ANATOMIC SIGNIFICANCE OF MAGNETIC-RESONANCE-IMAGING FINDINGS IN HIP FRACTURE

This study was done to determine the histologic etiology for the linea r black signal seen on magnetic resonance imaging at the site of proxi mal femoral fractures, No previous satisfactory explanation for this b lack line exists in the literature, To determine the pathologic etiolo gy of this linear black signal, the magnetic resonance imaging appeara nces of osteotomies and fractures of proximal femora were correlated w ith gross and histologic appearances in 12 freshly frozen porcine hips , In phase 1, a unilateral femoral neck osteotomy was performed in 1 h ip, and a sham operation was performed on the contralateral hip, The r adiologist was able to easily determine the site and side of the osteo tomy using magnetic resonance imaging, In phase 2, the remaining 8 fem oral specimens were stressed using the 1125 Instron Materials Testing Machine in a compression mode, In the 8 specimens, 4 fractures were cr eated that were visible on magnetic resonance imaging and plain radiog raphs; 2 fractures were apparent only on magnetic resonance images, an d 2 specimens did not have fractures identified by plain radiographs o r magnetic resonance images, Gross and microscopic analysis of the spe cimens confirmed the magnetic resonance imaging findings in all 8 case s (6 fractures and 2 nonfractures), Histologic evaluation showed trabe cular impaction at the 6 fracture sites corresponding to the linear bl ack signal on magnetic resonance images, No edema or hemorrhage was pr esent in these postmortem specimens, The authors conclude that the low signal band seen with proximal femoral fractures is produced by impac tion of the trabecular bone and is not the result of perifracture edem a or hemorrhage.