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 | ||