Validation of three-dimensional reconstructions of knee anatomy: CT vs MR imaging

This is the first investigation to validate the accuracy of spatial measurements based on computer-generated three-dimensional (3D) reconstructions of CT and magnetic resonance (MR) scans. Standard 3D reconstructions of one fresh frozen cadaveric knee specimen with implanted stereotactic reference markers were created. These reconstructions were based on the data from CT and MR scans performed before and after the resection of extraosseous soft tissues. The distances between the stereotactic reference markers in the 3D reconstructions were compared with the same measurements of the specimen using a Bridgeport milling machine as a precision 3D digitizer. The accuracy of intermarker distance measurements averaged 99% for CT-based reconstructions compared with 97.5% for MR-based reconstructions. Planar slices at a predetermined level and orientation through the femoral condyles were created by sequential milling of the specimen and were compared with reconstructed oblique planar CT and MR slices at the same level and orientation. The accuracy of condylar dimensional measurements was 94% for CT and 93% for MR compared with measurements of the milled slices. Three-dimensional reconstructions based on CT and MR scan data were of equally high quality and were unaffected by the status of the soft tissues.