Evaluation of biological and mechanical performance of Nylon 66 in rats for cerclage in orthopedic surgery

Abstract

Steel wires are currently being successfully used in stabilization and fixation of several kinds of fractures in both human and animal orthopedic surgery. In addition, new ceramic and plastic derivates have become available for those purposes. In oder to assess biocompatibility and to evaluate mechanical performance of sterilized Nylon 66 compared to the standard 316L steel wire, an experimental study in rat tibiae was carried out. Nylon 66 was looped extraperiostically around the right tibiae and steel was placed around the left tibiae , in the same animal. Different procedures (autoclave, formalin and ethylene oxid ), were used to sterilize Nylon 66. Mechanical properties (from deformation to rupture) of differently sterilized Nylon 66 were then quantitatively compared. Non-sterelized Nylon 66 served as control. To validate sterilizing procedures, microbiologic tests were performed on all sterilized Nylon 66. Results showed that both Nylon 66 and steel wires failed to induce cellular reaction (inflammation) at the implant sites. Mechanical testing of sterilized Nylon showed that formalin-exposed or autoclaved wires were quantitatively similar, and also similar to controls. Conversely, ethylene-oxid-sterilized material showed less resistance to deformation. Results were analyzed with a non-parametric statistical test (Kruskal-Wallis). All sterilized Nylon 66 samples failed to demonstrate microbiologic growth in cultures at 72 hours. Thus, Nylon 66 could be proposed as an acceptable alternative to steel for use in fracture fixation in small animal orthopedic surgery, since it shares the same biocompatibility and resistance to mechanical deformation properties with the standard (steel). Furthermore, it is an inexpensive material, widely available, and technically easy to handle. Further studies should be performed, however, to verify the results in long-term implanted material.