Retinacula of the foot and ankle: MRI with anatomic correlation in cadavers

The retinacula of the ankle are regions of localized thickening of superficial aponeurosis that provide mechanical strength to prevent tendon bowstringing. The purpose of this study was to define the foot and ankle retinacula as seen on MRI with anatomic correlation in cadavers.

Ten fresh foot and ankle specimens from humans were imaged with 1.5-T MRI. T1- and intermediate-weighted images were obtained in the axial, coronal, and sagittal planes. Specimens then were sectioned into 3-mm-thick sections in either the axial or the coronal plane to correspond with the MR images. Two radiologists interpreted the MR images and sections by consensus for the anatomic landmarks and best imaging planes for identification of the retinacula and discernment of their shape, thickness, and relations to adjacent tendons.

Normal retinacula of the ankle appeared as bands of low signal intensity in both MRI sequences. The bony landmarks were helpful in localization of the attachment sites of the retinacula. The superior extensor retinaculum and superior and inferior peroneal retinacula were optimally visualized on axial images. Their thicknesses averaged 0.9, 1.0, and 0.8 mm, respectively. The flexor retinaculum and three root components (medial, intermediate, and lateral) of the stem ligament of the inferior extensor retinaculum were well seen in the coronal plane. The average thicknesses of these structures were 0.9, 1.5, 1.0, and 0.9 mm, respectively.

MRI in standard orthogonal planes is a useful technique for visualizing the attachment sites, signal intensity, and normal thickness of foot and ankle retinacula.