Radiographic Morphology and Method for Localization of the Adductor Tubercle on Anterior-Posterior Knee Radiographs

The adductor tubercle (AT) is a landmark for joint line identification in knee arthroplasty. Up to now, there has not been a dedicated study to define its morphology on an anterior-posterior (AP) radiograph. As a result, radiographic localization of the AT has been inconsistent and confusing. Ten bone specimens, each with the AT labeled with a metal marker, were radiographed to demonstrate the AT appearance on AP radiographs. Based on this knowledge, a method to locate the AT was developed. A total of 200 clinical radiographs were examined to further confirm the observed radiographic morphology with emphasis on the visibility of the AT and its association with the rotational status of the knee on radiographs. One hundred of them were used to test the reliability of this method of AT identification. Of the 200 ATs, 153 (76%) were clearly visible on radiographs as a faint pyramid-shaped shadow protruding outward from the inflexion point of the concave-convex silhouette over the femoral shaft-condylar junction, allowing direct identification. For invisible ATs (24%), this inflexion point was found to be a useful surrogate landmark for their identification. Locating the AT using this technique showed a good intra- and interobserver reliabilities. The proposed method may be valuable for the consistent use of this landmark in joint line identification on radiographs.