Biomechanical investigation of the primary stability of intramedullary compression nails in the proximal tibia: experimental study using interlocking screws in cryopreserved human tibias

The biomechanical properties of the proximal tibia with respect to the application of compressible intramedullary nails were examined in a biomechanical model using human cadaver bones. A reference level was examined histomorphometrically in 24 cryopreserved human tibias. Three series of single or double interlocking fixations were tested at various distances from the tibial plateau. Yield strength, rigidity of the bone stock, maximum load, and compression distances were determined during axial strain. The positioning of the interlocking screws had a considerable influence on maximum load and deformation behavior of the bone. The double interlocking tended to display the best stability in the bone stock, and the distally placed single interlocking method was next best. Failure of the bone stock was observed with significant variations in compression distance and load, with great variations between individual specimens. The stability of the bone stock could not be accurately predicted using such clinical parameters as the patient's age, bone dimensions, radiographic parameters, and bone density. When using a tibial compression nail, the proximal interlocking screw should be placed relatively distal to achieve adequate support. It is possible to apply compression with one proximal interlocking screw under low preload or, preferably, with two interlocking screws.