Biomechanical evaluation of a novel orthogonal angle-stable interlocking nail in a canine femur model

Interlockings nails (IN) are orthopedic implants with superior mechanical and, potentially, biological qualities. Despite the countless and indisputable advantages of current angle-stable models, there are still limitations for their use in certain scenarios. The objective of the present study was to describe and biomechanically test a new orthogonal angle-stable intramedullary nail model for veterinary use. The proposed orthogonal angle-stable nail has two 3.8-mm threaded cylindrical holes in each of its portions: in the proximal portion, the holes are 11 mm apart; in the distal portion, the penultimate orifice is positioned at 90 degrees in relation to the last one, with a distance of 5.5 mm between them. The novel orthogonal nail (Group 3 - G3) was evaluated and compared biomechanically with the conventional interlocking nail (Group 1 - G1) and the uniplanar angle-stable nail (Group 2 - G2) by means of destructive torsion and axial compression tests. No statistically significant differences were observed in torsion resistance between the groups in the destructive tests. However, statistical differences were found in stiffness values in the compression tests between the orthogonal (G3) and conventional interlocking (G1) nails (p=0.01) and also between the uniplanar (G2) and interlocking (G1) nails (p=0.001). The new orthogonal nail proved to be biomechanically similar to the uniplanar angle-stable model and superior to the conventional nail. This new arrangement of interlocking screws (orthogonal and closer to each other) potentially enables the fixation of small fragments and at the extremities of long bones in dogs. Nonetheless, further clinical studies are necessary to validate such hypotheses.