Table 2.

Prevalence, origin, course, insertion and clinical significance of the accessory muscles around the ankle and hindfoot

	Muscles	Prevalence	Origin	Course	Insertion		Clinical significance
Lateral aspect	Accessory peroneus muscles (peroneus quartus)	16%	Variable Peroneus brevis (most common) Peroneus longus Fibula	Tendon is medial and posterior to the brevis and longus peroneal tendons	Peroneus accessorius	Peroneus longus	Potential crowding in the retinaculum, leading to subluxation of the peroneal tendons or tears due to friction Imaging pitfall—mistaken by tear
					Peroneocalcaneus externum	Calcaneus (79–91%)
					Peroneus digiti minimis	Head of the fifth metatarsal and base of the first phalanx
Posteromedial aspect	Flexor digitorum accessorius longus	6–8%	Medial margin of the tibia or from the lateral aspect of the fibula distal to the origin of the flexor hallucis longus	Beneath the flexor retinaculum, through the tarsal tunnel, superficial to the neurovascular bundle	Quadratus plantae or flexor digitorum longus		Tarsal tunnel syndrome Flexor hallucis longus tenosynovitis
	Peroneocalcaneus internus	1%	Internal aspect of the fibula, below the origin of the flexor hallucis longus	Posterior to flexor hallucis longus displacing it anteriorly and medially, with the tendons running parallel	Small tubercle on the medial aspect of the calcaneus, below the sustentaculum		Crowding in the tarsal tunnel Occasionally, limitation of movement, posterior ankle impingement and flexor hallucis longus tenosynovitis
	Accessory soleus	0.7–5.5%	Anterior surface of the soleus, partially sharing the soleus origin	Antero-medially to the Achilles, superficial to the flexor retinaculum	Achilles tendon		Soft tissue mass (incidental finding) Associated pain, triggered by exercise Tarsal tunnel syndrome
	Tibiocalcaneus internus	–	Medial tibia	Deep in the flexor retinaculum	Medial calcaneus		Tarsal tunnel syndrome
Anterior aspect	Peroneus tertius	95%	Anterior aspect of the distal fibula and the extensor digitorum longus muscle	Tendon normally running along the extensor digitorum longus tendon	Dorsal surface of the shaft of the fifth metatarsal		normally asymptomatic, however snapping of its tendon over the lateral dome of the talus has been described
	Extensor hallucis capsularis tendon	14%	Extensor hallucis longus tendon or muscle	Parallel extensor hallucis longus	First metatarsophalangeal joint capsule		Grafting if needed for reconstruction, especially in cases of hallux dysfunction
	Anterior fibulocalcaneus	Rare	Fibula, peroneus tertius	Tendon parallel to the extensors	Calcaneus, anterosuperior to fibular throclea		Pain due to impingement
	Accessory extensor digiti secundus	Rare	Extensor hallucis longus tendon or muscle	Tendons parallel to the extensors	Medial phalanx second digit		Incidental finding
	Tibioastragalus anticus of Gruber	Rare	Lower third of the anterolateral tibia and interosseous membrane	Tendon is deep to the tibialis anterior and extensor hallucis longus tendon	Anterolateral aspect of the neck of the talus		Potential tendon transfer