To distinguish segmental impaction from avascular necrosis of the femoral head, 26 consecutive patients who sustained an acute displaced acetabular fracture were assessed preoperatively with routine radiographs, computed tomography, and radionuclide imaging using pinhole collimation and single photon emission computed tomography (SPECT). The diagnostic criterion for avascular necrosis was a photopenic defect of the femoral head, whereas, the criterion for segmental impaction was an area of impaction of at least 1 cm2 noted at the time of surgery. Of this series, 3 incurred a segmental impaction while 1 showed evidence consistent with avascular necrosis on SPECT imaging. None of the patients possessed diagnostic features of both complications. The distinction between these two complications of an acetabular fracture should contribute to the application of appropriate surgical techniques to correct segmental impaction and avascular necrosis.
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Gruen et al. (1988) studied this question.