Anatomical Characteristics of the Flexor Digitorum Accessorius Longus Muscle and Their Relevance to Tarsal Tunnel Syndrome

by MASS4D® Prescription Orthotics February 27, 2017

In this systematic review, the aetiology of Tarsal Tunnel Syndrome (TTS) associated with the presence of the flexor digitorum accessorius longus (FDAL) muscle is described, with emphasis on clinical testing methods, diagnostic imaging, and nonsurgical and surgical management.

Studies about TTS caused by the FDAL muscle published in English as full papers or case reports were considered in this systematic review.

The FDAL muscle is an accessory muscle in the lower leg, the prevalence of which was reported as varying from 1.6 per cent to 12.2 per cent based on cadaver lower-limb dissections.

The most common configuration of the FDAL muscle is a single head that originates from the tibia or the fibula bone, from the deep fascia of the leg, or a combination of all.

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It can have a single-headed or a double-headed configuration.

In the tarsal tunnel, single- and double-headed FDAL tendons usually course posterior to the tendon of the flexor hallucis longus (FHL) muscle.

A total of 23 clinical cases were identified in the literature reporting a TTS caused by the FDAL muscle.

Clinically, all of the patients had a positive pseudo-Tinel’s sign and local tenderness behind the medial malleolus.

Electro-neurodiagnostic studies were performed in most cases.

The FDAL muscle is a known potential aetiology of TTS, despite MRI, this may be overlooked when tarsal tunnel symptoms are present.

Conservative Treatment in the literature consisted of a soft shoe profile, activity modification, custom orthoses, supportive taping, non-steroidal anti-inflammatory drug administration, and physical therapy.

Surgical intervention was performed in 20 of the 23 patients as a result of failure to alleviate symptoms by conservative management.

The dynamic compression of the nerve could potentially be caused by the contraction of the accessory muscle.

This literature review suggests that the FDAL muscle is important in terms of its functional and clinical significance.

Copyright 2017 MASS4D® All rights reserved. 

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References:

1. Deleu P., Bevernage D. B., Birch I., Maldague P., Gombault V., Leemrijse T. (2015) Anatomical Characteristics of the Flexor Digitorum Accessorius Longus Muscle and Their Relevance to Tarsal Tunnel Syndrome.  Journal of the American Podiatric Medical Association: July/August 2015, Vol. 105, No. 4, pp. 344-355

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