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Dual-energy CT is increasingly being used in the emergency department to help diagnose acute conditions. Its applications include demonstrating bone marrow edema (BME) seen in the setting of occult fractures and other acute conditions. Dual-energy CT acquires data with two different x-ray energy spectra and is able to help differentiate materials on the basis of their differential energy-dependent x-ray absorption behaviors. Virtual noncalcium (VNCa) techniques can be used to suppress the high attenuation of trabecular bone, thus enabling visualization of subtle changes in the underlying attenuation of the bone marrow. Visualization of BME can be used to identify occult or mildly displaced fractures, pathologic fractures, metastases, and some less commonly visualized conditions such as ligamentous injuries or inflammatory arthritis. The authors' major focus is use of dual-energy CT as a diagnostic modality in the setting of trauma and to depict subtle or occult fractures. The authors also provide some scenarios in which dual-energy CT is used to help diagnose other acute conditions. The causes and pathophysiology of BME are reviewed. Dual-energy CT image acquisition and VNCa postprocessing techniques are also discussed, along with their applications in emergency settings. The authors present potential pitfalls and limitations of these techniques and their possible solutions. © RSNA, 2020.

Traumatic and atraumatic fractures are entities with distinct but often overlapping clinical manifestations, imaging findings, and management protocols. This article is a review of terminology, etiology, and key imaging features that affect management of atraumatic fractures including stress fractures, atypical femoral fractures, and pathologic fractures. The terminology of atraumatic fractures is reviewed, with an emphasis on the distinctions and similarities of stress, atypical, and pathologic fractures. The basic biomechanics of normal bone is described, with an emphasis on the bone remodeling pathway. This framework is used to better convey the shared etiologies, key differences, and important imaging findings of these types of fractures. Next, the characteristic imaging findings of this diverse family of fractures is discussed. For each type of fracture, the most clinically relevant imaging features that guide management by the multidisciplinary treatment team, including orthopedic surgeons, are reviewed. In addition, imaging features are reviewed to help discriminate stress fractures from pathologic fractures in patients with challenging cases. Finally, imaging criteria to risk stratify an impending pathologic fracture at the site of an osseous neoplasm are discussed. Special attention is paid to fractures occurring in the proximal femur because the osseous macrostructure and mix of trabecular and cortical bone of the proximal femur can function as a convenient framework to understanding atraumatic fractures throughout the skeleton. Atraumatic fractures elsewhere in the body also are used to illustrate key imaging features and treatment concepts. © RSNA, 2018.

Hip dislocation is an important orthopedic emergency usually seen in young patients who have experienced high-energy trauma, often resulting in significant long-term morbidity. Rapid identification and reduction is critical, as prolonged dislocation increases the risk of developing avascular necrosis of the femoral head, and posttraumatic osteoarthritis is a common complication, even in the absence of associated fractures. Identification and timely management of hip dislocation are highly dependent on imaging, both at presentation and after attempted reduction. It is imperative for the radiologist to understand imaging features that guide management of hip dislocation to ensure timely identification, characterization, and communication of clinically relevant results. Although the importance of prompt identification of hip dislocation is universally recognized, the significance of imaging features that guide correct management and are thought to prevent complications is less emphasized in the radiology literature. In this article, the authors review the anatomy of the hip, common injury mechanisms for various types of dislocations, and imaging findings for associated injuries. They review the most commonly used classification systems and propose a simplified checklist approach to hip dislocation to aid rapid interpretation and communication of the most clinically relevant imaging features to the treating orthopedic surgeon. © RSNA, 2017.

Femoral fracture in the setting of a hip arthroplasty is an increasingly common complication encountered in the emergency department (ED). Diagnosis and management of periprosthetic fractures are complicated, and orthopedic surgeons rely on imaging findings to guide the appropriate management approach to the injury. Delay in identification and appropriate definitive management of periprosthetic fractures is associated with high morbidity and mortality. At present, the Vancouver classification system for periprosthetic hip fractures is the most common classification system used by orthopedic surgeons. It relies on three radiographic criteria-fracture location, prosthesis stability, and quality of the femoral bone stock-to characterize these fractures and to help guide management decisions. Familiarly with the Vancouver classification system allows radiologists to both recognize and communicate the most clinically relevant imaging findings to the treating orthopedic surgeon. This article reviews the imaging workup for hip pain in patients with a femoral prosthesis, risk factors for periprosthetic fracture, and the expected normal appearance of the most commonly encountered types of femoral prostheses. Fracture terminology and the Vancouver classification system are reviewed in a simplified algorithm with emphasis on the most common patterns of periprosthetic fractures, the radiologic determinants of prosthesis stability and bone quality, and the management implications of these imaging findings. Finally, multiple instructive clinical cases are used to demonstrate critical application of the classification system and to highlight the clinical implications of the imaging findings. © RSNA, 2017.

Each year, more than 250,000 hip fractures occur in the United States, resulting in considerable patient mortality and morbidity. The various types of adult proximal femoral fractures require different treatment strategies that depend on a variety of considerations, including the location, morphologic features, injury mechanism, and stability of the fracture, as well as the patient's age and baseline functional status. The authors discuss femoral head, femoral neck, intertrochanteric, and subtrochanteric fractures in terms of injury mechanisms, specific anatomic and biomechanical features, and important diagnostic and management considerations, including the diagnostic utility of imaging modalities. The authors review clinically important classification systems, such as the Pipkin, Garden, Pauwels, and Evans-Jensen classification systems, with emphasis on differentiating subchondral insufficiency fractures from avascular necrosis of the femoral head and typical subtrochanteric fractures from atypical (often bisphosphonate-related) subtrochanteric fractures. In addition, the authors describe the potential complications and management strategies for each fracture type on the basis of the patient's age and physical condition. A clear understanding of these considerations allows the radiologist to better provide appropriate and relevant diagnostic information and management guidance to the orthopedic surgeon., ((©)RSNA, 2015.)

Treating trauma patients with displaced pelvic fractures requires a multidisciplinary approach at a designated trauma center to reduce morbidity and mortality. Immediate recognition of pelvic ring disruption and determination of pelvic stability are critical components in the evaluation of such patients. Stability is achieved by the ability of the osseoligamentous structures of the pelvis to withstand physiologic stresses without abnormal deformation. The supporting pelvic ligaments, including the posterior and anterior sacroiliac, iliolumbar, sacrospinous, and sacrotuberous ligaments, play a crucial role in pelvic stabilization. Radiologists should be familiar with the ligamentous anatomy and biomechanics relevant to understanding pelvic ring disruptions, as well as the Young and Burgess classification system, a systematic approach for interpreting pelvic ring disruptions and assessing stability on the basis of fundamental force vectors that create predictable patterns. This system provides an algorithmic approach to interpreting images and categorizes injuries as anterioposterior (AP) compression, lateral compression, vertical shear, or combined. Opening and closing of the pelvis from rotational forces result in AP compression and lateral compression injuries, respectively, whereas vertical shear injuries result from cephalad displacement of the hemipelvis. AP and lateral compression fractures are divided into types 1, 2, and 3, with increasing degrees of severity. Knowledge of these injury patterns leads to prompt identification and diagnosis of other subtle injuries and associated complications at pelvic radiography and cross-sectional imaging, allowing the orthopedic surgeon to apply corrective forces for prompt pelvic stabilization., (©RSNA, 2014.)