Tibial intramedullary canal axis and its influence on the intramedullary alignment system entry point in Koreans

Using computerized tomographic data and three dimensional model, we studied the influence of tibial intramedullary canal axis and other morphologic factors of the tibia on the entry point for tibial intramedullary alignment guides. Various anatomical parameters including tibial anteroposterior dimensions (AP), mediolateral dimensions (ML), aspect ratio (ML/AP), bowing and the intramedullary canal axis were studied. In addition, the entry point for the intramedullary alignment guide for primary and revision total knee arthroplasty were studied. The averaged entry point at the level of the tibial plateau was $5.7{\pm}2.2$ mm anterior and $4.3{\pm}2.0$ mm lateral to the classical entry point (P<.001). Furthermore, this entry point was more anterolateral in females when compared to males (P<.001). At a depth 10 mm below the tibial plateau, the entry point was on average $8.8{\pm}1.9$ mm anterior and $2.9{\pm}1.9$ mm lateral to the center of the cut surface. With increasing tibial varus the entry point tended to shift laterally at both levels (r=0.49) (P<.001). In Korean, the entry point for tibial intramedullary alignment systems is anterolateral to the classically described entry point. Moreover, the increment of tibial varus necessitates more lateral placement of the entry point. Intraoperatively, the entry point can be localized during primary knee arthroplasty to a point $15.9{\pm}2.8$ mm anterior to and $1.2{\pm}2.8$ mm lateral to the lateral tibial spine. For revision knee arthroplasty the point is on average $8.8{\pm}1.9$ mm anterior and $2.9{\pm}1.9$ mm lateral to the center of the cut surface of the tibia at a depth of 10 mm from the articular surface.