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one) in 11 (26%), type II (failure of mechanism holding the liner to shell) in 6 (14%), type III(failure of the bipolar holding mechanism) in one (2%), type IV (dislocation of bipolar) in 9(21%), type V (dislocation of femoral prosthetic head from bipolar) in 3 (7%), and in 1 hip wecould not identify the failure mechanism; There were no instances found of type VI failure(disengagement of the prosthetic head from trunion) or catastrophic polyethylene wear.Conclusion:Constrained tripolar implants are complex devices with multiple interfaces. We have shownmultiple mechanisms of failure of these devices. Avoiding technical errors can reduce thenumber of failures. However, judiciously restricting their use to salvage situations seemswarranted.Friday, October 8, 2010, 15:00-16:00Session A15: Alternate Bearings 2An Original Hip Navigation System to Control Leg Lengthening, Offset andStability Without the Use of the Pelvic Anterior PlaneIntroduction:*Olivier Guyen - Edouard Herriot Hospital - Lyon, FranceVincent Pibarot - Edouard Herriot Hospital - LYON, FRANCESebastien Martres - Edouard Herriot Hospital - LYON, FRANCEChristophe Chevillotte - Edouard Herriot Hospital - LYON, FRANCEJacques Bejui-Hugues - ICOT - Latina, ITALYJean-Paul Carret - Edouard Herriot Hospital - LYON, FRANCE*Email: oguyen@hotmail.comDespite improvements in prosthesis design, the clinical outcome of total hip arthroplasty stillhas 10% failure rate after 10 years. Component malpositioning can lead to instability,impingement, excessive wear and loosening. Computer-assisted procedures are expected toimprove the accuracy of component positioning, and therefore the long-term outcome. Wepresent an original hip navigation system that allows controlling leg lengthening, offset andstability without the use of the pelvic anterior plane.Material and Methods:Because the reliability of the pelvic anterior plane (Lewinnek plane) remains discussed, wepresent a computer-assisted hip replacement using a functional femoral reference plane.Direction and depth of the acetabular reaming and progression of the femoral rasp arecalculated by a sophisticated algorithm, as well as the components’ final position, in order tocontrol leg lengthening and offset. In addition, the ROM to impingement (and therefore thestability) is continuously displayed relative to the position of the components. Simple graphicaland numerical data in addition to virtual instruments displayed on the screen aid the surgeonduring the entire procedure.file:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]