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Spontaneous anterior interosseous nerve palsy with hourglass-like fascicular constriction within the main trunk of the median nerve
Spontaneous Anterior Interosseous Nerve Palsy With Hourglass-like Fascicular Constriction Within the Main Trunk of the Median Nerve Akira Nagano, MD, Keiichi Shibata,MD, Humiaki Tokimura, MD, Seizo Yamamoto, MD, YasutoTajiri, MD, Tokyo, Japan Interfascicular neurolysis was performed in nine patients with Spontaneous anterior interosseous nerve palsy. In eight of these patients, an hourglass-like constriction in the fascicles forming the anterior interosseous nerve was found within the main trunk of the median nerve at 2-7.5 cm above the medial epicondyle. The clinical signs and symptoms of these eight patients were similar to those that have been described to isolated neuritis. While the etiology remains unknown, when spontaneous anterior interosseous nerve palsy is suspected to be caused by isolated neuritis, interfascicular neurolysis should be performed to confirm the lesion and to discover whether fascicular constriction is present. (/ Hand Surg 1996; 21 A:266-270.)
The suspected cause of spontaneous anterior interosseous nerve (AIN) palsy has been reported as neuralgic amyotrophy,1 isolated neuritis, 2 and entrapment neuropathy.3 We had performed exploratory surgery in 10 patients with spontaneous AIN palsy in 2 of whom the operative findings confirmed that the palsy was due to nerve compression by the pronator teres or a fibrous band. In the other eight patients, in whom the nerve was slightly swollen, scarred, hardened, or even normal, the cause was suspected to be isolated neuritis. 4 Recently, we encountered a patient in whom the AIN was partially swollen at external neurolysis, and an hourglass-like fascicular constriction was discovered in the AIN after interfascicular neurolysis. We suspected that same lesion could have existed in our
From the Department of Orthopaedic Surgery, The University of Tokyo Hospital Branch,Tokyo,Japan. Received for publicationApril 10, 1995; accepted in revised form July 18, 1995. No benefitsin any form have been received or will be received from a commercialparty relateddirectlyor indirectlyto the subjectof this article. Reprint requests: Akira Nagano, MD, Department of Orthopaedic Surgery, The Universityof Tokyo Hospital Branch, 3-28-6, Mejirodai, Bunkyo-ku,Tokyo, Japan.
266
The Journal of Hand Surgery
above-mentioned eight cases with no external compression. Since then, we have performed interfascicular neurolysis for all cases of AIN palsy with no clear cause. Here we report an additional eight patients with AIN palsy with hourglass-like fascicular constriction within the main trunk of the median nerve, as revealed by interfascicular neurolysis.
Materials and Methods Fourteen patients with spontaneous AIN palsy were referred to our hospital between 1992 and 1994. Of these, one patient showed recovery signs within 3 months after the onset, three patients showed no recovery at 3 months after the onset but refused an exploratory operation, and one patient was seen 1.5 years after the onset with M3 (Medical Research Council grading system) of the flexor pollicis longus (FPL) and the flexor digitorum profundus of the index finger (FDP1). These five patients were therefore treated conservatively. The other nine patients did not show any recovery by 3 months after onset and accepted surgical exploration of the AIN. The patients included eight men and one woman, with all average age at operation of 40 years (range, 26-64 years). The mean interval between
The Journal of Hand Surgery / Vol. 21A No. 2 March 1996
267
T a b l e 1. Preoperative Status
Muscle Strength Case
Age (years)
Sex
Affected Side
Pain at Elbow
1
30
M
L
2 3 4 5 6 7 8 9
64 34 57 26 43 31 34 44
M M M M M M M F
L R L R L R R R
+ + + + +
Interval Between Pain and Palsy (d) 1 42 12 2 2
-
+ + +
32 30 l
FTPL
FDP1
M0 M0 M2 M0 M0 M0 M0 M2 M0
M0 M0 M0 M4 M0 M2 M0 M0 M0
FPL, flexor pollicis longus; FDP1, flexor digitorum pr0fundus of index finger.
the onset and the operation was 5 months (range, 3-10 months). The fight side was affected in five patients and the left in four. The clinical signs and symptoms of these nine patients are shown in Table 1. Eight patients had pain in the elbow region before the onset of the palsy, and the palsy occurred at a mean of 15 days (range, 1-42 days) after the onset of the pain. No patient showed any clear physical cause due to manual work or sports activity. The strength of both the FPL and the FDP1 was M0 in five patients: the strength of the FPL was M2 and that of the FDP1 was M0 in two patients; the strength of the FPL was M0 and that of the FDP1 was M4 in one patient; and the strength of the FPL was M0 and that of the FPD 1 was M2 in one patient. No patient showed any sensory disturbance or muscular weakness in the flexor digitorum superficialis or the abductor pollicis brevis. The median nerve and the AIN were explored from the proximal one third of the forearm to about 5 cm above the elbow. When there was no external
compression, interfascicular neurolysis was performed under microscopic guidance.
Results No external compression was found anywhere along the course of the median nerve or the AIN in any patient. Three median nerves showed slight swelling, hardening, or adhesion to surrounding tissue at the elbow, and the other six were normal in appearance. By interfascicular neurolysis, an hourglass-like fascicular constriction was discovered in the fascicles of the AIN within the median nerve at 2.0-7.5 cm above the elbow in eight patients (Table 2). Only one fascicular constriction was found in two patients (Fig. 1A); two were found in one fascicle in four patients (Fig. 2B); one was found in each of two fascicles in one patient (Fig. 1B); and two were found in each of two fascicles in one patient (Fig. 1C). The clinical signs and
T a b l e 2. F i n d i n g s at O p e r a t i o n *
Fascicular Constriction Case
Duration Until Surgery (mo)
Appearance of Nerve
Distance Above Medial Epicondyle (cm)
Type
1
10.0
5.0
1 in 1 fascicle
2 3
5.5 3.0
Partially swollen; hardened, adhered Normal Strongly adhered
Absent 2.0, 3.0
4 5 6 7
7.5 3.5 7.0 3.5
Normal Normal Slightly adhered Normal
2.0, 3.5 5.5, 7.5 5.5 2.0, 3.0
8 9
5.0 4.0
Normal Normal
5.3, 6.0 2.5, 5.5
None 1 in each of 2 fascicles 2 in 1 fascicle 2 in 1 fascicle 1 in 1 fascicle 2 in each of 2 fascicles 2 in 1 fascicle 2 in l fascicle
*Patient 5 underwent nerve grafting using the sural nerve. All other patients were treated by interfascicular neurolysis alone.
268
Nagano et al. / Spontaneous Interosseous Nerve Palsy
A
A
B
G Figure 1. Hourglass-like fascicular constrictions. (A) One constriction only (case 1); (B) one constriction in each of two fascicles (case 3); (C) two constrictions in each of two fascicles (case 7). (From Shibata et alJ ~ with permission.)
s y m p t o m s of the one patient with no fascicular constriction were very similar to those of the patients with constriction. In seven of the eight patients with hourglass-like fascicular constriction, treatment was by interfascicular neurolysis only, and in the other patient the con-
G Figure 2. The right median and the anterior interosseous nerve were explored 3.5 months after onset. (A) The nerves were normal in appearance. The left white tape was passed under the anterior interosseous nerve, and the middle white tape was passed under the median nerve 1.0 cm proximal to the elbow. (B) Two hourglass-like fascicular constrictions were revealed in one fascicle, located 5.5 and 7.5 cm above the medial epicondyle, after interfascicular neurolysis. (C) Appearance under magnification.
striction was resected and nerve grafting was performed. Five patients treated by interfascicular neu-
The Journal of Hand Surgery / Vol. 21A No. 2 March 1996
269
Table 3. Postoperative Results* Time to M1 After Operation (mo) Case
Time to M1 After the Onset (too)
Results"
FPL
FDP1
FPL
FDP1
FPL
FDP1
Follow-up Period (too)
1
1.5
1.5
l 1.0
11.0
2 3 4 5 6 7 8 9
5.5 5.5 4.0 7.5
M4 M3 M5 M5 M3 M3 M5
M4 M3 M5 M5 M3 M3 M5 Too early to estimate Too early to estimate
20 15 18 20 12 12 15
6.0
9.0 13.0
2.0 3.0
7.5 14.5
6.5
*Surgery involved nerve grafting for patient 5, and intrafascicular neurolysis for all others. FPL, flexor pollicis longus; FDP1, flexor digitiorum profundus of index finger.
rolysis and the one treated by nerve grafting were followed for more than 1 year after the operation (Table 3). The strength of the FPL and the FDP1 returned to better than M3 in all patients. The strength of the FPL was M0 at the operation in four of the five patients treated by interfascicular neurolysis and recovered to M1 at 1.5-7.5 months after operation, which corresponded to 7.5-14.5 months after onset. The strength of the FDP1 was M0 at operation in three of these five patients and recovered to M1 at 1.5-6.3 months after operation (6.5-11.0 months after onset). In the one patient who underwent nerve grafting, the strength of the FPL recovered to M1 at 5.5 months after operation and that of the FDP1 to M1 at 2 months after operation.
Case Report A 26-year-old man who worked as a roof tiler noticed a severe pain at the anteromedial aspect of the fight elbow with no clear cause. Two days later, he noticed that he could not flex the interphalangeal joint of the fight thumb or the distal interphalangeal joint of the right index finger. He visited our outpatient clinic 3 days after the onset of these symptoms. The strength of both the FPL and FDP1 was M0. The patient was then followed conservatively for 3 months but showed no sign of recovery. The median nerve and the AIN were surgically explored 3.5 months after the onset. The nerves were normal in appearance (Fig. 2A). The AIN was explored in the forearm and traced proximally along the median nerve in the arm under microscopy. Two hourglass-like fascicular constrictions were seen 5.5 and at 7.5 cm proximal to the medial epicondyle (Fig. 2B, C). The lesion segment was resected for 5 cm, and nerve grafting using the
sural nerve was performed. The FDP1 and the FPL began contractions at 2.0 and 5.5 months after operation, respectively, and they had recovered to M4 by 1 year after operation. Pathologic examination of the specimen distal to the constriction showed a complete loss of axons and an increase in the number of Schwann cells, with no inflammatory infiltration. At 5 mm above the proximal constriction, no inflammatory infiltration was seen, but the nerve was edematous and the axon diameter was reduced.
Discussion We performed a surgical exploration of the AIN in nine patients with spontaneous AIN palsy. Hourglass-like fascicular constrictions were revealed in eight of these patients by interfascicular neurolysis. External neurolysis alone is not adequate for thorough exploration of the AIN, and interfascicular neurolysis should be performed to detect any lesion. An hourglass-like fascicular constriction in the AIN has been reported in the literature for only five patients. 5-9 However, we have found this lesion in most cases of AIN palsy not related to external compression. Seven of eight patients with this constriction had pain in the elbow, and palsy was evident 1-42 days after the onset of pain. Such cases had previously been attributed to isolated neuritis when there were no findings of entrapment neuropathy at exploration. An hourglass-like fascicular constriction should be suspected in AIN palsy when that is attributed to neuritis. The etiology of this lesion remains unknown. Haussmann and Kendel6 and Nakamura et al. s have reported that the cause may involve mechanical torsion by rolling of the fascicles during flexion-extension of the elbow or pronation-supination of the fore-
270
Nagano et al. / Spontaneous Interosseous Nerve Palsy
arm. Hosi et al. 9 reported that this constriction did not have a mechanical origin, because in their patient one lesion was found in each of two fascicles, which could not be explained by pronation-supination of the forearm. They suggested that the etiology might involve an inflammatory response due to infection or an autoimmune response. In our series, the constriction occurred in the fascicles of the main trunk of the median nerve, which gives rise to the AIN, and two or more constrictions were present in six of eight patients. These findings are not explained by rolling of the faScicles or pronation-supination motion of the forearm. We suggest that the cause is an inflammation in the nerve, causing edema, with the fascicle then adhering locally. Subsequent traction by flexion and extension of the elbow pulls more strongly on the fascicles forming the AIN than on those forming the main trunk of the median nerve, since the traction force is thought to be greater on the shorter segment, causing the fascicles to become constricted. With respect to the treatment of this constriction, Haussmann and Kendel6 and Nakamura et al.8 resected the portion containing the constriction and performed nerve grafting. We also performed nerve grafting in one patient, because the constriction in this patient was as severe as if the fascicle were completely ruptured, and we did not know the results of our first three operated cases at the time of his surgery. However, recovery from palsy after interfascicular neurolysis has generally been good. Therefore, we recommend only interfascicular neurolysis and believe that nerve grafting is unnecessary to treat this lesion. It is unknown whether the good recovery
in our series was spontaneous recovery or was due to the interfascicular neurolysis. The time intervals between the first muscle contraction and the operation and between the first muscle contraction and the onset was different in each case, which suggests that recovery was not spontaneous and was not clearly due to the operation. Further study is therefore required.
References 1. Kiloh LG, Nevin S. Isolated neuritis of the anterior interosseous nerve. BMJ 1952;1:850-1. 2. Parsonage MJ, Turner JWA. Neuralgic amyotrophy, the shoulder girdle syndrome. Lancet 1948; 1:973-8. 3. Fearn CBD, Goodfellow JW. Anterior interosseous nerve palsy. J Bone Joint Surg 1965;47B:91-3. 4. Nagano A. Anterior interosseous nerve palsy. J Jpn Soc Surg Hand 1987;3:894-7 (in Japanese with English abstract). 5. Englert HM. Partielle faszikulfire Medianus-Atropie ungekl~trter Genese. Handchirurgie 1976;8:61-2. 6. Haussmann R Kendel K. Oligofaszikul~ires MedianusKompressions Syndrom. Handchirurgie 1981; 13:268-71. 7. Haussmann R Intratrunkl~e faszikul~e Kompression des N. interosseus anterior. Handchirurgie 1982; 14:183-5. 8. Nakamura M, Suganuma E, Tanaka M, Ishizuki M, Huruya K. A case report of the anterior interosseous nerve palsy in which one of the two funiculi was found twisted at about five cm proximal to the elbow. J Jpn Soc Surg Hand 1992;8:986-9 (in Japanese with English abstract). 9. Hosi K, Ochiai N, Shinoda H, Kotani K, Matsuura H, Itokawa H et al. Median nerve paresis with hourglass deformed funiculi; a case report. Rinsho Useikeigeka 1993 ;28:1171--4 (in Japanese). 10. Shibata, K, Nagano A, Yamamoto S, Tokimua F, Ochiai N. Necessity of interfascicular neurolysis in anterior interosseous nerve palsy. J Jpn Soc Surg Hand 1994;10:985-9.
The suspected cause of spontaneous anterior interosseous nerve (AIN) palsy has been reported as neuralgic amyotrophy,1 isolated neuritis, 2 and entrapment neuropathy.3 We had performed exploratory surgery in 10 patients with spontaneous AIN palsy in 2 of whom the operative findings confirmed that the palsy was due to nerve compression by the pronator teres or a fibrous band. In the other eight patients, in whom the nerve was slightly swollen, scarred, hardened, or even normal, the cause was suspected to be isolated neuritis. 4 Recently, we encountered a patient in whom the AIN was partially swollen at external neurolysis, and an hourglass-like fascicular constriction was discovered in the AIN after interfascicular neurolysis. We suspected that same lesion could have existed in our
From the Department of Orthopaedic Surgery, The University of Tokyo Hospital Branch,Tokyo,Japan. Received for publicationApril 10, 1995; accepted in revised form July 18, 1995. No benefitsin any form have been received or will be received from a commercialparty relateddirectlyor indirectlyto the subjectof this article. Reprint requests: Akira Nagano, MD, Department of Orthopaedic Surgery, The Universityof Tokyo Hospital Branch, 3-28-6, Mejirodai, Bunkyo-ku,Tokyo, Japan.
266
The Journal of Hand Surgery
above-mentioned eight cases with no external compression. Since then, we have performed interfascicular neurolysis for all cases of AIN palsy with no clear cause. Here we report an additional eight patients with AIN palsy with hourglass-like fascicular constriction within the main trunk of the median nerve, as revealed by interfascicular neurolysis.
Materials and Methods Fourteen patients with spontaneous AIN palsy were referred to our hospital between 1992 and 1994. Of these, one patient showed recovery signs within 3 months after the onset, three patients showed no recovery at 3 months after the onset but refused an exploratory operation, and one patient was seen 1.5 years after the onset with M3 (Medical Research Council grading system) of the flexor pollicis longus (FPL) and the flexor digitorum profundus of the index finger (FDP1). These five patients were therefore treated conservatively. The other nine patients did not show any recovery by 3 months after onset and accepted surgical exploration of the AIN. The patients included eight men and one woman, with all average age at operation of 40 years (range, 26-64 years). The mean interval between
The Journal of Hand Surgery / Vol. 21A No. 2 March 1996
267
T a b l e 1. Preoperative Status
Muscle Strength Case
Age (years)
Sex
Affected Side
Pain at Elbow
1
30
M
L
2 3 4 5 6 7 8 9
64 34 57 26 43 31 34 44
M M M M M M M F
L R L R L R R R
+ + + + +
Interval Between Pain and Palsy (d) 1 42 12 2 2
-
+ + +
32 30 l
FTPL
FDP1
M0 M0 M2 M0 M0 M0 M0 M2 M0
M0 M0 M0 M4 M0 M2 M0 M0 M0
FPL, flexor pollicis longus; FDP1, flexor digitorum pr0fundus of index finger.
the onset and the operation was 5 months (range, 3-10 months). The fight side was affected in five patients and the left in four. The clinical signs and symptoms of these nine patients are shown in Table 1. Eight patients had pain in the elbow region before the onset of the palsy, and the palsy occurred at a mean of 15 days (range, 1-42 days) after the onset of the pain. No patient showed any clear physical cause due to manual work or sports activity. The strength of both the FPL and the FDP1 was M0 in five patients: the strength of the FPL was M2 and that of the FDP1 was M0 in two patients; the strength of the FPL was M0 and that of the FDP1 was M4 in one patient; and the strength of the FPL was M0 and that of the FPD 1 was M2 in one patient. No patient showed any sensory disturbance or muscular weakness in the flexor digitorum superficialis or the abductor pollicis brevis. The median nerve and the AIN were explored from the proximal one third of the forearm to about 5 cm above the elbow. When there was no external
compression, interfascicular neurolysis was performed under microscopic guidance.
Results No external compression was found anywhere along the course of the median nerve or the AIN in any patient. Three median nerves showed slight swelling, hardening, or adhesion to surrounding tissue at the elbow, and the other six were normal in appearance. By interfascicular neurolysis, an hourglass-like fascicular constriction was discovered in the fascicles of the AIN within the median nerve at 2.0-7.5 cm above the elbow in eight patients (Table 2). Only one fascicular constriction was found in two patients (Fig. 1A); two were found in one fascicle in four patients (Fig. 2B); one was found in each of two fascicles in one patient (Fig. 1B); and two were found in each of two fascicles in one patient (Fig. 1C). The clinical signs and
T a b l e 2. F i n d i n g s at O p e r a t i o n *
Fascicular Constriction Case
Duration Until Surgery (mo)
Appearance of Nerve
Distance Above Medial Epicondyle (cm)
Type
1
10.0
5.0
1 in 1 fascicle
2 3
5.5 3.0
Partially swollen; hardened, adhered Normal Strongly adhered
Absent 2.0, 3.0
4 5 6 7
7.5 3.5 7.0 3.5
Normal Normal Slightly adhered Normal
2.0, 3.5 5.5, 7.5 5.5 2.0, 3.0
8 9
5.0 4.0
Normal Normal
5.3, 6.0 2.5, 5.5
None 1 in each of 2 fascicles 2 in 1 fascicle 2 in 1 fascicle 1 in 1 fascicle 2 in each of 2 fascicles 2 in 1 fascicle 2 in l fascicle
*Patient 5 underwent nerve grafting using the sural nerve. All other patients were treated by interfascicular neurolysis alone.
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Nagano et al. / Spontaneous Interosseous Nerve Palsy
A
A
B
G Figure 1. Hourglass-like fascicular constrictions. (A) One constriction only (case 1); (B) one constriction in each of two fascicles (case 3); (C) two constrictions in each of two fascicles (case 7). (From Shibata et alJ ~ with permission.)
s y m p t o m s of the one patient with no fascicular constriction were very similar to those of the patients with constriction. In seven of the eight patients with hourglass-like fascicular constriction, treatment was by interfascicular neurolysis only, and in the other patient the con-
G Figure 2. The right median and the anterior interosseous nerve were explored 3.5 months after onset. (A) The nerves were normal in appearance. The left white tape was passed under the anterior interosseous nerve, and the middle white tape was passed under the median nerve 1.0 cm proximal to the elbow. (B) Two hourglass-like fascicular constrictions were revealed in one fascicle, located 5.5 and 7.5 cm above the medial epicondyle, after interfascicular neurolysis. (C) Appearance under magnification.
striction was resected and nerve grafting was performed. Five patients treated by interfascicular neu-
The Journal of Hand Surgery / Vol. 21A No. 2 March 1996
269
Table 3. Postoperative Results* Time to M1 After Operation (mo) Case
Time to M1 After the Onset (too)
Results"
FPL
FDP1
FPL
FDP1
FPL
FDP1
Follow-up Period (too)
1
1.5
1.5
l 1.0
11.0
2 3 4 5 6 7 8 9
5.5 5.5 4.0 7.5
M4 M3 M5 M5 M3 M3 M5
M4 M3 M5 M5 M3 M3 M5 Too early to estimate Too early to estimate
20 15 18 20 12 12 15
6.0
9.0 13.0
2.0 3.0
7.5 14.5
6.5
*Surgery involved nerve grafting for patient 5, and intrafascicular neurolysis for all others. FPL, flexor pollicis longus; FDP1, flexor digitiorum profundus of index finger.
rolysis and the one treated by nerve grafting were followed for more than 1 year after the operation (Table 3). The strength of the FPL and the FDP1 returned to better than M3 in all patients. The strength of the FPL was M0 at the operation in four of the five patients treated by interfascicular neurolysis and recovered to M1 at 1.5-7.5 months after operation, which corresponded to 7.5-14.5 months after onset. The strength of the FDP1 was M0 at operation in three of these five patients and recovered to M1 at 1.5-6.3 months after operation (6.5-11.0 months after onset). In the one patient who underwent nerve grafting, the strength of the FPL recovered to M1 at 5.5 months after operation and that of the FDP1 to M1 at 2 months after operation.
Case Report A 26-year-old man who worked as a roof tiler noticed a severe pain at the anteromedial aspect of the fight elbow with no clear cause. Two days later, he noticed that he could not flex the interphalangeal joint of the fight thumb or the distal interphalangeal joint of the right index finger. He visited our outpatient clinic 3 days after the onset of these symptoms. The strength of both the FPL and FDP1 was M0. The patient was then followed conservatively for 3 months but showed no sign of recovery. The median nerve and the AIN were surgically explored 3.5 months after the onset. The nerves were normal in appearance (Fig. 2A). The AIN was explored in the forearm and traced proximally along the median nerve in the arm under microscopy. Two hourglass-like fascicular constrictions were seen 5.5 and at 7.5 cm proximal to the medial epicondyle (Fig. 2B, C). The lesion segment was resected for 5 cm, and nerve grafting using the
sural nerve was performed. The FDP1 and the FPL began contractions at 2.0 and 5.5 months after operation, respectively, and they had recovered to M4 by 1 year after operation. Pathologic examination of the specimen distal to the constriction showed a complete loss of axons and an increase in the number of Schwann cells, with no inflammatory infiltration. At 5 mm above the proximal constriction, no inflammatory infiltration was seen, but the nerve was edematous and the axon diameter was reduced.
Discussion We performed a surgical exploration of the AIN in nine patients with spontaneous AIN palsy. Hourglass-like fascicular constrictions were revealed in eight of these patients by interfascicular neurolysis. External neurolysis alone is not adequate for thorough exploration of the AIN, and interfascicular neurolysis should be performed to detect any lesion. An hourglass-like fascicular constriction in the AIN has been reported in the literature for only five patients. 5-9 However, we have found this lesion in most cases of AIN palsy not related to external compression. Seven of eight patients with this constriction had pain in the elbow, and palsy was evident 1-42 days after the onset of pain. Such cases had previously been attributed to isolated neuritis when there were no findings of entrapment neuropathy at exploration. An hourglass-like fascicular constriction should be suspected in AIN palsy when that is attributed to neuritis. The etiology of this lesion remains unknown. Haussmann and Kendel6 and Nakamura et al. s have reported that the cause may involve mechanical torsion by rolling of the fascicles during flexion-extension of the elbow or pronation-supination of the fore-
270
Nagano et al. / Spontaneous Interosseous Nerve Palsy
arm. Hosi et al. 9 reported that this constriction did not have a mechanical origin, because in their patient one lesion was found in each of two fascicles, which could not be explained by pronation-supination of the forearm. They suggested that the etiology might involve an inflammatory response due to infection or an autoimmune response. In our series, the constriction occurred in the fascicles of the main trunk of the median nerve, which gives rise to the AIN, and two or more constrictions were present in six of eight patients. These findings are not explained by rolling of the faScicles or pronation-supination motion of the forearm. We suggest that the cause is an inflammation in the nerve, causing edema, with the fascicle then adhering locally. Subsequent traction by flexion and extension of the elbow pulls more strongly on the fascicles forming the AIN than on those forming the main trunk of the median nerve, since the traction force is thought to be greater on the shorter segment, causing the fascicles to become constricted. With respect to the treatment of this constriction, Haussmann and Kendel6 and Nakamura et al.8 resected the portion containing the constriction and performed nerve grafting. We also performed nerve grafting in one patient, because the constriction in this patient was as severe as if the fascicle were completely ruptured, and we did not know the results of our first three operated cases at the time of his surgery. However, recovery from palsy after interfascicular neurolysis has generally been good. Therefore, we recommend only interfascicular neurolysis and believe that nerve grafting is unnecessary to treat this lesion. It is unknown whether the good recovery
in our series was spontaneous recovery or was due to the interfascicular neurolysis. The time intervals between the first muscle contraction and the operation and between the first muscle contraction and the onset was different in each case, which suggests that recovery was not spontaneous and was not clearly due to the operation. Further study is therefore required.
References 1. Kiloh LG, Nevin S. Isolated neuritis of the anterior interosseous nerve. BMJ 1952;1:850-1. 2. Parsonage MJ, Turner JWA. Neuralgic amyotrophy, the shoulder girdle syndrome. Lancet 1948; 1:973-8. 3. Fearn CBD, Goodfellow JW. Anterior interosseous nerve palsy. J Bone Joint Surg 1965;47B:91-3. 4. Nagano A. Anterior interosseous nerve palsy. J Jpn Soc Surg Hand 1987;3:894-7 (in Japanese with English abstract). 5. Englert HM. Partielle faszikulfire Medianus-Atropie ungekl~trter Genese. Handchirurgie 1976;8:61-2. 6. Haussmann R Kendel K. Oligofaszikul~ires MedianusKompressions Syndrom. Handchirurgie 1981; 13:268-71. 7. Haussmann R Intratrunkl~e faszikul~e Kompression des N. interosseus anterior. Handchirurgie 1982; 14:183-5. 8. Nakamura M, Suganuma E, Tanaka M, Ishizuki M, Huruya K. A case report of the anterior interosseous nerve palsy in which one of the two funiculi was found twisted at about five cm proximal to the elbow. J Jpn Soc Surg Hand 1992;8:986-9 (in Japanese with English abstract). 9. Hosi K, Ochiai N, Shinoda H, Kotani K, Matsuura H, Itokawa H et al. Median nerve paresis with hourglass deformed funiculi; a case report. Rinsho Useikeigeka 1993 ;28:1171--4 (in Japanese). 10. Shibata, K, Nagano A, Yamamoto S, Tokimua F, Ochiai N. Necessity of interfascicular neurolysis in anterior interosseous nerve palsy. J Jpn Soc Surg Hand 1994;10:985-9.