Stress fractures are characterized by bone pain and tenderness without a history of direct trauma. The fatigue type of stress fracture results from repetitive cyclical loading and prolonged muscular force on bone that has normal elastic resistance. Conventional radiographs are often unremarkable at the onset of symptoms.
Fatigue fractures usually result from alteration of the duration, intensity, or manner in which a physical activity is performed. Stress fractures of the foot are relatively site specific based on the type of athletic activity. Recreational and competitive runners, basketball and football players, ice skaters, ballet dancers, and military recruits are particularly at risk.
The most common midfoot stress fracture in athletes occurs in the tarsal navicular [10,11]. It is typically oriented in the midsagittal plane of the navicular (Fig. 5). The fracture may be partial, isolated to the dorsal cortex, or complete. Complete fractures may be complicated by delayed or nonunion or osteonec-rosis of the lateral segment. Conventional radiographs are relatively insensitive for detection of navicular fracture. Historically, nuclear bone scintigraphy has been employed to detect clinically suspected, radiographically occult stress fractures. This has largely been supplanted by CT and MRI (Fig. 6). CT permits visualization of cortical defects, gapping at the fracture site and callus formation . CT may reveal cortication or sclerosis at the fracture margins suggesting delayed or nonunion, whereas fragmentation, sclerosis, and cyst formation of the lateral fragment might suggest osteonecrosis (Fig. 7). MRI depicts the fracture as linear marrow signal abnormality, with surrounding marrow edema appearing as a penumbra of reticulated, ill-defined low T1 or bright T2 signal,
diminishing over time unless there is chronic instability and motion at the fracture site.
Stress fracture of the ''lesser metatarsals'' most commonly occurs at the mid to distal shaft, typically affecting the second and third rays. Many factors can contribute to insufficiency of the first ray, shifting the stresses of weight bearing and ambulation from the first to the second and third rays. These include hallux valgus, metatarsus primus varus, previous corrective surgery of the first
ray, congenital shortening of the first ray, or a low-lying arch, all of which may predispose to stress fracture of the lesser metatarsals .
There are three different types of stress fracture of the proximal to midshaft fifth metatarsal. Fracture of the tip of the styloid process results from an inversion injury and results from avulsion either by the lateral cord of the plantar aponeurosis or by the peroneus brevis  (Fig. 8). A Jones fracture occurs approximately 1.5 to 2.0 cm distal to the tip of the tuberosity as a result dorsiflex-ion with the forefoot in supination [14,15] (Fig. 9); the distinction is important because of the tendency toward delayed healing or nonunion for these fractures at the junction of the metaphysis and proximal diaphysis. Midshaft fractures are related to chronic repetitive stress, and have been attributed in football players to fatigue resulting from insufficient diaphyseal support as a result of widely placed cleats .
Metatarsal stress fractures may be subtle or occult on conventional radiographs. Detection requires a discernible cortical defect, usually at the medial aspect of the mid to distal diaphysis. Cortical stress reaction or callus may obscure the lucent fracture line. MRI allows early visualization of stress-related marrow edema, which may be accompanied by parosteal soft tissue edema (Fig. 10). This marrow edema is nonspecific, but in the proper clinical context,
may permit proper diagnosis and clinical intervention before progression to fracture . On MRI a fracture appears as linear or band-like low signal on T1- or T2-weighted images contiguous with the cortex, with marrow edema most conspicuously demonstrated on fat-suppressed or STIR sequences
Freiberg's infraction is characterized by subchondral collapse of the second or third metatarsal head with osteonecrosis and cartilaginous fissuring  (Fig. 12). It may result from acute or repetitive injury with vascular compromise to the subchondral bone. Radiographically, occult lesions may be visible by MRI as subchondral dark T1 and bright T2 signal. Over time, flattening and sclerosis of the metatarsal head will become radiographically evident, at which point MRI will demonstrate dark signal on both T1 and T2 weighting.
Stress fractures of the phalanges are decidedly rare [18,19]. Case reports of stress fractures of the proximal phalanx of the great toe reveal a tendency toward the medial base, most commonly in the context of hallux valgus and a bipartite tibial hallucal sesamoid. Stress fracture of the proximal phalanx of the second toe is exceedingly rare, presenting with pain in the region of the meta-tarsal head. Most cases of phalangeal stress fractures occurred in young elite athletes engaged in basketball, volleyball, running, or ballet.
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