Selected topic: Emergency radiology
Imaging Choices in Occult Hip Fracture

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Abstract

Background: Hip fracture is a common injury, with an incidence rate of > 250,000 per year in the United States. Diagnosis is particularly important due to the high dependence on the integrity of the hip in the daily life of most people. Objectives: In this article we review the literature focused on hip fracture detection and discuss advantages and limitations of each major imaging modality. Discussion: Plain radiographs are usually sufficient for diagnosis as they are at least 90% sensitive for hip fracture. However, in the 3–4% of Emergency Department (ED) patients having hip X-ray studies who harbor an occult hip fracture, the Emergency Physician must choose among several methods, each with intrinsic limitations, for further evaluation. These methods include computed tomography, scintigraphy, and magnetic resonance imaging. Conclusion: We present an evidence-based algorithm for the evaluation of a patient suspected to have an occult hip fracture in the ED. Also outlined are future directions for research to distinguish more effective techniques for identifying occult hip fractures.

Introduction

Diagnosis of hip fractures is particularly important due to the high dependence on the integrity of this structure for people to function in their daily lives. Left unrecognized, patients face increasing morbidity and mortality as time from the original injury lengthens. A delay of just 2 days in surgical treatment for an acute hip fracture doubles mortality (1). In addition, an unrecognized non-displaced fracture may displace, requiring surgery of much higher risk (2). This may be part of the reason that the most frequent lawsuit against Emergency Physicians is for missed orthopedic injury (3).

There are more than 250,000 hip fractures annually in the United States, and that number is increasing as the population ages (4, 5). In fact, a doubling or even tripling of this number is projected by the year 2040 (6). An estimated 15% of the population will have a fracture of the proximal femur by the age of 80 years (7). Not all fractures are obvious clinically or radiographically. Detecting these occult fractures is complicated by the intrinsic limitations of contemporary imaging tools. In practice, a suspicion of hip fracture despite negative X-ray studies usually prompts additional imaging to detect or exclude pathology. Choices include computed tomography (CT), bone scanning, and magnetic resonance imaging (MRI).

In this article we review the literature focused on hip fracture detection and discuss advantages and disadvantages of each major imaging modality. Moreover, we present an evidence-based algorithm for the evaluation of a patient suspected to have an occult hip fracture in the Emergency Department (ED).

Section snippets

Plain Radiography

Imaging typically begins with plain radiography. This will reveal most fractures; however, occult hip fractures are not infrequent. The hip, in particular, is at risk for occult fracture as the proximal femur has a high percentage of trabecular bone, a type of bone in which disruption is more difficult to detect than in cortical bone (2). Figure 1 depicts a radiograph of a patient's hip harboring an occult femoral neck fracture after a fall, whereas Figure 2 shows the same patient who returned

The Patient with Occult Fracture

As the prevalence of occult fracture is significant, determining which patients are at risk for this diagnosis is imperative. Therefore, a physician must determine who belongs in the high- and low-risk groups. This promotes efficient allotment of appropriate imaging and streamlining of resource utilization. The literature gives definition to these groups. A Medline search using various combinations of the search terms “hip,” “femur,” “fracture,” “occult,” and “imaging” produced 17 studies from

Computed Tomography

Computed tomography is readily accessible in the ED and is a chief method of evaluating the multiply injured trauma patient. Addition of the third dimension with CT can often define a fracture when it is not seen on X-ray study, as a two-dimensional X-ray study may not be taken in coincident plane(s) with the fracture(s). However, the same problem is encountered with CT as with plain radiography: resolution of osteoporotic trabecular bone is limited and fracture can lie hidden within. Figure 3

Finding the Occult Hip Fracture

With little support for CT and negative data regarding scintigraphy, the available evidence favors MRI as the diagnostic modality of choice for occult hip fracture. The limited availability in many ED settings to perform MRI underscores the importance of defining low- and high-risk patients to determine appropriate diagnostic methods.

Using available data, we developed an algorithm for patients with hip trauma. A pictorial representation of this algorithm is presented in Figure 5. Clinical

Summary

Hip fracture is a common disease and deserves efficient and precise diagnosis. It has significant morbidity and mortality, which worsens as time from injury progresses. Plain radiographs are usually sufficient for diagnosis as they are at least 90% sensitive for hip fracture. However, in the 3–4% of ED patients having hip X-ray studies who harbor an occult hip fracture, the Emergency Physician must choose among several methods for further evaluation. The right tool is not always easy to pick as

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