Laboratory Studies
If in the course of the diagnostic workup for the stress injury the individual is discovered to have metabolic bone disease or another comorbidity (eg, inadequate nutritional status), the clinician should obtain the appropriate laboratory and imaging studies to permit definitive management of the condition (or request specialty-level consultation).
Low vitamin D levels have been associated with foot and ankle stress fractures. Assessment of the patient's vitamin D level may be beneficial. [22]
Imaging Studies
Imaging studies can help the physician confirm the suspected clinical diagnosis. Conventional radiographic findings are often unremarkable, particularly early in the continuum that leads from stress reaction to stress fracture. In the acute setting, conventional radiography may only detect 15% of stress fractures. [23] In most instances, conventional radiographic signs of a periosteal reaction are not evident within the first several weeks of symptoms. In some cases, conventional radiography remains negative, despite clear diagnostic evidence of fracture on bone scan or cross-sectional imaging.
Other conventional radiographic findings include an area of cortical lucency (ie, the so-called thin black line) that suggests a nonhealing stress fracture.
CT scanning is a useful diagnostic imaging tool, as is MRI. [2] These cross-sectional modes of imaging may be helpful in defining the extent of the suspected fracture.
A 3-phase bone scan (scintigraphy) may be indicated if conventional radiographic findings are negative or nondiagnostic and the clinical suspicion of stress fracture remains high. The bone scan is diagnostic of stress fracture if focal isotope uptake occurs in the area of clinical interest on the third phase of the scan.
Scintigraphy is extremely sensitive. If the scan shows no evidence of focal uptake, the diagnosis of stress fracture is quite unlikely. Note that as a result of the sensitivity of this imaging modality, focal radiotracer uptake may persist at healing stress fracture sites long after the patient has become asymptomatic. Furthermore, the bone scan may be positive even before the clinical onset of symptoms.
Drawbacks of scintigraphy include a relative lack of specificity and anatomic resolution. Nevertheless, the temporal pattern of uptake during the scan may be useful in distinguishing the etiology of the patient's symptoms. Radiotracer uptake on the third phase of the scan generally is specific to bony pathology. For example, tibial periostitis and acute tibial stress fracture both usually demonstrate uptake on the first and second phases of the 3-phase bone scan; however, only the stress fracture results in focal uptake on the third phase.
Note that other processes besides stress fracture, including osteomyelitis and tumor, can have a similar appearance on 3-phase bone scans. Thus, for the clinician to consider the imaging study result in the context of the patient's history and physical examination findings is important.
Because of the limitations inherent to scintigraphy, MRI may be a reasonable first-line imaging procedure. MRI provides greater anatomic detail of the area in question, and fat-suppressed (short TI inversion recovery [STIR]) and water-weighted (T2) signal sequences permit detection of marrow edema and/or periosteal reaction occurring during the earliest stages of stress fracture formation with a level of sensitivity that rivals bone scanning. MRI is considered the best imaging procedure for stress fractures. [23, 24, 25]
For example, a literature review by Wright et al indicated that MRI has the greatest sensitivity and specificity for diagnosing stress fractures of the lower extremity, when compared with conventional radiography, nuclear scintigraphy, CT scanning, and ultrasonography. According to the studies evaluated, MRI had a sensitivity of 68-99% and a specificity of 4-97%. [26]
MRI has been shown to have a 92% sensitivity in detecting stress reaction or fracture in the evaluation of spondylolysis. [27]
In 2003, Arendt et al described a radiographic grading system that incorporates both conventional radiographic findings and those from MRI. [28] The authors found that the grade of bone stress injury correlated with the average time to full recovery. For example, athletes with grade 1 stress injury who were treated with a standardized rehabilitation protocol returned to sporting activity in 3.3 weeks, on average, while those with grade 4 stress injury returned in 14.3 weeks.
Similarly, a study by Ramey et al found that in patients with femoral neck stress fractures, return-to-running time was significantly shorter for those with a grade 1 injury (mean period of 7.4 wks), as determined with MRI, than in patients with a grade 2, 3, or 4 fracture (mean periods of 13.8, 14.7, and 17.5 wks, respectively). [29]
High-resolution ultrasonography may detect bone stress injury or occult fractures before they are evident on radiographs. [10]
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This image is of a 17-year-old male wrestler with a 2-month history of left-sided low back pain, worse with extension. Total body scintigraphy findings were unremarkable. Courtesy of Michael Spieth, MD, and Nandita Bhattacharjee, MD, MHA; Marshfield Clinic Department of Radiology.
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Same patient as in the above image. Single-photon emission computed tomography (SPECT) images demonstrate abnormal delayed uptake in the posterior elements of L5. Courtesy of Michael Spieth, MD, and Nandita Bhattacharjee, MD, MHA; Marshfield Clinic Department of Radiology.
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Same patient as in the above 2 images. Subsequent MRI revealed an area of bright signal in the left pars interarticularis of L5 on T2-weighted images, confirming the diagnosis of acute unilateral spondylolysis. The patient was treated successfully with activity restriction and bracing with a lumbar corset for 3 months, at which point he was asymptomatic. Plain film imaging at follow-up (not shown) was unremarkable, with no evidence of spondylolysis on oblique views. Courtesy of Michael Spieth, MD, and Nandita Bhattacharjee, MD, MHA; Marshfield Clinic Department of Radiology.
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A 17-year-old female dancer with a 2-week history of left shin pain. Plain film imaging was unremarkable. Three-phase bone scanning demonstrated an area of linear uptake in the posterior medial aspect of the left tibia on blood pool images, but delayed images were considered normal. This scintigraphic pattern is consistent with medial tibial stress syndrome (shin splints), but not with stress fracture. Courtesy of Michael Spieth, MD, and Nandita Bhattacharjee, MD, MHA; Marshfield Clinic Department of Radiology.
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This is a 55-year-old female industrial worker with a 1-week history of right foot pain. Plain film imaging was unremarkable. Bone scanning revealed a stress fracture of the second metatarsal. Courtesy of Michael Spieth, MD, and Nandita Bhattacharjee, MD, MHA; Marshfield Clinic Department of Radiology.
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This image is of an 18-year-old female soccer player with a 3-week history of left leg pain, which was worse at night and with activity. Upon examination, she reported tenderness in response to palpation over the midtibia. Bilateral pes planus was noted. Plain film radiography failed to demonstrate a fracture. Bone scanning revealed a focal area of delayed uptake on the posterior medial aspect of the proximal third of the left tibia, confirming the diagnosis of stress fracture. Courtesy of Michael Spieth, MD, and Nandita Bhattacharjee, MD, MHA; Marshfield Clinic Department of Radiology.
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A 63-year-old man with metastatic thyroid carcinoma went for a walk and awoke the following morning with left hip girdle pain. Plain film imaging revealed a subtle area of linear cortical lucency at the proximal left femoral metadiaphysis, consistent with an insufficiency fracture through pathologic bone. The patient subsequently underwent internal fixation. Courtesy of Michael Spieth, MD, and Nandita Bhattacharjee, MD, MHA; Marshfield Clinic Department of Radiology.
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Enlarged view of the fracture shown in the above image. Plain film imaging revealed a subtle area of linear cortical lucency at the proximal left femoral metadiaphysis, consistent with an insufficiency fracture through pathologic bone. The patient subsequently underwent internal fixation. Courtesy of Michael Spieth, MD, and Nandita Bhattacharjee, MD, MHA; Marshfield Clinic Department of Radiology.
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This case involves a 16-year-old female basketball player with a 2-year history of left foot pain refractory to casting and reduced weight bearing. Bone scanning revealed a focal area of delayed uptake lateral to the left first metatarsal phalangeal joint, which corresponded to a bipartite sesamoid on plain films. Courtesy of Michael Spieth, MD, and Nandita Bhattacharjee, MD, MHA; Marshfield Clinic Department of Radiology.
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Sesamoid stress fractures are prone to nonunion, and sesamoidectomy is indicated for patients who do not respond to conservative management. Some clinicians recommend bone grafting as an alternative to complete or partial sesamoidectomy. Courtesy of Michael Spieth, MD, and Nandita Bhattacharjee, MD, MHA; Marshfield Clinic Department of Radiology.
