Accesssory peroneal muscles

Accesssory peroneal muscles are a group of accessory muscles that can occur in the foot region as a normal variant in some individuals.

Peroneus quartus muscle

Originally, several accessory muscles were distinguished in the peroneal compartment:

• peroneus quartus (Otto),
• peroneus-calcaneus externum (Hecker),
• peroneus accessorius (White),
• peroneus digiti quinti (Testut).

This terminology has been simplified by summarising all peroneal compartment variants under the definition of a peroneus quartus muscle as a muscle arising from the lower leg and inserting onto the lateral hind and middlefoot. This explains why there are variable insertion sites of the PQ muscle, which include:

• the retrotrochlear eminence of the calcaneus,
• the metatarsal bone of the V^th toe,
• the peroneal tendons,
• the lateral retinaculum of the ankle,
• the cuboid bone.

The origin of the PQ muscle is the distal lateral portion of the fibula. It typically descends medial and posterior to the peroneal tendons.

Related pathology

The PQ muscle is usually asymptomatic. Occasionally, it may lead to crowding in the retromalleolar groove, predisposing to peroneus brevis tendon attrition and tear.

Peroneus tertius muscle

This muscle is actually not a peroneal compartment muscle, for it runs in the same canal as the extensor digitorum longus. It arises from the lower third of the anterior surface of the fibula and the interosseous membrane, and from an intermuscular septum connecting it with the peroneus brevis muscle (septum of Otto). Its tendon passes under the superior and inferior extensor retinacula of the foot and inserts into the dorsal surface of the base of the Vth metatarsal bone.
It is a simple variant with no associated pathologies.