A generic precurved interlocking nail is more compatible with femoral and tibial morphology than a straight nail in dogs.

Objective: To study the morphology of canine and feline femurs and tibias in lateral radiographic projections and assess their compatibility with either a straight or a curved full-length interlocking nail (ILN).

Methods: Lateral projection radiographs of 50 tibias and 50 femurs (10 cats and 40 dogs per bone) were used to measure the minimum and maximum radius of curvature of an ILN compatible with each bone. These radii were defined by cranial and caudal endosteal points at the proximal entry point of the nail, at the isthmus, and at the most distal point of the ILN insertion into the femoral or tibial metaphysis. These points were figured by 2 proximal circles, 2 diaphyseal circles at the isthmus, and 2 distal circles in distal metaphyses of the bones. The diameter of these circles corresponded to 75% of the medullary canal width at the isthmus of the bone.

Results: An ILN with a radius between 750 and 806 mm fit 87% of all the bones reviewed. In dogs, an ILN within this radius range would fit 95% of the tibias, whereas a straight ILN would fit only 50%. For femurs, the curved ILN would fit 80% compared to 37.5% for a straight ILN. In cats, an ILN with a radius between 750 and 806 mm would fit 85% of the bones (femur, 100%; tibia, 70%), whereas a straight ILN would fit all tested bones.

Conclusions: A full-length ILN with a radius of curvature between 750 and 806 mm would fit 87% of the studied bones, whereas only 55% of them could accept a straight ILN.

Clinical relevance: A full-length ILN with a 750-806-mm curvature radius may provide a suitable option for treating most femoral and tibial diaphyseal fractures.