Accuracy of intramedullary versus extramedullary tibial alignment cutting systems in total knee arthroplasty

The postoperative standing 51-inch radiographs of 352 total knee arthroplasties were reviewed. The angle formed by the tibial tray to the mechanical axis of the tibia in the coronal plane was measured. The mean deviation from a perpendicular cut to the tibial mechanical axis was not significantly different between tibial cuts made with extramedullary alignment and with intramedullary alignment. With extramedullary alignment, 92% of the cuts were +/- 4 degrees of the ideal 90 degrees cut (perpendicular to the mechanical axis), whereas 94% of the cuts with intramedullary alignment were within 4 degrees of ideal. An analysis of the cuts that erred > or = 4 degrees with intramedullary alignment showed that for the majority the intra-medullary guide rod, if passed down the middle of the tibial shaft in the coronal plane, directly led to the less than ideal cut. In these tibias, bowing deformity in the coronal plane made passage of the intramedullary rod parallel to the tibial mechanical axis impossible.