Accessory flexor digitorum longus muscle

The accessory flexor digitorum longus muscle is an accessory muscle in the deep posterior compartment of the leg with a reported prevalence of 6-8%. Unilateral muscles are more common although bilateral cases have been reported.

Summary
origin: variable; either the medial margin of the tibia and deep posterior compartment fascia; or the fibula1,3
insertion: variable; either the quadratus plantae, tendon of flexor digitorum longus or both 1,3
Gross anatomy
The accessory flexor digitorum longus muscle arises from the medial margin of the tibia and the deep posterior compartment fascia or from the fibula. Its insertion may occur into the quadratus plantae muscle, tendon of flexor digitorum longus or both.

Related pathology
The accessory flexor digitorum longus muscle may compress the neurovascular bundle within the tarsal tunnel and cause tarsal tunnel syndrome 1,3. The accessory flexor digitorum longus muscle has also been reported to contribute to the development of flexor hallucis longus tenosynovitis 4.

References
Related Radiopaedia articles
Anatomy: Lower limb
skeleton of the lower limb[+]
joints[+]
spaces of the lower limb[+]
muscles of the lower limb
muscles of the pelvic group[+]
muscles of the thigh[+]
muscles of the leg
anterior compartment of the leg[+]
posterior compartments of the leg
superficial posterior compartment of the leg (calf)[+]
deep posterior compartment of the leg
accessory flexor digitorum longus muscle
flexor digitorum longus muscle[+]
flexor hallucis longus muscle
popliteus muscle
tibialis posterior muscle
lateral compartment of the leg[+]
muscles of the foot[+]
accessory muscles[+]
vascular supply[+]
innervation of the lower limb[+]
lymphatics[+]