How to Read an Ankle MRI: A Patient's Guide

Key MRI Sequences

• T1-weighted images: excellent bone detail, showing normal fatty marrow as bright signal
• T2-weighted with fat saturation: the workhorse for pathology detection, highlighting fluid and edema as bright signal
• STIR (Short Tau Inversion Recovery): highly sensitive for bone marrow edema and stress fractures
• Proton density sequences: excellent contrast between ligaments, tendons, and surrounding tissue

Lateral Ligaments on MRI

The ATFL is best seen on axial images as a thin, dark band connecting the anterior fibula to the talus. A torn ATFL shows discontinuity, thickening, or waviness with surrounding bright T2 signal indicating fluid and edema. The CFL is evaluated on both axial and coronal images, running from the fibular tip to the calcaneus. Chronic ligament injuries may show thickening or attenuation rather than acute signal changes. For treatment decisions, read our article on ankle ligament healing without surgery.

Tendons on MRI

Normal tendons appear uniformly dark on all MRI sequences. The Achilles tendon is the largest and is best evaluated on sagittal images, where tears show discontinuity or a gap filled with bright T2 signal. The peroneal tendons behind the lateral malleolus may show splits (particularly peroneus brevis), subluxation from the retromalleolar groove, or tendinosis with thickening and increased internal signal. The posterior tibial tendon on the medial side is evaluated for tendinosis or tears that contribute to flatfoot deformity. Learn about common tendon injuries in our ankle injury types guide.

Cartilage and Osteochondral Lesions

Osteochondral lesions of the talus are best detected on coronal and sagittal T2-weighted images. They appear as focal areas of bright signal in the subchondral bone with overlying cartilage irregularity. Stable lesions have intact cartilage coverage, while unstable lesions show fluid undermining the fragment or loose body formation. The medial talar dome is the most common location. Bone marrow edema patterns also help identify stress fractures, particularly of the calcaneus and navicular, which appear as areas of bright T2/STIR signal within the bone.

Key Takeaways

• T2 fat-saturated sequences are the primary tool for detecting ankle pathology
• The ATFL is best seen on axial images and is the most commonly torn lateral ligament
• Normal tendons appear dark on all sequences and any bright signal suggests pathology
• Osteochondral lesion stability on MRI guides conservative versus surgical management

Frequently Asked Questions