Ting D, Cabassu JB, Guillou RP, Sinnott MT, Meyer EG, Haut RC, Déjardin LM. Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, MI. Vet Surg 2009 Oct 38 7 881-7 OBJECTIVE: To investigate the effect of fracture configuration on the mechanical properties of standard interlocking nails (ILNs) and a novel angle-stable ILN (ILNn) in bending. STUDY DESIGN: In vitro experimental study. SAMPLE POPULATION: Synthetic tibial gap fracture bone models. METHODS: Bone models, featuring a 5 or 120 mm central defect, respectively, mimicking a simple diaphyseal and a comminuted fracture involving both metaphyses, were implanted with 6 or 8 mm screwed or bolted standard ILNs (ILN6s, ILN6b, ILN8s, ILN8b, respectively) or an ILNn. Specimens were tested in 4-point bending. Construct angular deformation (AD) and slack were statistically compared (P<.05). RESULTS: With increasing gap size, standard ILN construct AD increased significantly by approximately 27% in ILN8b and by up to 105% in ILN6s. Similarly, standard ILN construct slack significantly increased by approximately 33% in ILN8b (from approximately 4.2 degrees to approximately 5.6 degrees) and by up to approximately 130% in ILN6s (from approximately 7 degrees to approximately 16 degrees). Conversely, there was no difference in the ILNn construct AD (approximately 4 degrees) regardless of gap size. ILNn AD was the lowest of all groups and occurred without slack. CONCLUSIONS: This study demonstrated that the angle-stable ILNn provided construct stability regardless of fracture configuration, whereas the intrinsic slack of standard ILNs could jeopardize construct stability in a fracture configuration involving the metaphyses. CLINICAL RELEVANCE: Use of standard ILNs may be optimal in diaphyseal fractures where circumferential nail/cortical contact could augment repair stability. Conversely, the angle-stable ILNn may represent a reliable fracture stabilization method for diaphyseal fractures as well as fractures involving the metaphyseal regions.