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OBJECTIVE.Under the hypothesis that the anatomic relationship of the tibialis anterior tendon and extensor retinaculum of the foot and ankle is relevant to the clinical aspects of a tear in that tendon, we assessed the anatomic details of these structures using MRI in cadavers and evaluated MRI in patients with a tibialis anterior tendon tear.MATERIALS AND METHODS. Seven cadaveric feet underwent detailed MRI using standard and oblique coronal planes with respect to the course of the tibialis anterior tendon and extensor retinaculum. Cadaveric sections subsequently provided an anatomic correlation. MR images of seven patients with tibialis anterior tendon tear were analyzed by consensus of two musculoskeletal radiologists.RESULTS. Imaging-anatomic correlations allowed identification of the tibialis anterior tendon and extensor retinaculum. The tendon passed through three tunnels formed by the superior extensor retinaculum, oblique superomedial, and oblique inferomedial limbs of the inferior extensor retinaculum. Of seven patients with the tendon tear, three patients had complete tears and four patients had partial tears. In all partial tears, the level of the tear was at the ankle joint, corresponding to the approximate level of the oblique superomedial limb. In all complete tears, the proximal ends of torn tendons were retracted to a level below the oblique superomedial limb. In all tears, the oblique superomedial limb surrounding the torn tendon was seen with thickening in four patients and enhancement after IV gadolinium injection in two patients. Other findings included a bulbous appearance or swelling of the torn tendon in two complete and two partial tears and fluid collections within the tendon sheath and in an area confined by the extensor retinaculum in four patients.CONCLUSION. The relationship of the tibialis anterior tendon and extensor retinaculum is well depicted on MRI, even in patients with a tibialis anterior tendon tear, and is clinically relevant to the tear of this tendon. njuries of the ankle are among those most commonly encountered in sports-related and routine activities. This coupled with the fact that the anatomy of the ankle is quite complex requires a detailed understanding of the anatomy and common injuries around this articulation. The ankle joint is a composite joint reinforced by various ligaments. More than 10 tendons and many nerves and vessels cross the ankle and are held in place by several retinacula.The tibialis anterior tendon is the strongest of the anterior tendons. It is covered by the extensor retinaculum, which stabilizes the tendons in the frontal aspect of the ankle and foot [1]. Its injury in the distal leg or at the level of the ankle is infrequent [2]. Often the diagnosis can be confusing and is delayed. The injury may be overlooked by the patient, and the clinical presentation of a tender bulbous mass at the level of the ankle joint without awareness of any definite functional impairment may cause concern for a neoplasm [3,4]. I...