximal and distal stumps increases there is a greater fascicular mismatch between the stumps which leads to poorer outcomes, especially if the gap exceeds 5 cm.

Nerve Anatomy
A peripheral nerve contains connective tissue elements and axons. The connective tissue of nerves includes the outer epineurial layer, which contains loosely woven collagen fibers and elastin. The epineurium protects the nerve from compression and stretch and therefore tends to be thicker in places that experience repetitive shear force such as the ulnar nerve in the cubital tunnel. The perineurium separates groups of fascicles and acts as a diffusion barrier, which protects the axons from infection and chemical insult. The perineurium is relatively unyielding which allows for a positive endoneurial pressure. This same property can lead to a minicompartment syndrome when the endoneurial pressure increases such as occurs in compressive neuropathies. The individual axons may or may not be myelinated are surrounded by the endoneurium which provides support and a framework for regeneration of nerve fibers after injury.

II. NERVE REPAIR (link to median nerve repair video)
The location of fascicles varies somewhat within a nerve, and there are cross connections between them as fibers migrate from one fascicle to another. This migration occurs because axons destined for a specific end organ receptor may arise at more than one spinal cord level which results in a sorting and rearranging as it moves distally. The use of intraoperative motor and sensory nerve differentiation can diminish the risk of fascicular mismatch when repairing or grafting a nerve. There is the anatomic method based upon separate identification of groups of fascicles, the electrophysiologic method and histochemical methods that rely on staining for enzymes specific to motor or sensory nerves, which is time consuming and currently not in vogue.

Electrical Fascicle Identification
Motor and sensory fascicles can be differentiated by direct stimulation.14 The median and ulnar nerves in the distal forearm are most amenable to this technique.13 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, the author has used nerve action potentials (NAPs) in place of the muscle twitch to map the distal stump (Figure 1 A,B) .32 The compound motor action potential (CMAP) disappears at 7-9 days whereas the sensory nerve action potential (SNAP) disappears at day 10-11.5 CMAPs are recorded from the thenar/hypothenar muscles, and SNAPs are recorded from either the index or small finger using ring electrodes. A grouped fascicular repair is then performed as described below. In chronic injuries the awake stimulation of the proximal stump is unchanged. Since the NAPs are no longer present, it is necessary dissect the distal motor branch, and then follow the motor fascicles proximally to the nerve stump (Figure 2A).

Indications
The principle 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 1° repair is indicated.

Contraindications
Blast injuries which are heavily impregnated with debris or bacteria are better treated by staged reconstruction. 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 (link to ulnar nerve repair video)
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. Usually 3-4 sutures with 9-0 nylon is sufficient. Alternatively, fibrin glue can be used which allows the placement of fewer sutures. 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 (Figure 2 B,C).

External Epineurial Splint: Jabaley has employed the external epineurium as a splinting device.15 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 (Figure 3 A-D).

Postoperative Rehabilitation
After nerve repair the rehabilitation focuses on 3 areas: Initial immobilization to protect the repair, joint mobilization to promote longitudinal excursion of the nerve, and sensory re-education. Prior to wound closure, the adjacent joints are placed in various degrees of flexion and extension in order to determine the optimum limb position that unloads the repair site. This position is maintained with a blocking splint for 3 weeks but a protected short arc of motion may be instituted to provide some nerve gliding.

III. NERVE GRAFTING (link to ulnar nerve graft video)

Indications

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 is indicated to bridge a defect when >10% elongation of the nerve would be necessary to bridge the gap.38 This is a better indication for grafting than the nerve gap per se, although 4 cm is often used as a critical defect.

Contraindications
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 acts to provide a source of empty endoneurial tubes through which the regenerating axons can be directed. Any tissue which contains a basil lamina such as freeze dried muscle or tendon, can be substituted but only the autogenous nerve graft also provides a source of viable Schwann cells. 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 it’s 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 which ultimately impedes the advancement of any ingrowing axon sprouts. The donor site defect must be acceptable for the patient and the harvested nerve must be long enough to ensure a tension free anastomosis with the adjacent joints in full extension. 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 termination of the anterior and posterior interosseous nerves are suitable for digital nerve grafts at the DIP joint level.

Surgical Technique
Millessi has written extensively on this subject. 26 If the recipient nerve is the approximate diameter of the graft, the two stumps are transected until normal appearing tissue without fibrosis is seen and the graft is inserted by an epineurial repair. If the recipient nerve is larger than the graft the fascicular pattern determines the type of preparation. If the nerve contains 1 - 4 fascicles, the stump is resected until healthy tissue is encountered. Multiple nerve grafts are used to completely cover the cross sectional area of each fascicle in a 1:2 or 1:3 ratio (Figure 4 A,B). When there are 5 -12 fascicles that are the size of the nerve graft, then each fascicle is grafted individually. When there is a polyfascicular pattern with a group fascicular arrangement, interfascicular dissection is performed to isolate the fascicle groups, which are then grafted individually. 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.

Outcomes following repair/graft
Most series report the results of nerve repair using the British Medical research council grading system. which has been modified by Dellon and Mackinnon.10 In this classification S3 = recovery of pain and touch sensibility, with 2 point discrimination of > 15 mm. S3+ equates to 2 point discrimination of 7-15 mm. A grade of M3 equates to a recovery of muscle strength that is sufficient to overcome gravity. M4 is strength with gravity and added resistance.

Ruijs et al performed a meta-analysis after microsurgical nerve repair of 623 median or ulnar nerve injuries. Motor and sensory recovery were significantly associated. In ulnar nerve injuries, the chance of motor recovery was 71 percent lower than in median nerve injuries.30 Kallio and co-authors evaluated 132 patients (mean age 28 years) with injuries to the median nerve at an average 10.4 years after repair. Most of the nerve lesions were sharp (76) or blunt (47) injuries. Division was total in 87 cases, and most were at the wrist level. Secondary repair was performed in 34 cases and fascicular grafting in 98 cases. The average gap was 5.8 cm. Excellent or good results were obtained in only 49.2%. The result of nerve repair was poor in patients aged over 54 years, when the level of the injury was more than 56 cm proximal to the finger tip, if the pre-operative delay was more than 24 months, or if the graft length was more than 70 mm.17

Secer et al reported the results of 407 ulnar nerve injuries caused by gunshot wounds. A good outcome was noted in 15% of patients who underwent high-level repair, 29% of patients who underwent intermediate-level repair, and 49% of patients after low-level repair. The critical period for surgery was within 6 months of injury. Although the optimal graft length was found to be 5 cm, this finding was not statistically significant.31 Kim and coauthors examined 45 patients following surgically treated posterior interosseous nerve entrapments (21) or injuries (23). Seven underwent suture repair, 7 were grafted and the rest underwent neurolysis. Most muscles achieved LSUHSC Grade 3 or better.20
Kallio et al studied 95 patients with 254 completely divided digital nerves at an average of 12.4 (5-20) years after repair. Secondary epineurial suture was used in 53, fascicular grafting in 37 and fascicular suture in five. Useful sensory function was recovered in 79% of the nerves operated on with epineurial or fascicular suture and in 56% with fascicular grafting.16

It is commonly accepted that the results are far better in children than in adults. Tomei evaluated 25 nerve repairs at the wrist in children under age 15 years with a minimum follow-up of 12 months. The sensory results were often excellent (S4 or S3+ in 23 cases/25) whereas motor recovery ranged between from M2 and M3.37

Frykman and Gramyk reviewed 8 studies of nerve grafting published prior to 1990.12. This included 167 patients who underwent median nerve grafting. In this pooled data 81% achieved 81% achieved a grade of M3, while 79%achieved S3. In more recent series Dauotis et al. M3 or better was achieved in 68% and S3 or better in 75% of 47 patients with median nerve grafts.9 Kim et al reported M3/S3 in 72% of 50 patients.19 Milessi achieved M4 or better in 61% and S3 or better in 42%. For the ulnar nerve, he reported M4 or better in 49% and S3 or better in 27%, whereas he reported S3+ or better in only 22% for digital nerve repairs.26

IV. ALTERNATE METHODS OF NERVE RECONSTRUCTION

End-to-side Repairs
Experimental data in both rabbit and primate models have shown that intact donor nerves have the ability to sprout lateral branches from their axons that can grow through endo, peri- and epineurium and reinnervate target organs with functional sensory and motor results.18, 44 These results have also been duplicated in human studies which have included root avulsions of the brachial plexus, as well as patients with large gaps in peripheral nerves. A standard end-to-side anastomosis involves suturing the recipient nerve into an epineural window that is created in the donor nerve. An advantage of this technique is that the donor nerve does not lose any function.

End-to-side repairs cannot replace a sound primary repair, but they have been used as an adjunctive procedure in the following situations: intact nerve to the musculocutaneous to neurotise the biceps muscle, distal stump of the ulnar nerve to the median nerve at the wrist in high ulnar nerve palsies or vice versa and ulnar digital nerves to intact median sensory nerves (Figure 5). The limb is splinted for 3 weeks in a tension free position, followed by motor and sensory re-education. The procedure is best done early since the results deteriorate if delayed beyond 6 months. In Mennen’s series of 56 patients which included 33 ulnar to median and 7 median to ulnar repairs, $M3/S3 was achieved in 56%.25

Neurotization
Brunelli pioneered the concept of direct neurotization of denervated muscles in situations where the motor nerve has been avulsed and direct nerve suture or grafting is not possible.4 He demonstrated in rat and rabbit models that an axon that is in contact with a denervated muscular fiber can form a new neuromuscular junction. The motor end-plate is in fact, not an anatomical formation but rather a functional alteration of the axon endings and the muscular fibers that develop when they are in contact with each other. A prerequisite for this procedure is that there is some residual trophism of the muscle. This is manifested by the presence of fibrillation potentials on the EMG. The procedure in contraindicated if there is muscle atrophy without fibrillation potentials or if there is extensive scarring or joint stiffness.

The donor nerve is retrieved and sectioned transversely until healthy fascicles are seen. The junction of the proximal _ and distal _ of the muscular belly is exposed. A sural nerve graft of adequate length is harvested and sutured end to end to the donor nerve. The distal part of the nerve graft is freed from the epineurium and is divided into as many artificial fascicles as possible. The epineurium of the graft is sutured to the muscle epimysium in order to prevent graft retraction. A number of slits are made at different depths and as widely separated as the graft will permit. The artificial fascicles are then implanted into the muscle and held in place with fibrin glue and epineurial sutures. The limbs are immobilized for 15 days in order to prevent avulsion of the implanted nerve. Re-education is started with joint mobilization and electrotherapy. In Brunelli’s series of 80 patients, M4/M5 motor strength was achieved in 72 of the cases.3

Nerve Conduits
Neurotrophism is the ability of chemotactic hormonal or growth factors to enhance the rate of nerve regeneration. Neurotrophic factors produced by the target end-organ undergo retrograde axonal transport and help support the cell body. Neurotropism describes the directional accuracy of that regeneration. The growth cone is attracted to neurotropic proteins that are derived from the distal degenerating nerve segment after nerve transection. These phenomena have been exploited through the use of synthetic or natural conduits to bridge the nerve gap. Histologically, fibrin clot develops inside the tube within hours. Within the first week longitudinally oriented fibrin matrix bridges span the nerve gap. In the second week, fibroblasts, Schwann cells, macrophages and endothelial cells permeate the matrix. Axon sprouts from proximal nerve reach the distal stump and become myelinated by the 4th week. The axons elongate down intact the distal endoneurial tubes and reinnervate the target organs. Nondegradable tubes out of silicone were initially used. More recently natural prosthetic tubes have included freeze/thawed muscle (which contains a basal lamina) and autogenous vein grafts. Biodegradable synthetic material includes polyglycolic acid, caprolactone, and collagen. The postoperative rehabilitation includes early mobilization of the part since tension on the repair site is not a consideration, followed by appropriate sensory and/or motor retraining.
Lundborg compared tubulation with a silicone conduit, after intentionally leaving a 3-4 mm nerve gap (11 cases) v.s. conventional microsurgical repair of transected median and ulnar nerve repairs (7 cases) in the forearm. The results showed no significant differences between the two techniques although the silicone tubes had to be removed at a later date due to compression of the reformed nerve.23. Chiu et al did a series of animal experiments bridging gaps of 1.0 - 6.0 cm using autogenous vein grafts.6 The technique includes suturing a reversed vein graft in place distally so that the valves in the vein cannot collapse and block axonal migration. The proximal repair is performed after filling the vein with saline to present clot formation that will produce scarring that can obstruct the axons (Figure 6 A-C) In their clinical series, Chiu and Strauch reported comparable results to those obtained with nerve repair and grafting for sensory nerve defects of < 3 cm.7

Weber et al performed a randomized prospective multicenter evaluation on 98 subjects with 136 nerve transections in the hand comparing a polyglycolic conduit with either end-to-end or a nerve graft for nerve repair. There were 56 nerves repaired in the control group and 46 nerves repaired with a conduit available for follow-up. The overall results showed no significant difference between the two groups as a whole. Nerves with gaps of 4 mm or less had better sensation when repaired with a conduit; the mean moving two-point discrimination was 3.7 +/- 1.4 mm for polyglycolic acid tube repair and 6.1 +/- 3.3 mm for end-to-end repairs (p = 0.03). All injured nerves with deficits of 8 mm or greater were reconstructed with either a nerve graft or a conduit. This subgroup also demonstrated a significant difference in favor of the polyglycolic acid tube. The mean moving two-point discrimination for the conduit was 6.8 +/- 3.8 mm, with excellent results obtained in 7 of 17 nerves, whereas the mean moving two-point discrimination for the graft repair was 12.9 +/- 2.4 mm, with excellent results obtained in none of the eight nerves (p < 0.001 and p = 0.06, respectively).40 Bertleff et al examined the results of using a caprolactone tube v.s. primary repair in 34 digital nerve lesions with gaps < 2 cm. The results with the conduits were equal to those of repair as evaluated by Pressure-Specified-sensory testing device and 2 pd.1

Nerve Transfers (link to FDS nerve transfer video)
Perhaps one of the most exciting recent developments in peripheral nerve reconstruction has been through the use of nerve transfers. They are indicated when there is a need to direct a large number of motor axons quickly to the denervated muscle in situations where there is insufficient time for axonal ingrowth. For motor nerves, an expendable donor nerve with pure motor fibers and a large number of axons near the target muscle is selected. It is preferable if the donor muscle is synergistic to the target muscle. Motor re-education is crucial and involves the recruitment of the donor muscle and then contraction of the reinnervated muscle. Sensory nerve transfers require sensory retraining. Some specific examples of upper limb nerve transfers are described below.

Biceps Reinnervation
In 1994, Oberlin described a series of 4 patients who had undergone successful nerve transfer using redundant fascicles to the flexor carpi ulnaris (FCU) from the ulnar nerve to the motor branch of the musculocutaneous nerve for biceps reinnervation. 28 His group then modified this by performing a double fascicular nerve transfer using redundant fascicles of the median and ulnar nerve to reinnervate the biceps and brachialis muscles. 21 These transfers are indicated in C5-C7 plexus lesions where direct nerve reconstruction is not possible. Mixed plexus injuries can also be treated by this method if there is adequate clinical recovery in the lower roots. Since the neurorraphy is placed close to the target muscles, this nerve transfer is particularly useful in patients who have had a delay in surgical treatment. Successful restoration of elbow flexion has been reported even in cases done one year after injury. The absolute contraindication for this nerve transfer is a global brachial plexus palsy with no recovery of ulnar nerve function since the transfer requires intact function of the C8 ,T1 nerve roots.

Following an isolated Oberlin transfer the patient is treated with a sling for the initial 2 weeks followed by passive elbow motion. Once there is evidence of reinnervation the patient is started on muscle reeducation and isometric strengthening. Elbow flexion is enhanced by activation of the flexor carpi ulnaris which is achieved by having the patient grip while simultaneously trying to flex the elbow. In their review of the literature, Sharpe and Stevanovic identified a total of 100 cases. Eighty percent of patients recovered > M4 motor strength for elbow flexion, 9 percent recovered M3 function, and 11 percent with < M3 recovery. Clinical evidence of biceps reinnervation was seen at an average of 3 months, with a range from 2-7 months. Recovery of M3 function ranged between 4-13 months. For those patients who recovered M4 motor function, the range of elbow flexion strength was between 0.5 and 7 kg.33

Wrist and Finger Extension
Mackinnon et al have demonstrated that redundant median nerve branches to the flexor digitorum sublimus (FDS), flexor carpi radialis (FCR) or palmaris longus (PL) may be used for transfer. In a dissection of 31 cadaver arms, they noted that double innervation of the FDS was found in 94% of the specimens.39 They described two successful cases of transfer of the FDS fascicles to the pronator teres branch to restore pronation. They subsequently reported the use of this transfer to the extensor carpi radialis (ECRB) branch and the posterior interosseous nerve (PIN) in a case of a high radial nerve palsy and a brachial plexopathy with excellent results.22 In a separate study they noted that the FCU branch of ulnar nerve can also be used, but this required a second incision.2

Proximal to the elbow, the median nerve is found to condense into 3 bundles. Branches arising from the anterior bundle can be seen innervating the FCR and pronator teres (PT) (Figure 7A). The FDS branches along with the FCR and PL fascicles arise from the middle group. They are carefully differentiated from the hand intrinsics using a hand held stimulator. The radial nerve is isolated through the same incision. It can be found between the brachioradialis and brachialis as it divides into the superficial sensory nerve branch and the PIN branch. MacKinnon recommends use of the PL and the FDS or FCR branches to the PIN and the ECRB branch. The redundant median nerve fascicles are harvested in close proximity to the PIN to avoid undue tension on the repair site. An end to end coaptation is then performed (Figure 7 B,C). If need be a short nerve graft can be interposed. Postoperatively an above elbow splint is applied with the elbow at 90 degrees and the shoulder, wrist, and fingers free. Gentle elbow flexion is started after the first week followed by gradual elbow extension. Motor retraining is akin to tendon transfers. The patient is instructed in active sublimus contractions, which will ultimately produce wrist and finger extension.

Published clinical series on this transfer are still lacking. In Mackinnon’s series a 51 y.o. male with a proximal left radial nerve palsy underwent transfer of the nerve branch to the PL and the FDS to the PIN and ECRB branch respectively. He achieved 4/5 power for wrist extension but lacked simultaneous finger extension at 14 months postoperatively. The second patient was a 24 y.o. female following an iatrogenic radial nerve injury at the plexus level. The nerve branch from the PL and FDS were transferred to the PIN. A 2nd FDS branch was transferred to the ECRB. The patient achieved 4/5 power of wrist and finger extension.22

Intrinsic Muscle Reinnervation
The only donor nerve for intrinsic muscle reinnervation that fulfills all of the requirements for nerve transfer is the distal anterior interosseous nerve (AIN). It may be used to neurotize either the recurrent motor branch of the median nerve or the deep motor branch of the ulnar nerve. It is almost purely a motor nerve save for proprioceptive fibers to the wrist capsule and it is expendable since there is minimal functional loss resulting from denervation of the pronator quadratus (PQ) muscle. Just prior to entering the PQ, the axon count of the AIN is equal to $ 75% of the deep motor branches of the median and ulnar nerves. With sufficient proximal interfascicular dissection of the distal median or ulnar nerves, direct coaptation of the transected distal anterior interosseous nerve to the fascicular origins of the thenar branch of the median nerve or the deep motor branch of the ulnar nerve is possible.42

For thenar reinnervation Wood has noted that a transfer of the distal anterior interosseous nerve may be used only in those patients with median nerve loss distal to the origin of the anterior interosseous nerve and with sparing of the entire anterior interosseous nerve branch.43 This technique should be considered in those patients who are unlikely to recover median innervated thenar motor function by a median nerve repair or reconstruction. Similarly, for intrinsic muscle reinnervation transfer of the distal AIN should be considered in any patient with an ulnar nerve transection at or proximal to the upper forearm because in such patients recovery of intrinsic motor function with ulnar nerve repair or reconstruction is both poor and unpredictable, especially if there a nerve gap. In either case, the injury should not be so distal as to interfere with identification of the median or ulnar nerve motor fascicles. The procedure should be carried out within 6 months from the date of injury.

Sensory Nerve Transfers
The goal of nerve transfers for digital sensation is to redirect intact sensory input from less critical to more critical contact points. The distal thumb, radial side of the index and ulnar side of the small finger have priority with regards to sensory reconstruction from a functional standpoint. Anesthesia in the thumb and index finger limit pinch and fine motor tasks whereas anesthesia in the small finger causes a loss of proprioception of the hand. The adjacent sides of the 3rd and 4th webspaces are by comparison relatively expendable. When a nerve transfer is indicated for a proximal median nerve injury, a failed distal median nerve repair/graft or an upper trunk ( C5,6) injury, the ulnar-innervated fourth web space nerves can be transferred into the first web space nerves in and end-to-end manner to restore thumb and index finger sensation (Figure 8 A,B). In the case of ulnar nerve loss, the median-innervated third web space nerves are selected as donors for transfer to the small finger. The donor site sensory loss may be treated with a secondary series of end-to-side transfers into the existing sensory nerve supply which may provide at least protective sensation. For example, after the fourth web space nerves are transferred to the first web space using end-to-end repair, the distal end of the fourth web space nerves are coapted end-to-side into the intact ulnar proper digital nerve of the small finger. With proximal median and ulnar nerve injuries the superficial radial nerve (SRN) is the only available sensory donor. Ducic et al reported 2 cases of SRN transfer to the ulnar digital nerve of the thumb and the radial digital nerve of the index finger in a proximal median nerve injury with recovery of protective sensation.11. Similarly with a C6,7 injury the dorsal cutaneous branch of the ulnar nerve (DCBUN) provides an additional source of sensory axons.

Timing is not as crucial for sensory nerve reconstruction due to the lack of a motor end-plate hence this can be performed at the surgeons and patient’s discretion. As nerve regeneration progresses specific training for sensory localization is integral to the outcome. Stock et al reported a recovery of S3+ or S4 in 85% of patients. Some tip sensibility returns within 3 to 4 months, with gradual maturation continuing past 2 years after nerve transfer.34 In MacKinnon’s experience recovery of at least protective sensation can be expected following end-to-end coaptations with primary nerve transfers for digital sensation. Using the “ten test” designed by Strauch et al 35 evaluation, sensory recovery even in the absence of sensory re-education will be approximately 6/10 following end-to-end repair and 3/10 following end-to-side repair.27 Localization of sensory stimuli to the donor digits persists for 2 to 3 years, with localization to the recipient digit improving with time, use, and sensory re-education.

Legends
Figure 1. Intraoperative stimulation of Ulnar nerve at wrist
A. Stimulation of deep motor branch
B. CMAP with normal latency but low amplitude (recorded from ADM).
( From Slutsky, DJ. A Practical Approach to Nerve Grafting in the Upper Extremity. Atlas of the Hand Clinics. Nerve Repair and Reconstruction: A Practical Guide. Vol 10, No 1, March 2005, pp 73-92, with permission.)
Figure 2. Ulnar Nerve Laceration
A. Ulnar nerve motor fascicles traced from the distal stump to the deep motor branch (*) in the palm.
B. Group fascicular repair of motor group of fascicles (*).
C. Epineurial repair of remaining sensory fascicles
( From Slutsky, DJ. A Practical Approach to Nerve Grafting in the Upper Extremity. In Peripheral Nerve Surgery: Practical Applications in the Upper Extremity. Slutsky DJ, Hentz VR, eds. Elsevier. Philadelphia, 2006, with permission.)
Figure 3. One month old proximal radial nerve laceration.
A. Minuscule exit wound (arrow) following a stabbing with a knife from the medial arm.
B. Knife tract (arrow) with separation of proximal and distal nerve ends (*).
C. Strip of posterior epineurium is sutured (arrow) to take the tension off the repair
D. Completed epineurial repair.

Figure 4. Proximal Median and Radial Nerve Grafts
A. Laceration through antecubital fossa.
B. Multiple fascicular grafts to median nerve, superficial radial nerve and posterior interosseous nerve (PIN) nerve.
( From Slutsky, DJ. A Practical Approach to Nerve Grafting in the Upper Extremity. In Peripheral Nerve Surgery: Practical Applications in the Upper Extremity. Slutsky DJ, Hentz VR, eds. Elsevier. Philadelphia, 2006, with permission.)
Figure 5. High Ulnar nerve palsy
End-to-side repair of common digital nerve of the small finger (*) to the median derived common digital nerve to the 3rd web (arrow).
Figure 6. Digital neuroma
A. Neuroma of radial digital nerve.
B. Resection back to healthy fascicles and reversed autogenous vein graft interposition.
C. Completed repair.
Figure 7. Posterior Interosseous Nerve Palsy
A. Proximal median nerve dissection demonstrating the 3 different bundles of fascicles. AIN = anterior interosseous nerve, PIN = posterior interosseous nerve, FDS = flexor digitorum sublimus.
B. Isolation of FDS branch.
C. End to end coaptation of FDS branch (*) to posterior interosseous nerve (arrow).
Figure 8. Sensory nerve transfer in the palm after failed median nerve graft.
A. Median nerve (MN) dissection with isolation of 1st webspace branches (arrows) and ulnar derived common digital nerve to the 4th webspace (*).
B. The 4th common digital nerve (*) is transposed and coapted to the ulnar digital nerve of the thumb and the radial digital nerve of the index (arrows).

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