Methods

Between March 2012 and May 2012 thirty consecutive patients with primary gonarthrosis were selected for unilateral total knee arthroplasty (TKA) using a handheld surgical navigation system to perform the tibial resection.

Navigation procedure: The entire system is provisionally secured to the tibia using a spring placed around the leg and is fixed to the proximal aspect of the tibia using 2-headed pins. Before fixing the system proximally, an aiming arm is used to align the top of the device with the anterior cruciate ligament footprint and the medial one third of the tibial tubercle. Distally, a footplate connected to the tibial jig is used to keep the EM jig a set distance off of the tibial surface. A gyrometer within the navigation unit is then able to calculate the posterior slope of the tibial jig. Subsequent anatomical landmarkings of both the lateral and medial malleoli are identified using the distal aspect of the EM jig to establish the tibia's mechanical axis. Similarly, the gyrometer within the navigation unit is able to calculate the varus or valgus alignment of the tibial jig relative to the tibia's established mechanical axis. Once anatomical registration has been performed, the tibial cutting block is placed at the proximal aspect of the device, and real-time feedback is provided by the navigation unit to the surgeon, who is then able to set the cutting block's varus/valgus and posterior slope alignment before performing the tibial resection.

Postoperatively, standing anteroposterior hip-to-ankle radiographs and lateral knee-to-ankle radiographs were performed to determine the varus/valgus alignment and the posterior slope of the tibial components relative to the mechanical axis in both the coronal and sagittal planes. The difference between the intraoperative reading of the tibial varus/valgus alignment and posterior slope provided by the system was compared to the radiographic measurements obtained postoperatively for each respective case. Differences were analysed via standard t test. The critical level of significance was set at P <0.05.