Image Quiz

Hip Pain in an Athletic Fourteen-Year-Old Boy (continued)

Answer: Tension-sided femoral neck stress fracture.


Fig. 1		 Fig. 1 Anteroposterior radiograph of the right hip, made four weeks after the onset of symptoms, showing a nondescript, linear disruption of the normal trabecular pattern (arrow) on the lateral side of the right femoral neck.

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Fig. 2-A		 Fig. 2-A T2-weighted coronal magnetic resonance image showing the fracture line commencing at the cortex of the lateral portion of the femoral neck, with surrounding bone edema and high signal intensity.

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Fig. 2-B		 Fig. 2-B T1-weighted spin-echo coronal magnetic resonance image demonstrating decreased signal intensity in the femoral neck.

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Since the fracture had not responded to nonoperative treatment for several months and because of the potential for displacement and subsequent complications, we recommended operative stabilization. Under fluoroscopic visualization, we performed internal fixation by placing two 7.3-mm cannulated screws percutaneously across the femoral neck without permitting them to extend across the physis. The patient reported a rapid resolution of hip discomfort after the operation. Follow-up radiographs showed satisfactory healing of the fracture. At eight weeks, he exhibited a full, painless range of motion as well as a normalization of gait. Radiographs made at one year revealed good alignment with no evidence of a fracture line (Figs. 3-A and 3-B). At the time of the latest follow-up, 1.5 years after the operation, the patient was symptom-free and had resumed all of his preinjury activities.


Fig. 3-A
Fig. 3-B		 Figs. 3-A and 3-B Anteroposterior (Fig. 3-A) and frog-leg lateral (Fig. 3-B) radiographs, made one year after the operation, showing healing of the fracture in normal alignment.

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Discussion

The differential diagnosis for a child or adolescent who has a limp with pain in the hip or the proximal portion of the thigh is extensive and includes infection, lower-extremity limb-length discrepancy, developmental dysplasia of the hip, slipped capital femoral epiphysis, transient synovitis, Legg-Calvé-Perthes disease, trauma, leukemia, tumor, and fracture. Achieving a correct diagnosis in children can be difficult. In most instances, the information gained from a thorough medical history of the patient, appropriate radiographs, and the physical examination will lead to a proper diagnosis. In particular, the diagnosis of slipped capital femoral epiphysis must be placed high on the list of differential diagnoses for an adolescent; adequate radiographs, physical examination, and, on occasion, magnetic resonance imaging are necessary to rule out this common diagnosis. In the case of our patient, magnetic resonance imaging did not reveal any periphyseal edema, which is a common finding in patients who have a slipped capital femoral epiphysis.

The history of a patient who has a femoral neck stress fracture will usually be consistent with that of an active individual who has recently increased his or her training schedule or intensity. The pain typically is localized to the groin or the medial aspect of the thigh or is referred to the distal portion of the femur or the knee, and it is aggravated by activity or passive internal rotation of the hip. The symptoms can mimic transient synovitis, slipped capital femoral epiphysis, muscle strains, or benign bone lesions. Stress fractures also can occur in pathologic bone in association with tumors, osteoporosis, and rheumatoid arthritis. However, when most of the common diagnoses of a painful limp have been excluded, additional studies will be necessary to determine the exact cause. Basic hematologic studies usually include a complete blood-cell count, determination of the erythrocyte sedimentation rate, and measurement of the level of C-reactive protein to assess the possibility of infection. Additional imaging studies, such as bone scintigraphy, computed tomography, and magnetic resonance imaging, may be helpful. Routine radiographs of the pelvis and hip may not show evidence of a stress fracture for up to four to six weeks after the onset of symptoms. A technetium bone scan is extremely sensitive and may show a stress fracture much sooner than radiographs will; however, such scans are often nonspecific. A technetium bone scan probably would not have differentiated between a compression-sided and a tension-sided stress fracture in our patient, and it may have been misinterpreted as demonstrating a slipped capital femoral epiphysis. Magnetic resonance imaging is a very useful technique because of its increased specificity and its greater ability to identify soft-tissue lesions about the hip. Short tau inversion recovery magnetic resonance images are especially helpful in that they can better delineate the chronology of a stress fracture. They are particularly useful for determining the phase of healing and for ascertaining whether a recurrent or new fracture has occurred at the same site. Also, in comparison with spin-echo images, short tau inversion recovery images have been shown to provide superior contrast between normal and abnormal marrow. Magnetic resonance imaging should be performed when there is concern regarding the possibility of an occult fracture or when there is evidence of increased uptake on bone scintigraphy. Umans et al. showed the value of magnetic resonance imaging in depicting slipped capital femoral epiphysis. Physeal widening was apparent on the T1-weighted images in every case of slipped capital femoral epiphysis, including the case of one presumed so-called pre-slip. T2-weighted images demonstrated synovitis and marrow edema but did not reveal physeal abnormalities. The authors concluded that magnetic resonance imaging clearly delineates physeal changes associated with both pre-slip and slipped capital femoral epiphysis and demonstrates very early changes at a time when routine radiographs and computed tomographic images may appear normal.

In cases of occult fractures, magnetic resonance imaging tends to show areas of low signal intensity on T1-weighted spin-echo images and high signal intensity on T2-weighted images in the area of concern, sometimes exhibiting a continuous so-called black line within the cortex in the high-signal area. Keene and Lash reported the case of a patient who had a negative bone scan but who was later discovered to have a femoral neck stress fracture on the basis of magnetic resonance imaging. There have been other studies, of both children and adults, in which magnetic resonance imaging was the only modality that depicted the femoral neck stress fracture. Cases in which occult fractures have simulated stress fractures on magnetic resonance images also have been reported.

In the case of our patient, the history and the findings of the physical examination were consistent with a stress fracture. Plain radiographs revealed a nondescript abnormality on the lateral side of the femoral neck, and magnetic resonance images were acquired to delineate the nature of the abnormality. These images revealed a tension-sided femoral neck stress fracture that we chose to treat in a manner similar to that used for adults. The patient underwent a successful stabilization procedure with use of two cannulated screws. At the time of the latest follow-up, 1.5 years after the operation, the patient was asymptomatic and had returned to full activities, and there was radiographic evidence of healing of the fracture. Although compression-sided (medial) femoral neck stress fractures may be treated nonoperatively with restriction of weight-bearing and modification of activity, we believe that tension-sided (lateral) femoral neck stress fractures should be stabilized operatively because of the risk of displacement and the associated complications such as osteonecrosis. The clinician should consider a tension-sided stress fracture of the femoral neck in the differential diagnosis of pain and limping in an adolescent.

Reference

1. Lehman RA Jr, Shah SA. Tension-sided femoral neck stress fracture in a skeletally immature patient: a case report. J Bone Joint Surg Am. 2004;86:1292-5.