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peak dynamic varus angle over time.Results: TKA corrected static knee alignment from 2.2 (2.5) degrees varus to 3.5 (2.7) degreesvalgus (P < 0.001). Peak dynamic varus angle during gait was reduced from 9.7 (6.5) degrees to3.6 (5.8) degrees at 6 months and 5.2 (7.6) degrees at 1 year (Main Effect of Time; P=0.005).Peak adduction moment was significantly reduced to 85% of pre-op level at 6 months(P=0.037) but subsequently increased to 94% of pre-op level at 1 year (P = 0.539). Post-opimprovement in static alignment did not correlate with the change in adduction moment at anyfollow-up period (P = 0.671). A significant correlation was found between the increase indynamic varus angle and the subsequent increase in adduction moment from the six-month tothe one-year follow-up (P = 0.008).Conclusion: TKA improves knee adduction moment at 6 months but this effect is lost with time(1 year). Despite restoration of static knee alignment and soft tissue balance, loading conditionsat medial compartment remain high, predisposing to medial polyethylene wear, a findingreported by retrieval studies.Friday, October 8, 2010, 8:40-9:50Session B10: Navigation and Robotics in ArthroplastyImproving Accuracy by Patient Specific Instruments*Emmanuel Thienpont - University Hospital Saint Luc - Woluwe, BELGIUM*Email: ethienpont@yahoo.comIntroduction: The importance of frontal and rotational alignment in total knee arthroplasty hasbeen published. Together with conventional instrumentation, computer navigation has beenused for many years now. The pro’s and con’s of navigation are well known since.Materials & Methods: We present the results of our first 200 total knee arthroplasties with aPatient Specific Instrument System, called Signature (Biomet). With this system an MRI of thehip, knee and ankle is performed. Based on these images, mechanical axis and rotationallandmarks are decided. Preoperative planning and templating is done with a computer program.Alignment, rotation, slope, size, positioning and gaps are planned with the software. Based onthis templating a femoral guide and a tibial guide are custom made (Materialise) for eachpatient that will allow only one unique fit and position. Both of these guides are no cuttingguides but pinning guides. From that stage on Vanguard Total Knee (Biomet) is implanted withthis system applying conventional surgical techniques and rules.Preoperative alignment was measured on standing full leg X-rays. Rotational alignment was setaccording to the epicondylar axis. Slope was by default fixed at 3° posterior slope. Femoralflexion was set at 3° by default. Sizing was done with the system. Tourniquet time, blood loss,mean Hb drop and lateral release rate as hospital stay were analyzed. Postoperative full leg X-rays and CT scan were analyzed.Results: Preoperative alignment range between 18° varus and 19° valgus. Sizing was accuratein 82% of cases. Postoperative alignment was accurate in 90% of cases with a range between 0°file:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]