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A Man with Hand Pain
Case 4
A Man with Hand Pain
A 48-year-old man had a 6-month history of pain in the right hand, occasionally radiating to the shoulder. He also had numbness with tingling in the first two digits, and was referred for an EMG. The neurologic examination was normal, except for mild weakness of the thenar muscle on the right and a positive
Phalen test. There was a sensory deficit in the median nerve distribution on the right and left hands. Strength, reflexes, and sensory examinations in the legs were essentially normal.
AN EMG TEST WAS PERFORMED Motor Nerve Studies
Motor Nerve Studies—cont’d
Nerve and Site
Latency (ms)
Amplitude (mV)
Conduction Velocity (m/s)
Median Nerve R.
Normal £ 4.2
Normal ≥6
Normal ≥ 50
6.4 8.4
6.9 10.9
— 120
Normal £ 3.6
Normal ≥8
Normal ≥ 50
2.8 6.4
18.0 14.4
— 63
Normal £ 4.2
Normal ≥6
Normal ≥ 50
Wrist Elbow Ulnar Nerve R. Wrist Below elbow Median Nerve L. Wrist Elbow
5.2 9.2
13 12
— 55
Nerve and Site
Latency (ms)
Amplitude (mV)
Conduction Velocity (m/s)
Ulnar Nerve L.
Normal £ 3.6
Normal ≥8
Normal ≥ 50
2.8 6.6
18 18
— 62
Wrist Below elbow
Median Nerve R. Recording at Adductor Digiti Minimi Muscle Wrist NR NR — Elbow 8 3 —
F-wave Studies Nerve
Latency (ms)
Median nerve R. Ulnar nerve R. Median nerve L. Ulnar nerve L.
Normal Latency £ (ms) 30 30 30 30
31.2 26.2 30.0 27.2
Sensory Nerve Studies
Nerve Median nerve R. Ulnar nerve R. Median nerve L. Ulnar nerve L.
Onset Latency (ms)
Normal Onset Latency £ (ms)
Peak Latency (ms)
Normal Peak Latency £ (ms)
4.2 1.9 4.2 1.8
2.6 2.6 2.6 2.6
4.7 2.4 4.7 2.3
3.1 3.1 3.1 3.1
Amp (µV)
Normal Amp ≥ (µV)
Conduction Velocity (m/s)
Normal Conduction Velocity ≥ (m/s)
4 16 12 14
20 13 20 13
31 63 31 67
50 50 50 50
111
112
Case 4
EMG Data Muscle
Insrt Activity
Fibs
Pos Waves
Fasc
Amp
Dur
Poly
Pattern
Deltoid R. Biceps brachii R. Flexor carpi radialis R. Flexor carpi ulnaris R. Extensor dig. communis R. Abductor pollicis brevis R. 1st dorsal interosseous R.
Norm Norm Norm Norm Norm Norm Norm
None None None None None None None
None None None None None None None
None None None None None None None
Norm Norm Norm Norm Norm Norm Norm
Norm Norm Norm Norm Norm Norm Norm
None None None None None None None
Full Full Full Full Full Full Full
WHAT WERE THE EMG FINDINGS? This test revealed prolonged SNAP latencies and slow velocities of both median nerves but not the ulnar nerve, indicating the patient had bilateral median neuropathy at the wrist. The motor studies were unusual: although there was prolongation of the distal latencies of both median CMAPs, supporting the diagnosis of median entrapment, the conduction velocity of the right median nerve from elbow to wrist was faster than normal. There was also higher amplitude of the median CMAP when stimulated at the elbow compared with the response obtained with stimulation at the wrist. There was a positive “dip” at the beginning of the right median CMAP when stimulating at the elbow but not at the wrist (Fig. 4-1). The right ulnar CMAP was larger from wrist stimulation than from elbow stimulation (Fig. 4-2). The needle test was normal. 5 ms
These electrophysiologic findings are highly suggestive that the patient not only had bilateral carpal tunnel syndrome (CTS), but also a right Martin-Gruber anastomosis (MGA). The larger amplitude CMAP from median elbow stimulation is caused by the contribution to the CMAP of ulnar-innervated muscles that receive innervation from the anomaly above the wrist. The initial positive deflection of the median CMAP obtained from elbow stimulation is caused by volume-conducted responses of the ulnar muscles innervated by the anomaly. The abnormally fast median motor conduction velocity is explained by the contribution of axons traveling within the ulnar nerve that cross above the wrist, and do not pass through the carpal tunnel. The higher amplitude of the ulnar nerve CMAP from wrist stimulation compared with that obtained from the elbow stimulation is caused by stimulation of axons that incorporate in the ulnar nerve from the crossover below the elbow, but above the wrist. This finding should always be considered with caution as it can be confused with a conduction block. The stimulation should always be supra2 ms
A 1
221 V 2 mV
A 1 A 2
320 V 5 mV
222 V 2 mV A 2
400 V 5 mV
FIGURE 4-1 Right median nerve motor conduction studies. Notice large amplitude median CMAP on elbow stimulation with an initial positive deflection.
FIGURE 4-2 Normal CMAP configuration of the adductor digiti minimi (ADM) muscle with a lower amplitude on ulnar elbow stimulation compared with wrist stimulation.
A Man with Hand Pain 2 ms
A
356 V
1
2 mV
A
327 V
2
2 mV
FIGURE 4-3 CMAP obtained from median nerve stimulation at the elbow (A2) but not at the wrist when recording at the ADM muscle (A1).
maximal, as less-than-supramaximal stimulation can also cause low-amplitude CMAPs.
HOW DOES ONE PROVE THE DIAGNOSIS OF A MARTIN-GRUBER ANASTOMOSIS? In this case the anastomosis was proved by stimulating the median nerve at the elbow and recording a response in the abductor digiti minimi (ADM) muscle (Fig. 4-3) not obtained by stimulating the wrist. This indicates that the fibers from the median nerve travel through the anastomosis to the ADM muscle. In suspected cases, ulnar stimulation while recording at the first dorsal interosseous muscle could demonstrate the abnormality not seen using the standard recording at the ADM muscle. There was no cross-innervation in the left median nerve, which had equal CMAPs from proximal and distal stimulation (Fig. 4-4).
WHAT IS THE MARTIN-GRUBER ANASTOMOSIS? This anomalous cross-innervation from median to ulnar nerves was initially described by Martin in 17631 and later by Gruber in 1870.2 The MGA consists of a crossover of
113 5 ms
A
232 V
1
5 mV
A
400 V
2
5 mV
FIGURE 4-4 Normal configuration of both median nerve CMAP responses on the left side.
fibers going from the median to the ulnar nerve in the forearm (Fig. 4-5). It has been reported that more frequently the anomalous axons go through the anterior interosseous nerve.3 In a recent cadaveric study, however, it was found that the most common anastomosis was between the branches to the flexor digitorum profundus muscle.4 This study also demonstrated that some cases of anomalous innervation cannot be demonstrated by EMG. In MGA there is cross-innervation of motor axons, but crossover of sensory axons can also occur.5 MGA has been found in about 31% of subjects.6 In one study it was present in 62% of family members, suggesting an autosomal dominant inheritance.7 The crossover is bilateral in 68% of cases,8 and its presence is demonstrated by the methods described earlier and by the use of collision techniques.9 In a group of 22 subjects Wilbourn and Lambert6 found that the anomaly innervated the ADM in 9 cases (this is considered MGA type I), the first dorsal interosseous in 21 cases (MGA type II), and the thenar muscles normally innervated by the ulnar nerve in 3 cases (MGA type III) (Fig. 4-6). There are variations of these, and they can also occur in combination. In addition, there are variations in the site of the anomalous connection in the forearm. MGA is only one of the various anomalous nerve connections; some persons have an anastomosis from the ulnar to the median nerve, and in some all muscles of the hand are innervated by the median nerve. Variations of innervation occurring in the hand were described by Riche and by Cannieu.10,11 These cross-innervations have not been studied in detail but should be taken under consideration
114
Case 4 5 ms
Type II
A
130 V
1
1 mV
A
235 V
2
1 mV
Type III Type I
Ulnar nerve
FIGURE 4-6 Another patient with CTS. Notice the normal CMAP median nerve with prolonged latency on wrist stimulation and a double wave CMAP with stimulation at the elbow.
Median nerve
Anastomosis
FIGURE 4-5 Diagram of the different median-ulnar anatomies of the forearm (MGA types I, II, III).
when unusual electrophysiologic findings are being interpreted. For example, Dumitru et al.12 documented denervation of the abductor pollicis brevis muscle (normally innervated by the median nerve) in a patient with ulnar neuropathy at the elbow. To summarize, type I MGA is demonstrated by the presence of a response in the ADM upon stimulating the median nerve at the elbow. Type II is demonstrated by the presence of a response in the first dorsal interossei upon stimulation at the median nerve at the elbow. Type III is difficult to document, but sometimes is recognized by a double hump of the median response upon stimulation at the elbow (see Fig. 4-6).
SUMMARY This patient with bilateral CTS had unusual electrophysiologic findings caused by an MGA. He responded to surgery.
MGA should be suspected when there is a higheramplitude CMAP of the median nerve from elbow stimulation, compared with the one obtained with stimulation at the wrist, and a lower amplitude of the ulnar nerve CMAP when stimulated at the elbow compared with the wrist. MGA in a patient with CTS is suggested by the following: 1. Prolonged distal median motor and SNAP latencies 2. A larger proximal than distal median CMAP amplitude 3. A positive deflection of the median CMAP during elbow stimulation13,14 4. A larger ulnar CMAP with wrist stimulation compared with elbow stimulation (this and numbers 2 and 3 are seen in MGA without CTS) 5. A falsely fast elbow-to-wrist median motor conduction velocity15 6. A double response of the median nerve CMAP, when stimulated at the elbow, caused by a much slower conduction of the median nerve than the ulnar nerve16 The treatment of CTS in patients with MGA is the same as in those without the anomaly. This patient was treated unsuccessfully with wrist splints and later underwent carpal tunnel release surgery with excellent response.
A Man with Hand Pain
IMPORTANT POINTS • MGA occurs in about 31% of all people. This anomalous innervation consists of a crossover of axons from the median nerve to the ulnar nerve in the forearm, so that muscles normally innervated by the ulnar nerve are innervated by axons traveling with the median nerve, and then crossing over to the ulnar nerve. • Electrophysiologic diagnosis of MGA is based on the presence of larger-amplitude median CMAPs obtained with elbow stimulation compared with that obtained with wrist stimulation. The reverse occurs during the ulnar nerve stimulation, and should not be confused with conduction block. • The crossover is confirmed by observing a CMAP in ulnar-innervated muscles, when stimulating the median nerve at the elbow and not at the wrist. • MGA should be suspected in cases with CTS when there is not only prolongation of the distal median SNAPs and motor latencies but also an initial positive “dip” of the median CMAP with elbow stimulation, a falsely fast conduction velocity from elbow to wrist, and higher amplitude of the median CMAP when stimulated at the elbow.
REFERENCES 1. Martin R: Tal om Nervus allmam na Egenskaperi Manniskans Kropp. Stockholm, L Salviu, 1763. 2. Gruber W: Uber die Verbindung des Nervus medianus mit dem Nervus Ulnaris am Unteerarme des Menschen und der Saugetiere. Arch Anat Physiol Med Leipzig 37:501–522, 1870. 3. Srinivasan R, Rhodes J: The median-ulnar anastomosis (Martin-Gruber) in normal and congenitally abnormal fetuses. Arch Neurol 38:418–419, 1981.
115
4. Lee KS, Oh CS, Chung IH, Sunwoo IN: An anatomic study of the Martin-Gruber anastomosis: Electrodiagnostic implications. Muscle Nerve 31:95–97, 2005. 5. Santoro L, Rosato R, Caruso G: Median-ulnar nerve communications: Electrophysiological demonstration of motor and sensory fibre cross-over. J Neurol 229:227–235, 1983. 6. Wilbourn J, Lambert EH: The forearm median to ulnar nerve communication: Electrodiagnostic aspects. Neurology 26:368, 1976. 7. Crutchfield CA, Gutmann L: Hereditary aspects of medianulnar nerve communications. J Neurol Neurosurg Psychiatry 43:53–55, 1980. 8. Kimura J, Murphy MJ, Varda DJ: Electrophysiological study of anomalous innervation of intrinsic hand muscles. Arch Neurol 33(12):842–844, 1976. 9. Kimura J: Collision technique. Physiologic block of nerve impulses in studies of motor nerve conduction velocity. Neurology 26:680–682, 1976. 10. Riche P: Le nerf cubital et less muscles de l’eminece thenar. Bull Mem Soc Anat Paris 5:251–252, 1897. 11. Cannieu JMA: Note sur une anastomose entre la branch profonde du cubital et le median. Bull Soc d’Anat Physiol Bordeaux 18:339–349, 1897. 12. Dumitru D, Walsh NE, Weber CF: Electrophysiologic study of the Riche-Cannieu anomaly. Electromyogr Clin Neurophysiol 28:27–31, 1988. 13. Gutmann L, Gutierrez A, Riggs JE: The contribution of median to ulnar communication in diagnosis of mild carpal tunnel syndrome. Muscle Nerve 9:319–321, 1986. 14. Gutmann L: Median-ulnar communications and carpal tunnel syndrome. J Neurol Neurosurg Psychiatry 40:982– 986, 1977. 15. Iyer V, Fenichel GM: Normal median nerve proximal latency in carpal tunnel syndrome: A clue to coexisting MartinGruber anastomosis. J Neurol Neurosurg Psychiatry 39:449– 452, 1976. 16. Lambert EH: Diagnostic value of electrical stimulation of motor nerves. Electroencephalogr Clin Neurophysiol 22(Suppl):9–16, 1962.
A Man with Hand Pain
A 48-year-old man had a 6-month history of pain in the right hand, occasionally radiating to the shoulder. He also had numbness with tingling in the first two digits, and was referred for an EMG. The neurologic examination was normal, except for mild weakness of the thenar muscle on the right and a positive
Phalen test. There was a sensory deficit in the median nerve distribution on the right and left hands. Strength, reflexes, and sensory examinations in the legs were essentially normal.
AN EMG TEST WAS PERFORMED Motor Nerve Studies
Motor Nerve Studies—cont’d
Nerve and Site
Latency (ms)
Amplitude (mV)
Conduction Velocity (m/s)
Median Nerve R.
Normal £ 4.2
Normal ≥6
Normal ≥ 50
6.4 8.4
6.9 10.9
— 120
Normal £ 3.6
Normal ≥8
Normal ≥ 50
2.8 6.4
18.0 14.4
— 63
Normal £ 4.2
Normal ≥6
Normal ≥ 50
Wrist Elbow Ulnar Nerve R. Wrist Below elbow Median Nerve L. Wrist Elbow
5.2 9.2
13 12
— 55
Nerve and Site
Latency (ms)
Amplitude (mV)
Conduction Velocity (m/s)
Ulnar Nerve L.
Normal £ 3.6
Normal ≥8
Normal ≥ 50
2.8 6.6
18 18
— 62
Wrist Below elbow
Median Nerve R. Recording at Adductor Digiti Minimi Muscle Wrist NR NR — Elbow 8 3 —
F-wave Studies Nerve
Latency (ms)
Median nerve R. Ulnar nerve R. Median nerve L. Ulnar nerve L.
Normal Latency £ (ms) 30 30 30 30
31.2 26.2 30.0 27.2
Sensory Nerve Studies
Nerve Median nerve R. Ulnar nerve R. Median nerve L. Ulnar nerve L.
Onset Latency (ms)
Normal Onset Latency £ (ms)
Peak Latency (ms)
Normal Peak Latency £ (ms)
4.2 1.9 4.2 1.8
2.6 2.6 2.6 2.6
4.7 2.4 4.7 2.3
3.1 3.1 3.1 3.1
Amp (µV)
Normal Amp ≥ (µV)
Conduction Velocity (m/s)
Normal Conduction Velocity ≥ (m/s)
4 16 12 14
20 13 20 13
31 63 31 67
50 50 50 50
111
112
Case 4
EMG Data Muscle
Insrt Activity
Fibs
Pos Waves
Fasc
Amp
Dur
Poly
Pattern
Deltoid R. Biceps brachii R. Flexor carpi radialis R. Flexor carpi ulnaris R. Extensor dig. communis R. Abductor pollicis brevis R. 1st dorsal interosseous R.
Norm Norm Norm Norm Norm Norm Norm
None None None None None None None
None None None None None None None
None None None None None None None
Norm Norm Norm Norm Norm Norm Norm
Norm Norm Norm Norm Norm Norm Norm
None None None None None None None
Full Full Full Full Full Full Full
WHAT WERE THE EMG FINDINGS? This test revealed prolonged SNAP latencies and slow velocities of both median nerves but not the ulnar nerve, indicating the patient had bilateral median neuropathy at the wrist. The motor studies were unusual: although there was prolongation of the distal latencies of both median CMAPs, supporting the diagnosis of median entrapment, the conduction velocity of the right median nerve from elbow to wrist was faster than normal. There was also higher amplitude of the median CMAP when stimulated at the elbow compared with the response obtained with stimulation at the wrist. There was a positive “dip” at the beginning of the right median CMAP when stimulating at the elbow but not at the wrist (Fig. 4-1). The right ulnar CMAP was larger from wrist stimulation than from elbow stimulation (Fig. 4-2). The needle test was normal. 5 ms
These electrophysiologic findings are highly suggestive that the patient not only had bilateral carpal tunnel syndrome (CTS), but also a right Martin-Gruber anastomosis (MGA). The larger amplitude CMAP from median elbow stimulation is caused by the contribution to the CMAP of ulnar-innervated muscles that receive innervation from the anomaly above the wrist. The initial positive deflection of the median CMAP obtained from elbow stimulation is caused by volume-conducted responses of the ulnar muscles innervated by the anomaly. The abnormally fast median motor conduction velocity is explained by the contribution of axons traveling within the ulnar nerve that cross above the wrist, and do not pass through the carpal tunnel. The higher amplitude of the ulnar nerve CMAP from wrist stimulation compared with that obtained from the elbow stimulation is caused by stimulation of axons that incorporate in the ulnar nerve from the crossover below the elbow, but above the wrist. This finding should always be considered with caution as it can be confused with a conduction block. The stimulation should always be supra2 ms
A 1
221 V 2 mV
A 1 A 2
320 V 5 mV
222 V 2 mV A 2
400 V 5 mV
FIGURE 4-1 Right median nerve motor conduction studies. Notice large amplitude median CMAP on elbow stimulation with an initial positive deflection.
FIGURE 4-2 Normal CMAP configuration of the adductor digiti minimi (ADM) muscle with a lower amplitude on ulnar elbow stimulation compared with wrist stimulation.
A Man with Hand Pain 2 ms
A
356 V
1
2 mV
A
327 V
2
2 mV
FIGURE 4-3 CMAP obtained from median nerve stimulation at the elbow (A2) but not at the wrist when recording at the ADM muscle (A1).
maximal, as less-than-supramaximal stimulation can also cause low-amplitude CMAPs.
HOW DOES ONE PROVE THE DIAGNOSIS OF A MARTIN-GRUBER ANASTOMOSIS? In this case the anastomosis was proved by stimulating the median nerve at the elbow and recording a response in the abductor digiti minimi (ADM) muscle (Fig. 4-3) not obtained by stimulating the wrist. This indicates that the fibers from the median nerve travel through the anastomosis to the ADM muscle. In suspected cases, ulnar stimulation while recording at the first dorsal interosseous muscle could demonstrate the abnormality not seen using the standard recording at the ADM muscle. There was no cross-innervation in the left median nerve, which had equal CMAPs from proximal and distal stimulation (Fig. 4-4).
WHAT IS THE MARTIN-GRUBER ANASTOMOSIS? This anomalous cross-innervation from median to ulnar nerves was initially described by Martin in 17631 and later by Gruber in 1870.2 The MGA consists of a crossover of
113 5 ms
A
232 V
1
5 mV
A
400 V
2
5 mV
FIGURE 4-4 Normal configuration of both median nerve CMAP responses on the left side.
fibers going from the median to the ulnar nerve in the forearm (Fig. 4-5). It has been reported that more frequently the anomalous axons go through the anterior interosseous nerve.3 In a recent cadaveric study, however, it was found that the most common anastomosis was between the branches to the flexor digitorum profundus muscle.4 This study also demonstrated that some cases of anomalous innervation cannot be demonstrated by EMG. In MGA there is cross-innervation of motor axons, but crossover of sensory axons can also occur.5 MGA has been found in about 31% of subjects.6 In one study it was present in 62% of family members, suggesting an autosomal dominant inheritance.7 The crossover is bilateral in 68% of cases,8 and its presence is demonstrated by the methods described earlier and by the use of collision techniques.9 In a group of 22 subjects Wilbourn and Lambert6 found that the anomaly innervated the ADM in 9 cases (this is considered MGA type I), the first dorsal interosseous in 21 cases (MGA type II), and the thenar muscles normally innervated by the ulnar nerve in 3 cases (MGA type III) (Fig. 4-6). There are variations of these, and they can also occur in combination. In addition, there are variations in the site of the anomalous connection in the forearm. MGA is only one of the various anomalous nerve connections; some persons have an anastomosis from the ulnar to the median nerve, and in some all muscles of the hand are innervated by the median nerve. Variations of innervation occurring in the hand were described by Riche and by Cannieu.10,11 These cross-innervations have not been studied in detail but should be taken under consideration
114
Case 4 5 ms
Type II
A
130 V
1
1 mV
A
235 V
2
1 mV
Type III Type I
Ulnar nerve
FIGURE 4-6 Another patient with CTS. Notice the normal CMAP median nerve with prolonged latency on wrist stimulation and a double wave CMAP with stimulation at the elbow.
Median nerve
Anastomosis
FIGURE 4-5 Diagram of the different median-ulnar anatomies of the forearm (MGA types I, II, III).
when unusual electrophysiologic findings are being interpreted. For example, Dumitru et al.12 documented denervation of the abductor pollicis brevis muscle (normally innervated by the median nerve) in a patient with ulnar neuropathy at the elbow. To summarize, type I MGA is demonstrated by the presence of a response in the ADM upon stimulating the median nerve at the elbow. Type II is demonstrated by the presence of a response in the first dorsal interossei upon stimulation at the median nerve at the elbow. Type III is difficult to document, but sometimes is recognized by a double hump of the median response upon stimulation at the elbow (see Fig. 4-6).
SUMMARY This patient with bilateral CTS had unusual electrophysiologic findings caused by an MGA. He responded to surgery.
MGA should be suspected when there is a higheramplitude CMAP of the median nerve from elbow stimulation, compared with the one obtained with stimulation at the wrist, and a lower amplitude of the ulnar nerve CMAP when stimulated at the elbow compared with the wrist. MGA in a patient with CTS is suggested by the following: 1. Prolonged distal median motor and SNAP latencies 2. A larger proximal than distal median CMAP amplitude 3. A positive deflection of the median CMAP during elbow stimulation13,14 4. A larger ulnar CMAP with wrist stimulation compared with elbow stimulation (this and numbers 2 and 3 are seen in MGA without CTS) 5. A falsely fast elbow-to-wrist median motor conduction velocity15 6. A double response of the median nerve CMAP, when stimulated at the elbow, caused by a much slower conduction of the median nerve than the ulnar nerve16 The treatment of CTS in patients with MGA is the same as in those without the anomaly. This patient was treated unsuccessfully with wrist splints and later underwent carpal tunnel release surgery with excellent response.
A Man with Hand Pain
IMPORTANT POINTS • MGA occurs in about 31% of all people. This anomalous innervation consists of a crossover of axons from the median nerve to the ulnar nerve in the forearm, so that muscles normally innervated by the ulnar nerve are innervated by axons traveling with the median nerve, and then crossing over to the ulnar nerve. • Electrophysiologic diagnosis of MGA is based on the presence of larger-amplitude median CMAPs obtained with elbow stimulation compared with that obtained with wrist stimulation. The reverse occurs during the ulnar nerve stimulation, and should not be confused with conduction block. • The crossover is confirmed by observing a CMAP in ulnar-innervated muscles, when stimulating the median nerve at the elbow and not at the wrist. • MGA should be suspected in cases with CTS when there is not only prolongation of the distal median SNAPs and motor latencies but also an initial positive “dip” of the median CMAP with elbow stimulation, a falsely fast conduction velocity from elbow to wrist, and higher amplitude of the median CMAP when stimulated at the elbow.
REFERENCES 1. Martin R: Tal om Nervus allmam na Egenskaperi Manniskans Kropp. Stockholm, L Salviu, 1763. 2. Gruber W: Uber die Verbindung des Nervus medianus mit dem Nervus Ulnaris am Unteerarme des Menschen und der Saugetiere. Arch Anat Physiol Med Leipzig 37:501–522, 1870. 3. Srinivasan R, Rhodes J: The median-ulnar anastomosis (Martin-Gruber) in normal and congenitally abnormal fetuses. Arch Neurol 38:418–419, 1981.
115
4. Lee KS, Oh CS, Chung IH, Sunwoo IN: An anatomic study of the Martin-Gruber anastomosis: Electrodiagnostic implications. Muscle Nerve 31:95–97, 2005. 5. Santoro L, Rosato R, Caruso G: Median-ulnar nerve communications: Electrophysiological demonstration of motor and sensory fibre cross-over. J Neurol 229:227–235, 1983. 6. Wilbourn J, Lambert EH: The forearm median to ulnar nerve communication: Electrodiagnostic aspects. Neurology 26:368, 1976. 7. Crutchfield CA, Gutmann L: Hereditary aspects of medianulnar nerve communications. J Neurol Neurosurg Psychiatry 43:53–55, 1980. 8. Kimura J, Murphy MJ, Varda DJ: Electrophysiological study of anomalous innervation of intrinsic hand muscles. Arch Neurol 33(12):842–844, 1976. 9. Kimura J: Collision technique. Physiologic block of nerve impulses in studies of motor nerve conduction velocity. Neurology 26:680–682, 1976. 10. Riche P: Le nerf cubital et less muscles de l’eminece thenar. Bull Mem Soc Anat Paris 5:251–252, 1897. 11. Cannieu JMA: Note sur une anastomose entre la branch profonde du cubital et le median. Bull Soc d’Anat Physiol Bordeaux 18:339–349, 1897. 12. Dumitru D, Walsh NE, Weber CF: Electrophysiologic study of the Riche-Cannieu anomaly. Electromyogr Clin Neurophysiol 28:27–31, 1988. 13. Gutmann L, Gutierrez A, Riggs JE: The contribution of median to ulnar communication in diagnosis of mild carpal tunnel syndrome. Muscle Nerve 9:319–321, 1986. 14. Gutmann L: Median-ulnar communications and carpal tunnel syndrome. J Neurol Neurosurg Psychiatry 40:982– 986, 1977. 15. Iyer V, Fenichel GM: Normal median nerve proximal latency in carpal tunnel syndrome: A clue to coexisting MartinGruber anastomosis. J Neurol Neurosurg Psychiatry 39:449– 452, 1976. 16. Lambert EH: Diagnostic value of electrical stimulation of motor nerves. Electroencephalogr Clin Neurophysiol 22(Suppl):9–16, 1962.