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Occult Hip Fracture
An elderly woman presented to the Emergency Room with chief complaint of left hip pain after an accidental fall at home. Her vital signs were unremarkable. Physical examination revealed tenderness about the left hip region. There was some guarding with range of motion of the left hip. Radiographs of the left hip demonstrated no evidence of acute hip fracture (Figure 1). Deformity of the left inferior ischiopubic ramus of indeterminate age was present. CT scan of the left hip (Figure 2) was obtained. Apart from old healed fractures of the ischiopubic rami and generalized osteopenia, the CT scan revealed no abnormalities. Left hip MRI without contrast was obtained. MRI (Figure 3) clearly demonstrated a non-displaced intertrochanteric fracture of the left femur. All of the studies were obtained within 24 hours from the initial radiographs.
Figure 1. Radiograph of the hip demonstrates no evidence of acute hip fracture. There is generalized osteopenia. Deformity of the inferior ischiopubic ramus is present.
Figure 2. Coronal CT image (A) demonstrates no evidence of acute hip fracture. Axial image (B) demonstrates old healed fractures of the ischiopubic rami.
Figure 3. T1 weighted MR image (A) demonstrates a non displaced fracture (arrow) through the intertrochanteric region of the left femur. Bone marrow edema is demonstrated in the proximal left femur on fluid sensitive STIR image (B). Please note the soft tissue edema (small arrow in B) adjacent to the fracture site.
Imaging choices for the evaluation of suspected hip injuries include radiography, CT, MRI and bone scans. There are a few published small studies that address utility of various modalities.
Radiographs can usually be easily obtained and should be the first step in imaging evaluation of suspected hip injury. At least two images are needed and should include a frontal view of the hip and an axial view. Addition of frontal view of the pelvis to the initial work up may also be advisable to provide an overview of the surrounding osseous structures. Pelvic radiograph, when obtained using proper technique in patients with little overlying bowel gas may allow for occasional diagnosis of sacral fracture, which sometimes presents as pain referred to the hip joint. However, it should be noted that a negative pelvic radiograph does not exclude an occult sacral fracture.
Does a negative hip radiograph exclude a hip fracture? The answer depends on many factors, but the two most important ones are the quality of the images and the presence of osteoporosis. The body habitus also becomes a factor quiet frequently. One study (1) included 92 patients and reported that radiographs were normal in 14% of patients with fractures subsequently demonstrated by MRI.
MRI is a reasonable next step for patients with negative radiographs, high osteoporosis risk and persistent clinical concern for presence of occult fracture (2). Common risk factors for osteoporosis include advanced age, female gender, steroid use, inactivity and others. In addition to detecting occult fracture as demonstrated by this case, MRI can also evaluate for presence or absence of stress reaction or bone marrow contusion, presence or absence of joint effusion, avascular necrosis of the femoral head, peritrochanteric bursal fluid collections, and other conditions, which may explain hip pain.
What about CT scan? A distinction should be made between a patient with high energy trauma and a patient with routine daily life activity that resulted in low energy injury. High energy trauma will likely be detected by the CT scan. Low energy injuries are unlikely to be demonstrated on the CT scan. In cases of negative CT scan, but persistent clinical concern for an occult fracture, MRI should be considered. Age of the patient should also be a consideration in this era of radiation dose reduction attempts. Even under the best conditions and best technologist efforts, gonads and other structures are usually on the way of the radiation beam during CT imaging of the hip.
Bone scan sensitivity for hip fractures ranges from 75.0% to 97.8% in the literature (3, 4, 5). Bone scan is a reasonable modality in patients who cannot undergo MRI. However, abnormal MDP uptake demonstrated on bone scan only indicates that there is increased bone turnover without the specificity afforded by other modalities.
In summary, radiographs should be the first modality used for evaluation of hip injury. MRI is an excellent choice for patients with osteoporosis and low energy trauma who present with negative radiographs. CT should be considered for patients with high energy trauma. Bone scan is an alternative modality for patients who cannot undergo MRI.
1. Kirby MW; Spritzer C. Radiographic detection of hip and pelvic fractures in the emergency department. AJR Am J Roentgenol. 2010; 194(4):1054-60
2. Cannon J., Silvestri, S, Munro M. Imaging choices in Occult Hip Fracture. Medscape.
3. Holder LE, Schwarz C, Wernicke PG, et al. Radionuclide bone imaging in the early detection of fractures of the proximal femur (hip): multifactorial analysis. Radiology. 1990;174:509-515.
4. Lewis SL, Rees JI, Thomas GV, et al. Pitfalls of bone scintigraphy in suspected hip fractures. Br J Radiol. 1991;64:403-408.
5. Evans PD, Wilson C, Lyons K. Comparison of MRI with bone scanning for suspected hip fracture in elderly patients. J Bone Joint Surg Br. 1994;76:158-159.