The medial and inferior calcaneal nerves: an anatomic...

Surg Radiol Anat (1999) 21:169-173

S u r g i c a l a I Radiolog,c Anatomy Journal of Clinical Anatomy

© Springer-Verlag 1999

The medial and inferior calcaneal nerves: an anatomic study

S. Louisia and A.C. Masquelet

Department of Orthopaedic Surgery, Paris Nord University, 74, rue Marcel Cachin, F-93012 Bobigny Cedex, France

Summary: The existence of chronic heel pain induced by the compress ion of nerves prompted us to conduct an anatomic study of the innervation of the heel. Fifteen cadaver feet were dissected to inves t igate the origin, course and branches of the medial calcaneal nerve (MCN) and the inferior calcaneal nerve (ICN). Despite a variable origin (tibial n. (TN) or lateral plantar n. (LPN)), the medial calcaneal nerve branches which lay superficial to the abductor hallucis muscle (AH) were quite constant. The medial calcaneal nerve gave branches to the abductor hallucis muscle and innervated the posterior part of the medial face of the heel. It terminated in the superficial heel pad at the inferior part of the heel. In our study, the inferior calcaneal nerve always originated from the lateral plantar nerve. Its relationship to the deep fascia of the abductor hallucis muscle and anter ior tubercle of calcaneus may explain the entrapment syndrome of the inferior calcaneal nerve.

Etude anatomique des nerfs calcan6ens m6dial et inf6rieur

R6sum~ : L'existence de talalgies chro- niques li6es h des compressions ner- reuses a motiv6 cette ~tude de l'innerva-

Correspondence to: S. Louisia

tion du talon. Quinze pieds de cadavres ont 6t6 diss6qu6s pour explorer l'origine, le trajet, et les cotlatdrates des nerfs cal- canden mddial (NCM) et calcan6en inf6- rieur (NCI). L 'or ig ine du NCM 6tait variable : nerf tibial post6rieur ou nerf plantaire lat6ral, la distribution de ses branches, superficielles par rapport au muscle abducteur de l'hallux, 6tant relati- vement constante. Elles 6taient destindes au muscle abducteur de l'hallux et ?~ la pattie post6rieure de la face mddiale du talon. La portion terminale du neff calca- n6en m6dial s'dpuisait dans le coussin adipeux superficiel du talon h la face infdrieure du calcan6us. Le nerf calca- n6en inf6rieur naissait toujours du nerf plantaire latdral. Ses rapports avec le fascia profond du muscle abducteur de l'hallux et le tubercule ant6rieur du calcandus accrdditent la possibilit6 d'un syndrome canalaire.

Key words: Medial calcaneal nerve - - Inferior calcaneal nerve - - Heel pain - - Entrapment neuropathy - - Anatomy

Heel pain is a very common symptom among patients who seek orthopaedic care. Most of the literature on the subject has focused on the tarsal tunnel syndrome or the role of a heel spur in such pains [4, 8, 24]. Even when systemic etiologies have been ruled out, some cases remain unexplained. Some authors have sugges- ted that the medial calcaneal nerve (MCN) and/or the inferior calcaneal n.

(ICN) may be involved in such heel pain [1, 2, 24]. Two types of clinical situations prompted us to study the sensory innervation of the medial and inferior aspects of the heel: first, heel pain arising from the screws of an external fixator implan- ted in the medial aspect of the calcaneus; and second, persistant heel pain which cannot be explained either by tarsal tunnel syndrome, or by the existence of a heel spur or hindfoot deformity. In order to clarify the sites of the calcaneal nerves and explore their relationship to neuropathy entrapments, we conducted this anatomic study and reviewed the literature.

Material and methods

To name the calcaneal nn., we used the same terminology as Didia [5], Park [15], Arenson [1] and Roegholt [t8], i.e., the medial calcaneal n. (MCN) and the inferior calcaneal n. (ICN). Fifteen cadaver feet were dissected. Thirteen cadavers were embalmed, while the remaining two were fresh-frozen. None of them were injected. The feet used in the study were both left and right and male and female. The choice was based on the availability of the cadavers. 2 out of the 15 belonged to the same cadaver. The tibial n. (TN) was dissected from the middle third of the leg to its bifurcation into the medial plantar n. (MPN) and lateral plantar n. LPN. We dissected the branches of the MCN and those of the ICN. The origin of these two nerves with relationship to the

170 s. Louisia and A.C. Masquelet: The medial and inferior calcaneal nerves

TN's division, their course, and the num- ber of their branches were documented. The bifurcation of the TN was defined in terms of its distance along a line drawn from the center of the medial malleolus to the center of the calcaneus [4]. All of our dissections were undertaken with fine instruments (Metzembanm scissors, Ste- vens scissors, classical forceps both too- thed and untoothed) without having to resort to microsurgical instruments. We did not use optical magnification. The objective of our study was to define the anatomy of the MCN, ICN and their main branches. The study of all the colla- teral branches of both nerves would require optical magnification and that was not the aim of our study.

Resul t s

The rate of occurrence of the MCN and ICN in our dissection was 100%. Details of the results in the 15 cadaver dissections are shown in Table 1.

Medial calcaneal n.

The MCN originated from the TN in 10 out of 15; from the LPN in 3 out of 15 and from both the TN and LPN in 2 out of 15 (Fig. 1). When the MCN's origin consisted of two distinct trunks we considered that these branches belonged to the MCN, since their course and terminations corresponded to those of an MCN with a single truncal origin. The MCN's origin was highly variable. We found it originating from 10 cm above the division of the TN to 4 cm below this point, with a mean distance of 1.58 cm above this division. It coursed obliquely plantarward and backward to the heel.

The MCN and its branches had an overall direction from the depth to the surface. Most of the branches lay superficial to the abductor hallucis m. (AH). The medial calcaneal branches provide sensory innervation to most of the heel pad and to the superficial tissues overlying the inferior aspect of the calcaneum. The MCN consisted of 2 major branches in 9 out of 15 feet; 1 major branch in 2 out of 15; 3 major branches in 2 out of 15 and 4 major branches in 2 out of 15. Each of these branches ended in ramifications. When the MCN consisted of several

Fig, 1 Note the MCN's origin consisting of two distinct trunks from the TN

Fig. 2 This is an example of the most common variant whereby the origin of the MCN consists of only one trunk from the TN

Fig. 3 This picture shows the superficial course of the CPN

branches (Figs. 1, 2, 3), the anterior branch (ABMCN) ended close to the proximal insertion of the AH. The posterior branch (PBMCN) innervated the superficial tissues of the medial aspect of the calcaneus opposite the insertion of the calcaneal tendon. These 2 branches arose

either independently or from a common trunk with a medial branch (MBMCN). This medial branch crossed the infero- medial edge of the heel. The location of this branch on the medial aspect of the heel was constant in all 15 feet. It followed its course through the alveolar struc-

S. Louisia and A.C. Masquelet: The medial and inferior catcaneal nerves

Table 1. Details of the dissections

t71

Patients Origin ICN Origin MCN MCN/div. TN ICN/div. TN Branches of MCN Branches of ICN Div. TN/axis

t LPN TN 0.5 - 3 2 2 3.5 2 LPN TN 1.8 - 4.7 1 2 3 3 MCN LPN - 0.9 - 2.2 4 2 1.5 4 LPN TN/LPN* * 2.8/- 0.5 * - 1 2 2 0 5 LPN TN 0 - 1.1 2 2 2 6 LPN TN 1.4 - 0.7 2 2 0 7 LPN*** TN 10 0 2 2 0 8 LPN TN 6.5/I.5" - 1.5 2 2 1 9 LPN*** TN 2.5 0 2 2 0 10 LPN TN 3 - 2 2 2 2.5 11 LPN LPN - 2 - 2.5 1 2 1.5 I2 LPN LPN - 4 - 6 3 2 3.5 13 LPN TN 1.5 0 4 2- 0.5 t4 LPN TN 4/1" - 0.5 2 2 0.8 15 LPN TN/LPN** 1.5/- 0.5* -- 1 3 2 - i

The figures are in cm. LPN, lateral plantar n.; TN, final n.; MCN, medial calcaneal n.; ICN, inferior calcaneal n.; div, division; axis, malleolar-calcaneal axis; nega- tive figures, distal to division of the TN; positive figures, proximal to division of the TN; **, the MCN's origin consisted of two distinct trunks, one from the TN, one from the LPN; *, the MCN's origin consisted of two distinct minks;***, the ICN arose from the LPN just after the division of the TN

Fig. 4 This is a specimen where the ICN arises from the MCN. Abbreviations'. TN, tibial nerve; LPN, lateral plantar n.; MPN, medial plantar n.; MCN, medial calcaneal n.; AB MCN, anterior branch of the medial calcaneal n.; MB MCN, medium branch of the medial calcaneal n.; PB MCN, posterior branch of the medial calcaneal n.; ICN, inferior calcaneal n.; CB ICN, calcaneal branch of the ICN; CPi~; cutaneous plantar n.

ture of the fatty pad of the heel on the media l and plantar aspects of the heel.

Reaching the plantar aspect of the heel, this branch had a course which was ini-

tially backward and lateral and then for-

ward and lateral in a curved shape that

followed the edge of the plantar aspect of the heel. This nerve corresponds to Rou- vi~re's description of the cutaneous plan-

tar n. (CPN) (Figs. 1, 3, 4).

Inferior calcaneal n.

The ICN arose from the LPN in 14 out of

15 and in l out of 15 from the M C N (Fig. 4). In the latter the M C N originated from

the LPN. The o r i g i n o f the I C N was always distal to the origin of the medial

c a l c a n e a l n. The I C N o r i g i n a t e d at a mean distance of 1.74 cm below the T N divis ion. The detai ls of the dissect ions

reported in Table 1 show that the more proximal the division of the TN, the fur-

ther f rom this d iv i s ion the I C N arose. Thus, the point of emergence of the ICN in relationship to Del lon ' s reference l ine

[4] was no t as var iable as the point of division of the TN.

The ICN traveled downward, forward

and laterally. Passing into the deeper tissue structures it crossed over the upper

edge of the A H go ing d o w n w a r d and laterally. Its course passed be tween the uppe r edge o f the A H and the med ia l edge of the quadratus plantae m. (QP). It

then passed between the deeper fascia of the A H and the anterior tubercle of calca-

neus. The nerve continued its course late-

ral ly be tween the QP above and flexor d ig i tomm brevis m, below. The nerve ran

along the lower side of the QP and then,

c r o s s e d ove r the l a t e r a l edge of tha t muscle terminating at the most proximal portion of the abductor digiti minimi m..

In i ts course , the I C N gave r ise to a constant calcaneal branch to the anterior

tubercle of calcaneus innervating its per-

ios teum (CBICN) (Figs. 1, 2, 3, 4). W e

named this nerve the calcaneal branch of

the ICN. Othe r b r a n c h e s were f o u n d regularly innervating the flexor digitorum

brevis and QP ram. No at tempts were

made to record these muscular branches

precisely. T h e b r a n c h e s o f t h e s e 2 n e r v e s

(MCN, ICN) were closely accompanied by corresponding vessels.

By using the definition of the M M C axis defined by Dellon [4], the results of our study showed that the TN bifurcated

in 73% of cases within the tarsal tunnel a n d in 26% a b o v e the t a r sa l t u n n e l .

Discuss ion

The M C N and the I C N

The M C N has no t been greatly studied [5, 15]; n o n e of its b ranches has been accurately described. The anatomy of the

172

ICN is also poorly documented [1]. Moreover, the ICN has received nume- rous appellations in the literature: first branch of the LPN [2, 3, 19]; muscular branch of the LPN to the abductor digiti quinti m. [17]; calcaneal branch [24], deep caicaneai n. [11], anterior branch of the calcaneal n. [9]. Cruvelhier's medial calcaneal nerve branch [14]. Anatomic descriptions of the MCN found in classical anatomic texbooks such as Rouvirre [20], Grays [6], etc are either succinct or do not match with our results. The anatomy of the ICN is not described in these books.

More recent anatomic studies, toge- ther with our results, allow clarification of the anatomy of the two calcaneal rm.

The bifurcation of the tibial n. (TN)

Our findings were consistent with the literature regarding the bifurcation of the TN. Davis found that the TN bifurcated in 90% of cases within the tarsal tunnel. Dellon and Havel found similar results: 95% and 93% respectively.

The origin and branches of the medial calcaneal n.

Our results corroborate those of Didia [5], who studied 16 cadavers. He found that the MCN arose f rom the TN in 62.5%, from the bifurcation of the TN in 18.75% and from the LPN in 18.75% of the cases. He reported the same variability concerning the point of emergence of the MCN and the same cons tancy concerning the distr ibution of the branches to the skin of the medial and plantar aspects of the heel.

Park [ 15] found similar results on the origin of the MCN. Out of 14 feet, he found a great variability of the origin of the MCN, which ranged from 8.2 cm proximal to 1.3 cm distal to the lowest point of the medial malleolus. In his study, the MCN arose from the TN in 58%, from the division of the TN in 21% and from the LPN in 21%. He described one principal trunk for the MCN in 71% and two trunks in 29%. Like Park, we found that the MCN could arise from two distinct branches in 13% of cases. These trunks gave rise to 2 branches destined for the heel in 64% and to 3 branches in

S. Louisia and A.C. Masquelet: The medial and inferior calcaneal nerves

36%. He confirmed that there was a constant distribution of the terminal branches of the MCN and that this distribution was superficial. For this author this constancy and superficial location allows specific electrophysiologic study of the MCN. He defined a point G1 as the best point to perform such a study; it was situated at one third of the distance from the apex of the heel to a point mid- way between the navicular tuberosity and the prominence of the medial malleolus.

Davis [3] found innervation of the abductor hallucis (AIt) m. from the FB of the LPN (corresponding to the ICN) in 3 out of 20 specimens. We never found this feature. On the other hand, we found that the anterior branch of the MCN innervated the proximal part of the AH m. Our findings focused on the distribution of previously undescribed branches of the MCN. It was interesting to note that the MCN provided almost constantly an anterior branch to the proximal portion of the abductor hallucis, a posterior branch to the superficial soft tissues in the poste- ro-superior part of the medial aspect of the heel and a medial or terminal branch which innervated the superficial portion of the inferior aspect of the heel. This terminal branch should be named the cutaneous plantar n. as Rouvi~re [20] had already named it.

The origin and branches of the ICN

Our results regarding the ICN matched with those of Arenson [I], who studied 30 feet. This author insisted on the close relationship between the ICN and the anterior tubercle of the calcaneus. He found an average distance of 5.5 mm between these 2 structures. Didia [5] found the origin of the ICN to be from the LPN in 81.25% of cases, f rom the TN in 12.5% and in 6.25% from the TN sharing a common origin with the MCN. Despite the use of a different terminology, Schon [23], Przylucki [17], Davis [3] and Rond- huis [19] reported anatomic findings that correspond closely to our results regarding the ICN. Davis [3] found calcaneal branches originated from the MPN in 3 out of 20 cases. We never found calcaneal branches originating from the MPN. Moreover, we found the first branch of the ICN to be constant and to innervate

the periosteum of the medial calcaneum. In 1 out of 15 we found a previously undescribed variation of the ICN. In this case (n ° 3, Table 1) the ICN arose from the MCN, which originated from the LPN (Fig. 4). Harem [7] reported variations of the nerve for the abductor digiti quinti m.. In a study of 39 specimens, he found this nerve originating as the posterior branch of a trifurcation of the TN in 46%, as a branch of the LPN in 49% and as a direct branch from the TN in 5% of the specimens.

Clinical and surgical implications

Our new knowledge about the anatomy of the ICN allows a better understanding of the role of ICN entrapment in heel pain. In 1940, Roegholt [18] was the first to suggest the role of the ICN in the heel pain syndrome. Przylucki [17] emphasi- sed the fact that the greatest compression is at a point just anterior to the attach- ment of the fascial structures to the anterior tubercle of the calcoaleus.This area is where the muscular branch to the abductor digiti quinti m. is observed to be subject to these compressive forces with each step taken. According to Rondhuis [19] it is very likely that the ICN contains sensory fibres especially in its branch to the periosteum of the anterior tubercle of the calcaneus (CBICN). When such fibres are caught in an entrapment, severe and welt-localised pain may occur, as can be observed in patients with heel pain syndrome, An entrapment of a motor nerve would produce a dull pain hard to locate [19].

Both Henricson [9] and Tanz [24] described a calcaneal branch that corresponded to the ICN "interposed between the deep fascia of the proximal part of the AH and the anterior tubercle of the calcaneus". Kenzora [11] identified two different sites of possible entrapment of the ICN. The first would be in the area where the nerve crosses the deep fascia of the AH between the AH and QP ram. The second site, more distal, would be where the nerve hugs the periosteum just distal to the anterior tubercle of the calcaneus. For this author, a hypertrophy of any tissue in this area so that the nerve cannot move out of the way could be a cause of entrapment (calcaneal spur, scar tissue,

S. Louisia and A.C. Masquelet: The medial and inferior calcaneal nerves 173

inflammation etc). He reported 6 cases of surgical release using a longitudinal plantar approach. Henricson [9] and Baxter [2] reported respectively the results in 11 and 69 patients with chronic heel pain who benefited from surgical release of the ICN (named the first branch of the LPN by these authors). The procedure consisted of partial resection of the deep fascia of the AH facing the entrapment zone of the nerve. All these authors reported good results after such a surgical release.

Park [16] reported a case of isolated inferior calcaneal neuropathy with specific electrophysiologic findings suggesting denervation of the ICN. In a review, MaNn [13]reported the clinical and electrophysiologic features of compression of both the MeN and ICN. The clinical features can easily be explained by our anatomic study. ICN entrapment can be identified by tenderness where the nerve passes between the AH and QP mm [13, 23]. Schon [22] reported the same clinical findings in all of his 38 cases. He found electromyographic abnormalities which correlated with the affected side of patients with unilateral symptoms. These findings concerned the MPN and LPN. This author considered it impossible to investigate specifically the ICN or the MeN electrophysiologically. According to Mabin [ 13] repeated microtraumata or major loss of fatty tissue could cause entrapment of the MCN and its branches. A more accurate knowledge of the anatomy of the MCN and the ICN should allow a better understanding of heel pain, especially at the medial and inferior

aspects of the heel. This more accurate knowledge may also be useful concerning safe screw insertion for external fixation across the calcaneus. To minimi- ze iatrogenic injuries of these two nerves we recommend, like Santi [21] the use of blunt dissection down to the bone for screw insertion.

Acknowledgements. We would like to thank Mr Haudy from the School of Surgery of Pads for his

technical support in producing the illustrations.

References

1. Arenson DJ, Cosentino GL, Suran SM (1980) The inferior calcaneal nerve: an anatomic study. J Am Podiatr Ass 70:552-560

2. Baxter DE, Pfeffer GB (1992) Treatment of chronic heel pain by surgical release of the first branch of the lateral plantar nerve. Clin Orthop 279:229-236

3. Davis TJ, Schon LC (1995) Branches of the tibial nerve: anatomic variations. Foot Ankle Int 16:21-29

4. Dellon AL, Mackinnon SE (1984) Tibial nerve branching in the tarsal tunnel. Arch Nearol, 41: 645-646

5. Didia BC, Horsefall AU (1990) Medial catcaneal nerve: an anatomic study. J Am Podiatr Ass 80:115-119

6. Gray H (1989) Gray's Anatomy.37th edition, Churchill Livingstone

7. Harem JT, Sanders M (1987) Anatomic variations of the nerve to the abductor digiti quinti muscle. Foot Ankle 8:123

8. HaveI PE, Ebraheim NA, Clark SE, Jackson WT, Didio L (1988) Tibial nerve branching in the tarsal tunnel. Foot Ankle 9:117-119

9. Henricson AS, Westlin NE (1984) Chronic calcaneal pain in athletes: entrapment of the calcaneal nerve ? Am J Sports Med 12:152-154

10. Horwitz MT (1938) Normal anatomy and variations of the peripheral nerves of the leg and foot. Arch Surg 36:626-636

11. Kenzora JE (1987) The painful heel syndrome: an entrapment neuropathy. Bull Hosp Jt Dis Ortho Inst 47:178-89

12. Kopell HP, Thompson AL (1960) Peripheral entrapment neuropathies of the lower extre- mity. N Engl J Med 262:56-60

t3. Mabin D (1997) Compressions nerveuses dis- tales du membre infrrieur. Etude clinique et 61ectrophysiologique. Neurophysiol Clin 27: 9-24

14. Mestdagh H, Houcke M, Moulront S, Laraki A (1980) Contribution ~t l'&ude de l'innervation sensitive de la coque talonnibre. Acta anat 108:124-131

15. Park TA, Del Tor t DR (t995) The medial calcaneal nerve: anatomy and nerve conduc- tion technique. Muscle and Nerve 18:32-38

16. Park TA, Del Tort DR (1996) Isolated inferior calcaneal neuropathy. Muscle and Nerve I9:106-108

17. Przylucki H, Jones CL (1981) Entrapment neuropathy of muscle branch of lateral plantar nerve. J Am Podiatry Assoc 71:119-124

18. Roegholt MN (1940) Een nervus calcaneus inferior als overbrenger, Van de pijn bij cal- caneodynie of calcaneuss poor en de daaruit volgen therapie. Ned Tijdschr Geneeskd 84: 1898-1902

19. Rondhuis JJ, Huson A (1986) The first branch of the lateral plantar nerve and heel pain. Acta Morphol Neert Scand 24 :269-279

20. Rouviere H, Delmas A (1984) Anatomic Humaine Tome III. 12~me edition, Masson, Paris

21. Santi MD, Botte MJ (1996) Exmmal fixation of the catcaneus and talus: an anatomic study for safe pin insertion. J Orthop Trauma 10: 487-491

22. Schon LC, Glennon TP, Baxter DE (1993) Heel pain syndrome: electrodiagnostic support for nerve entrapment. Foot Ankle 14: 129-35

23. Schon LC, Baxter DE (1990) Neuropathies of the foot and ankle in athletes. Clin Sports Med 9:489-509

24. Tanz SS (1963) Heel pain. Clin Orthop 28: 169-177

Received February 24, 1998 / Accepted in final form March 15, 1999

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