Subcapital fractures of the femoral neck: prevalence and cause of radiographic appearance simulating pathologic fracture.

OBJECTIVE Subcapital fractures of the femoral neck are common in elderly persons who have osteoporosis. Occasionally, radiographs of the hip in these patients show a radiolucency in the superolateral, subcapital region of the femoral neck that mimics the features of a pathologic fracture. Our purpose was to determine the prevalence of this finding and the anatomic variations of fracture alignment that cause this appearance. MATERIALS AND METHODS All subcapital nonpathologic hip fractures (n = 111) that occurred at our institution during a 5-year period were reviewed. Radiographs were available in 100 of these cases. Review of intraoperative biopsy specimens, available in 69 patients, revealed no evidence of neoplasm in any case. In the other patients, follow-up radiographs, clinical evaluation, and pathology reports were used to exclude neoplastic involvement. Preoperative radiographs were analyzed for the presence of findings suggesting a pathologic fracture. Fracture configuration was classified by using the Garden staging system. Cadaveric femurs (n = 6) were fractured and studied radiographically. RESULTS Seventeen (17%) of the 100 subcapital fractures had a radiographic appearance similar to that of a pathologic fracture. This finding occurred only with Garden stage III fractures (n = 7, 32% of Garden stage III fractures) or Garden stage IV fractures (n = 10, 24% of Garden stage IV fractures). Study of the cadaveric femoral specimens showed that the radiographic appearance simulating a pathologic fracture was primarily caused by external rotation of the distal fracture fragment and was accentuated by displacement between fracture fragments. CONCLUSION The radiographic appearance of subcapital fractures of the femoral neck unrelated to neoplasm is often similar to that of pathologic fractures. This appearance is caused primarily by rotation of the fracture fragments, and the finding is accentuated by displacement. Recognition of the appearance of subcapital hip fractures mimicking pathologic fractures and knowledge of the cause of this finding are important for prescribing appropriate treatment.