Imaging Studies
The Ottawa Foot and Ankle Rules are validated clinical decision rules designed to assist the clinician in determining which individuals with foot and ankle pain require radiographic evaluation. [10, 11] The guidelines include: individuals who are unable to bear weight for at least 4 steps immediately following the injury and in the emergency department, or those individuals who demonstrate tenderness over the posterior aspect of the medial and lateral malleoli, over the navicular, or over the base of the fifth metatarsal. Such individuals should have radiographic evaluation performed. The clinical rules have a high sensitivity in adult patients (0.3% false-negative rate) and a 100% sensitivity rate in pediatric patients, although the specificity approaches 30-40%. [10]
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Sesamoiditis: Stress radiographs, axial silhouette views, bone scans, and computed tomography (CT) scans are helpful diagnostic aids. Radiographic examination of the contralateral foot is useful. The radiographs are often normal, although a bipartite sesamoid bone is a common normal variant that can be mistaken for a stress fracture. Additional testing may be needed to help evaluate this possibility further, depending on the patient's symptoms.
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Turf toe: Plain radiographs may reveal a small avulsion fracture from the plantar metatarsal head. If the diagnosis is unclear, MRI may more thoroughly evaluate the integrity of the MTP joint.
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Posterior tibial tendinitis: A weight-bearing plain radiograph may help determine the degree and type of flatfoot abnormality. Magnetic resonance imaging (MRI) is the imaging modality of choice for imaging posterior tibial tendon tenosynovitis and degenerative tears. Ultrasound (US) imaging can provide a dynamic picture of the tendon.
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Peroneal tendon subluxation/dislocation: The diagnosis is made on clinical grounds. Most peroneal dislocations reduce spontaneously; therefore, most of these injuries are unrecognized.
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Peroneal tendinitis: Plain radiographs may reveal hindfoot varus. US imaging and MRI are usually not necessary, but these modalities may reveal synovitis, peroneal retinaculum, or tendon tearing.
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FHL tenosynovitis: Plain radiographs of the foot are helpful with the differential diagnosis (see Differentials and Other Problems to Be Considered), and US imaging or MRI can help to rule out a tear.
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Jones fracture: Standard foot radiographs demonstrate most metatarsal base fractures. Note any intra-articular fractures, and determine the percentage of articular surface that is involved, as this percentage is essential to determining clinical management. Avulsion of the fifth metatarsal apophysis should not be confused for a Jones fracture, as the apophyseal avulsion is parallel to the shaft of the fifth metatarsal compared with the perpendicular fracture of the standard Jones fracture.
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Morton neuroma: Radiographic imaging may be employed if the diagnosis is in question. US can help the physician make a reliable estimate of the size of the neuroma.
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Stress fractures
Plain radiography is the first imaging study recommended to help confirm the diagnosis of stress fractures. However, radiographic changes may not be evident for 2-3 weeks following the onset of symptoms. Periosteal and endosteal callus formation is typically seen within 2 weeks of injury, whereas callus formation reaches its maximum at 6 weeks. Moreover, only 50% of stress fractures are seen on plain radiographs. Findings of radionuclide bone scanning or MRI help confirm the diagnosis.
The criterion standard for the diagnosis of stress fractures is a technetium (Tc) bone scan. The osteoblast incorporates the isotopes in new bone formation and may be positive as early as 48-72 hours following clinical signs of injury. MRI has been found to be just as sensitive and more specific. However, MRI may be cost prohibitive or may not be available, depending on the medical center.
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Lisfranc fracture dislocation
Meticulous evaluation of weight-bearing foot radiographs is essential for confirmation of suspected Lisfranc fracture dislocation. A fracture of the base of the second metatarsal is virtually pathognomonic for TMT joint disruption.
The medial aspects of the first, second, and third metatarsals should align evenly with the medial borders of the first, second, and third cuneiform bones, respectively. The medial border of the fourth metatarsal should align evenly with the medial border of the cuboid bone. Comparison views of the feet may reveal a widening of the space between the first and second metatarsals or between the second and third metatarsals. Disruption of these anatomic relationships suggests a Lisfranc fracture dislocation. US imaging and MRI can indicate ligamentous disruption by showing fluid in the ligaments and intertarsal joint spaces.
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The hindfoot is composed of the talus and the calcaneus.
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Select tendons of the foot.
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Select bones of the foot (dorsal and plantar views).
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Select bones of the foot (medial and lateral views).
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Select bones of the foot (superolateral view).
