Presentation
High-level sportsman. Presents with pain in the lateral aspect of the left foot.
Patient Data
there is a linear T1 hypointensity involving the base of the 3rd metatarsal with marked bone edema (sagittal, coronal), in keeping with a probable fatigue fracture.
moderate amount of fluid within the fibular tendon sheath
there is a small bony fleck located at the lateral plantar aspect of the calcaneus within the substance of the fibularis longus tendon, that looks fractured, in keeping with an os peroneum (see on T1, on T1 FS C+)
thickening of the plantar aponeurosis (coronal, sagittal) measuring up to 9 mm, in keeping with a plantar fascitis due to probable repetetive trauma
linear non-transmural intrasubstance slit of a T2 hyperintense signal of the proximal portion of the plantar aponeurosis, with surrounding edema
Case Discussion
The os peroneum was not initially seen on MRI, and the plain radiographs were the clue to the diagnosis.
The differential diagnosis for this case was fibularis longus tenosynovitis due to a fibular trochlea hypertrophy. Although it could be associated with an os peroneum syndrome, it's not the case since the trochlea measured less than 5 mm.