FINITE-ELEMENT ANALYSIS (FEA) FOR THE POINT-CONTACT FIXATOR - SCREW DRIVE, PLATE DESIGN, OVERCUTS

Finite Element (FE) analysis was performed to ensure that the newly de signed plate for internal fixation, the Point Contact Fixator (PC-Fix) , was at least as strong as existing implants used for the same clinic al indications. The smaller holes of the PC-Fix allow for some reducti on of the cross-sectional dimensions in comparison to a comparable Dyn amic Compression Plate. The cross section of the PC-Fix changes along the length in order to provide for point contacts at the level of the screws and to reduce the strength between the holes. These major geome trical characteristics are produced by a longitudinal undercut and a s et of transverse undercuts. They are supplemented by shallow cuts on t he upper surface of the plate which reduce the effects of bending-indu ced stress concentration. All of these parameters have been optimized by iterative FE analysis. Equal strength requirement resulted in a mod est, but important reduction of the implant size for the critical use in the forearm. In addition, the locking of the conical screw head int o the PC-Fix has been analyzed and optimized in order to ensure proper locking of the screw. This has been achieved by a measured geometrica l mismatch between the screw head and the hole in the fixator. The max imum compressive stress between the screw head and the fixator, which is considered a critical risk for galling, has been reduced by approxi mately 50 percent at the required insertion torque.