Differences between extramedullary, intramedullary, and computer-aided surgery tibial alignment techniques for total knee arthroplasty.

Traditionally, intramedullary and extramedullary tibial alignment techniques are used to obtain neutral alignment during total knee arthroplasty. Computer-assisted techniques are available to aid in obtaining alignment intraoperatively. This study analyzed the difference in tibial alignment using intramedullary and extramedullary techniques, and compared them to the resulting tibial axis as determined by a computer navigation system. The tibial alignment standard measure was determined by a spiral computed tomography (CT) study of each lower extremity. Intramedullary techniques resulted in a 1.3 degrees +/- 1.4 degrees of varus alignment and 4 degrees +/- 2.1 degrees increase in posterior slope while the extramedullary techniques resulted in 1.5 +/-1.8 degrees of valgus alignment and 1.8 degrees +/-1.1 degrees increase in posterior slope compared to the navigation system alignment. Direct measurement of metal markers on CT-scan analysis using the navigation system resulted in <0.5 degrees difference from the navigation data. Although the traditional alignment techniques are within a few degrees, the addition of the errors in all planes gives a much higher degree of error. Direct measurement of the mechanical axis using computer-guided surgical techniques for the tibia give a greater degree of accuracy compared to traditional alignment techniques.