2 Skeletal Assessment of Fractures of the Proximal Femur
Evaluation of the painful hip is a daily occurrence in most hospital settings. A painful hip is most commonly seen in the elderly osteoporotic population. Plain film radiographs are the initial study of choice to evaluate these patients.
Although most proximal femur fractures are easily detected on routine x-ray studies, nondisplaced fractures of the hip are a reality and a challenge for imagers and surgeons alike. Radio-occult fractures of the hip are fractures that escape detection on routine x-ray imaging. A high index of suspicion is needed for patients in excessive pain or those refusing to bear weight. When the clinical situation does not correspond to a “negative hip x-ray,” these patients warrant further investigation. Imaging choices include computed tomography (CT), magnetic resonance imaging (MRI), and bone scan. Bone tomograms are of historical interest but are no longer performed. Rapid diagnosis and early treatment of occult fractures are in the patient’s best interest because this approach reduces the chance that a nondisplaced fracture will displace, a situation that requires more invasive management and increases morbidity.1
The routine radiographs used to evaluate hip fractures include anteroposterior (AP) and lateral views of the hip (Fig. 2-1). Frog leg views are not recommended in an acute hip fracture for fear of dislocation or displacement of fragments. An AP view of the pelvis is also recommended because so many elderly patients with hip pain and inability to bear weight have pubic rami fractures, which may be more visible on the pelvic x-ray film. In suspected cases of avascular necrosis (AVN) of the hip, a frog leg view can be helpful to evaluate for subchondral fracture of the femoral head (Fig. 2-2).
Figure 2-1 A, Anteroposterior radiograph of the left hip shows an intertrochanteric fracture. B, Lateral radiograph of the left hip shows anterior displacement of the femoral shaft relative to the neck. The ischial tuberosity is an excellent anatomic landmark that is posteriorly located.
Figure 2-2 A, Frog leg radiograph of the hip shows a subchondral radiolucent fracture line referred to as a crescent sign. This indicates a relatively advanced stage of avascular necrosis (AVN). B, Anteroposterior radiograph of another hip with a more advanced stage of AVN, with fracture and depression of the articular surface of the femoral head.
The choice of CT, MRI, or bone scan depends partly on what is available to patients. For example, some centers do not offer nuclear medicine imaging at night or on weekends. In addition, some MRI technologists are available only on an on-call basis after hours, and this service is generally reserved for dire emergencies such as spinal cord compression. Some institutions have a 24-hour in-house CT technologist, so it is much easier for an emergency department patient to obtain a CT scan than an MRI. Hence, CT is often the next imaging test used to follow up on an equivocal or negative hip x-ray study at some institutions.
CT is a modality that is often readily available in the hospital setting, especially after hours. The CT imaging protocol has changed significantly in the last few years. Thin-cut slices that are 0.6 mm thick have become routine, whereas in the past much thicker slices, such as 3-mm cuts, were used. The older, thick slices had very choppy reformations, which made fracture detection more difficult. Today’s thin slices allow one to obtain beautifully detailed coronal and sagittal reformatted images (Fig. 2-3). Reformatted images, especially in the coronal plane, are recommended and often show a proximal femur hairline fracture more clearly (Fig. 2-4). In theory, the use of only axial imaging may fail to reveal fractures that are parallel to the axial imaging plane.2
Figure 2-3 A, Anteroposterior radiograph of the right hip shows an intertrochanteric fracture. B, A computed tomography (CT) scan was performed to evaluate for other fractures in this 29-year-old male cyclist who fell off his bike. Coronal reformatted CT image shows an impacted intertrochanteric fracture. C, Axial CT image in same patient, displayed on soft tissue windows. The fat-fluid level indicates lipohemarthrosis.
Figure 2-4 Coronal reformatted computed tomography image shows a subtle hairline intertrochanteric fracture. The plain film was negative, even in retrospect.
CT can be vital to operative planning in the established proximal femur fracture. This imaging technique allows excellent assessment of intra-articular bone fragments, such as in a patient with a history of hip dislocation3 (Figs. 2-5 and 2-6). It also shows such fine bony detail that articular collapse can be assessed in cases of AVN.
Figure 2-5 A, Anteroposterior radiograph in a 55-year-old man who fell onto his backyard deck shows anterolateral dislocation of the femoral head. B, Cross-table lateral radiograph of the hip shows anterolateral dislocation of the femoral head. C, Coronal reformatted computed tomography image of the hip performed after reduction shows a large osteochondral impaction injury of the superolateral aspect of the femoral head. The femoral head is located well within the acetabulum, and no intra-articular fracture fragments were found.
Figure 2-6 A, Anteroposterior radiograph taken after reduction of a hip dislocation. A vague lucency is noted in the superolateral femoral head and neck. A tiny linear bone fragment is noted inferior to the femoral head. B, Axial computed tomography image of the same patient performed within 1 hour of A shows an oblique fracture of the femoral head. A small fracture fragment lies at the posterior wall of the acetabulum, and a subtle intra-articular bone fragment was identified.
One study showed MRI to be a more accurate modality than CT scan for early diagnosis of occult hip fractures4 (Fig. 2-7). The image slice thickness in that study was 3.2 mm, much thicker than what would be used today.
Figure 2-7 A, Axial computed tomography (CT) image of the right hip shows a hairline fracture of the superior aspect of the femoral neck. B, Anteroposterior radiograph in the same patient shows a hairline vertical fracture of the superior femoral neck. A hip fracture was not suspected clinically in this 28-year-old female intravenous drug abuser who gave no history of trauma. The CT scan had been performed to rule out intramuscular abscess.
A CT scan takes approximately 5 minutes to perform, although patient immobility may increase this time because it may take longer to transfer the patient from the hospital stretcher to the CT table. The actual scanning time is approximately 30 seconds; therefore, CT may be preferred in patients who are unable to remain still. CT scan of the pelvis is not degraded by quiet respiratory motion, but it is degraded by patients who cannot keep still for 30 seconds, such as demented elderly patients in extreme pain.
Magnetic Resonance Imaging
MRI is excellent at detecting occult fractures. A study of 15 osteopenic patients with normal plain radiographs and suspected hip fractures were imaged with MRI. Ten of the 15 patients showed a clear fracture on MRI, and these patients then underwent surgery based on the MRI study. The other 5 patients had no fracture noted on MRI and were successfully treated nonoperatively.5 MRI can also delineate disorders adjacent to fractures, such as infarcts or metastases, and nonsurgical entities such as pubic rami fractures (Fig. 2-8), bursitis, and muscle strain (Fig. 2-9).
Figure 2-8 Coronal T1-weighted magnetic resonance image in a patient with hip pain shows a low signal intensity fracture line in the superior pubic ramus.
Figure 2-9 Axial T2-weighted magnetic resonance imaging scan with fat saturation in an elderly woman who would not bear weight. Note the extensive high signal intensity throughout the adductor muscle group. An inferior pubic ramus fracture is also noted, and it was better seen on the T1-weighted image (not shown).