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Sciatic Nerve Intercommunications: New Finding
Accepted Manuscript Sciatic Nerve Intercommunications: A New Finding R. Shane Tubbs, Peter G. Collin, Anthony V. D’Antoni, Marios Loukas, Rod J. Oskouian, Robert J. Spinner PII:
S1878-8750(16)31107-X
DOI:
10.1016/j.wneu.2016.10.118
Reference:
WNEU 4786
To appear in:
World Neurosurgery
Received Date: 3 October 2016 Revised Date:
22 October 2016
Accepted Date: 24 October 2016
Please cite this article as: Tubbs RS, Collin PG, D’Antoni AV, Loukas M, Oskouian RJ, Spinner RJ, Sciatic Nerve Intercommunications: A New Finding, World Neurosurgery (2016), doi: 10.1016/ j.wneu.2016.10.118. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Sciatic Nerve Intercommunications: A New Finding
Oskouian1, Robert J. Spinner4
Seattle Science Foundation, Seattle, WA 98122, USA; 2 Department of Pathobiology, CUNY School of Medicine / The Sophie Davis School of Biomedical Education, The City College of New York, CUNY, New York, NY 10031, USA; 3Department of Anatomical Sciences, St. George’s University, Grenada; 4 Department of Neurosurgery, Mayo Clinic, Rochester, Minnesota, 55905 USA
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R. Shane Tubbs1, Peter G. Collin2, Anthony V. D’Antoni2, Marios Loukas3, Rod J.
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Introduction The sciatic nerve is composed of L4-S3 spinal nerve contributions and is the
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thickest nerve in the body.1, 2 Its width is 2 cm at its origin, ranging across its length from 1.5 to 2.0 cm.1-3 It comprises two nerves, the common fibular and tibial nerves, which are encased in a common epineurial sheath.4-6 The tibial nerve comprises the ventral
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branches of the ventral rami of L4-S3 while the common fibular nerve comprises the
dorsal branches of the ventral rami of L4-S2.1, 3 The two nerves/divisions are separated
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within the nerve sheath by the Compton-Cruveilher septum, which is composed of connective and adipose tissues.7 These two components of the sciatic nerve are mixed nerves supplying the posterior thigh muscles, the ischial aspect of the adductor magnus and most structures inferior to the knee except for the sensory distribution of the saphenous nerve on the medial aspect of the leg and foot.1, 2 The sciatic nerve also sends
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articular branches to the hip, knee, and ankle joints.1, 2 As the sciatic nerve, the two encased tibial and common fibular divisions exit
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through the greater sciatic foramen and inferior to the piriformis muscle.3 Anatomical variations of the sciatic nerve involving the piriformis muscle are well documented, with
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particular debt to the early work of Beaton and Anson.4, 8-11 More rarely, the common fibular component of the sciatic nerve innervates the gluteus maximus, as demonstrated in a case reported by Sumalatha et al.12 The sciatic nerve continues to descend deep to the gluteus maximus muscle and along the posterior aspect of the acetabulum.2, 3 It courses over the obturator internus, quadratus femoris and superior and inferior gemelli muscles,2,3 continuing inferiorly between the greater trochanter and the ischial tuberosity; halfway between these bony features is the surface marking of the nerve.1-3 Through the
2
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posterior compartment of the thigh, the sciatic nerve courses along the posterior aspect of the adductor magnus.2 It separates into the tibial and common fibular nerves proximal to the knee as it is crossed by the long head of the biceps femoris muscle and enters the apex
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of the popliteal fossa, but the location of the bifurcation is highly variable.1, 2, 11, 13-15
The aim of the present study was to identify communicating branches between the
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common fibular and tibial components of the sciatic nerve.
Materials and Methods
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Twenty unembalmed adult cadavers (40 sides) underwent dissection of the sciatic nerve from its exit from the greater sciatic foramen to its division into common fibular and tibial components above the knee. The cadavers were aged 46-97 years (mean 77 years) at death. Twelve specimens were male and eight were female. With the specimen
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in the prone position, a linear skin incision was made from the top of the iliac crest to the popliteal fossa. The fascia lata was then identified and opened in a cranial to caudal direction. The overlying gluteus muscle was transected and retractors placed. The sciatic
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nerve was identified inferior to the piriformis muscle and followed distally to the popliteal fossa. The outer layer of connective tissue uniting the common fibular and tibial
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components of the sciatic nerve was dissected with scissors using a spreading motion in a caudal to cranial direction. No specimen showed evidence of prior surgery or trauma to the areas studied. Calipers and a ruler were used for measurements. Random nerve communication samples (15) were sent for routine histological analysis to prove their neural nature. The classification developed by Testut.16 (Fig. 1) was used to describe the
3
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various nerve communications when any were present. Statistica for Windows was used for statistical analysis, with significance set at p<0.05.
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Results
Thirty of the 40 sides (75%) had communications between the parts of the sciatic nerve in the gluteal/posterior thigh regions before the normal bifurcation of the nerve just
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above the knee (Figs. 2-7). All neural connections were located in the gluteal region or proximal thigh. This was always within 20 cm of the greater sciatic notch with the
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majority of these interconnections occurring in the proximal superior half of the thigh. Most connections were represented by Testut intercommunicating branches types A (14 sides), F (8 sides) and D (2 sides). Two sides had a configuration similar to a Testut type H intercommunication. One side was similar to Testut’s type B but was more complex by
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having an additional crisscrossing branch traveling in the opposite direction from the two parallel nerves. This side was classified as a type B2 intercommunication. Three sides were not represented by the Testut classification and were described by us as “complex”
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or type H2 configuration (Figs. 6 and 7). On one right side from a male cadaver we identified a high bifurcation of the sciatic nerve, with clear communication between the
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tibial and common fibular components in the gluteal region just inferior to point at which the nerve was split by the piriformis muscle (Fig. 8). The majority of sides were found to have one location for sciatic nerve intercommunications. However, four sides (13%) had multiple locations (up to thee) for these intercommunications (Figs. 5 and 6). The lengths of the communications between the tibial and common fibular nerves ranged from 1.0 to 9.2 cm (mean 4.1 cm). Their diameters ranged from 1.0 to 5.5 mm (range 2.4 mm). The
4
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number of connections on each side ranged from one to three, and they traveled in opposite directions in many specimens, i.e. lateral to medial and medial to lateral. Histologically, all the communications examined were found to be neural (Fig. 9). No
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statistically significant difference was found between sides or sexes. Discussion
In our study, 75% of cadaveric sides had neural intercommunications between the
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tibial and common fibular components of the sciatic nerve in the gluteal or proximal thigh regions. However, the extant medical literature included no accounts of such
20-29
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communicating branches within the common epineurial sheath of the sciatic nerve.1, 3, 14, On the contrary, such scant comments as could be found stated that no neural
connections were present. For example, Hollinshead’s Anatomy for Surgeons: Volume 3 Second Edition from 1969 states: “In spite of their [the tibial and common fibular nerves]
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common connective sheath, these two nerves do not interchange fibers.” The second edition of Nerve and Nerve Injuries by Sunderland (1978) states: “There is no exchange of bundles between the two in the sciatic trunk and so no difficulty is experienced in
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identifying and separating them macroscopically.” Sunderland’s statement has served as a foundation for anatomical and clinical studies of the sciatic nerve and there are similar
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statements in many anatomy textbooks and published literature.1-3, 26, 30 Although the tibial and common fibular components of the sciatic nerve communicate at, for example, the posterior leg via the communicating sural nerve, no other source to our knowledge has reported communications between these parts within the sciatic nerve in the gluteal region and posterior thigh.
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This division of the sciatic nerve can occur as the nerve leaves the greater sciatic foramen where it can be segregated into its tibial and common fibular components by the piriformis muscle. This is found in 4.0-20.9% of specimens.13, 14, 17-19 There have been no
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reports of neural communicating branches between the tibial and common fibular nerves in the gluteal or thigh regions after such early divisions.5, 13, 14 However, on one right side, we identified a high bifurcation of the sciatic nerve with clear communication
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between the tibial and common fibular parts in the gluteal region just inferior to the point at which the nerve was split by the piriformis muscle. The connections found in our study
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could have been missed in previous anatomical descriptions of the sciatic nerve because of the dissection necessary to access the common fibular and tibial nerves within the common epineurial sheath.3,4,7,10,32-38 Additionally, though the intercommunications were very prevalent, their disruption may go clinically unnoticed potentially due to the nerve
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conveying only minor innervation. Alternatively, neural loss resulting from damage to the intercommunications may have previously been attributed to complications of either the lesion of the sciatic nerve that necessitated the surgery or the surgery itself.
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For lesions of the sciatic nerve, Kline and colleagues describe sciatic nerve dissection so that the extent of a lesion can be assessed by Nerve Action Potential (NAP)
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recordings.24, 25, 31 In order to perform NAP recordings for the tibial and common fibular components separately, the two divisions are split proximally and distally relative to the site of the sciatic nerve lesion.24, 25 Both divisions are then independently stimulated and recordings are monitored distal to the site of the lesion.24, 25 Millesi (1987) and Aydin et al. (2009) also indicated the ease of dissecting between the two nerves and stated that they should be handled independently. In the Second Edition of Management of
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Peripheral Nerve Problems (1998), the authors highlight a similar point, stating: “At the junction of the upper and middle thirds of the thigh, the common peroneal and posterior (sic) tibial nerves have formed separate structures and can be easily separated into their
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components though they are loosely held together until approximately the mid-thigh.”
Conclusions
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Contrary to descriptions in common anatomy and surgical textbooks, we have
demonstrated that neural communications between tibial and common fibular divisions of
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the sciatic nerve exist in most specimens. Knowledge of such connections could help to explain unusual clinical presentations and help surgeons to avoid injuring such fibers during surgical procedures involving the sciatic nerve.
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References
[1] Standring S. Gray's anatomy: the anatomical basis of clinical practice. 41sted. New York, NY: Elsevier Health Sciences; 2015.
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[2] Tubbs RS, Rizk E, Shoja MM, Loukas M, Barbaro N, Spinner RJ. Nerves and Nerve Injuries: Vol 1: History, Embryology, Anatomy, Imaging, and Diagnostics. 1st ed.
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London, UK: Academic Press; 2015. [3] Berihu BA, Debeb YG. Anatomical variation in bifurcation and trifurcations of sciatic nerve and its clinical implications: in selected university in Ethiopia. BMC Res Notes. 2015;8:1.
[4] Cejas C, Aguilar M, Falcón L, Caneo N, Acuña M. High resolution (3T) magnetic resonance neurography of the sciatic nerve. Radiologia (Eng). 2013;55:195-202.
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[5] Vloka JD, Hadzic A, Lesser JB, Kitain E, Geatz H, April EW, et al. A common epineural sheath for the nerves in the popliteal fossa and its possible implications for sciatic nerve block. Anesth Analg. 1997;84:387-90.
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[6] Stewart JD. Peripheral nerve fascicles: anatomy and clinical relevance. Muscle Nerve. 2003;28:525-41.
nerve. Surg Radiol Anat. 2008;30:619-26.
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[7] Sladjana UZ, Ivan JD, Bratislav SD. Microanatomical structure of the human sciatic
[8] Beaton LE, Anson BJ. The relation of the sciatic nerve and of its subdivisions to the
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piriformis muscle. Anat Rec. 1937;70:1-5.
[9] Carare R, Goodwin M. A unique variation of the sciatic nerve. Clin Anat. 2008;21:800-1.
[10] Kanawati AJ. Variations of the sciatic nerve anatomy and blood supply in the gluteal
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region: a review of the literature. ANZ J Surg. 2014;84:816-9.
[11] Tubbs RS, Shoja MM, Loukas M. Bergman's Comprehensive Encyclopedia of Human Anatomic Variation. 1st ed. Hoboken, NJ: John Wiley & Sons; 2016.
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[12] Sumalatha S, Souza ASD, Yadav JS, Mittal SK, Singh A, Kotian SR. An unorthodox innervation of the gluteus maximus muscle and other associated variations: A case report.
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Australas Med J. 2014;7:419.
[13] Prakash BA, Devi M, Sridevi N, Rao P, Singh G. Sciatic nerve division: a cadaver study in the Indian population and review of the literature. Singapore Med J. 2010;51:721-3.
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[14] Saleh H, El-fark M, Abdel-Hamid G. Anatomical variation of sciatic nerve division in the popliteal fossa and its implication in popliteal nerve blockade. Folia Morphol (Warsz). 2009;68:256-9.
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[15] Vloka JD, Hadžic A, April E, Thys DM. The division of the sciatic nerve in the popliteal fossa: anatomical implications for popliteal nerve blockade. Anesth Analg. 2001;92:215-7.
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[16] Testut J. Tratado de Anatomia Humana. 6th ed. Barcelona, Spain: Salvat; 1902.
[17] Pokorný D, Jahoda D, Veigl D, Pinskerová V, Sosna A. Topographic variations of
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the relationship of the sciatic nerve and the piriformis muscle and its relevance to palsy after total hip arthroplasty. Surg Radiol Anat. 2006;28:88-91.
[18] Ugrenović SZ, Jovanović ID, Krstić V, Stojanović VR, Vasović LP, Antić S, et al. The level of the sciatic nerve division and its relations to the piriform muscle. Vojnosanit
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Pregled. 2005;62:45-9.
[19] Adibatti M, Sangeetha V. Study on variant anatomy of sciatic nerve. J Clin Diagn Res 2014;8:AC07.
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[20] Sunderland S, Walshe F. Nerves and Nerve Injuries. 2nd ed. New York, NY: Churchill Livingstone; 1968.
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[21] Tomaszewski KA, Graves MJ, Henry BM, Popieluszko P, Roy J, Pękala PA, et al. Surgical anatomy of the sciatic nerve: A meta-analysis. J Orthop Res. 2016. [22] Burks SS, Levi DJ, Hayes S, Levi AD. Challenges in sciatic nerve repair: anatomical considerations: Laboratory investigation. J Neurosurg. 2014;121:210-8. [23] Gousheh J, Arasteh E, Beikpour H. Therapeutic results of sciatic nerve repair in Iran-Iraq war casualties. Plast Reconstr Surg. 2008;121:878-86.
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[24] Kim DH, Murovic JA, Tiel R, Kline DG. Management and outcomes in 353 surgically treated sciatic nerve lesions. J Neurosurg. 2004;101:8-17. [25] Kline DG, Kim D, Midha R, Harsh C, Tiel R. Management and results of sciatic
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nerve injuries: a 24-year experience. J Neurosurg. 1998;89:13-23.
[26] Aydin A, Ozkan T, Aydin HU, Topalan M, Erer M, Ozkan S, et al. The results of surgical repair of sciatic nerve injuries. Acta Orthop Traumatol Turc. 2009;44:48-53.
nerve injuries. WB Saunders; 1987:239-251.
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[27] Millesi H. Lower extremity nerve lesions. In: Terzis JK, ed. Microreconstruction of
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[28] Hollinshead WH. Anatomy for Surgeons: Volume 3. 2nd ed. New York, NY: Harper & Row; 1969.
[29] Van Beek A, Omer GE, Spinner M. Management of Peripheral Nerve Problems. 2nd ed. Philadelphia, PA: WB Saunders Company; 1998.
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[30] Agur AM, Dalley AF. Grant's Atlas of Anatomy. 12th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2009.
[31] Robert EG, Happel LT, Kline DG. Intraoperative nerve action potential recordings:
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technical considerations, problems, and pitfalls. Neurosurgery. 2009;65:A97-A104. [32] Selkirk GD, Mclaughlin AC, Mirjalili SA. Revisiting the surface anatomy of the
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sciatic nerve in the gluteal region in children using computed tomography. Clin Anat. 2016;29:211-216.
[33] Siquara De Sousa AC, Capek S, Amrami KK, Spinner RJ.Neural involvement in endometriosis: Review of anatomic distribution and mechanisms. Clin Anat. 2015;28:1029-38. [34] Prasad NK, Capek S, de Ruiter GC, Amrami KK, Spinner RJ. The subparaneurial
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compartment: A new concept in the clinicoanatomic classification of peripheral nerve lesions. Clin Anat. 2015;28:925-30. [35] Colombo EV, Howe BM, Amrami KK, Spinner RJ.Elaborating upon the descent
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phase of fibular and tibial intraneural ganglion cysts after cross-over in the sciatic nerve. Clin Anat. 2014;27:1133-6.
[36] Currin SS, Mirjalili SA, Meikle G, Stringer MD.Revisiting the surface anatomy of
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the sciatic nerve in the gluteal region. Clin Anat. 2015;28:144-9.
[37] Capek S, Sullivan PS, Howe BM, Smyrk TC, Amrami KK, Spinner RJ, Dozois EJ.
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Recurrent rectal cancer causing lumbosacral plexopathy with perineural spread to the spinal nerves and the sciatic nerve: an anatomic explanation. Clin Anat. 2015;28:136-43. [38] Takizawa M, Suzuki D, Ito H, Fujimiya M, Uchiyama E.The adductor part of the adductor magnus is innervated by both obturator and sciatic nerves. Clin Anat.
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Figure Legends:
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2014;27:778-82.
Figure 1: Classification system used by Testut.
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Figure 2: Left posterior thigh with sciatic nerve dissected. Note the simple neural interconnection traveling between the tibial nerve medially to the common fibular nerve laterally. This represents a Testut type A interconnection. Figure 3: Right posterior view of the sciatic nerve in the thigh illustrating two branches from the medial tibial nerve fusing to a single branch attaching to the common fibular nerve. This represents a Testut type F interconnection.
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Figure 4: Left sciatic nerve viewed from behind illustrating a Testut type D interconnection. Figure 5: Left sided sciatic nerve seen from behind illustrating two connections traveling
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from the tibial to the common fibular nerve and a single branch traveling from the
common fibular to the tibial nerve. This configuration is not represented by Testut’s classification but has components similar to his type B intercommunication.
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Figure 6: Right sciatic nerve from the posterior thigh and seen from behind. Multiple
interconnections are seen. The upper and middle connections represent Testut type A and
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F interconnections and the lowest connections are not represented by this classification system.
Figure 7: Dissection of the sciatic nerve from behind at the left greater sciatic foramen. The common fibular nerve is lateral and has multiple connections traveling in a
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superolateral to inferomedial direction. Although not exact, this configuration is closest to a Testut type H configuration.
Figure 8: Right-sided posterior dissection illustrating a sciatic nerve prematurely divided
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into medial tibial and lateral common fibular parts due to the common fibular nerve piercing the piriformis muscle (white arrow). A neural intercommunication (Testut type
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A connection) is seen just distal to the split (black arrow). Figure 9: Neural histology of an intercommunication found between the tibial and common fibular nerves as parts of the sciatic nerve in the posterior thigh.
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Highlights
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Neural intercommunications of the proximal sciatic nerve were found. The extant literature on the sciatic nerve indicates no neural intercommunications. Knowledge of neural intercommunications could decrease iatrogenic neural injuries.
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• • •
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Abbreviations
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NAP- Nerve Action Potential
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Disclosure- Conflict of Interest R. Shane Tubbs Conflict of interest: none
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Peter G. Collin Conflict of interest: none Anthony V. D’Antoni Conflict of interest: none
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Marios Loukas Conflict of interest: none
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Robert J. Spinner Conflict of interest: none
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Rod J. Oskouian Conflict of interest: none
S1878-8750(16)31107-X
DOI:
10.1016/j.wneu.2016.10.118
Reference:
WNEU 4786
To appear in:
World Neurosurgery
Received Date: 3 October 2016 Revised Date:
22 October 2016
Accepted Date: 24 October 2016
Please cite this article as: Tubbs RS, Collin PG, D’Antoni AV, Loukas M, Oskouian RJ, Spinner RJ, Sciatic Nerve Intercommunications: A New Finding, World Neurosurgery (2016), doi: 10.1016/ j.wneu.2016.10.118. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Sciatic Nerve Intercommunications: A New Finding
Oskouian1, Robert J. Spinner4
Seattle Science Foundation, Seattle, WA 98122, USA; 2 Department of Pathobiology, CUNY School of Medicine / The Sophie Davis School of Biomedical Education, The City College of New York, CUNY, New York, NY 10031, USA; 3Department of Anatomical Sciences, St. George’s University, Grenada; 4 Department of Neurosurgery, Mayo Clinic, Rochester, Minnesota, 55905 USA
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R. Shane Tubbs1, Peter G. Collin2, Anthony V. D’Antoni2, Marios Loukas3, Rod J.
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Introduction The sciatic nerve is composed of L4-S3 spinal nerve contributions and is the
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thickest nerve in the body.1, 2 Its width is 2 cm at its origin, ranging across its length from 1.5 to 2.0 cm.1-3 It comprises two nerves, the common fibular and tibial nerves, which are encased in a common epineurial sheath.4-6 The tibial nerve comprises the ventral
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branches of the ventral rami of L4-S3 while the common fibular nerve comprises the
dorsal branches of the ventral rami of L4-S2.1, 3 The two nerves/divisions are separated
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within the nerve sheath by the Compton-Cruveilher septum, which is composed of connective and adipose tissues.7 These two components of the sciatic nerve are mixed nerves supplying the posterior thigh muscles, the ischial aspect of the adductor magnus and most structures inferior to the knee except for the sensory distribution of the saphenous nerve on the medial aspect of the leg and foot.1, 2 The sciatic nerve also sends
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articular branches to the hip, knee, and ankle joints.1, 2 As the sciatic nerve, the two encased tibial and common fibular divisions exit
EP
through the greater sciatic foramen and inferior to the piriformis muscle.3 Anatomical variations of the sciatic nerve involving the piriformis muscle are well documented, with
AC C
particular debt to the early work of Beaton and Anson.4, 8-11 More rarely, the common fibular component of the sciatic nerve innervates the gluteus maximus, as demonstrated in a case reported by Sumalatha et al.12 The sciatic nerve continues to descend deep to the gluteus maximus muscle and along the posterior aspect of the acetabulum.2, 3 It courses over the obturator internus, quadratus femoris and superior and inferior gemelli muscles,2,3 continuing inferiorly between the greater trochanter and the ischial tuberosity; halfway between these bony features is the surface marking of the nerve.1-3 Through the
2
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posterior compartment of the thigh, the sciatic nerve courses along the posterior aspect of the adductor magnus.2 It separates into the tibial and common fibular nerves proximal to the knee as it is crossed by the long head of the biceps femoris muscle and enters the apex
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of the popliteal fossa, but the location of the bifurcation is highly variable.1, 2, 11, 13-15
The aim of the present study was to identify communicating branches between the
SC
common fibular and tibial components of the sciatic nerve.
Materials and Methods
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Twenty unembalmed adult cadavers (40 sides) underwent dissection of the sciatic nerve from its exit from the greater sciatic foramen to its division into common fibular and tibial components above the knee. The cadavers were aged 46-97 years (mean 77 years) at death. Twelve specimens were male and eight were female. With the specimen
TE D
in the prone position, a linear skin incision was made from the top of the iliac crest to the popliteal fossa. The fascia lata was then identified and opened in a cranial to caudal direction. The overlying gluteus muscle was transected and retractors placed. The sciatic
EP
nerve was identified inferior to the piriformis muscle and followed distally to the popliteal fossa. The outer layer of connective tissue uniting the common fibular and tibial
AC C
components of the sciatic nerve was dissected with scissors using a spreading motion in a caudal to cranial direction. No specimen showed evidence of prior surgery or trauma to the areas studied. Calipers and a ruler were used for measurements. Random nerve communication samples (15) were sent for routine histological analysis to prove their neural nature. The classification developed by Testut.16 (Fig. 1) was used to describe the
3
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various nerve communications when any were present. Statistica for Windows was used for statistical analysis, with significance set at p<0.05.
RI PT
Results
Thirty of the 40 sides (75%) had communications between the parts of the sciatic nerve in the gluteal/posterior thigh regions before the normal bifurcation of the nerve just
SC
above the knee (Figs. 2-7). All neural connections were located in the gluteal region or proximal thigh. This was always within 20 cm of the greater sciatic notch with the
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majority of these interconnections occurring in the proximal superior half of the thigh. Most connections were represented by Testut intercommunicating branches types A (14 sides), F (8 sides) and D (2 sides). Two sides had a configuration similar to a Testut type H intercommunication. One side was similar to Testut’s type B but was more complex by
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having an additional crisscrossing branch traveling in the opposite direction from the two parallel nerves. This side was classified as a type B2 intercommunication. Three sides were not represented by the Testut classification and were described by us as “complex”
EP
or type H2 configuration (Figs. 6 and 7). On one right side from a male cadaver we identified a high bifurcation of the sciatic nerve, with clear communication between the
AC C
tibial and common fibular components in the gluteal region just inferior to point at which the nerve was split by the piriformis muscle (Fig. 8). The majority of sides were found to have one location for sciatic nerve intercommunications. However, four sides (13%) had multiple locations (up to thee) for these intercommunications (Figs. 5 and 6). The lengths of the communications between the tibial and common fibular nerves ranged from 1.0 to 9.2 cm (mean 4.1 cm). Their diameters ranged from 1.0 to 5.5 mm (range 2.4 mm). The
4
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number of connections on each side ranged from one to three, and they traveled in opposite directions in many specimens, i.e. lateral to medial and medial to lateral. Histologically, all the communications examined were found to be neural (Fig. 9). No
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statistically significant difference was found between sides or sexes. Discussion
In our study, 75% of cadaveric sides had neural intercommunications between the
SC
tibial and common fibular components of the sciatic nerve in the gluteal or proximal thigh regions. However, the extant medical literature included no accounts of such
20-29
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communicating branches within the common epineurial sheath of the sciatic nerve.1, 3, 14, On the contrary, such scant comments as could be found stated that no neural
connections were present. For example, Hollinshead’s Anatomy for Surgeons: Volume 3 Second Edition from 1969 states: “In spite of their [the tibial and common fibular nerves]
TE D
common connective sheath, these two nerves do not interchange fibers.” The second edition of Nerve and Nerve Injuries by Sunderland (1978) states: “There is no exchange of bundles between the two in the sciatic trunk and so no difficulty is experienced in
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identifying and separating them macroscopically.” Sunderland’s statement has served as a foundation for anatomical and clinical studies of the sciatic nerve and there are similar
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statements in many anatomy textbooks and published literature.1-3, 26, 30 Although the tibial and common fibular components of the sciatic nerve communicate at, for example, the posterior leg via the communicating sural nerve, no other source to our knowledge has reported communications between these parts within the sciatic nerve in the gluteal region and posterior thigh.
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This division of the sciatic nerve can occur as the nerve leaves the greater sciatic foramen where it can be segregated into its tibial and common fibular components by the piriformis muscle. This is found in 4.0-20.9% of specimens.13, 14, 17-19 There have been no
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reports of neural communicating branches between the tibial and common fibular nerves in the gluteal or thigh regions after such early divisions.5, 13, 14 However, on one right side, we identified a high bifurcation of the sciatic nerve with clear communication
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between the tibial and common fibular parts in the gluteal region just inferior to the point at which the nerve was split by the piriformis muscle. The connections found in our study
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could have been missed in previous anatomical descriptions of the sciatic nerve because of the dissection necessary to access the common fibular and tibial nerves within the common epineurial sheath.3,4,7,10,32-38 Additionally, though the intercommunications were very prevalent, their disruption may go clinically unnoticed potentially due to the nerve
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conveying only minor innervation. Alternatively, neural loss resulting from damage to the intercommunications may have previously been attributed to complications of either the lesion of the sciatic nerve that necessitated the surgery or the surgery itself.
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For lesions of the sciatic nerve, Kline and colleagues describe sciatic nerve dissection so that the extent of a lesion can be assessed by Nerve Action Potential (NAP)
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recordings.24, 25, 31 In order to perform NAP recordings for the tibial and common fibular components separately, the two divisions are split proximally and distally relative to the site of the sciatic nerve lesion.24, 25 Both divisions are then independently stimulated and recordings are monitored distal to the site of the lesion.24, 25 Millesi (1987) and Aydin et al. (2009) also indicated the ease of dissecting between the two nerves and stated that they should be handled independently. In the Second Edition of Management of
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Peripheral Nerve Problems (1998), the authors highlight a similar point, stating: “At the junction of the upper and middle thirds of the thigh, the common peroneal and posterior (sic) tibial nerves have formed separate structures and can be easily separated into their
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components though they are loosely held together until approximately the mid-thigh.”
Conclusions
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Contrary to descriptions in common anatomy and surgical textbooks, we have
demonstrated that neural communications between tibial and common fibular divisions of
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the sciatic nerve exist in most specimens. Knowledge of such connections could help to explain unusual clinical presentations and help surgeons to avoid injuring such fibers during surgical procedures involving the sciatic nerve.
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References
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[2] Tubbs RS, Rizk E, Shoja MM, Loukas M, Barbaro N, Spinner RJ. Nerves and Nerve Injuries: Vol 1: History, Embryology, Anatomy, Imaging, and Diagnostics. 1st ed.
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London, UK: Academic Press; 2015. [3] Berihu BA, Debeb YG. Anatomical variation in bifurcation and trifurcations of sciatic nerve and its clinical implications: in selected university in Ethiopia. BMC Res Notes. 2015;8:1.
[4] Cejas C, Aguilar M, Falcón L, Caneo N, Acuña M. High resolution (3T) magnetic resonance neurography of the sciatic nerve. Radiologia (Eng). 2013;55:195-202.
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[5] Vloka JD, Hadzic A, Lesser JB, Kitain E, Geatz H, April EW, et al. A common epineural sheath for the nerves in the popliteal fossa and its possible implications for sciatic nerve block. Anesth Analg. 1997;84:387-90.
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[6] Stewart JD. Peripheral nerve fascicles: anatomy and clinical relevance. Muscle Nerve. 2003;28:525-41.
nerve. Surg Radiol Anat. 2008;30:619-26.
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[7] Sladjana UZ, Ivan JD, Bratislav SD. Microanatomical structure of the human sciatic
[8] Beaton LE, Anson BJ. The relation of the sciatic nerve and of its subdivisions to the
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piriformis muscle. Anat Rec. 1937;70:1-5.
[9] Carare R, Goodwin M. A unique variation of the sciatic nerve. Clin Anat. 2008;21:800-1.
[10] Kanawati AJ. Variations of the sciatic nerve anatomy and blood supply in the gluteal
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region: a review of the literature. ANZ J Surg. 2014;84:816-9.
[11] Tubbs RS, Shoja MM, Loukas M. Bergman's Comprehensive Encyclopedia of Human Anatomic Variation. 1st ed. Hoboken, NJ: John Wiley & Sons; 2016.
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[12] Sumalatha S, Souza ASD, Yadav JS, Mittal SK, Singh A, Kotian SR. An unorthodox innervation of the gluteus maximus muscle and other associated variations: A case report.
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Australas Med J. 2014;7:419.
[13] Prakash BA, Devi M, Sridevi N, Rao P, Singh G. Sciatic nerve division: a cadaver study in the Indian population and review of the literature. Singapore Med J. 2010;51:721-3.
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[14] Saleh H, El-fark M, Abdel-Hamid G. Anatomical variation of sciatic nerve division in the popliteal fossa and its implication in popliteal nerve blockade. Folia Morphol (Warsz). 2009;68:256-9.
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[15] Vloka JD, Hadžic A, April E, Thys DM. The division of the sciatic nerve in the popliteal fossa: anatomical implications for popliteal nerve blockade. Anesth Analg. 2001;92:215-7.
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[16] Testut J. Tratado de Anatomia Humana. 6th ed. Barcelona, Spain: Salvat; 1902.
[17] Pokorný D, Jahoda D, Veigl D, Pinskerová V, Sosna A. Topographic variations of
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the relationship of the sciatic nerve and the piriformis muscle and its relevance to palsy after total hip arthroplasty. Surg Radiol Anat. 2006;28:88-91.
[18] Ugrenović SZ, Jovanović ID, Krstić V, Stojanović VR, Vasović LP, Antić S, et al. The level of the sciatic nerve division and its relations to the piriform muscle. Vojnosanit
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Pregled. 2005;62:45-9.
[19] Adibatti M, Sangeetha V. Study on variant anatomy of sciatic nerve. J Clin Diagn Res 2014;8:AC07.
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[20] Sunderland S, Walshe F. Nerves and Nerve Injuries. 2nd ed. New York, NY: Churchill Livingstone; 1968.
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[21] Tomaszewski KA, Graves MJ, Henry BM, Popieluszko P, Roy J, Pękala PA, et al. Surgical anatomy of the sciatic nerve: A meta-analysis. J Orthop Res. 2016. [22] Burks SS, Levi DJ, Hayes S, Levi AD. Challenges in sciatic nerve repair: anatomical considerations: Laboratory investigation. J Neurosurg. 2014;121:210-8. [23] Gousheh J, Arasteh E, Beikpour H. Therapeutic results of sciatic nerve repair in Iran-Iraq war casualties. Plast Reconstr Surg. 2008;121:878-86.
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[24] Kim DH, Murovic JA, Tiel R, Kline DG. Management and outcomes in 353 surgically treated sciatic nerve lesions. J Neurosurg. 2004;101:8-17. [25] Kline DG, Kim D, Midha R, Harsh C, Tiel R. Management and results of sciatic
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nerve injuries: a 24-year experience. J Neurosurg. 1998;89:13-23.
[26] Aydin A, Ozkan T, Aydin HU, Topalan M, Erer M, Ozkan S, et al. The results of surgical repair of sciatic nerve injuries. Acta Orthop Traumatol Turc. 2009;44:48-53.
nerve injuries. WB Saunders; 1987:239-251.
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[27] Millesi H. Lower extremity nerve lesions. In: Terzis JK, ed. Microreconstruction of
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[28] Hollinshead WH. Anatomy for Surgeons: Volume 3. 2nd ed. New York, NY: Harper & Row; 1969.
[29] Van Beek A, Omer GE, Spinner M. Management of Peripheral Nerve Problems. 2nd ed. Philadelphia, PA: WB Saunders Company; 1998.
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[30] Agur AM, Dalley AF. Grant's Atlas of Anatomy. 12th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2009.
[31] Robert EG, Happel LT, Kline DG. Intraoperative nerve action potential recordings:
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technical considerations, problems, and pitfalls. Neurosurgery. 2009;65:A97-A104. [32] Selkirk GD, Mclaughlin AC, Mirjalili SA. Revisiting the surface anatomy of the
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sciatic nerve in the gluteal region in children using computed tomography. Clin Anat. 2016;29:211-216.
[33] Siquara De Sousa AC, Capek S, Amrami KK, Spinner RJ.Neural involvement in endometriosis: Review of anatomic distribution and mechanisms. Clin Anat. 2015;28:1029-38. [34] Prasad NK, Capek S, de Ruiter GC, Amrami KK, Spinner RJ. The subparaneurial
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compartment: A new concept in the clinicoanatomic classification of peripheral nerve lesions. Clin Anat. 2015;28:925-30. [35] Colombo EV, Howe BM, Amrami KK, Spinner RJ.Elaborating upon the descent
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phase of fibular and tibial intraneural ganglion cysts after cross-over in the sciatic nerve. Clin Anat. 2014;27:1133-6.
[36] Currin SS, Mirjalili SA, Meikle G, Stringer MD.Revisiting the surface anatomy of
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the sciatic nerve in the gluteal region. Clin Anat. 2015;28:144-9.
[37] Capek S, Sullivan PS, Howe BM, Smyrk TC, Amrami KK, Spinner RJ, Dozois EJ.
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Recurrent rectal cancer causing lumbosacral plexopathy with perineural spread to the spinal nerves and the sciatic nerve: an anatomic explanation. Clin Anat. 2015;28:136-43. [38] Takizawa M, Suzuki D, Ito H, Fujimiya M, Uchiyama E.The adductor part of the adductor magnus is innervated by both obturator and sciatic nerves. Clin Anat.
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Figure Legends:
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2014;27:778-82.
Figure 1: Classification system used by Testut.
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Figure 2: Left posterior thigh with sciatic nerve dissected. Note the simple neural interconnection traveling between the tibial nerve medially to the common fibular nerve laterally. This represents a Testut type A interconnection. Figure 3: Right posterior view of the sciatic nerve in the thigh illustrating two branches from the medial tibial nerve fusing to a single branch attaching to the common fibular nerve. This represents a Testut type F interconnection.
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Figure 4: Left sciatic nerve viewed from behind illustrating a Testut type D interconnection. Figure 5: Left sided sciatic nerve seen from behind illustrating two connections traveling
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from the tibial to the common fibular nerve and a single branch traveling from the
common fibular to the tibial nerve. This configuration is not represented by Testut’s classification but has components similar to his type B intercommunication.
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Figure 6: Right sciatic nerve from the posterior thigh and seen from behind. Multiple
interconnections are seen. The upper and middle connections represent Testut type A and
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F interconnections and the lowest connections are not represented by this classification system.
Figure 7: Dissection of the sciatic nerve from behind at the left greater sciatic foramen. The common fibular nerve is lateral and has multiple connections traveling in a
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superolateral to inferomedial direction. Although not exact, this configuration is closest to a Testut type H configuration.
Figure 8: Right-sided posterior dissection illustrating a sciatic nerve prematurely divided
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into medial tibial and lateral common fibular parts due to the common fibular nerve piercing the piriformis muscle (white arrow). A neural intercommunication (Testut type
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A connection) is seen just distal to the split (black arrow). Figure 9: Neural histology of an intercommunication found between the tibial and common fibular nerves as parts of the sciatic nerve in the posterior thigh.
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Highlights
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Neural intercommunications of the proximal sciatic nerve were found. The extant literature on the sciatic nerve indicates no neural intercommunications. Knowledge of neural intercommunications could decrease iatrogenic neural injuries.
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Abbreviations
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NAP- Nerve Action Potential
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Disclosure- Conflict of Interest R. Shane Tubbs Conflict of interest: none
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Peter G. Collin Conflict of interest: none Anthony V. D’Antoni Conflict of interest: none
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Marios Loukas Conflict of interest: none
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Robert J. Spinner Conflict of interest: none
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Rod J. Oskouian Conflict of interest: none