Technetium-99 scintigraphy has been valuable for detecting stress fractures of metatarsal and tarsal bones, and CT has high accuracy for detecting osteochondral fracture. In foot pain of undetermined etiology, however, MRI is an excellent screening modality because it permits direct evaluation of all osseous and soft-tissue structures.
MRI is superior to any other modality in displaying tendon pathology (47,48). In tenosynovitis, MRI detects fluid within the tendon sheath as having moderate signal intensity on T1-weighted images and as hyperintense on T2-weighted images. Tendinosis is commonly observed in the Achilles, tibialis posterior, flexor hallucis longus, tibialis anterior, and peroneal tendons (Fig. 6-37). Tendinosis is visualized as a focal or diffuse thickening of the tendon that may show areas of increased signal intensity on T2-weighted images. Plantar fasciitis shows similar changes within the plantar aponeurosis (Fig. 6-38). With a complete tendon rupture, axial MR images show absence of the tendon and its replacement by edema. Sagittal and coronal MR images display the site of discontinuity, with edema occupying the gap and surrounding the torn ends of the tendon.
FIGURE 6-37. A: Axial T1-weighted image at the level of the talar dome. There is thickening and splitting to the fibers of the peroneus brevis (short arrows). Note normal signal and configuration to the peroneus longus (PL). B: Axial PD fat suppressed sequence. The split fibers of the peroneus brevis are better depicted (arrowheads). There is an effusion within the tendon sheath (short arrow).
FIGURE 6-38. A: Sagittal T1-weighted image of the hindfoot. There is thickening and increased signal (short arrow) within the proximal fibers of the plantar fascia (PF). TT tarsal tunnel; ST, sustentaculum talus. B: Coronal T2-weighted fat suppressed sequence. There is asymmetric thickening and increased signal to the medial bundle of the plantar fascia (MB). Edema extends into the adjacent fat (arrowhead ). Note normal thickness and signal to the lateral bundle (LB).
Stress fractures of the tarsal or metatarsal bones appear on MRI as linear areas of decreased marrow signal intensity. There are adjacent areas of marrow edema that are hypointense relative to marrow fat on T1-weighted images and hyperintense on T2-weighted images (47). By MRI, osteochondral fractures (e.g., of the talar dome) have an appearance similar to that of osteochondritis dissecans of the knee. The primary task of MRI is to determine the stability of the fragment by demonstrating the integrity of the articular cartilage and the absence of fluid between the osteochondral fragment and the parent bone. Synovial cysts of intertarsal joint origin demonstrate moderate signal intensity on T1-weighted images and high signal intensity on T2-weighted images.