The peroneus digiti minimi is an accessory muscle to the little toe present in approximately 22% of individuals, arising from the lower fibula or peroneus brevis and inserting on the little toe extensor mechanism. It occupies the lateral compartment or the dorsal foot and may contribute to the lateral ankle tendon crowding. It is also called the fibularis digiti minimi and is the foot equivalent of the extensor digitorum brevis manus.
| Origin | Lower portion of the fibula or the peroneus brevis, between the peroneus brevis and the extensor digitorum longus |
|---|---|
| Insertion | Dorsal surface of the proximal phalanx of the little toe or the extensor digitorum longus slip to the fifth toe |
| Nerve Supply | Superficial peroneal nerve |
| Blood Supply | Peroneal artery perforators |
| Actions | Extension and abduction of the little toe; functionally equivalent to an accessory EDL slip to the fifth toe |
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The peroneus digiti minimi is occasionally identified on ankle MRI as an additional muscle in the lateral compartment or at the fifth metatarsal base level, and must be distinguished from peroneus quartus (which inserts on the calcaneus or peroneal trochlea rather than the toe). When present, it may contribute to lateral ankle tendon crowding predisposing to peroneus brevis splitting. Its identification prevents misdiagnosis as a lateral ankle soft tissue mass.
An accessory peroneus digiti minimi identified incidentally on lateral ankle MRI for pain may be mistaken for a soft tissue tumour or accessory muscle causing impingement; recognition of its muscular signal characteristics and its continuity with the lateral compartment muscles prevents unnecessary biopsy or excision.
