Dr. Bartolotta is an assistant professor of radiology at Weill Cornell Medical College in New York City and assistant attending radiologist at New York-Presbyterian Hospital/Weill Cornell Medical Center.
Post-traumatic hip pain is a common chief concern among ED patients. While routine radiography, the standard imaging modality for the initial evaluation of suspected hip fracture, detects most fractures, its sensitivity is decreased in the setting of osteoporosis—particularly with nondisplaced fractures. Thus, though elderly/osteoporotic patients are more likely to fracture, these fractures are harder to detect on radiography. In a study of 70 patients with negative radiographs but high clinical concern for fracture, magnetic resonance imaging (MRI) detected occult femoral fractures in 37% and occult pelvic fractures in 23%.1
Hip fractures in elderly patients are associated with substantial mortality and morbidity, the risks for which increase with delayed diagnosis.2 When there is high clinical suspicion for a radiographically occult hip fracture in this population, cross-sectional imaging should be considered for further evaluation (Figure). The decision of whether to use computed tomography (CT) or MRI for the cross-sectional examination must be made on both an institutional and patient-specific basis. CT is faster, less expensive, and more widely and temporally available. Although CT has increased sensitivity for fracture detection compared to radiography, studies have demonstrated false-negative CT examinations in the setting of nondisplaced proximal femoral fractures, especially in osteoporotic patients. Hakkarinen et al3 reported that among 235 hip fractures, 10% were occult radiographically; approximately 17% of these fractures (4 out of 24) were also occult on CT but visible on MRI. Moreover, while radiography and CT may demonstrate a seemingly isolated fracture at the femoral greater trochanter, a subset of these fractures exhibit intertrochanteric extension that is only evident on MRI (Figure). Isolated greater trochanteric fractures are typically treated conservatively, while some incomplete intertrochanteric fractures warrant internal fixation, especially fractures that cross the intertrochanteric midline on coronal MRI.4,5
In addition to improved fracture detection, MRI also provides superior evaluation of the underlying bone marrow for coexisting conditions, such as osteomyelitis, osteonecrosis, and primary or metastatic neoplasm in the setting of pathologic fracture. Additional benefits of MRI over radiography and CT include its lack of ionizing radiation and improved evaluation of adjacent soft tissue injuries, such as labral and/or musculotendinous tears.
MRI, however, does require a longer examination time in which the patient must remain still. This may be difficult for acutely post-traumatic patients, notably those with baseline dementia and/or claustrophobia. For patients in whom MRI is indicated (eg, patients who do not have an implantable device such as a cardiac pacemaker) and where it is institutionally available, the decision to utilize it over CT is largely rooted in health-care economics. MRI is more expensive than radiography and CT, and even in the largest medical centers, the examination requires substantially more time than CT, which inherently decreases patient throughput in the ED. Cannon et al6 present an evidence-based algorithm for patient stratification, in which patients at high-risk for osteoporosis and low-energy trauma should be considered for immediate MRI rather than CT. These risk factors optimize MRI utilization by selecting those patients with the greatest likelihood of nondisplaced, radiographically occult fracture.
References
1. Bogost GA, Lizerbram EK, Crues JV 3rd. MR imaging in evaluation of suspected hip fracture: frequency of unsuspected bone and soft-tissue injury. Radiology. 1995;197(1):263-267.
2. Zuckerman JD, Skovron ML, Koval KJ, Aharonoff G, Frankel VH. Postoperative complications and mortality associated with operative delay in older patients who have a fracture of the hip. J Bone Joint Surg Am. 1995;77(10):1551-1556.
3. Hakkarinen DK, Banh KV, Hendey GW. Magnetic resonance imaging identifies occult hip fractures missed by 64-slice computed tomography. J Emerg Med. 2012;43(2):303-307.
4. Feldman F, Staron RB. MRI of seemingly isolated greater trochanteric fractures. AJR Am J Roentgenol. 2004;183(2):323-329.
5. Schultz E, Miller TT, Boruchov SD, Schmell EB, Toledano B. Incomplete intertrochanteric fractures: imaging features and clinical management. Radiology. 1999;211(1):237-240.
6. Cannon J, Silvestri S, Munro M. Imaging choices in occult hip fracture. J Emerg Med. 2009;37(2):144-152.