Muscular variation on the dorsum of the foot and alteration of structures passing under cover of

the extensor retinacula of the lower limb – a case report

1 Huban Thomas. R *,2Prasanna, LC, 3Suhani S, 4Sneha G, 5 Prakash Babu B

1. Senior Grade Lecturer,Department of Anatomy, Kasturba Medical College, Manipal University, Manipal, India.

2. Associate Professor,Department of Anatomy, Kasturba Medical College, Manipal University, Manipal, India.

3. Senior Grade Lecturer,Department of Anatomy, Kasturba Medical College, Manipal University, Manipal, India.

4. Professor and HeadDepartment of Anatomy, Kasturba Medical College, Manipal University, Manipal, India.

5. Associate Professor,Department of Anatomy, Kasturba Medical College, Manipal University, Manipal, India.

Corresponding Author

Huban Thomas RSenior Grade Lecturer,Department of Anatomy, Kasturba Medical College, Manipal University, Manipal, India.

E-mail:huban_anatomy@yahoo.co.in, Mobile No: +91 9844343546

Muscular variation on the dorsum of the foot and alteration of structures passing under cover of

the extensor retinacula of the lower limb – a case report

1 Huban Thomas. R *,2Prasanna, LC, 3Suhani S, 4Sneha G, 5 Prakash Babu B

1Senior Grade Lecturer and Corresponding Author, 2 Associate Professor, 3Senior Grade

Lecturer,4Associate Professor, 5Additional Professor.

Department of Anatomy,Kasturba Medical College, Manipal University, Manipal. Karnataka State,

India.

Abstract

Extensor digitorum longus is one of the muscle of the anterior crural region of the leg, arises from the

upper part of the medial surface of the shaft of fibula, a small area of lateral tibial condyle, interosseous

membrane and anterior intermuscular septum of the leg. The tendon of the extensor digitorum longus

lies on the lower part of the tibia passes beneath the superior and inferior extensor retinaculum, finally

split into four digital slips and joins with the lateral three slips of extensor digitorum brevis to form the

dorsal digital expansion. Anterior tibial artery is the main artery of the anterior crural region which lies

between the extensor halluces longus and extensor digitorum longus in the lower third of the leg and

appears on the dorsum of the foot as dorsalis pedis artery.During routine dissection for undergraduate

medical students,in a middle aged male cadaver an additional tendon was observed in the extensor

digitorum longus and is attached to the middle of the shaft of the fifth metatarsal bone.Anterior tibial

artery lies lateral to the peroneus tertius muscle in the lower third of the leg, then it passes medially deep

to the peroneus tertius and extensor digitorum longus muscles. Lateral tarsal artery arises from the

dorsalis pedis artery and lies lateral to the deep peroneal nerve while the main trunk lies medial to the

nerve beneath the inferior extensor retinaculum of the lower limb. Awareness of presence of an

additional tendon in the dorsum of the foot and variation in the course of the anterior tibial artery is

crucial while treating the compartment syndrome.

Key Words: Extensor digitorum longus, anterior tibial artery, compartment syndrome

Introduction

The retinacula of the ankle are distinct structures defined as regions of localized thickening of the

superficial aponeurosis covering the deep structures of the distal portion of the leg, ankle, and foot.

These retinacula are sites of reinforcement of the superficial aponeurosis, maintaining approximation

of tendons to the underlying bone. The retinacula act as a pulley like mechanism that appears to

represent an adaptation of the body to provide both a smooth gliding surface and the mechanical strength

to prevent tendon bowstringing [1].

The superior extensor retinaculum is a transverse, roughly rectangular band located above the tibiotalar

joint. It attaches laterally on the lateral crest of the lower fibula and the lateral surface of the lateral

malleolus and medially on the anterior crest of the tibia and the medial malleolus. The structures that

pass deep in relation to this retinaculum include the tibialis anterior muscle, extensor hallucis

Longus muscle, anterior tibial blood vessels, deep peroneal nerve, extensor digitorum longus muscle,

and peroneus tertius muscle. [2].

Case Presentation

During routine dissection for undergraduate medical students in middle aged male cadaver, an additional

tendon was observed in the extensor digitorum longus and is attached to the middle of the shaft of the

fifth metatarsal bone. Anterior tibial artery lies lateral to the peroneus tertius muscle in the lower third of

the leg and deep to the superior extensor retinaculum, then it passes medially deep to the peroneus

tertius and extensor digitorum longus muscles. Lateral tarsal artery arises from the dorsalis pedis artery

and lies lateral to the deep peroneal nerve while the main trunk lies medial to the nerve beneath the

inferior extensor retinaculum of the lower limb. Arrangement of structures beneath the superior extensor

retinaculum also altered; from medio laterally these are tibialis anterior muscle, extensor hallucis

Longus muscle, deep peroneal nerve, extensor digitorum longus muscle, peroneus tertius muscle,

anterior tibial blood vessels.

Figure – Anterior view of the left leg

TA – tibialis anterior , EHL – extensor hallucis

Longus, DPA – dorsalis pedis artery, DPN– deep peroneal nerve,

EDL- extensor digitorum longus , ATA- anterior tibial artery, PT- peroneus tertius

Discussion

The extensor digitorum longus muscle frequently shows variation in the arrangement and insertion of its

tendons. It may give an additional slip to the base of the proximal phalanx of the second toe, the first

interosseous muscle and the anterior end of the fifth metatarsal bone. Sometimes, it may be connected to

the extensor hallucis longus by a slip, extensor digitorum brevis by a cross band and peroneus tertius by

a slip. Further, the digital tendon to each toe may be doubled or rarely tendon to the second and little

toes alone may be doubled. [3] Presence of an additional tendon in extensor digitorum longus muscle is

seldomly reported in the past and can be used for tendon transfer surgeries. Course of the anterior tibial

artery is deep to the peroneus tertius and extensor digitorum longus muscles. This may cause transient

compression of the anterior tibial artery leading to ischemia of the muscles of the anterior tibial

compartment of the leg causing anterior tibial compartment syndrome.

Conclusion

Knowledge of these variations is necessary for the surgeon to perform tendon transfer surgeries.

Furthermore, Knowledge of vascular anatomy of foot is essential for arterial reconstruction flap

surgeries of the foot. This can avoid amputation of foot in cases of arterial trauma like thromboangitis

obliterans, industrial automobile accidents, diabetes and severe ischaemia of lower limb. [4]

References

1. Numkarunarunrote, N., Malik, A., Aguiar, RO., Trudell, DJ., Resnick, D,. (2007) ‘Retinacula of

the Foot and Ankle:MRI with Anatomic Correlation in Cadavers’. American Journal of

Roentgenology. Vol 188, pp 348-354.

2. Sarrafian SK. Anatomy of the foot and ankle: descriptive, topographic, functional, 2nd ed.

(1993)Philadelphia, PA: Lippincott Williams & Wilkins,:113–158

3. Jetti, R., Sirasanagandla, S R., Nayak, B S., Gorantla, V R., Shetty, A S,. (2014) ‘Higher division

of the extensor digitorum longus muscle: A cadaveric case report;. OA Case Reports Vol 25,

pp:12.

4. Kulkarni, J., Paranjpe, V., Vatsalaswamy. (2012) ‘Anterior Tibial Artery Terminating as Tarsal

arteries). IOSR Journal of Dental and Medical Sciences (JDMS) Vol 1, Issue 2, PP 21-22

Declaration:

Authors declare that this Manuscript has not been published or submitted for publication

elsewhere.