Wire cerclage is one of the oldest forms of internal fixation. Cerclage has numerous applications in orthopaedics as a primary method of fracture fixation and as a supplement to other forms of fixation. Traditional wire cerclage, however, has several disadvantages. Monofilament wire is prone to breakage. Multifilament braided cables tend to undergo fatigue failure and fray, releasing metallic particulate debris into the body. Both have a limited ability to maintain compression. This paper presents performance data on a novel flexible, high strength, high fatigue life cable that addresses the inherent problems associated with traditional metal wire cerclage. The iso-elastic cerclage cable consists of a nylon core encased in a jacket of UHMWPE braided fibers. A tensioning instrument tightens the assembly with a metal clasp. Cable assemblies were tested under in vitro static and dynamic loading conditions. Viscoelastic response and wear behavior under in vitro loading conditions were characterized. The iso-elastic cerclage cable displayed an ultimate tensile strength of pproximately 650 MPa and withstood over one million cycles of simulated physiologic load without failure. After 8 weeks of static loading, initial cable tension decreased by approximately 40%. After one million loading cycles against a bone plate, the iso-elastic cable displayed no evidence of fraying or fiber breakage. The ultimate strength of the iso-elastic cable is comparable to that of traditional metal cable while its fatigue strength is clearly superior. After initial relaxation, the iso-elastic cable maintained compressive forces that are typical of the initial compression held by metal cerclage wires. The wear characteristics of the iso-elastic cable are clearly superior to those of multifilament metal cerclage cables. The iso-elastic cable shows high tensile strength and fatigue life. An iso-elastic cable has been developed to compensate for micro-movement within the bone fracture construct while maintaining a continuous compressive force across the fracture.
