Anatomy of the sural nerve complex

Anatomy of the sural nerve complex The anatomy of the sural nerve complex in 20 cadaveric limbs was determined by dissection. The nerve usually consists of four named components: the medial sural cutaneous nerve, the lateral sural cutaneous nerve, the peroneal communicating branch, and the sural nerve. In most instances (80%), the sural nerve is formed in the distal portion of the leg by the union of the medial sural cutaneous nerve and the peroneal communicating branch. In 20% of cases, the peroneal communicating branch is absent. In such cases, the sural nerve is derived from the medial sural cutaneous nerve alone. The lateral sural cutaneous nerve is laterally situated and usually divides into medial and lateral branches. In a few cases, its medial division may contribute to the sural nerve through the peroneal communicating branch. The peroneal communicating branch can be of substantial caliber and may be useful as a source of nerve graft without complete sacrifice of the sural nerve. We describe a technique of isolation of the peroneal communicating branch for use as a nerve graft. (J HAND SURG 1987;12A:1119-23.)

Maria E. Ortigiiela, M.D.*, Michael B. Wood, M.D., and Donald R. Cahill, Ph.D., Rochester, Minn.

T

he sural nerve is the most frequent donor nerve used for peripheral nerve grafting. 1' 9 It is particularly advantageous because it provides a generous length of expendable nerve and is of an ideal caliber for revascularization and for interfascicular graft placement. Despite the widespread use of the sural nerve, there is scant attention reported in the literature to associated donor site problems. In their study on sural nerve donor sites, Staniforth and Fisher reported that 44% of the patients complained that the sensory deficit over the lateral aspect of the foot and ankle was "uncomfortable." Furthermore, 42% complained of calf tenderness, characteristic of neuroma, and in 16% of patients, this was associated with significant pain. A recent review of our own experience with sural donor sites used for interfascicular nerve grafting noted a 6.1 % (4 of 66 patients) incidence of neuromas producing symptoms in the legs of donors and a 9.1 % (6

From the Department of Orthopedics and the Department of Anatomy, Mayo Clinic and Mayo Foundation, Rochester, Minn. Received for publication March 31, 1987; accepted in revised form April 17, 1987. *Visiting scientist. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Reprint requests: Section of Publications, Mayo Clinic, 200 First St. S.W., Rochester, MN 55905.

of 66 patients) incidence of some degree of patient dissatisfaction related to altered sensibility over the lateral aspect of the foot and ankle (Strecker Wand Wood MB: Unpublished data). The complaints in the latter group were generally related to mild hyperpathia, but one patient experienced neurotrophy-related skin loss over the fifth metatarsal base because of poorly fitting footwear. We have attempted to define the optimal method of sural nerve isolation on the basis of the normal anatomic arrangement and common variations ofthe sural nerve. We propose a modified method of sural nerve graft harvest for situations that require a limited length of graft material.

Materials and methods The course of the sural nerves and their components from distal thigh to ankle was determined in 20 lower limbs by dissection aided with magnifying loupes. The study material included 19 embalmed limbs and one fresh limb of lengths between 40 and 45 cm from ankle to trans femoral condylar line. Nine of the limbs were from the left side, 11 from the right, and the malefemale distribution was equal. In all instances, the component tributaries forming the sural nerves were identified and measured for length and caliber. In four specimens, histologic sections stained with Masson's trichromic tincture, periodic acid-Schiff, and Luxol fast-blue methods were made from the sural nerve and THE JOURNAL OF HAND SURGERY

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't \(

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medial br-..........

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MEDIAL SURAL

I

CUTANEOUS N

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_SURAL N

~ Fig. 2. Photomicrograph of medial sural cutaneous nerve. (Original magnification, x 40.)

Fig. 1. Cutaneous nerves on back of leg that contribute to sural nerve. In 3 of 19 cases, medial branch of lateral sural cutaneous nerve was anastomosed to peroneal communicating branch.

its components to evaluate fascicular cross-sectional makeup. In all cases, the tissue sections were obtained within 1 cm of nerve origin. Results All limbs had a medial sural cutaneous nerve and a sural nerve. A lateral sural cutaneous nerve was present in 19 of 20 limbs, and in 16 of 20 limbs, a peroneal communicating branch from the lateral sural cutaneous contributed to the sural nerve (Fig. 1). Medial sural cutaneous nerve. The medial sural cutaneous nerve originated from the posterior surface of the tibial nerve within the popliteal fossa near the origin of the tibial nerve from the sciatic nerve (Fig. 1). It descended between the two heads of the gastrocnemius deep to the fascia overlying the gastrocnemius muscle and became superficial by piercing the crural fascia at the junction of the distal and middle thirds of the leg. In all specimens, the point of penetration of the fascia was characterized by a rather welldeveloped fibrous arcade. The medial sural cutaneous nerve always joined the sural nerve. However, the precise site of union differed because the length of the medial sural cutaneous nerve ranged from 21 to 33 cm. The diameter of the medial sural cutaneous nerve ranged from 1.0 to 1.5 mm at its origin and 1.5 to 1.6

mm at its termination. Histologic sections of the medial sural cutaneous nerve revealed one to three fasciculi and a small peripheral nutrient artery and group of veins (Fig. 2). Lateral sural cutaneous nerve. The lateral sural cutaneous nerve originated from the common peroneal nerve and gave off the peroneal communicating branch within 3.0 to 8.5 cm beyond the place at which it left the common peroneal nerve. As it continued, it usually (78.1 %) divided into a medial branch and a lateral branch. These branches coursed superficially within 1 cm of their formation. The medial branch ran toward the posterior midline, where, in 15.8% of cases (3 of 19), it broke into a plexus of branches or anastomosed (or both) with the peroneal communicating branch. When anastomosis with the peroneal communicating branch did not exist (84%), the medial branch terminated into multiple superficial branches in the distal one half of the leg. Similarly, the lateral branch terminated into the skin of the leg. The length of the lateral sural cutaneous nerve ranged from 5 to 13 cm before division. The length of the medial division ranged from 7 to 21 cm, and the lateral division ranged from 2 to 10 cm before arborizing. The diameters of the lateral sural cutaneous nerve just distal to the origin of the peroneal communicating branch, its medial division, and its lateral division at point of origin were 1.0 to 1.5 mm, 0.5 to 0.6 mm, and 1.0 mm, respectively. Distally, these diameters were 2.0, 0.2, and 0.2 mm, respectively. After giving off the peroneal communicating branch, the lateral sural cutaneous nerve appeared, by histologic cross-section, to be composed of

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Fig. 3. Photomicrograph of lateral sural cutaneous nerve from same anatomic specimen as that in Fig. 2. (Original magnification X 40.)

five to seven fasciculi of different calibers and an accompanying nutrient arteriovenous system (Fig. 3). Peroneal communicating branch. The peroneal communicating branch to the sural nerve originated from the lateral sural cutaneous nerve. In a single instance, the peroneal communicating branch and the lateral sural cutaneous nerve had separate origins from the common peroneal nerve. The peroneal communicating branch descended medially and superficially to the gastrocnemius fascia. It joined the medial sural cutaneous nerve just at the point where the latter pierced the fascia to form the sural nerve. The junction point was 11 to 20 cm proximal to the lateral malleolus. The length of the peroneal communicating branch was from 20 to 38 cm and in some cases was significantly larger in diameter than the medial sural cutaneous nerve. The diameter ranged from 1.5 to 3.0 mm at its origin and 2.5 to 3.0 mm at its distal portion. Histologic sections of the peroneal communicating branch revealed one to three fasciculi of generally larger caliber than those of the medial sural cutaneous nerve. A small peripheral nutrient arteriovenous complex was consistently present (Fig. 4). Sural nerve. The sural nerve was present in all specimens. In 80% of the specimens, it was formed by the union of the medial sural cutaneous nerve with the peroneal communicating branch at a point 11 to 20 cm proximal to the lateral malleolus (Fig. 1). In the remaining 20%, the sural nerve was simply the continuation of the medial sural cutaneous nerve, with no contribution from the peroneal communicating branch

Anatomy of sural nerve complex

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Fig. 4. Photomicrograph of peroneal communicating branch from same anatomic specimen as that in Figs . 2and 3. (Original magnification X 40.)

LATERAL SURAL

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Fig. 5. Formation of sural nerve as direct continuation of medial sural cutaneous nerve.

(Fig. 5). The sural nerve coursed distally and laterally near the lesser saphenous vein to pass from 1.0 to 1.5 cm posterior to the lateral malleolus. Two to three centimeters distal to the lateral malleolus, the nerve arborized into multiple cutaneous branches that sometimes coursed as far as the fifth toe. In addition, two or three cutaneous branches usually left the sural nerve

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Table I. Lengths and diameters of nerves of the sural nerve complex

Nerve Medial sural cutaneous Lateral sural cutaneous Common Lateral branch Medial branch Sural Peroneal communicating branch

Fig. 6. Photomicrograph of sural nerve from same anatomic specimen as that in Figs . 2, 3, and 4. (Original magnification x40.)

proximal to the ankle. The length of the sural nerve proper ranged from 11 to 20 cm. Its diameter proximally ranged from 2.5 to 4.0 mm and distally from 2.0 to 3.0 mm. Histologic evaluation demonstrated 9 to 14 fasciculi with a central nutrient artery and vein or veins . In some specimens, there was an additional peripheral arteriovenous system (Fig. 6). Discussion With certain differences, the anatomy of the sural nerve complex in this report is similar to that reported in the literature. Most authors agree that the most common and consistent components of sural cutaneous innervation are the sural nerve, the medial and lateral sural cutaneous nerves, and the peroneal communicating branch of the lateral sural cutaneous nerve. IO- 17 Kosinskil 8 did not distinguish between the medial sural cutaneous nerve and the sural nerve nor did he find that the sural nerve was consistently present However, our study and most reports suggest that the sural nerve is consistently present and most commonly is formed by the union of the medial sural cutaneous nerve and the peroneal communicating branch. Except for unmyelinated autonomic fibers, the sural nerve is entirely sensory. It supplies the skin of the lateral and posterior lower third of the leg and the lateral aspect of the foot and heel. It also provides sensibility for the ankle, subtalar, and calcaneocuboid joints and perhaps for the little toe as well. 19 de Moura and Gilbert20 pointed out that communication can exist between the medial division of the

Length (em)

Diameter at origin (mm)

Distal diameter (mm)

21-33

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1.5-1.6

5-13 2-10 7-21 11-20 20-38

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2.0 0.2 0.2 2.0-3 .0 2.5-3 .0

lateral sural cutaneous nerve and the sural but stated that these joined by way of the medial sural cutaneous nerve. Our results suggest that when such communications are present, they exist between the medial division of the lateral sural cutaneous nerve and the peroneal communicating branch. The array of potential contributing branches to the sural nerve must be kept in mind when one deals with a symptomatic neuroma involving the sural nerve in the distal part of the leg. In many cases, simple section of the medial sural cutaneous nerve in the popliteal region is not effective management because of the contributions from the peroneal communicating branch or the medial branch of the lateral sural cutaneous nerve to the sural nerve. Furthermore, the variety of contributing nerves to the sural nerve may complicate and interfere with the technique of nerve graft harvest by use of a tendon stripper, as advocated by some. 6 • 8 We believe that the most significant findings of this study are related to the peroneal communicating branch of the lateral sural cutaneous nerve. In most specimens, this nerve branch was of larger caliber than, and of comparable length to, the medial sural cutaneous nerve. This finding is at variance with that of Hill, Vasconez, and Jurkiewicz,6 who reported that the medial sural cutaneous nerve was always larger than any contribution from the peroneal nerve. Moreover, the peroneal communicating branch was present in 80% of specimens and had a reasonably consistent point of entry into the sural nerve. The peroneal communicating branch lies superficial to the fascia of the triceps surae muscles and thus is readily accessible to surgical harvest Therefore, in situations requiring a limited length of nerve graft material, the peroneal communicating branch alone can be harvested and the medial sural cutaneous nerve can be preserved. In this way, some sensibility in the sural nerve distribution will be pre-

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served and the risk of symptomatic neuroma at the transection site of the sural nerve or its component branches will likely be diminished. We now use the peroneal communicating branch, when present, for clinical situations requiring 20 cm or less of nerve graft material 2 mm in diameter. For exposure in such cases, a linear incision, 15 to 20 cm in length, is made at a point 10 cm proximal to the lateral malleolus in the posterior midline and is extended proximally in the midline. The peroneal communicating branch is identified distally where it unites with the sural nerve. Without disturbance of the sural nerve or the medial sural cutaneous nerve, this branch is excised over the required length, provided that its caliber is sufficient for grafting. If at exposure a peroneal communicating branch is not present, the medial sural cutaneous nerve deep to the fascia and the sural nerve are both available and accessible through the incision. Conclusions Table I provides lengths and diameters of all nerves investigated. Our main conclusions are: 1. In 80% of cases, the sural nerve is formed by the union of the medial sural cutaneous nerve and the peroneal communicating branch. 2. In the other 20% of cases, the sural nerve originates from the medial sural cutaneous nerve only. 3. In 95% of cases, a lateral sural cutaneous nerve is present. 4. In 93.7% of cases, the peroneal communicating branch originates from the lateral sural cutaneous nerve. 5. In 15.8% of cases, the medial division of the lateral sural cutaneous nerve contributes branches to the peroneal communicating branch. 6. The peroneal communicating branch is often of larger caliber than the medial sural cutaneous nerve. 7. The peroneal communicating branch, when present, is a useful source of nerve graft material and can be readily harvested through a superficial incision, with preservation of the medial sural cutaneous nerve functional contribution.

REFERENCES I. Brooks D. The place of nerve-grafting in orthopaedic surgery. J Bone Joint Surg [Am] 1955;37:299-304.

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2. Seddon H. Surgical disorders of the peripheral nerves. Baltimore: Williams & Wilkins Co, 1972. 3. Fisher TR, Cox P. The sural nerve as autogenous nerve graft [Abstract]. J Bone Joint Surg [Br] 1974;56:571-2. 4. Millesi H. Interfascicular grafts for repair of peripheral nerves of the upper extremity. Orthop Clin North Am 1977;8:387-404. 5. Staniforth P, Fisher TR. The effects of sural nerve excision in autogenous nerve grafting. Hand 1978;10: 187-90. 6. Hill HL, Vasconez LO, Jurkiewicz MJ. Method for obtaining a sural nerve graft. Plast Reconstr Surg 1978; 61: 177-9. 7. Merle M, Amend P, Cour C, Foucher G, Michon J. Microsurgical repair of peripheral nerve lesions. Peripheral Nerve 1986;1:17-26. 8. Hankin FM, Jaeger SH, Beddings A. Autogenous sural nerve grafts: A harvesting technique. Orthopedics 1985; 8:1160-4. 9. Narakas AO. The treatment of brachial plexus injuries. Int Orthop 1985;9:29-36. 10: Bardeen CR. Development and variation of the nerves and the musculature of the inferior extremity and of the neighboring regions of the trunk in man. Am J Anat 1906;6:259-390. II. Cunningham's text-book of anatomy. Brash JC, ed. 9th ed. London: Oxford University Press, 1951:1106,1110. 12. Gray H. Anatomy of the human body. 26th ed. Edited by CM Goss. Philadelphia: Lea & Febiger, 1973:9981000. 13. Williams DD. A study of the human fibular communicating nerve. Anat Rec 1954;120:533-43. 14. Huelke DF. A study of the formation of the sural nerve in adult man. Am J Phys Anthropol 1957;15:137-47. 15. Huelke DF. The origin of the peroneal communicating nerve in adult man. Anat Rec 1958;132:81-92. 16. Mann MD. The nervous system and behavior. Philadelphia: Harper & Row, 1981 :91. 17. Bergman RA, Thompson SA, Afifi AK. Catalog of human variation. Baltimore: Urban & Schwarzenberg, 1984:161. 18. Kosinski C. The course, mutual relations and distribution of the cutaneous nerves of the metazonal region of leg and foot. J Anat 1926;60:274-97. 19. Thomas PK, Ochoa J. Microscopic anatomy of peripheral nerve fibers. In: Dyck PJ, Thomas PK, Lambert EH, Bunge R, eds. Peripheral neuropathy. Vol 1. 2nd ed. Philadelphia: WB Saunders Company, 1984:46. 20. de Moura W, Gilbert A. Surgical anatomy of the sural nerve. J Reconstr Microsurg 1984;1:31-9.