«A Practical Approach to Nerve Grafting in the Upper Extremity David J. Slutsky, MD, FRCS(C) Private Practice, South Bay Hand Surgery Center, 3475 ...»
Neuromuscular function in humans, as in other mammals, disappears 3 to 5 days after nerve section . The preservation of nerve action potentials for 10 days after nerve transection can be used in place of the muscle twitch to map the distal stump (unpublished data); this prevents the need to dissect the nerve to its distal motor branch. Nerve action potential recordings after acute nerve transection are characterized by diminishing amplitudes with preserved latencies until the action potential is no longer present. The compound motor action potential (CMAP) disappears at 7 to 9 days versus the sensory nerve action potential (SNAP), which disappears at 10 to 11 days .
The initial dissection is performed with nitrous oxide because fentanyl can abolish the response. The nerve stimulation is performed after the tourniquet has been deﬂated for 20 minutes using a pulse width duration of 0.05 ms and a repeat rate of 1 to 2 per second.
Averaging is used for small-amplitude nerve action potentials. CMAPs are recorded from the thenar/hypothenar muscles, and SNAPs are recorded from either the index or small ﬁnger using ring electrodes (Fig. 6). A grouped fascicular repair is performed as described previously.
In chronic injuries, the awake stimulation of the proximal stump is unchanged. Because the nerve action potentials are no longer present, it is necessary dissect the distal motor branch, then follow the motor fascicles proximally to the nerve stump (Fig. 7).
Nerve lesions in continuity
Electrical stimulation is useful to determine if there are any intact fascicles in a neuroma in continuity . Bipolar hook electrodes are used with the stimulating and recording electrodes separated by at least 4 cm. The stimulus frequency is two to three times per second with a pulse duration of less than 0.1 ms. The intensity is slowly increased to the range where a response is expected (3–15 V). The recorder sensitivity is increased to a maximum of 20 lV/cm. The nerve is stimulated proximal to, across, and below the lesion. It is estimated that there must be at least 4000 myelinated axons for a recordable nerve action potential to conduct through a neuroma
(Fig. 8) . A neurolysis is performed to single out any normal-appearing fascicles; this is conﬁrmed electrically. Nonconducting fascicles are excised and grafted.
Grafting speciﬁc nerves Median nerve Anatomy The median nerve arises from the medial and lateral cords of the brachial plexus. It contains the nerve root ﬁbers from C6-T1. It provides the motor supply to the pronator teres, the ﬂexor digitorum sublimus, the palmaris longus, the ﬂexor carpi radialis, the thenar muscles, and the radial two lumbricals. Its anterior interosseous branch supplies the ﬂexor pollicus longus, the pronator quadratus, and the ﬂexor digitorum profundus to the index and middle ﬁngers. Its sensory distribution includes the palmar surface of the thumb, index, middle, and radial half of the ring ﬁnger. It lies lateral to the axillary artery, but then crosses medial to it at the level of the coracobrachialis. At the elbow, the median nerve travels behind the bicipital aponeurosis but in front of the brachialis. It enters the forearm between the two heads of the pronator teres and is adherent to the undersurface of the ﬂexor digitorum sublimus muscle until it becomes superﬁcial, 5 cm proximal to the wrist. It then passes underneath the carpal transverse ligament, giving oﬀ the recurrent motor branch and sensory branches to the thumb and ﬁngers.
Injury at the elbow The median nerve is located through an S-shaped anteromedial incision at the cubital fossa.
The lacertus ﬁbrosus is divided taking care to preserve the LABCN. The median nerve and brachial vein lie medial to the artery. At this level, the motor branches of the median nerve consistently collect into three fascicular groups. There is an anterior group (to the pronator teres and ﬂexor carpi radialis), a middle group (to the ﬂexor digitorum sublimus and hand intrinsics), and a posterior group (to the AIN branch) . These branch groups can be traced proximally without harm, within the main trunk of the median nerve for 2.5 to 10 cm .
Injury in the forearm The median nerve is approached through an S-shaped incision over the volar forearm. The nerve is identiﬁed on the undersurface of the sublimus muscle. In the upper third of the forearm, the motor branches usually lie peripherally, typically on the radial and ulnar sides. The motor fascicles from the recurrent motor branch are in a slightly radial position at 100 mm proximal to the radial styloid. The central core of the proximal stump should be connected distally with the motor and sensory components of the hand. Any large identiﬁable forearm motor branches should be attached about the periphery (Fig. 9).
Injury at the wrist The median nerve at the wrist has approximately 30 fascicles. The motor recurrent branch often consists of two fascicles, which are situated in a volar position, with the various sensory groups in the radial, ulnar, and dorsal positions. The motor branch can be separated from the main trunk without harm for 100 mm proximal to the thenar muscles . The motor fascicles in the recurrent motor branch are identiﬁed where they leave the median nerve trunk, then are followed proximally to the distal nerve end. To maintain motor continuity when there is a median nerve gap at the wrist level, a sural nerve graft should be sutured to the large bifascicular group of fascicles along the volar aspect of the distal stump and connected to a matching radial group of fascicles in the proximal stump (Fig. 10).
Injury in the hand The median nerve is approached through an extensile carpal tunnel approach, with division of the transverse carpal ligament. The recurrent motor branch most commonly is found distal to the transverse carpal ligament as it enters the thenar muscles (Fig. 11) . The terminal portion of the AIN provides a good-caliber match at this level.
A PRACTICAL APPROACH TO NERVE GRAFTING IN THE UPPER EXTREMITYFig. 6. Intraoperative stimulation of ulnar nerve (UN) at wrist. (A) Stimulation of deep motor branch. (B) CMAP with normal latency but low amplitude [recorded from abductor digiti minimi (ADM)]. (C) Stimulation of superﬁcial (Sup) sensory fascicles. (D) SNAPs with normal latencies but low amplitudes (recorded from small and ring ﬁngers).
84 SLUTSKY Fig. 7. Ulnar nerve motor fascicles (arrows) traced from the distal stump to the deep motor branch in the palm.
The sensory ﬁbers travel within the common digital nerves to the thumb, index ﬁnger, and middle ﬁnger and the communicating branch to the third web space. The LABCN and MABCN are suitable grafts for nerve gaps at this level (Fig. 12). When the median nerve defect is greater than 5 cm and extends from the wrist to the common digital nerve bifurcation, sural grafts are more appropriate (Fig. 2).
Digits Many authors recommend nerve grafting when the gap exceeds 1 cm with the wrist and all three ﬁnger joints extended . The digital nerves are approached through a midlateral or a volar Brunner incision. The LACBN is a good-caliber match at this level. The dorsal sensory branch that arises from the proper digital nerve also can be used as graft material. This branch most commonly arises proximal to the PIP ﬂexion crease, then crosses superﬁcial or deep to the digital artery to lie just above the extensor mechanism, innervating the dorsum of the middle phalanx . This branch can be provide a 1- to 2-cm nerve graft (see Fig. 2). Distal to the DIP joint, the nerve trifurcates. The terminal PIN is a suitable graft at this level.
Fig. 8. Neuroma in continuity of ulnar nerve. (A) Nerve stimulation with bipolar electrodes proximal to a neuroma-incontinuity (NIC), with recording over a common digital nerve (*). (B) Nerve action potential (nerve action potentials) recorded from the common digital nerve (top tracing). Nerve stimulation also elicited a CMAP from the ﬁrst dorsal interosseous (fdi).
A PRACTICAL APPROACH TO NERVE GRAFTING IN THE UPPER EXTREMITYFig. 9. Proximal median and radial nerve grafts. (A) Laceration through antecubital fossa. (B) Note median nerve laceration and radial nerve laceration at bifurcation of SRN and PIN. (C) Multiple fascicular grafts to median nerve, SRN, and PIN.
Ulnar nerve Anatomy The ulnar nerve arises from the medial cord of the brachial plexus. It contains the nerve root ﬁbers from C8-T1. It provides the motor supply to the hypothenar muscles, the ulnar two lumbricals, the interosseous muscles, the adductor pollicis, the FCU, and the profundus to the ring and small ﬁngers. Its sensory distribution includes the palmar surface of the small ﬁnger, the ulnar half of the ring ﬁnger, and the dorsoulnar carpus. It lies medial to the axillary artery and continues distally to the midarm, where it pierces the medial intermuscular septum. The nerve often is accompanied by the superior ulnar collateral artery. At the elbow, it lies between the medial epicondyle and the olecranon, where it is covered by Osborne’s ligament. It enters the forearm between the two heads of the FCU covered by a ﬁbrous aponeurosis (the cubital tunnel). It runs deep to the FCU until the distal forearm. At the wrist, it passes over the transverse carpal ligament, medial to the ulnar artery through Guyon’s canal. The deep motor branch is given oﬀ at the pisiform and passes underneath a ﬁbrous arch to lie on the palmar surface of the interossei. It crosses the palm deep to the ﬂexor tendons, to terminate in the adductor pollicis and ulnar head of the ﬂexor pollicis brevis.
Injury at the elbow The ulnar nerve is located through a curved posteromedial incision behind the medial epicondyle. At the elbow, the ulnar nerve contains about 20 fascicles, including the motor branches to the forearm muscles. The motor fascicles to the FCU and the intrinsics are centrally located, whereas the sensory ﬁbers are superﬁcially located. The proximal motor branches to the FCU and ﬂexor digitorum profundus often can be traced for 6 cm before interfascicular connections . It is possible to distinguish between sensory and motor fascicles in the distal nerve end using low-intensity electrical stimulation, if performed within a few days of the injury.
86 SLUTSKY Fig. 10. Median nerve (MN) laceration near wrist. (A) A 4-cm defect between MN ends. (B) Sural nerve grafts with matching of volar radial fascicle groups.
Occasionally, fascicles innervating the ﬂexor muscles can be separated from fascicles supplying the intrinsic muscles in the hand . The sural nerve commonly is used as graft material at this level (Fig. 13).
Injury in the forearm The motor fascicles lie dorsal and slightly ulnarly to the sensory fascicles at the wrist level and usually maintain a dorsal relationship as one moves proximally. The motor component remains as a distinct entity 90 mm proximal to the styloid . At 50 to 85 mm proximal to the radial Fig. 11. Median nerve laceration. (A) Laceration of median nerve at junction of motor recurrent branch (RB) and digital sensory nerves to the thumb (*). (B) Repair of recurrent branch, LABCN grafts to digital nerves.
A PRACTICAL APPROACH TO NERVE GRAFTING IN THE UPPER EXTREMITYFig. 12. Blast injury. (A) Disrupted common digital nerves and artery (forceps). (B) Repair of nerve to index, graft of second and third common digital nerves. (C) Close-up view.
styloid, the dorsal sensory branch joins the other groups. At the level of the midforearm, 50 mm from the ulnar styloid, the motor fascicles lie dorsal to the sensory fascicles . A sural nerve graft should be placed in the dorsal quadrant of the proximal nerve end and the dorsoulnar quadrant of the distal nerve end to restore motor continuity.
Injury at the wrist The ulnar nerve has 15 to 25 fascicles at the wrist. It can be divided into a volar sensory component and a dorsal motor component. The ulnar nerve is approached through an S-shaped incision over the volar ulnar forearm. The nerve is identiﬁed medial to the ulnar artery underneath the FCU muscle. If a muscle twitch is no longer present, the motor branch can be traced from the takeoﬀ of the deep motor branch to the distal nerve end (see Fig. 7).
Hand The nerve is approached through a volar ulnar incision in line with the ring ﬁnger. The deep motor and more superﬁcial sensory fascicles are separated easily at this level and allow separate grafting (Fig. 14). The sural nerve, LABCN, or MABCN provides suitable sized grafts. The DCBUN usually is not grafted because neuromas of this nerve are uncommon.
Digits Grafting in the digits is similar to grafting in the median nerve.
88 SLUTSKY Fig. 13. Avulsion injury. (A) Thumb amputation associated with avulsion of the palmar arch and median nerve branches in the palm. (B) Thumb replant plus reconstruction of palmar arch with vein graft. (C) 12-cm sural nerve grafts from proximal median nerve to digital nerves (DN).
Guidelines for digital nerve graft selection
Higgins et al  investigated the fascicular cross-sectional area and number of fascicles of ﬁve nerve graft sites to speciﬁc digital nerve segments. In the ﬁngertip distal to the DIP, the AIN, PIN, and MABCN all were appropriate choices for caliber-matched grafts. The LABCN was the only similar donor nerve, however, when number of fascicles was assessed. The LABCN also is the best match in caliber and fascicle number for digital nerve deﬁcits from the metacarpophalangeal joint to the DIP joint and from the common digital nerve bifurcation to the metacarpophalangeal joint. The sural nerve was the most appropriate choice when grafting defects between the wrist and the common digital nerve bifurcation, even though there were considerably fewer fascicles and a smaller cross-sectional area than the common digital nerve.
Radial nerve Anatomy The radial nerve arises from the posterior cord of the brachial plexus. It receives contributions from C5-8 spinal roots. It runs medial to the axillary artery. At the level of the