Peroneus Quartus Muscle

The peroneus quartus is an accessory peroneus muscle that is seen in about 15%-20% of the population. The muscle is name the fourth peroneal because the name peroneus (fibularis) tertius was already been assigned to the muscle that runs with the extensor digitorum longus to insert on the dorsal surface of the base of the fifth metatarsal.

The peroneus quartus muscle commonly originates from the peroneal muscles in the distal leg and attaches to either the retrotrochlear eminence of the calcaneus, the cuboid, or the peroneus longus tendon. The muscle can be further classified based on these insertions as peroneocalcaneus externum (calcaneus), peroneocuboideus (cuboid), or peroneoperoneolongus (peroneus longus tendon).

While peroneus quartus muscles are usually asymptomatic, they may cause crowding in the retromalleolar groove and predispose people with this normal variant to peroneus brevis tendon dislocation and tear.

Axial images are usually best for defining the muscle (white arrow). It is found posteromedial to the peroneus brevis muscle (pink arrow) and is usually separated from the peroneus brevis muscle by a fat plane. The peroneus longus muscle is indicated by the blue arrow.

Interestingly, it has been suggested that the peroneus quartus muscle represents an intermediate evolutionary stage in the development of bipedal posture, with the muscle allowing our ancestors to lift the lateral edge of their feet and stabilizing hind-foot pronation.

References

• Cheung YY, Rosenberg ZS, Ramsinghani R, Beltran J, Jahss MH. Peroneus quartus muscle: MR imaging features. Radiology. 1997 Mar;202(3):745-50.
• Saupe N, Mengiardi B, Pfirrmann CW, Vienne P, Seifert B, Zanetti M. Anatomic variants associated with peroneal tendon disorders: MR imaging findings in volunteers with asymptomatic ankles. Radiology. 2007 Feb;242(2):509-17.
• Wang XT, Rosenberg ZS, Mechlin MB, Schweitzer ME. Normal variants and diseases of the peroneal tendons and superior peroneal retinaculum: MR imaging features. Radiographics. 2005 May-Jun;25(3):587-602.