The Radiographic approach in Diagnosis of Peroneal Tendon T
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Radiographs of the foot and ankle (weight-bearing anteroposterior, lateral, and oblique views) can be useful to assess deformity and related osseous pathology. The diagnosis of a peroneus longus rupture can sometimes be made on radiographs, based on the position of the os peroneum, when present. Approximately 20% of the population has an ossified os peroneum, visible on internal rotation oblique foot radiographs at the level of the calcaneocuboid joint. Under physiologic conditions, the os peroneum should not appear proximal to the calcaneocuboid joint.1 Migration of the os proximal to the calcaneocuboid joint is indicative of a tear of the peroneus longus tendon distal to the os peroneum. If the tendon tear is associated with fragmentation of the os, the telltale fragment distraction can also be visualized on radiographs.

When peroneal tendon pathology is suspected and nonoperative treatment has not resulted in satisfactory results, magnetic resonance (MR) imaging is indicated. Although the early literature reported inaccuracies of imaging, MR imaging is currently a useful diagnostic aid, despite conflicting results regarding the reliability of this method. There is a consensus, however, that the utility is increased with better understanding of the “magic angle effect,” a phenomenon in MR imaging in which there is a factitious appearance of heterogeneity and increased signal in a tendon when it intersects the main magnetic vector at an angle of 55°. The peroneal tendons are susceptible to this artifact, especially at the tip of the lateral malleolus. Thus, it is essential that MR imaging of the peroneals include sections formatted in a parasagittal oblique plane that is perpendicular to the tendons where they turn at the lateral malleolus. Peroneus brevis tears will be diagnosed most easily in this plane. Imaging the ankle in 20° of plantarflexion can also increase the accuracy of the study by separating the peroneal tendons in the sheath and decreasing the magic angle effect.

Tears of the peroneus longus are seen well on axial images. Additionally, it can be helpful to include sections in the oblique coronal plane perpendicular to the axis of the metatarsals to better visualize the extent of peroneus longus tendon tears in the midfoot. A recent study by Res et al observed increased fatty infiltration of the muscle on MRI in cases of peroneus brevis tendon tears. The clinical implications of this observation remain to be determined.

Despite the increasing sensitivity of MR imaging, the importance of correlation with a careful physical examination cannot be overstated. Tears found incidentally on imaging that are asymptomatic do not require treatment.

Ultrasound imaging for the diagnosis of peroneal tendon pathology can be useful and accurate. In a study of 30 patients (60 peroneal tendons) who underwent both dynamic ultrasound assessment and operative exploration, the sensitivity of ultrasonography in predicting a tendon tear was 100%. The specificity was 85%, and the accuracy was 90%. A practical limitation is that the technique is operator dependent and less readily available than MRI in many centers.