Extensor hallucis capsularis tendon

Last revised by Dr Joachim Feger on 10 Sep 2021

The extensor hallucis capsularis tendon, also known as secondary extensor hallucis longus, accessory extensor tendon of the first metatarsophalangeal joint, extensor ossis metatarsi hallucis or extensor ossis primi internodii hallucis is an accessory tendon or muscle of the ankle and an anatomical variant. Prevalence has been estimated up to 90% 1-3 and in ~14% it might be suitable to be used as a tendon graft 3.

  • origin: extensor hallucis longus muscle or tendon
  • insertion: dorsomedial aspect of the first metatarsophalangeal joint capsule and/or base of the first proximal phalanx
  • action:
    • agonist of the extensor hallucis longus, dorsiflexion
    • stabilization of the first metatarsophalangeal joint capsule during hallux extension

The extensor hallucis capsularis tendon originates from the extensor hallucis tendon or muscle and travels along the anterior aspect of the ankle medially and parallel to the extensor hallucis longus within the extensor compartment to insert onto the first metatarsophalangeal joint capsule  1-3.  

The extensor hallucis capsularis tendon is a thin tendon usually ≤4 mm in width that can be found medially to the extensor hallucis longus tendon.

The extensor hallucis capsularis tendon was first reported by the Irish anatomist Alexander MacAlister (1844-1919) 6 in 1886 2,5.

The tendon can be used as an autologous tendon graft and has been found especially useful in hallux dysfunction 1-3.

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