Peroneocalcaneus Internus Muscle

The peroneocalcaneus internus muscle (arrow) originates along the inner aspect of the inferior fibula, below the origin of the flexor hallucis longus origin. The peroneocalcaneus internus muscle descends posterior and lateral to the flexor hallucis longus muscle and displaces it anteriorly and medially. Its tendon inserts onto a small tubercle on the medial aspect of the calcaneus below the sustentaculum tali.

Most patients with a peroneocalcaneus internus muscle are asymptomatic; however, there may be encroachment on the neurovascular bundle in the tarsal tunnel in some.

References

• Mellado JM, Rosenberg ZS, Beltran J, Colon E. The peroneocalcaneus internus muscle: MR imaging features. AJR Am J Roentgenol. 1997 Aug;169(2):585-8.
• Sookur PA, Naraghi AM, Bleakney RR, Jalan R, Chan O, White LM. Accessory muscles: anatomy, symptoms, and radiologic evaluation. Radiographics. 2008 Mar-Apr;28(2):481-99.