Biomechanical considerations in 'biological' femoral osteosynthesis: an experimental study of the 'bridging' and 'wave' plating techniques.

Although traditional compression plate fixation aims to abolish interfragmentary movement and achieve primary bone healing, the more recent 'biological' plate fixation methods such as the 'bridging' and wave' plate techniques aim to maintain fracture alignment without absolute stability and promote union by callus formation. Furthermore, some mechanical advantages have been attributed to the 'wave' plate fixation. Since no data have been published on the mechanical characteristics of the 'bridging' and 'wave' plate fixation methods, the aim of this biomechanical comparative study was to investigate the rigidity of those fixation methods in various types of femoral diaphyseal fractures. Using a composite femoral model, the rigidity characteristics of three fixation methods (short DCP, 'bridging' and 'wave' plates) were investigated. The results showed that when cortical contact between the main fragments is present, a 'bridging' plate can be equally rigid to the 'wave' plate in mediolateral bending by displaying a similar tension-band effect. Furthermore, in the absence of cortical contact, the axial fixation rigidity of the long 'bridging' plate is superior to that of the 'wave' plate. Both methods showed a significant 'stress-shielding' effect on the intact femur. In conclusion, this in vitro study failed to show any significant mechanical advantages of the 'wave' plate technique over the 'bridging' plating method. It appears that the 'bridging' plate fixation may be the mechanically optimal 'biological' plating method for the femoral diaphysis.