A Novel Method for Evaluating Position of the Stem of Hip Prostheses

This study examined a novel method designed to assess the position of the stem of hip prostheses following Total Hip Arthroplasty (THA). Fifteen hip prostheses were scanned with a CT scanner in accordance with Gruen's zones. At the fourth zoninglayer of CT scanning, an XY coordinate system was attached to CT images. The origin of the coordinate system was placed at the center of the femoral medullary cavity. The X-axis was parallel to the posterior condylar axis of the distal femur; the arrowhead of the X-axis was directed toward the body's midline. Based on this observational methodology, stem tip position in the femoral medullary cavity was readily apparent in CT images when the CT window level ranged from 500 HU (hounsfield) to 600 HU and CT window width was 1500-2000 HU. These data -- including the center-to-center distance (distance between the center of the femoral medullary cavity and the center of the stem tip), the ratio of the center-to-center distance to the radius of the femoral medullary cavity and the quadrant value -- may be treated as the evaluative parameters of stem position in the femoral medullary cavity.