Magnetic resonance imaging (MRI) has created a new opportunity in the diagnosis and treatment of musculoskeletal diseases of the ankle and foot. The superior soft tissue contrast resolution, multiplanar capability, and noninvasive nature of MRI make it highly valuable in the detection and evaluation of soft tissue pathology of the ligaments, tendons, ankle impingement syndrome, sinus tarsi syndrome, compressive neuropathies, and synovial disorders. MRI is also excellent for early detection and evaluation of osseous abnormalities including bone marrow edema.1
Routine ankle MRI is performed in the axial, coronal, and sagittal planes relative to the tabletop. The foot is imaged in the oblique axial plane, oblique coronal plane, and oblique sagittal plane. The patient is supine with the foot in about 20° of plantar flexion. An extremity surface coil is used to enhance spatial resolution. A combination of anatomical pulse sequences such as spin-echo T1 or fast-spin echo proton density (FSE PD) and fluid-sensitive sequences such as fat-suppressed FSE T2 or short-tau inversion recovery (STIR) is used. In general, T1-weighted (T1W) images provide good anatomic detail and T2-weighted (T2W) images are useful for assessing the abnormal increase in water that characterizes most pathologic conditions.
MRI ANATOMY OF THE ANKLE TENDONS AND LIGAMENTS
Normal MRI Tendon Anatomy
Tendons around the ankle are divided into four groups: anterior, posterior, medial, and lateral. The posterior group includes the Achilles (Figure 18-1A,B) and plantaris tendons. The medial (flexor) group from medial to lateral is composed of the posterior tibialis tendon (PTT), flexor digitorum longus (FDL), and flexor hallucis longus (FHL), which are associated with the mnemonic “Tom, Dick, and (posterior tibial artery and nerve) Harry” (Figure 18-1A,C). The lateral (peroneal) tendons include the peroneus brevis medially and the peroneus longus tendon laterally (Figure 18-1A,D). The anterior (extensor) group from medial to lateral is composed of anterior tibialis tendon (ATT), extensor hallucis longus (EHL), and extensor digitorum longus (EDL), which are associated with the mnemonic “Tom, Harry, and (anterior tibial artery and nerve) Dick” (Figure 18-1A,E).2
Normal tendon anatomy. (A) Axial T1W image shows normal, low-signal tendons of the ankle. The medial (flexor) group pneumonic “Tom (T), Dick (D) and Harry (H)” stands for posterior tibialis tendon (PTT), flexor digitorum longus tendon (FDL), and flexor hallucis longus tendon (FHL). The anterior (extensor) pneumonic “Tom (T), Harry (H) and Dick (D)” stands for anterior tibialis tendon (ATT), extensor hallucis longus (EHL), and extensor digitorum longus (EDL). The lateral (peroneal) group includes peroneus brevis (PB) medially and peroneus longus (PL) tendons laterally. The posterior group includes Achilles tendon and plantaris tendon (not shown). M = medial, L = lateral, A = anterior, P = posterior. (B) Sagittal STIR image shows normal, low-signal Achilles tendon with parallel anterior and posterior walls (arrow). (...