FTI Headquarters
401 Andover Park East
Seattle, WA 98188 USA

Phone: 206.246.2010
Fax: 206.244.9886

sales@fatiguetech.com

Cold Expansion Products in the Medical Industry


Derived from the aerospace industry, the FTI split sleeve cold expansion has found applications in a diverse array of industries including the medical field.  A proven application is the use of FTI’s technology in Interlocking Intramedully Nails.

Interlocking Intramedullary Nails are used to treat complex femoral or tibial fractures.  The “nail” is used to support and stabilize the bone during the healing process.  These interlocking nails are typically held in place by screws which attach to the bone to the nail.  Although breakages of these nails were rare, the failure was most often associated with the presence of the screw hole - which reduced the local cross sectional area of the nail.  It was speculated that unstable fracture of the interlocking nail was due to an increased level of stress placed on the nail.  Smaller screws, which would reduce the stress concentration, were not the solution because of the potential for broken screws.  Thicker nails would also increase stiffness of the nail system and adversely affect the performance of the inserted nail.

Split sleeve cold expansion of the screw holes was evaluated to shield the holes from the applied stress, which would reduce the peak stress in the region of the screw hole under load.  The study revealed that using the FTI split sleeve cold expansion system resulted in no apparent deformation of the screw holes and a 35% increase in fatigue strength under torsional loading at two million cycles.  For finite life load condition, a near-one order of magnitude improvement in fatigue life at the fixation screw holes may be achieved using cold expansion.  The findings were published by Smith and Nephew in an article titled, “Improved Fatigue Strength of Interlocking Intramedullary Nails.”

For more information on medical applications, please contact us.