Distal fibular notch: a frequent manifestation of the rheumatoid ankle

To describe the distal fibular notch, an infrequently described manifestation of rheumatoid arthritis, and to speculate on its etiology through gross dissection, histologic correlation and MR imaging.

One hundred and twenty-one conventional ankle radiographs were obtained and reviewed in 76 patients with clinically diagnosed rheumatoid arthritis. Additional imaging of three ankles was obtained utilizing CT and MR imaging. In addition to evaluating erosive changes, note was made of the presence and location of a well-defined scalloped defect along the medial border of the distal fibula. Ankle specimen dissection and histoanatomic examination was performed in an attempt to determine the exact pathogenesis of this fibular notch.

The distal fibular notch was identified in 52 of 121 ankles (43%). Seventy-five percent of notches were syndesmotic and extended down to the horizontal ankle joint level, while 25% of notches were syndesmotic with extension below the joint. The majority of ankles (79%) demonstrated coexistent marginal erosions and/or joint narrowing. Ankle specimen dissection revealed a single-celled synovial fold within the distal tibiofibular syndesmotic recess without underlying articular cartilage extension.

The fibular notch within the distal tibiofibular syndesmosis is a frequent manifestation of rheumatoid arthritis and appears to result from synovial proliferation rather than from mechanical instability.