A Review of Extensor Hallucis Longus Variants Featuring a Novel Extensor Primi Internodii Hallucis Muscle Merging With Extensor Hallucis Brevis

Abstract

The extensor hallucis longus (EHL) muscle/tendon complex has been used in a variety of tendon transfer and tenodesis surgeries to correct iatrogenic hallux varus deformity, equinovarus foot deformity, clawed hallux associated with a cavus foot, and dynamic hyperextension of the hallux and, even, to prevent pedal imbalance after transmetatarsal amputation. Although it is usually considered a unipennate muscle inserting into the dorsum of the base of the distal phalanx of the hallux, a vast majority of EHL muscles possess ≥1 accessory tendinous slips that insert into other neighboring bones, muscles, or tendons, which can complicate these surgeries. The present report reviewed the reported data on EHL variants and describe a new variant, in which the tendons of the extensor primi internodii hallucis muscle of Wood and extensor hallucis brevis muscle merged together proximal to the tarsometatarsal (Lisfranc) joint, a site of rupture for extensor tendons of the foot. The reported variant might have contributed to the development of the clawed hallux seen in our patient and could complicate its operative management by mimicking the normal extensor digitorum longus tendon. Knowledge of the EHL variants and the particular muscular pattern described in the present review could improve the diagnosis and tendon transfer and tenodesis operative planning and outcomes.

A cadaveric study of the morphology of the extensor hallucis longus - a proposal for a new classification

“…The EHL is characterized by morphological variability with regard to the number of its additional bands and their insertion [1, 3–7]. Most previous research has focused on its possible morphological variations, particularly those regarding the additional bands.…”

Unraveling the anatomy of toe extensors: An aid to the clinical implications

“…Many studies are documented to show multiple muscular variations, unilateral, or bilateral, in extensors of foot in cadavers. [6][7][8][9][10][11][12][13][14][15] In the present study, bifurcation of EHL tendon was having medial and lateral slips. Medial slip was the main extensor tendon of great toe, whereas lateral slip was extensor tendon of 2 nd toe.…”

“…4 These variations manifest as painful foot on some occasions due to impingement of the surrounding structures. 5 Although various studies have already been conducted representing the variations in extensor tendons of foot, [6][7][8][9][10][11][12][13][14][15] the variations found in our study are rare and have not been previously reported in the literature. Description of tendons in foot is prerequisite for the surgeons to decide for suitable graft in various reconstructive surgeries and for the analysis of injuries in tendons.…”

Muscle Activation During Forehand and Backhand Drives in the Sport Discipline of Tennis

“…Ancillary muscles are the sartorius muscle, the gracilis, the popliteus muscle, the gastrocnemius and the soleus muscle. In addition, for the left foot to move right and in front of the above walking muscles, the adductor muscles (the adductor magnus, the adductor minimus, the adductor longus and the gracilis) also participate (Zdilla, Paulet, Lear, Addie, & Lambert, 2018;Olewnik, Podgorski, M., Polguj, M. Ruzik, K., & Topol, 2019;Bordoni & Varacallo, 2020).…”