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Penetration of the Digital Nerves by the Common Palmar Digital Arteries in Human Cadavers
SCIENTIFIC ARTICLE
Penetration of the Digital Nerves by the Common Palmar Digital Arteries in Human Cadavers Ju-Young Lee, BS, Yoo-Ri Kim, BS, Jeong-Nam Kim, BS, Hyun-Gon Choi, MD, Wu-Chul Song, MD, Ki-Seok Koh, PhD
Purpose To investigate the incidence of digital nerve loop penetration by digital arteries (neural loops) in cadaver palms and to classify these neural loops according to their topography and morphology. Methods In total, 121 palms (from 57 right and 64 left hands) were dissected from 70 preserved cadavers (50 male and 20 female; mean age 66.1 y). Results Of the 121 palms, 98 had neural loops; 184 cases of neural loop were observed in total. The neural loops could be classified into 4 topographical types, according to their position relative to the digital arteries: ulnar (in which the ulnar proper palmar digital nerve of the finger is penetrated), radial (in which the radial proper palmar digital nerve of the finger is penetrated), common (in which the common palmar digital nerve of the finger is penetrated), and bridge (in which the neural loop is formed by connecting the ulnar and radial proper palmar digital nerves). The neural loops were also classified morphologically according to their size: form A (ⱖ10 mm), form B (4.0 –9.9 mm), and form C (ⱕ3.9 mm). The mean lengths in these groups were 16.1, 7.2, and 3.0 mm, respectively, and the overall mean length of all neural loops was 10.8 mm. Conclusions It was confirmed that neural loops are a common occurrence in humans; hence, it is surprising that it is a little-known variation in the palm. (J Hand Surg 2010;35A:2022– 2026. Copyright © 2010 by the American Society for Surgery of the Hand. All rights reserved.) Key words Anatomy, common palmar digital artery, hand, neural loop, penetration, proper palmar digital nerve. the neurovascular distribution of the hand are observed frequently. However, digital nerve penetrations (neural loops), which form where a digital artery passes through a digital nerve, have received little attention;
A
NATOMIC VARIATIONS OF
From the Department of Anatomy, School of Medicine, Konkuk University, Seoul, Korea; Department of Plastic and Reconstructive Surgery, School of Medicine, Konkuk University, Seoul, Korea. Received for publication May 13, 2010; accepted in revised form August 30, 2010. This work was supported by Konkuk University in 2010. No benefits in any form have been received or will be received related directly or indirectly to the subject of this article. Correspondingauthor:Ki-SeokKoh,PhD,DepartmentofAnatomy,SchoolofMedicine,Konkuk University, 1, Hwayang-dong, Gwangjin-gu, Seoul 143-701, Korea; e-mail: [email protected]. 0363-5023/10/35A12-0017$36.00/0 doi:10.1016/j.jhsa.2010.08.025
2022 䉬 © ASSH 䉬 Published by Elsevier, Inc. All rights reserved.
little is known about them, even though the structures are occasionally encountered in hand surgery.1 To our knowledge, only a few articles have been written about these variations.1–7 The first description of a variation of the digital nerve loop by Hartmann was published a century ago.7 Edgerton et al.6 also found an anomalous neural ring of the common palmar digital nerve (CPDN) or proper palmar digital nerve (PPDN) that encircled the common palmar digital artery (CPDA), and Barreiro and Huelin5 found neural loops in all 30 palms that they studied. Spinner et al.4 discussed the clinical significance of such a neural loop. Indeed, neural loops have even been described in several atlases and textbooks, but without special comments.8 Therefore, although it is not well known, this phenomenon is considered common in the human palm.
DIGITAL NERVE LOOP PENETRATION
2023
The neural loop is important to clinicians such as hand surgeons, because it can sometimes cause paralysis or pain due to compression of the CPDN by the pulses of CPDA.2,9 –11 The purposes of the present cadaver study were to investigate the incidence of neural loops and to classify them according to their topography and morphology. MATERIALS AND METHODS A total of 121 palms (from 57 right and 64 left hands) were dissected from 70 preserved cadavers (50 male and 20 female; mean age 66.1 y). Skin, subcutaneous tissue, and palmar aponeurosis were removed carefully from the palm. The radial and ulnar arteries were then identified at the wrist, and the superficial palmar arch and radialis indicis artery of the palm were exposed. The radialis indicis artery (which branches from the deep palmar arch) and each CPDA (which branch from the superficial palmar arch), CPDN, and PPDN were dissected carefully. The princeps pollicis artery to the thumb was not included in this study. After dissection, the presence of a neural loop was identified and classified according to its relationship with the radialis indicis artery, the CPDA, or both. The neural loops were classified topographically according to how they divide and the position at which the palmar digital nerve is penetrated by the artery: ulnar (in which the ulnar PPDN of the finger is penetrated), radial (in which the radial PPDN of the finger is penetrated), common (in which the CPDN of the finger is penetrated), and bridge (in which the neural loop is formed by connecting the ulnar and radial PPDNs) types (Fig. 1). The neural loops were also classified into 3 forms according to their morphology and the diameter of the neural loop (from largest to smallest), as follows: form A, in which the diameter of the neural loop is ⬎10.0 mm; form B, in which the diameter of the neural loop is 4.0 –9.9 mm; and form C, in which the digital artery fits tightly into the neural loop and the diameter of the neural loop is ⬍3.9 mm. The length of the neural loop and diameter of the digital artery were measured using digital calipers (CD-15CP; Mitutoyo, Japan). All photographs and diagrams are viewed from the perspective of the right hand. RESULTS The superficial palmar arch was located in the proximal palm, palmar to the median and ulnar nerves, in all cases. In general, the CPDA ran superficial to the CPDN, toward the junction dividing the PPDNs, and deep to the PPDN thereafter, regardless of penetration.
FIGURE 1: Schematic presentation of the 4 topographically different types of neural loop. (U, ulnar PPDN of the finger penetrated; R, radial PPDN of the finger penetrated; C, CPDN of the finger penetrated; and B, formation of the neural loop connecting the ulnar and radial PPDNs. UA, ulnar artery; RA, radial artery; SPA, superficial palmar arch; MN, median nerve; UN, ulnar nerve; arrow, some CPDNs were proximally penetrated by the superficial palmar arch itself.)
Of the 121 palms, 98 had neural loops; 184 cases of neural loop were observed in total. Thus, there was an average of 1.5 neural loops per hand, and about 2 neural loops per palm if a neural loop was present (184 neural loops in 98 palms). The most common neural loop was made by the second CPDA, followed by the first and the third CPDA (Table 1). Only a few neural loops were made by the radialis indicis artery and the fourth CPDA. There were 3 cases in which 2 neural loops were developed by a CPDA; this phenomenon was labeled double penetration (Fig. 2A). In addition, 8 neural loops developed by some CPDNs were penetrated proximally by the superficial palmar arch itself (Figs. 1, 2B). The neural loops were classified into the 4 topographically different types. The most common type was the ulnar, followed by the radial, common, and bridge types, in that order (Table 1, Fig. 1). They were also
JHS 䉬 Vol A, December
2024
TABLE 1.
DIGITAL NERVE LOOP PENETRATION
The Types of Neural Loop Relative to the Involved Palmar Artery Location of Neural Loop
Type
Radialis Indicis
Ulnar
34
Radial Common
First CPDA
4
Bridge
Second CPDA
Third CPDA
28
6
8
31
16
8
15
8
6
6
3
Fourth CPDA
4 (2%)
56 (30%)
80 (44%)
33 (18%)
Total 68 (37%) 55 (30%)
3
38 (21%) 15 (8%)
CPDNs penetrated by superficial palmar arch Total
Superficial Palmar Arch
3 (2%)
8
8 (4%)
8 (4%)
184
FIGURE 2: The special types of neural loop: A double penetration and B some CPDNs were proximally penetrated by the superficial palmar arch itself (SPA, superficial palmar arch).
classified into the 3 morphologically different forms (ie, forms A–C, as defined earlier); the most common was form A, followed by forms B and C, in that order (Table 2, Fig. 3).
The lengths of the neural loops are listed according to their type and form in Table 3. The ulnar and radial types had similar lengths. The mean lengths of neural loops of form A, form B, and form C were 16.1, 7.2,
JHS 䉬 Vol A, December
2025
DIGITAL NERVE LOOP PENETRATION
TABLE 2.
The Forms of Neural Loop Relative to the Involved Palmar Artery Location of Neural Loop Radialis Indicis
Form Form A (ⱖ10 mm)
4
Form B (4.0–9.9 mm) Form C (ⱕ3.9 mm) Total
4
First CPDA
Second CPDA
Third CPDA
Fourth CPDA
Superficial Palmar Arch
Total 86 (47%)
28
38
9
1
6
22
35
15
2
2
6
7
9
56
80
33
77 (42%) 21 (11%)
3
8
184
FIGURE 3: The 3 morphological forms of neural loop: A form A, 19.6 mm; B form B, 8.2 mm; and C form C, 3.0 mm.
TABLE 3. Mean Length of Neural Loop According to Type and Form Type
Length (mm)
Form
Length (mm)
Ulnar
11.0
Form A
16.1
Radial
11.0
Form B
7.2
8.1
Form C
3.0
Common Bridge
14.4
and 3.0 mm, respectively. Form A was about twice as long as form B, which in turn was about twice as long as form C. The overall mean length of the neural loops was 10.8 mm. DISCUSSION Neural loops were found in 98 of 121 palms (81%) in the present study, which is within the range of previously reported incidences (67%, 92%, and 100%).1,5,7 Thus, it appears that neural loops are a normal phenomenon rather than a little-known variation, regardless of patient race. There is no mention of this variation in
anatomy textbooks, presumably because the palm is difficult to dissect and many branches of nerves and vessels are distributed in the narrow part of hand. In addition, it might be that the existence of a neural loop itself has not previously been associated with clinical symptoms such as pain, paralysis, and decreased cold intolerance, in contrast to the case of carpal tunnel syndrome. Gotani and Gilbert1 classified neural loops according to the digital nerve and the interdigital space. However, because the palmar digital arteries were located more superficially than the digital nerves and it was relatively easy to trace the arteries to find neural loops, we classified them according to their relationship with the palmar digital arteries in the present study. It is generally well known that blood vessels grow earlier than the nerves in order to provide nutrition and oxygen to particular sites of the embryo during development.12 A neural loop around an artery is usually considered to be a phylogenetic or developmental remnant, because this structural feature is common in lower primates and is correlated with extreme muscular development and the requisite extensive blood supply.13
JHS 䉬 Vol A, December
2026
DIGITAL NERVE LOOP PENETRATION
The digital nerve sometimes cannot grow straight toward the finger during development due to the early presence of a digital artery, which forces the digital nerve to turn around the digital artery or to divide its bundle proximal to the artery and rejoin it distally. The latter mechanism might underlie the formation of a neural loop. The localization of neural loops according to the palmar digital artery is a better classification criterion than are the digital nerve or the interdigital space. In a report of a patient with neurovascular symptoms due to a neural loop, Spinner et al.4 suggested that a neural loop was responsible for intermittent numbness or pain in the web space between the fingers and decreased strength in the hand due to compression of the CPDN by the pulses of the CPDA and was also responsible for cold intolerance in the hand due to dynamic occlusion of the CPDA. To our knowledge, that report was the first presentation of the clinical signification of neural loop. In the present study, the neural loop was classified into 3 forms. The neural loop described in the report of Spinner et al. resembles our form A or B, but not C. Nevertheless, clinical symptoms were observed, because the pulse pressure could be increased and the compression was thus more direct. In the present study, form C was defined as having a small-diameter neural loop (ⱕ3.9 mm) and a tightly fitting digital nerve within the neural loop. Therefore, clinical symptoms are more likely to occur with this form, which accounted for about 11% of the cases observed in the present study, and it could help to explain the symptoms of cold intolerance and sensory disturbance in the palm. In addition to the 4 main types of neural loop, there were 2 additional, special types. The first is the double neural loop type (or double penetration) in a digital artery, which was observed in 3 cases (Fig. 2A). This is an uncommon form of neural loop but one that has been reported previously as a variant.1,7 The other, the arch type occurs when some CPDNs are penetrated proxi-
mally by the superficial palmar arch itself, and it was observed in 8 of the present cases (Fig. 2B). The most frequent arch type was present between the first and second CPDAs, and it can exist either independently or together with another type of neural loop in the same palm. It has been confirmed that the little-known neural loop variation is indeed a common occurrence in the palm. This knowledge about digital artery neural loops provides useful information for both hand surgeons and anatomists with respect to both clinical and developmental applications. REFERENCES 1. Gotani H, Gilbert A. Hartmann’s boutonnière: an anatomical study of digital neural loop penetrations in the palm. J Hand Surg 1999; 24B:35–37. 2. Vathsala V, Ratnasamy S, Kalpana S. Digital neural loops—A rare anatomic variation. J Anat Soc India 2008;57:155–157. 3. Sener M, Yildiz M, Aydin H. Anomalous digital nerve loop: a case report. Microsurgery 1998;18:170 –171. 4. Spinner RJ, Varela CD, Urbaniak JR. Digital nerve penetration by a digital artery in a patient with neurovascular symptoms: a case report. J Hand Surg 1996;21A:1101–1103. 5. Barreiro FJJ, Huelin JG. Etude des rapports vasculaires des nerfs superficiels de la region palmaire. Compte Rendu Soc Anat Paris 1976;1:1–7. 6. Edgerton MT, Snyder GB, Webb WL. Surgical treatment of congenital thumb deformities (including psychological impact of correction). J Bone Joint Surg 1965;47A:1453–1474. 7. Hartmann H. Note sur l’anatomie des nerfs de la paume de la main. Bull Mem Soc Anat Paris 1887;62:860 – 864. 8. Abrahams PH, Boon JM, Spratt JD, Hutchings RT. McMinn’s clinical atlas of human anatomy. 6th ed. St. Louis: Mosby Elsevier, 2008:161–162. 9. Gross PT, Tolomeo EA. Proximal median neuropathies. Neurol Clin 1999;17:425– 445. 10. Monstrey SJ, Jones NF. Intermittent occlusion of the ulnar artery. J Hand Surg 1994;19B:27–29. 11. Jabaley ME, Wallace WH, Heckler FR. Internal topography of major nerves of the forearm and hand: a current view. J Hand Surg 1980;5:1–18. 12. Roy TS. Median nerve penetration by a muscular branch of the brachial artery. Clin Anat 2003;16:335–339. 13. Miller RA. Observations upon the arrangement of the axillary artery and brachial plexus. Am J Anat 1939;64:143–163.
JHS 䉬 Vol A, December
Penetration of the Digital Nerves by the Common Palmar Digital Arteries in Human Cadavers Ju-Young Lee, BS, Yoo-Ri Kim, BS, Jeong-Nam Kim, BS, Hyun-Gon Choi, MD, Wu-Chul Song, MD, Ki-Seok Koh, PhD
Purpose To investigate the incidence of digital nerve loop penetration by digital arteries (neural loops) in cadaver palms and to classify these neural loops according to their topography and morphology. Methods In total, 121 palms (from 57 right and 64 left hands) were dissected from 70 preserved cadavers (50 male and 20 female; mean age 66.1 y). Results Of the 121 palms, 98 had neural loops; 184 cases of neural loop were observed in total. The neural loops could be classified into 4 topographical types, according to their position relative to the digital arteries: ulnar (in which the ulnar proper palmar digital nerve of the finger is penetrated), radial (in which the radial proper palmar digital nerve of the finger is penetrated), common (in which the common palmar digital nerve of the finger is penetrated), and bridge (in which the neural loop is formed by connecting the ulnar and radial proper palmar digital nerves). The neural loops were also classified morphologically according to their size: form A (ⱖ10 mm), form B (4.0 –9.9 mm), and form C (ⱕ3.9 mm). The mean lengths in these groups were 16.1, 7.2, and 3.0 mm, respectively, and the overall mean length of all neural loops was 10.8 mm. Conclusions It was confirmed that neural loops are a common occurrence in humans; hence, it is surprising that it is a little-known variation in the palm. (J Hand Surg 2010;35A:2022– 2026. Copyright © 2010 by the American Society for Surgery of the Hand. All rights reserved.) Key words Anatomy, common palmar digital artery, hand, neural loop, penetration, proper palmar digital nerve. the neurovascular distribution of the hand are observed frequently. However, digital nerve penetrations (neural loops), which form where a digital artery passes through a digital nerve, have received little attention;
A
NATOMIC VARIATIONS OF
From the Department of Anatomy, School of Medicine, Konkuk University, Seoul, Korea; Department of Plastic and Reconstructive Surgery, School of Medicine, Konkuk University, Seoul, Korea. Received for publication May 13, 2010; accepted in revised form August 30, 2010. This work was supported by Konkuk University in 2010. No benefits in any form have been received or will be received related directly or indirectly to the subject of this article. Correspondingauthor:Ki-SeokKoh,PhD,DepartmentofAnatomy,SchoolofMedicine,Konkuk University, 1, Hwayang-dong, Gwangjin-gu, Seoul 143-701, Korea; e-mail: [email protected]. 0363-5023/10/35A12-0017$36.00/0 doi:10.1016/j.jhsa.2010.08.025
2022 䉬 © ASSH 䉬 Published by Elsevier, Inc. All rights reserved.
little is known about them, even though the structures are occasionally encountered in hand surgery.1 To our knowledge, only a few articles have been written about these variations.1–7 The first description of a variation of the digital nerve loop by Hartmann was published a century ago.7 Edgerton et al.6 also found an anomalous neural ring of the common palmar digital nerve (CPDN) or proper palmar digital nerve (PPDN) that encircled the common palmar digital artery (CPDA), and Barreiro and Huelin5 found neural loops in all 30 palms that they studied. Spinner et al.4 discussed the clinical significance of such a neural loop. Indeed, neural loops have even been described in several atlases and textbooks, but without special comments.8 Therefore, although it is not well known, this phenomenon is considered common in the human palm.
DIGITAL NERVE LOOP PENETRATION
2023
The neural loop is important to clinicians such as hand surgeons, because it can sometimes cause paralysis or pain due to compression of the CPDN by the pulses of CPDA.2,9 –11 The purposes of the present cadaver study were to investigate the incidence of neural loops and to classify them according to their topography and morphology. MATERIALS AND METHODS A total of 121 palms (from 57 right and 64 left hands) were dissected from 70 preserved cadavers (50 male and 20 female; mean age 66.1 y). Skin, subcutaneous tissue, and palmar aponeurosis were removed carefully from the palm. The radial and ulnar arteries were then identified at the wrist, and the superficial palmar arch and radialis indicis artery of the palm were exposed. The radialis indicis artery (which branches from the deep palmar arch) and each CPDA (which branch from the superficial palmar arch), CPDN, and PPDN were dissected carefully. The princeps pollicis artery to the thumb was not included in this study. After dissection, the presence of a neural loop was identified and classified according to its relationship with the radialis indicis artery, the CPDA, or both. The neural loops were classified topographically according to how they divide and the position at which the palmar digital nerve is penetrated by the artery: ulnar (in which the ulnar PPDN of the finger is penetrated), radial (in which the radial PPDN of the finger is penetrated), common (in which the CPDN of the finger is penetrated), and bridge (in which the neural loop is formed by connecting the ulnar and radial PPDNs) types (Fig. 1). The neural loops were also classified into 3 forms according to their morphology and the diameter of the neural loop (from largest to smallest), as follows: form A, in which the diameter of the neural loop is ⬎10.0 mm; form B, in which the diameter of the neural loop is 4.0 –9.9 mm; and form C, in which the digital artery fits tightly into the neural loop and the diameter of the neural loop is ⬍3.9 mm. The length of the neural loop and diameter of the digital artery were measured using digital calipers (CD-15CP; Mitutoyo, Japan). All photographs and diagrams are viewed from the perspective of the right hand. RESULTS The superficial palmar arch was located in the proximal palm, palmar to the median and ulnar nerves, in all cases. In general, the CPDA ran superficial to the CPDN, toward the junction dividing the PPDNs, and deep to the PPDN thereafter, regardless of penetration.
FIGURE 1: Schematic presentation of the 4 topographically different types of neural loop. (U, ulnar PPDN of the finger penetrated; R, radial PPDN of the finger penetrated; C, CPDN of the finger penetrated; and B, formation of the neural loop connecting the ulnar and radial PPDNs. UA, ulnar artery; RA, radial artery; SPA, superficial palmar arch; MN, median nerve; UN, ulnar nerve; arrow, some CPDNs were proximally penetrated by the superficial palmar arch itself.)
Of the 121 palms, 98 had neural loops; 184 cases of neural loop were observed in total. Thus, there was an average of 1.5 neural loops per hand, and about 2 neural loops per palm if a neural loop was present (184 neural loops in 98 palms). The most common neural loop was made by the second CPDA, followed by the first and the third CPDA (Table 1). Only a few neural loops were made by the radialis indicis artery and the fourth CPDA. There were 3 cases in which 2 neural loops were developed by a CPDA; this phenomenon was labeled double penetration (Fig. 2A). In addition, 8 neural loops developed by some CPDNs were penetrated proximally by the superficial palmar arch itself (Figs. 1, 2B). The neural loops were classified into the 4 topographically different types. The most common type was the ulnar, followed by the radial, common, and bridge types, in that order (Table 1, Fig. 1). They were also
JHS 䉬 Vol A, December
2024
TABLE 1.
DIGITAL NERVE LOOP PENETRATION
The Types of Neural Loop Relative to the Involved Palmar Artery Location of Neural Loop
Type
Radialis Indicis
Ulnar
34
Radial Common
First CPDA
4
Bridge
Second CPDA
Third CPDA
28
6
8
31
16
8
15
8
6
6
3
Fourth CPDA
4 (2%)
56 (30%)
80 (44%)
33 (18%)
Total 68 (37%) 55 (30%)
3
38 (21%) 15 (8%)
CPDNs penetrated by superficial palmar arch Total
Superficial Palmar Arch
3 (2%)
8
8 (4%)
8 (4%)
184
FIGURE 2: The special types of neural loop: A double penetration and B some CPDNs were proximally penetrated by the superficial palmar arch itself (SPA, superficial palmar arch).
classified into the 3 morphologically different forms (ie, forms A–C, as defined earlier); the most common was form A, followed by forms B and C, in that order (Table 2, Fig. 3).
The lengths of the neural loops are listed according to their type and form in Table 3. The ulnar and radial types had similar lengths. The mean lengths of neural loops of form A, form B, and form C were 16.1, 7.2,
JHS 䉬 Vol A, December
2025
DIGITAL NERVE LOOP PENETRATION
TABLE 2.
The Forms of Neural Loop Relative to the Involved Palmar Artery Location of Neural Loop Radialis Indicis
Form Form A (ⱖ10 mm)
4
Form B (4.0–9.9 mm) Form C (ⱕ3.9 mm) Total
4
First CPDA
Second CPDA
Third CPDA
Fourth CPDA
Superficial Palmar Arch
Total 86 (47%)
28
38
9
1
6
22
35
15
2
2
6
7
9
56
80
33
77 (42%) 21 (11%)
3
8
184
FIGURE 3: The 3 morphological forms of neural loop: A form A, 19.6 mm; B form B, 8.2 mm; and C form C, 3.0 mm.
TABLE 3. Mean Length of Neural Loop According to Type and Form Type
Length (mm)
Form
Length (mm)
Ulnar
11.0
Form A
16.1
Radial
11.0
Form B
7.2
8.1
Form C
3.0
Common Bridge
14.4
and 3.0 mm, respectively. Form A was about twice as long as form B, which in turn was about twice as long as form C. The overall mean length of the neural loops was 10.8 mm. DISCUSSION Neural loops were found in 98 of 121 palms (81%) in the present study, which is within the range of previously reported incidences (67%, 92%, and 100%).1,5,7 Thus, it appears that neural loops are a normal phenomenon rather than a little-known variation, regardless of patient race. There is no mention of this variation in
anatomy textbooks, presumably because the palm is difficult to dissect and many branches of nerves and vessels are distributed in the narrow part of hand. In addition, it might be that the existence of a neural loop itself has not previously been associated with clinical symptoms such as pain, paralysis, and decreased cold intolerance, in contrast to the case of carpal tunnel syndrome. Gotani and Gilbert1 classified neural loops according to the digital nerve and the interdigital space. However, because the palmar digital arteries were located more superficially than the digital nerves and it was relatively easy to trace the arteries to find neural loops, we classified them according to their relationship with the palmar digital arteries in the present study. It is generally well known that blood vessels grow earlier than the nerves in order to provide nutrition and oxygen to particular sites of the embryo during development.12 A neural loop around an artery is usually considered to be a phylogenetic or developmental remnant, because this structural feature is common in lower primates and is correlated with extreme muscular development and the requisite extensive blood supply.13
JHS 䉬 Vol A, December
2026
DIGITAL NERVE LOOP PENETRATION
The digital nerve sometimes cannot grow straight toward the finger during development due to the early presence of a digital artery, which forces the digital nerve to turn around the digital artery or to divide its bundle proximal to the artery and rejoin it distally. The latter mechanism might underlie the formation of a neural loop. The localization of neural loops according to the palmar digital artery is a better classification criterion than are the digital nerve or the interdigital space. In a report of a patient with neurovascular symptoms due to a neural loop, Spinner et al.4 suggested that a neural loop was responsible for intermittent numbness or pain in the web space between the fingers and decreased strength in the hand due to compression of the CPDN by the pulses of the CPDA and was also responsible for cold intolerance in the hand due to dynamic occlusion of the CPDA. To our knowledge, that report was the first presentation of the clinical signification of neural loop. In the present study, the neural loop was classified into 3 forms. The neural loop described in the report of Spinner et al. resembles our form A or B, but not C. Nevertheless, clinical symptoms were observed, because the pulse pressure could be increased and the compression was thus more direct. In the present study, form C was defined as having a small-diameter neural loop (ⱕ3.9 mm) and a tightly fitting digital nerve within the neural loop. Therefore, clinical symptoms are more likely to occur with this form, which accounted for about 11% of the cases observed in the present study, and it could help to explain the symptoms of cold intolerance and sensory disturbance in the palm. In addition to the 4 main types of neural loop, there were 2 additional, special types. The first is the double neural loop type (or double penetration) in a digital artery, which was observed in 3 cases (Fig. 2A). This is an uncommon form of neural loop but one that has been reported previously as a variant.1,7 The other, the arch type occurs when some CPDNs are penetrated proxi-
mally by the superficial palmar arch itself, and it was observed in 8 of the present cases (Fig. 2B). The most frequent arch type was present between the first and second CPDAs, and it can exist either independently or together with another type of neural loop in the same palm. It has been confirmed that the little-known neural loop variation is indeed a common occurrence in the palm. This knowledge about digital artery neural loops provides useful information for both hand surgeons and anatomists with respect to both clinical and developmental applications. REFERENCES 1. Gotani H, Gilbert A. Hartmann’s boutonnière: an anatomical study of digital neural loop penetrations in the palm. J Hand Surg 1999; 24B:35–37. 2. Vathsala V, Ratnasamy S, Kalpana S. Digital neural loops—A rare anatomic variation. J Anat Soc India 2008;57:155–157. 3. Sener M, Yildiz M, Aydin H. Anomalous digital nerve loop: a case report. Microsurgery 1998;18:170 –171. 4. Spinner RJ, Varela CD, Urbaniak JR. Digital nerve penetration by a digital artery in a patient with neurovascular symptoms: a case report. J Hand Surg 1996;21A:1101–1103. 5. Barreiro FJJ, Huelin JG. Etude des rapports vasculaires des nerfs superficiels de la region palmaire. Compte Rendu Soc Anat Paris 1976;1:1–7. 6. Edgerton MT, Snyder GB, Webb WL. Surgical treatment of congenital thumb deformities (including psychological impact of correction). J Bone Joint Surg 1965;47A:1453–1474. 7. Hartmann H. Note sur l’anatomie des nerfs de la paume de la main. Bull Mem Soc Anat Paris 1887;62:860 – 864. 8. Abrahams PH, Boon JM, Spratt JD, Hutchings RT. McMinn’s clinical atlas of human anatomy. 6th ed. St. Louis: Mosby Elsevier, 2008:161–162. 9. Gross PT, Tolomeo EA. Proximal median neuropathies. Neurol Clin 1999;17:425– 445. 10. Monstrey SJ, Jones NF. Intermittent occlusion of the ulnar artery. J Hand Surg 1994;19B:27–29. 11. Jabaley ME, Wallace WH, Heckler FR. Internal topography of major nerves of the forearm and hand: a current view. J Hand Surg 1980;5:1–18. 12. Roy TS. Median nerve penetration by a muscular branch of the brachial artery. Clin Anat 2003;16:335–339. 13. Miller RA. Observations upon the arrangement of the axillary artery and brachial plexus. Am J Anat 1939;64:143–163.
JHS 䉬 Vol A, December