Anatomical Science International (2002) 77, 140–144

Blackwell Science, LtdShort Report

Sural–tibial nerve communications in humans

Shin-ichi Sekiya1 and Katsuji Kumaki2

1 Niigata College of Nursing, Joetsu, and 2 Department of Anatomy, School of Medicine, Niigata University, Niigata, Japan

AbstractWe investigated the occurrence of a communication between the sural and tibial nerves in 49 legs of 28Japanese cadavers. In front of the calcanean tendon, we found the communication in 7 legs (14.3%) or in 5cadavers (18.9%). The sural nerve gave rise to a number of medial and lateral branches, including the lateralcalcanean branch at the lateral side of the ankle. The communicating branch with the tibial nerve arose fromthe first medial branch and pierced the deep fascia of the leg. In 4 cases, the U-shaped communication wasformed between the sural and tibial nerves, and in 3 cases, the Y-shaped communication. Electrophysiologi-cal evidence of an anomalous motor function of the sural nerve has been reported recently. We consider thatthe U-shaped communication between the sural and tibial nerves gives a morphological basis to the motorfunction of the sural nerve.

Key words: lateral plantar nerve, nerve communication, sural nerve, tibial nerve.

Introduction

The sural nerve is well known as a typical sensorynerve. It supplies not only the skin of the lateral sideof the ankle, heel, foot and the fourth and fifth toes,but also some joints of the foot (Lippert, 1962; Gardner& Gray, 1968), the achilles tendon (Stilwell, 1957), anddeep tissues (Chang et al., 1983). It usually commu-nicates on the dorsum of the foot with the superficialperoneal nerve. The cutaneous areas supplied by thesural nerve are variable in association with the com-munication with the superficial peroneal nerve.

On the other hand, the sural nerve is usuallyformed by the union of the medial sural cutaneousnerve and the peroneal communicating branch of thelateral sural cutaneous nerve. Several variations inthe formation of the nerve have long been reported(Bardeen, 1906; Ssokolow, 1933; Mogi, 1938; P’an,1939; Williams, 1954; Huelke, 1957, 1958). Kosinski(1926) investigated the origin, course and distributionof the sural nerve from the standpoint of comparativeanatomy, and Tani (1974) considered the morphologicaldiversity of the sural nerve as successive variationsusing the methods of fiber analysis.

Despite many such anatomical studies of the suralnerve, communications between the sural and thetibial or lateral plantar nerves, which are well knownin some experimental animals, rats (Nakanishi &

Norris, 1970), dogs (Evans & Christensen, 1979), andmonkeys (Howell & Straus, 1961), are not yet reportedin humans. Based on observation of the sural nerveof Japanese macaques, Sekiya (1999) suggestedthat the human sural nerve might communicate withthe lateral plantar nerve at the ankle.

In this paper, we describe the communicationbetween the sural and tibial nerves in humans.

Materials and methods

This study used 28 Japanese bodies (19 women andnine men), ranging 56–94 years (mean age ± standarddeviation (SD) = 80 ± 10.0 years), totalling 49 legs,which were dissected in anatomical practice duringa period of 2 years (1997 and 1998) at the NiigataUniversity School of Medicine.

The length of the fibula and six other distanceswere measured with a sliding caliper (Fig. 1). Thelength of the fibula was defined as the distancebetween the lateral summits of the head and the lateralmalleolus. The distances between the head of thefibula and the points of origins of the medial and lateralsural cutaneous nerves from the tibial and commonperoneal nerves, respectively, were measured. Othermeasured lengths were the distances from the lateralmalleolus to the point of union of the medial suralcutaneous nerve with the peroneal communicatingbranch of the lateral sural cutaneous nerve, and fromthe lateral malleolus to the sites of origins of threebranches, the lateral calcanean branch, and the firstmedial and first lateral branches. The lateral brancheswere defined as some branches arising anteriorlyfrom the sural nerve in the lower leg and supplying

Correspondence: Shin-ichi Sekiya, Niigata College of Nursing, 240 Shin-nan-cho Joetsu 943–0147, Japan. Email: sekiya@niigata-cn.ac.jpReceived 27 November 2001; accepted 19 November 2001.

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the skin of the lateral lower part of the leg, especiallyaround the lateral malleolus. The lateral calcaneanbranch supplied the lateral side of the skin of theheel. The medial branches were branches arisingmedially from the sural nerve and entering the spacelying in front of the calcanean tendon.

The sural nerve was usually formed by the unionof two nerves, the medial sural cutaneous nerve andthe peroneal communicating branch of the lateralsural cutaneous nerve. Although there is some con-troversy about the nomenclature of the sural nerve(Kosinski, 1926; Tani, 1974), we follow here thenomenclature of Huelke (1957).

Results

Communication between the sural nerve or themedial sural cutaneous nerve and the tibial nervewere found in seven of 49 legs (14.3%), bilaterallyin four legs and unilaterally in three legs. In 20 legs,we found medial branches arising from the sural orthe medial sural cutaneous nerve and supplying theconnective tissues lying in front of the calcaneantendon. The communication was made between acommunicating branch arising from the first medialbranch and that arising from the tibial nerve. Themedial branch left the parent nerve at a higher levelthan the lateral branches and lateral calcaneanbranch (Table 1). Two types of communication wereobserved in front of the calcanean tendon, a U-shapedcommunication and a Y-shaped communication(Table 2).

In case 1, the sural nerve was formed by the unionof the medial sural cutaneous nerve and two pero-neal communicating branches from the lateral sural

Figure 1. Measurements made on intact sural nerves. Thedistances, 1–6, from the bifurcating or joining points of nervesto the lateral summits of the head or the lateral malleolus of thefibula was measured. The asterisk indicates communicationbetween the sural and tibial nerves. CA, calcaneus; NCSL,lateral sural cutaneous nerve; NCSM, medial sural cutaneousnerve; NPC, common peroneal nerve; NS, sural nerve; NT,tibial nerve; RCL, lateral calcanean branch; RCP, peronealcommunicating branch; RL, lateral branch; RM, medial branch.

Table 2. Source of the communicating branch with the tibial nerve, position of the communication to the deep crural fascia, and typeof communication

Case Sex Age LegSource of communicating branch with tibial nerve

Position to deep crural fascia

Type of communication

1 F 81 Left Sural nerve over U2 Right Medial sural cutaneous nerve under Y3 M 82 Left Sural nerve over U4 Right Medial sural cutaneous nerve over U5 F 87 Left Medial sural cutaneous nerve over Y6 F 89 Left Sural nerve over Y7 M 94 Left Medial sural cutaneous nerve over U

Table 1. Distance to the head of the fibula or the lateralmalleolus from the points of origins of nerves

Nerves Mean ± SD (n, mm)

1 Lateral sural cutaneous nerve 81 ± 19.1 (42)2 Medial sural cutaneous nerve 60 ± 20.0 (47)3 Sural nerve 124 ± 60.6 (37)4 Lateral branch of the sural nerve 63 ± 14.9 (10)5 Medial branch of the sural nerve *72 ± 26.0 (20)6 Lateral calcanean branch *41 ± 19.9 (38)Length of the fibula 297 ± 20.3 (49)

See Fig. 1 for details of 1–6.*P < 0.01.

142 S. Sekiya and K. Kumaki

cutaneous nerve. The sural nerve gave rise to twomedial branches towards the anterior space of thecalcanean tendon. The proximal branch arose fromthe sural nerve at a site 65 mm proximal to the lateralmalleolus and gave off a communicating branch withthe tibial nerve. The communicating branch piercedthe deep fascia of the leg and joined the tibial nerveascending slightly under the fascia, thereby forminga U-shaped communication (Figs 2, 3a). A few finetwigs arose from this communication and suppliedthe deep fascia. The whole sciatic nerve, includingthis communication, was removed from the lower leg,and is shown in Fig. 4.

In case 2, the medial sural cutaneous nervedescended free from the lateral sural cutaneousnerve under the deep fascia of the leg until the pointof 50 mm above the lateral malleolus, where the twonerves united and coursed normally as the suralnerve. A Y-shaped communication between themedial sural cutaneous nerve and the tibial nervewas found under the deep fascia (Fig. 3b). A medialbranch that left the medial sural cutaneous nerve ata site 50 mm proximal to the lateral malleolus and a

Figure 2. Communication between the sural nerve (NS) andthe tibial nerve (NT). Posterior aspect of the left ankle removingthe calcanean tendon (CA) in case 1. A communicating branch(arrowheads) arising from a medial branch (RM) of the suralnerve is lying on the deep crural fascia, piercing it to reach thetibial nerve. A part of the deep crural fascia has been removedto show the tibial nerve. MP, tendon of the plantar muscle; RCL,lateral calcanean branch; RCP, distal peroneal communicatingbranch; VSP, small saphenous vein. Bar = 2 cm.

Figure 3. (below) Left ankle in case 1 (a), the right ankle in case2 (b), and in case 4 (c) in posterior aspect. In all cases, thecalcanean tendon (CA) has been removed. The communication(asterisk) between the sural and tibial nerves is U-shaped (a,c)or Y-shaped (b). In case 1, only the distal of the two peronealcommunicating branches (RCP) from the lateral sural cutaneousnerve is shown (a). The communication under the deep cruralfascia (FCP) in case 2 is shown by cutting open the fascia.MAL, lateral malleolus; MAM, medial malleolus; MP, tendon ofthe plantar muscle; MS, soleus muscle; NCSM, medial suralcutaneous nerve; NS, sural nerve; NT, tibial nerve; RCL, lateralcalcanean branch; VSP, small saphenous vein.

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communicating branch from the tibial nerve unitedto form one nerve that supplied the synovial sheath ofthe flexor hallucis muscle and the connective tissue.

In case 3, a medial branch arose from the suralnerve at a site 120 mm proximal to the lateral malle-olus. The medial branch gave off a fine commun-icating branch with the tibial nerve. These formed aU-shaped communication between the sural andtibial nerves. The same U-shaped communicationwas found in cases 4 (Fig. 3c) and 7. The medialbranch arose from the medial sural cutaneous nerveat a site 80 mm in case 4 and 100 mm in case 7 prox-imal to the lateral malleolus. The sural–tibial nervecommunication of case 5 was a Y-shaped one formedby the union of a branch of the tibial nerve and amedial branch that left the medial sural cutaneousnerve at a site 60 mm proximal to the lateral malle-olus. In case 6, the same Y-shaped communicationwas observed, and the medial branch arose from thesural nerve at a site 100 mm proximal to the lateralmalleolus. The branches formed by these Y-shapedcommunications were distributed to connective tis-sues lying in front of the calcanean tendon.

Discussion and conclusion

The 14.3% incidence of a communicating branchbetween the sural and tibial nerves in 49 legs in thisstudy is surprisingly high, considering that the com-munication has not been reported in the literature. Itmight have been overlooked in routine anatomicalprocedures because the communicating branchesare extremely thin and the sural nerve has beenconsidered as a pure sensory nerve supplying theskin and joint capsule.

The branch communicating with the tibial nervearose from the first medial branch of the sural nerveor the medial sural cutaneous nerve. In any case,the medial branch arose at a higher level comparedwith the lateral branches and the lateral calcaneanbranch. The communication showed either a U- orY-shaped appearance. In the former type, the direc-tion of the nerve fibers in the communicating branchremained obscure. In a preliminary study using thefiber analysis method, however, we found that somenerve fibers in the communication were derived fromthe medial sural cutaneous nerve and supplied theinterosseous muscle via the lateral plantar nerve

Figure 4. Nerves of the left lower limb in case 1, posterioraspect. The sural nerve (NS) is formed by the union of themedial sural cutaneous nerves from the tibial nerve (NT) and theproximal peroneal communicating branch of the lateral suralcutaneous nerve from the common peroneal nerve (NPC).Asterisk indicates the communication between the sural andtibial nerves. Scale check = 5 cm.

144 S. Sekiya and K. Kumaki

(Sekiya & Kumaki, 2000). In the Y-shaped commun-ication, the fibers appeared to be derived from boththe sural and tibial nerves united into a bundle, whichsupplies the connective tissue lying in front of thecalcanean tendon. Accordingly, this type of com-munication might not be a genuine one betweenthe two nerves.

We have been unable to find any description ofsuch a communication between the sural and tibialnerves in the research concerning the human suralnerve, while a communication between the sural andlateral plantar nerves has been found in some exper-imental animals (Howell & Straus, 1961; Nakanishi &Norris, 1970; Evans & Christensen, 1979), and var-ious primate species (Ssokolow, 1933; Sekiya, 1999).Therefore, we surmised that the communication be-tween the sural nerve and the lateral plantar nervemight also appear in humans (Sekiya, 1999), discovereda similar communication between the sural nerve andthe tibial nerve in the preliminary study (Sekiya &Kumaki, 2000), investigated the occurrence of it anddescribed it in the present study. Although the suralnerve does not directly communicate with the lateralplantar nerve in humans, fibers from the sural nervecan proceed to the lateral plantar nerve via the com-munication and the tibial nerve. In fact, we foundthat some fibers in the communication supplied theinterosseous muscle via the lateral plantar nerve(Sekiya & Kumaki, 2000). We consider that there isno essential difference between the human-type com-munication and the animal type. But further studiesusing the fascicle and fiber analysis methods arerequired.

In recent electrophysiological studies, severalinvestigators clarified that in some patients, motor fibersare contained in the sural nerve (Liguori & Trojaborg,1990; Ragno & Santoro, 1995; Amoiridis et al., 1997).Amoiridis et al., (1997) investigated 207 patients andfound motor fibers in 15 sural nerves (4.5%) or in 13individuals (6.2%). They recorded compound muscleaction potentials in the abductor digiti minimi muscle,which is innervated by the lateral plantar nerve, afterstimulation of the sural nerve. They postulated thecourse of motor fibers of the sural nerve in frontof the Achilles tendon. This course is compatiblewith that via the U-shaped communication betweenthe sural and tibial nerves. We consider that the

U-shaped communication gives a morphologicalbasis to the motor function of the sural nerve.

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