Os styloideum is an accessory ossicle located dorsally on the wrist that represents an anatomic variant. Association between the os styloideum and wrist pain is clinically known as "carpal boss syndrome". The authors report a case of bone marrow edema in the os styloideum diagnosed by magnetic resonance imaging in a young tennis player, and present a literature review on this finding.

Keywords: Os styloideum, Bone marrow edema, Magnetic resonance imaging

OBJECTIVE: To describe morphological aspects, and radiographically evaluate the segment of the peroneus longus tendon adjacent to the cuboid bone, in cadavers, and reporting the incidence of a fibular ossicle, in some cases with the help of histological analysis. MATERIALS AND METHODS: Fifty tendon segments were evaluated and radiographed for determining the presence or absence of an accessory ossicle inside the tendon. The specimens where such presence was dubious were sectioned and submitted to macroscopic evaluation. In the cases where doubts persisted, the specimens were submitted to hematoxylin-eosin staining for histological analysis. One specimen where the accessory ossicle had been detected was also histologically evaluated for illustration purposes. RESULTS: All the specimens presented a fusiform dilatation of the area under the arc of the cuboid bone. Radiographic images demonstrated 29 specimens without ossification, 13 with ossification and 8 were doubtful. After macroscopic analysis, only one presented ossification, five did not, and two remained dubious, being submitted to histological analysis that demonstrated no ossification. CONCLUSION: All the specimens presented focal thickening of the tendon under the arc of the cuboid bone. However, quantitative analysis of both specimens submitted to histological evaluation demonstrated that the tendon consisted of fibrocartilaginous tissue lined by hyaline cartilage on the surface of contact with the bone. Thus, under the morphological point of view, fibular ossicle was found in 28% of cases, and, under the radiographic point of view, in 26%.

Keywords: Peroneus longus, Os peroneum, Sesamoid