Biomechanics and Surface Activity in Simulated Body Fluid of Antibiotic Intramedullary Nail

Abstract

Intramedullary nail continues to evolve with the introduction of new technologies as it is considered a gold standard in treating bone defects caused by disease, trauma and accidents which are evidently higher in developing countries like the Philippines. Recently, Philippine Orthopedic Center introduced the usage of Antibiotic Intramedullary Nails (ABIMN), a threaded stainless rod coated with antibiotic cement to treat infections that commonly occurs in bone defects. The product has been widely used, however, no biomechanical study was made to demonstrate and test the coronal bending, cyclic axial loading and chemical properties of the ABIMN. The researchers compared the biomechanical properties and surface activity when immersed in Simulated Body Fluid (SBF) of the Antibiotic Intramedullary Nail (ABIMN), Küntscher Intramedullary Nail (KIMN), and Intramedullary Nail with Interlocking screws (IMNIS). A total of 37 Intramedullary Nail (IMN) models were used for the biomechanical study, while the 4 remaining nails were used for the SBF immersion test. A very high positive correlation between bending rigidity and radius to the 4th power in ABIMN was found. Median Young’s modulus of elasticity on the other hand, significantly differs across the three groups. Further analysis showed that the median value was significantly lower in ABIMN compared to KIMN (p=0.0027) and IMNIS (p=0.0025) concluding that the ABIMN can be left for 6 weeks, with the patient on partial weight bearing up to 25% of an average 75kg man. The chemical properties of the ABIMN however, revealed that it is safe to use and has qualitatively comparable corrosion properties of KIMN when immersed in SBF. For easier removal of the ABIMN and after completion of both oral and IV antibiotics at 6 weeks post op; it still advisable to remove the ABIMN and perform exchange nailing at the said timeframe.