This 64-year-old female fell approximately three weeks ago, and presents with right ankle pain.
Prior to this incident, this patient’s foot was assessed in 2015 and 2017. Images 1 and 2 are radiographs of the patient’s foot from 2015. Images 3 and 4 are radiographs of the patient’s foot from 2017. Images 5 and 6 are MRIs of the patients foot from the current visit (2018).
Q1 – From images 1 through 6, what do you think the most likely diagnosis would be?
A1 – The most likely diagnosis is a full-thickness tear of the peroneus longus tendon. The diagnosis can be made using plain film radiographs. The os peroneum,noted on the 2015 and 2017 exams (images 7 through 10, green arrows), is fractured and distracted on the 2017 study (images 9 and 10, blue arrows).
Followup MRI in 2018 confirms a complete full-thickness tear (image 11, blue arrow). The fracture of the os peroneum is most clearly identified on sagittal images (image 12, green arrow).
*Given how uncommon fractures of the os peroneum are, they may be mistaken for bipartite or multipartite sesamoids. Typically, association of such fractures are with either acute or chronic peroneal longus tendon dysfunctions where:
- Acute – Result from peroneal longus tendon rupture upon injury
- Chronic – Degeneration / Tearing resulting from friction of fragments along the tendon
With distal peroneus longus ruptures, displacement and proximal migration of an intact os peroneum can be seen.
Conservative or surgical treatment methods may include:
- Conservative – Casting, soft dressing, and steroid injections
- Surgical – Excision of fragments complemented by repair of associated peroneal longus tendon abnormalities
Pearl: Very small tears of the peroneus longus tendon may be seen as the tendon passes around the os peroneum and prove highly symptomatic.
Peterson, J.J. and Bancroft, L.W. Os Peroneal Fracture with Associated Peroneus Longus Tendinopathy. American Journal of Roentgenology. 2001;177: 257-258.