Convened under the auspicious of esteemed endorsers - ISTA

Figure 1: Typical steps used for computer assisted patient specific templating for total kneearthroplastyThe navigation system used in this experiment was VectorVision (BrainLab, Heimstetten,Germany). The navigation was just used as a measurement tool, without playing any role inguiding the observers, while placing the templates, since observers were not facing thenavigation monitor. The routine steps for using navigation systems in TKA 45 were adopted.Two tracking pins were inserted into the distal femur, about a handbreadth from the knee jointand another 2 pins were inserted into the proximal tibia about 2 handbreadths from the kneejoint. The tracking pins were 2 mm each and they served as rigid bodies to which one femoraland one tibial tracker were inserted. Each tracker has at least 3 reflectors (spheres) to reflect theinfrared light, which is emitted by an optical camera. This allowed the camera to track theposition of the trackers in 3 planes. A continuous line of sight has to be maintained between thetrackers and the camera. The optical camera was connected to the navigation system, wheredata were computed and relevant information was displayed in a computer monitor. Anatomicaldata of the plastic knee specimen were collected using a pointed probe that is attached to atracker. These data included a series of landmarks such as the centre of the hip, knee and anklejoints to allow the calculation of the mechanical axis by the navigation system. The centre ofthe hip (centre of the femoral head) was kinemtically calculated by the navigation system whilethe operator rotated the femur in a circular fashion (circumduction). The centre of the knee wasdetermined by touching the midpoint of the distal femur by the tracking probe. The centre of theankle was calculated by the navigation system after touching the medial and lateral malleoli.Epicondylar axis was used to determine the rotation of the femur. The operator collected data onthe bone surfaces by sliding the pointed probe over the surfaces of the distal femur andproximal tibia. The navigation system used all data to create a model specific to the plasticspecimen. This allowed the measurement of alignment, rotation and level of bone cutting in realtime by tracking a tracking plate that was inserted one at a time into the slits of the templatesthat corresponded to the reference bone cuts. This step is typically performed during navigatedTKA, where the tracking plate is inserted into the tibial, distal femoral and anterior femoral slitsof the conventional cutting blocks to measure alignment and level of bone cutting, before actualbone cuts are performed.Each observer was asked to position the tibial templates one at a time, with the tracking platein-situ (Figure 2). The navigation system continuously tracked the position of the trackingplates and subsequently measured alignment (coronal and sagittal) and level of bone cutting,which were displayed on a computer monitor in real time. When the observer was satisfied withthe template position, an independent assessor recorded the measurements that were displayedon the navigation monitor. These measurements were done before bone cutting, as is typicallyperformed, when using navigation systems in TKA. The same process was repeated for thefemoral template positioning, with 5 observers and 5 times each. However, in this case therewere 2 reference cuts and the template was first positioned, with the tracking plate inserted intothe distal femoral slit and then positioned again, with the tracking plate inserted into the anteriorfemoral slit. The distal femoral slit was meant to measure alignment (coronal and sagittal) andlevel of bone cutting and the anterior slit was for femoral rotation.Figure 2: An observer is positioning the femoral template while a navigation system istracking and measuring the alignment and level of bone cuttingfile:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]