Unusual accessory tendon connecting the hallucal extensors

Abstract

During routine dissection of an adult human cadaver, a suite of tendinous anomalies was discovered in the left hallucal region. Whereas the main tendon of the extensor hallucis longus muscle inserted normally, two accessory tendons were found coursing medial and lateral to the main tendon. The most lateral tendon originated from a supernumerary muscle belly and merged with the tendon of extensor hallucis brevis to form a composite tendon. The most medial tendon crossed the metatarsophalangeal joint and joined the composite tendon deep to the tendon of extensor hallucis longus. A terminal tendon, consisting of these three contributions, inserted upon the proximal hallucal phalanx. This variant likely arose due to atypical differentiation of the common extensor muscle mass during development, and is of particular significance to clinicians performing arthroscopy, tendon transfers, and other surgical procedures.

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

“…The example presented in the our review documented a unique communication between the tendons of the EPIH and the EHB. The EPIH variant also possessed its own muscle belly, which is exceedingly rare (12,13,17,25,28,36). Moreover, 90% of EHL accessory tendons have been reported to exist medially to the EHL (29).…”

“…The described EPIH should, therefore, be considered unique because of its presence lateral to the primary tendon of the EHL. Also, because of its position, it can be confused with the extensor digitorum longus tendon during surgery (36). Likewise, the communication between the EPIH and EHB medial to the base of the second metatarsal adds complexity to the unique variant pattern.…”

“…Also, individuals with cavus foot deformity, such as the individual described in our case study, often have excessive rubbing stressors to the dorsum of the foot, which can lead to the rupture of the EHL tendon at the level of the tarsometatarsal (Lisfranc) joint (37)(38)(39). The location of the EPIH-EHB communication is in an area that can be of particular risk of excessive mechanical stressors and subsequent dorsal foot pain and has also been demonstrated as a region prone to rupture of the EHB tendon (36,37). Albeit speculative in the absence of largescale studies, the forces that have been demonstrated to predispose the EHL and EHB damage along the dorsum of the cavus foot, might also predispose this variation to similar damage.…”

An additional tendon of the extensor digitorum brevis muscle of the foot: is there an accessory muscle?

“…Hill and Gerges [4] reported two accessory tendons coursing medial and lateral to the main tendon, whereas the main tendon of the extensor hallucis longus muscle inserted normally. Asomugha et al [5] described an acces-An additional tendon of the extensor digitorum brevis muscle of the foot: is there an accessory muscle?…”