Peroneus longus tendon rupture associated with an os peroneum

Case contributed by Dr Andrew Dixon


Sudden onset lateral midfoot pain.

Patient Data

Age: 45
Gender: Male

An os peroneum is present but sits around 1cm proximal to its normal location along side the cuboid. On the lateral image a tiny fragment avulsed from the os peroneum is seen just distal to the cuboid. Given that the os peroneum is an ossicle that exists within the substance of the peroneus longus tendon, this x-ray appearance is consistent with complete rupture of the peroneus longus tendon just distal to the os peroneum.   

MRI confirms the plain film suspicion of complete peroneus longus tendon rupture just distal to the os peroneum. There is approximately 2cm of tendon separation at the site of rupture. 

Blue arrow indicates where an os peroneum would normally be expected to be seen. The white arrows show how the majority of the os peroneum is retracted proximally with a tiny fragment displaced distally due to complete rupture of the peroneus longus tendon

Case Discussion

Complete rupture of the peroneus longus tendon just distal to an intrasubstance os peroneum. This case highlights how an understanding of the normal location of the os peroneum is essential to accurate plain film interpretation. The os peroneum should normally be located along side the cuboid. If it is displaced proximal to this, then a complete peroneus longus tear should be suspected. 

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Case information

rID: 30218
Published: 26th Jul 2014
Last edited: 14th Aug 2019
Inclusion in quiz mode: Included

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