The position of the joint line in relation to the trans-epicondylar axis of the knee: complementary radiologic and computer-based studies.

Two complementary studies that seek to establish the relationship between the length and position of the trans-epicondylar axis (TEAL) of the distal femur and the position of the knee joint line were presented. A radiologic study of 50 patients having computerized axial tomography of the knee showed that there is a good correlation between TEAL and the depths of the femoral condyles distal to the trans-epicondylar axis. A retrospective review of the anatomical data gathered on 99 patients having computer-assisted total knee arthroplasties (TKAs) provided equivalent information. The 2 studies suggest that TEAL determined by the process of registration, as a preliminary to computer-assisted TKA, can be used to predict the position of the joint line using the derived constant k at a value of 3.4. Thus, the joint line of the knee lies at a distance (TEAL / 3.4) expressed in millimeters from the trans-epicondylar axis. This is potentially very useful information during TKA especially where there is extensive femoral bone loss.