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 Table of Contents  
Year : 2021  |  Volume : 10  |  Issue : 2  |  Page : 66-69

The study of anatomy of tarsal tunnel in human fetuses by dissection method

1 Associate Professor, Department of Anatomy, Akash Institute of Medical Sciences and Research Centre, Bengaluru, Karnataka, India
2 Associate Professor, Department of Anatomy, Sapthagiri Institute of Medical Sciences and Research Centre, Bengaluru, Karnataka, India
3 Additional Professor, Department of Anatomy, SDM College of Medical Sciences and Hospital, Dharwad, Karnataka, India
4 Consultant, Department of Ophthalmology, Sakra World Hospital, Bengaluru, Karnataka, India

Date of Submission09-Dec-2020
Date of Decision12-Jan-2021
Date of Acceptance26-Jan-2021
Date of Web Publication09-Apr-2021

Correspondence Address:
B R Chaithra Rao
Department of Anatomy, Akash Institute of Medical Sciences and Research Centre, Prasannahalli Main Road, Near Kempegowda International Airport, Devanahalli, Bengaluru - 562 110, Karnataka
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/NJCA.NJCA_85_20

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Background: The flexor retinaculum of foot extends from the medial malleolus to the calcaneus to form the roof of tarsal tunnel. The structures passing through the tunnel are tendons of tibialis posterior, flexor digitorum longus & flexor hallucis longus, the tibial nerve & the posterior tibial artery with its venae comitantes. In order to understand the pathogenesis and improve the treatment of tarsal tunnel syndrome, we investigated the tarsal region of human foetuses anatomically. Methodology: The study was done on aborted/ stillborn foetuses in the Department of Anatomy of Sapthagiri Institute of Medical, Sciences, Bangalore. The structures passing under the flexor retinaculum of foot were dissected in 68 normal limbs of 34 foetuses of gestational age ranging from 10 weeks to term. Results: It was noted that the structures were arranged in two planes. Most commonly the superficial plane contained the tendon of tibialis posterior, posterior tibial artery & tibial nerve from medial to lateral side. In the deeper plane were the tendons of flexor digitorum longus medial to that of flexor hallucis longus. The bifurcation of tibial nerve mostly occurred under cover of flexor retinaculum and that of posterior tibial artery was distal to it. Conclusion: The understanding of arrangement of structures under cover of flexor retinaculum is important for diagnosis and treatment of tarsal tunnel syndrome in adults and also for the surgical correction of clubfoot, poliomyelitis & other deformities of foot in children.

Keywords: Club foot, flexor retinaculum, tibial nerve, posterior tibial artery, tarsal tunnel syndrome

How to cite this article:
Chaithra Rao B R, Annam S, Sunkeswari S, Patil S. The study of anatomy of tarsal tunnel in human fetuses by dissection method. Natl J Clin Anat 2021;10:66-9

How to cite this URL:
Chaithra Rao B R, Annam S, Sunkeswari S, Patil S. The study of anatomy of tarsal tunnel in human fetuses by dissection method. Natl J Clin Anat [serial online] 2021 [cited 2021 Jul 30];10:66-9. Available from: http://www.njca.info/text.asp?2021/10/2/66/313519

  Introduction Top

The tarsal tunnel is the region where the tendons of flexor digitorum longus, flexor hallucis longus, and tibialis posterior stretch from leg to sole of the foot, along the medial part of ankle joint. Between these tendons are the posterior tibial artery, the tibial nerve and their bifurcations held in their place by the flexor retinaculum. This tunnel is roofed by the flexor retinaculum and the floor is formed by parts of talus and calcaneus. The flexor retinaculum is a connective tissue band attached to the tibial malleolus above and to the medial calcaneal tubercle below. It sends in septa to the underlying bones and divides this region into four compartments, one for each tendon and one for the neurovascular bundle.[1] The medial and lateral plantar nerves are the terminal branches of the tibial nerve inside the tunnel.

Tarsal tunnel syndrome is a compression neuropathy of the posterior tibial nerve or its branches under the flexor retinaculum in this fibro-osseous tunnel.[2],[3] In surgeries involving medial part of ankle, information on the structural anatomy of the neurovascular bundle is important. It also assists in understanding the pathophysiology and manifestations of the syndrome such as paresthesia, numbness, burning pain involving the sole, and radiating toward the medial side of the leg at nights.[3],[4] The systemic evaluation of newborn involves a thorough examination of feet which is comforting to new parents. Early diagnosis of foot deformities in infants encourages timely remedial care.[5] The tendons in the tarsal tunnel can also get trapped in the fracture callus of distal tibia/fibula.[6]

The study aims to describe the arrangement of structures passing under the flexor retinaculum of fetal foot and to determine the level of branching of tibial nerve and posterior tibial artery in relation to the flexor retinaculum.

  Materials and Methods Top

An exploratory study was done in the Anatomy Department of the Sapthagiri Institute of Medical Sciences, Bangalore, over a span of 1 year by bilateral anatomical dissection of 34 formalin-fixed (10%) aborted/stillborn fetuses of gestational age ranging from 10 to 40 weeks (68 limbs). The Institutional Ethics Committee clearance was obtained for this descriptive study concept (IEC NO: SIMSandRC/IECC/64/2018). Consent was taken at the time of miscarriage or birth of the stillborn fetus for the use of these fetuses for academic and research purposes. A convenience sample of 34 (68 limbs) (all fetuses available in the Department of Anatomy for more than 10 weeks) was considered for research as this is a novel study performed on fetuses. Due to difficulty in dissecting the area, the fetuses with gross abnormality of limbs and gestational age <10 weeks were not considered. A longitudinal incision midway between the medial malleolus and the tendocalcaneus was utilized for dissection. Two more horizontal incisions were made above and below the ankle, one at each finish of the longitudinal incision, to make a window for approaching the structures at the medial ankle. At the flexor retinaculum, dissection was completed using blunt techniques to preserve to the deeper structures. The arrangement of structures in the tarsal tunnel and the relative position of tibial nerve and posterior tibial artery division with the flexor retinaculum were observed when the flexor retinaculum was partly removed to reveal the structures. For informative analysis, detailed results were reported and tabulated in Microsoft Excel. Using a digital camera, experimental photographic recording of anatomical dissections was carried out.

  Results Top

After dissecting the medial ankle region of 68 fetal lower limbs, the following findings were made. The structures were arranged in two planes, in 98.5% (67) cases, superficial and deep. There were seven varieties of structure arrangement patterns found, which are briefly described in [Table 1]. The most common pattern of arrangement seen in 59% of the limbs was that, from medial to lateral side, the tibialis posterior tendon, posterior tibial artery, and tibial nerve were in superficial plane [Figure 1] and the long digitorum and hallucis tendons were in deeper plane [Figure 2]. In 6%, 68%, and 26% of cases, the tibial nerve bifurcated into medial and lateral plantar nerves proximal to, deeper to, and distal to the flexor retinaculum, respectively [Table 2]. In 90% of cases, the posterior tibial artery was bifurcating into medial and lateral plantar arteries distal to and in 10% deep to the flexor retinaculum [Table 3]. Nerve division has consistently been proximal to that of the artery.
Table 1: Arrangement of structures undercover of flexor retinaculum (n=68)

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Figure 1: Arrangement of structures in superficial plane

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Figure 2: Arrangement of structures in deeper plane

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Table 2: Branching of tibial nerve (n=68)

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Table 3: Branching of posterior tibial artery (n=68)

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  Discussion Top

The human foot is an intricate system made out of bones, muscles, ligaments, and tendons. The exploration builds up an appropriate understanding of association of structures present under flexor retinaculum of fetal foot. By localized thickening of the deep fascia, creating retinacular bands, the tendons of leg muscles are held in place. As indicated by most researchers,[1],[7],[8],[9] there was no definite demarcation between the flexor retinaculum and fascia cruris both proximally and distally. Like the findings of Nagaoka and Inthasan and Mahakkanukrauh, fibrous septae extended from the deep surface of the flexor retinaculum providing separate compartments for every tendon and neurovascular structures.[1],[9]Joshi et al.[8] affirmed our finding of a distinct superficial and deep association among tendons and neurovascular structures within the tarsal tunnel.

Heel pain in adults with foot issues has an incidence of 11%–15%, and up to 88% of patients with long-standing heel pain have some level of nerve entrapment. Tarsal tunnel syndrome might be precipitated due to numerous space-occupying conditions. It has been identified in connection with neurofibroma, intraneural ganglion, lipoma, or systemic diseases such as diabetes mellitus[4],[10],[11],[12],[13],[14],[15] in addition to ganglia arising from tendon sheaths and talocalcaneal coalition.

Attention to varieties in tibial nerve bifurcation levels during surgeries of tarsal bone fracture fixation using external nailing, arthrodesis, medial displacement osteotomy, extensive release of contractures and tendon transfers, corticosteroid injections, and ganglion aspiration can forestall injury to the tibial nerve.[2],[7],[16],[17],[18] The majority of our cases (68%) showed the tibial nerve bifurcation within the tarsal tunnel which was similar to other researchers such as Joshi et al. (99.9%), Torres and Ferreira (88%), Warchol et al. (76.7%), Bilge et al. (84%), Premchand and Benjamin (77%), and Louisia and Masquelet (73%).[4],[8],[13],[18],[19],[20],[21],[22] In most limbs (90%), the posterior tibial artery bifurcation was distal to the flexor retinaculum and to the tibial nerve bifurcation. This was similar to 98% of limbs dissected by Joshi et al., and most of the cases dissected by Nabil et al., Bilge et al., and Yang et al.[8],[14],[15],[20] It is important to be aware of the relative positions of the artery, the nerve and its bifurcations to identify the surgical safe zone and to direct a therapeutic nerve block. Similarly, the situation of these neurovascular structures relative to recognized surface anatomical landmarks is logically helpful for the accurate detection and treatment of these clinical conditions.[14],[23],[24],[25] These findings should be noted during surgical correction of deformities brought about by injury, osteomyelitis, malunion, burn contractures, poliomyelitis, neuromuscular lesions, and resistant congenital contractures of vertical talus and clubfoot that happen in infancy as they require early correction before permanent compensatory changes ensue. The study fails to establish a measurable safe zone for surgeries because of variable size of limbs in fetuses of different gestational age considered here.


Although it is a novel study done on fetuses with convenience sampling, results cannot be generalized. Yet this study stresses the need for further studies in this area.

  Conclusion Top

In fetal foot, the structures are orchestrated underneath the flexor retinaculum in superficial and deep planes. The division of posterior tibial artery does not occur within the tarsal tunnel but distal to it. The tibial nerve branching is within the tarsal tunnel and is always proximal to that of the artery.

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Conflicts of interest

There are no conflicts of interest.

  References Top

Inthasan C, Mahakkanukrauh P. Tarsal tunnel syndrome: Anatomical facts and clinical implications. J Anat Soc India 2019;68:236-41.  Back to cited text no. 1
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Warchol Ł Walocha JA, Mizia E, Bonczar M, Liszka H, Koziej M. Ultrasound guided topographic anatomy of the medial calcaneal branches of the tibial nerve. Folia Morphol (Warsz) 2020. DOI: 10.5603/FM.a2020.0062.  Back to cited text no. 4
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Nagaoka M, Satou K. Tarsal tunnel syndrome caused by ganglia. J Bone Joint Surg Br 1999;81:607-10.  Back to cited text no. 11
Hong CH, Lee YK, Won SH, Lee DW, Moon SI, Kim WJ. Tarsal tunnel syndrome caused by an uncommon ossicle of the talus: A case report. Medicine (Baltimore) 2018;97:1-4.  Back to cited text no. 12
Torres AL, Ferreira MC. Study of the anatomy of the tibial nerve and its branches in the distal medial leg. Acta Ortop Bras 2012;20:157-64.  Back to cited text no. 13
Nabil NM, Al Homosani N, Biram D. Topographic anatomy of the neurovascular bundle at the tarsal tunnel and its applied significance. J Exp Clin Anat 2018;17:70-5.  Back to cited text no. 14
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Yang Y, Du ML, Fu YS, Liu W, Xu Q, Chen X, et al. Fine dissection of the tarsal tunnel in 60 cases. Sci Rep 2017;7:46351.  Back to cited text no. 15
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Kirienko A, Peccati A, Abdellatif I, Elbatrawy Y, Mostaf ZM, Necci V. Correction of poliomyelitis foot deformities with Ilizarov method. Strategies Trauma Limb Reconstr 2011;6:107-20.  Back to cited text no. 17
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Kalpana R, Komala N. Branching pattern of tibial nerve in the tarsal tunnel – A cadaveric study. Natl J Clin Anat 2017;6:120-5.  Back to cited text no. 19
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Premchand S, Benjamin W. Variations in the branching pattern of the tibial nerve in the posterior compartment of the leg. Natl J Clin Anat 2020;9:127-31.  Back to cited text no. 21
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Shalaby H, Hefny H. Correction of complex foot deformities using the V-osteotomy and the Ilizarov technique. Strategies Trauma Limb Reconstr 2007;2:21-30.  Back to cited text no. 23
Batista JP, Javier J, Vega J, De Prado M, Ghioldi ME. Inconstant high bifurcation of tibial nerve found in posterior ankle arthroscopy. A case report. Tobillo y Pie 2017;9:74-7.  Back to cited text no. 24
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  [Figure 1], [Figure 2]

  [Table 1], [Table 2], [Table 3]


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