Influence of intramedullary nail diameter and locking mode on the stability of tibial shaft fracture fixation

Fracture healing is affected by the type and the magnitude of movements at the fracture site. Mechanical conditions will be a function of the type of fracture management, the distance between the fracture fragments, and the loading of the fracture site. The hypothesis to be tested was that the use of a larger-diameter intramedullary nail, together with compressed interlocking, would enhance the primary stiffness and reduce fracture site movements, especially those engendered by shearing forces. Six pairs of human tibiae were used to study the influence on fracture site stability of two different diameters (9 and 11 mm) of intramedullary nails, in tension/compression, torsional, four-point bending, and shear tests. The nails were used with two interlocking modes (static interlocking vs. dynamic compression). With static interlocking, the 11-mm-diameter nail provided significantly (30-59%) greater reduction of fracture site movement, as compared with the 9-mm-diameter nail. Using an 11-mm-diameter nail, the stiffness of the bone-implant construct was enhanced by between 20 and 50%. Dynamic compression allowed the interfragmentary movements at the fracture site to be further reduced by up to 79% and the system stiffness to be increased by up to 80%. On biomechanical grounds, the largest possible nail diameter should be used, with minimal reaming, so as to minimize fracture site movement. Compression after meticulous reduction should be considered in axially stable fractures.