Introduction In a Finite Element Analysis we calculated that in order to obtain a dynamic plate osteosynthesis a long plate with few screws and if possible no lag screw must be applied. These principles were employed in most shaft fractures at our institution since January 1999. We present the preliminary results of tibial shaft fractures treated with dynamic plate osteosynthesis.

Methods Forty-seven consecutive patients treated from January 1999 until August 2001 were followed clinically and radiologically. Fractures of the distal third and mid-shaft not suitable for a nail such as anatomical bends or narrow intramedullary canal were fixed with a long plate (titanium LCDCP) and few screws. In eight cases no lag screws were used. Six fractures were open fractures. Two cases needed a local flap for coverage of the defect.

Results There were no deep infections. There was one delayed union necessitating re-osteosynthesis and cancellous bone graft after four months. All other fractures healed within six months. No axis deviation was noticed. Due to the dynamic osteosynthesis all cases without lag screws healed with visible callus formation. However, breakage of three screws was seen.

Conclusion Intramedullary nails have become the gold standard for most tibial shaft fractures. However, a significant risk of malunion is associated with nails and in some anatomical instances a nail is not feasible. Dynamic plate osteosynthesis allows good bone healing with callus formation and restores length, axis and rotation of the bone. We consider it a safe and biological method for the treatment of most tibial shaft fractures.

Introduction: For plate osteosynthesis (OS) many surgeons use a rigid fixation which prevents callus formation. The present paper applies biomechanical laws and a FE analysis for optimal screw placement to turn a rigid plate OS into a dynamic and biological OS.

Methods: A Finite Element Analysis was performed. The bone was modeled as a cylinder with an outer diameter of 30 mm and an inner diameter of 22 mm. An E-modul of 18 GPa was assumed for cortical bone. A DC steel plate was modeled with a preload of 300 N for each screw. Fracture motion and stress on the screw head was calculated for different screw placements and a load of 300 N angulated at 30 deg.

Results: The number of screws did not influence fracture motion. This could only be controlled by the distance of the first screw to the fracture site, the use of a lag screw and the material of the plate. When one screw hole was omitted close to the fracture site, motion doubled. Using A lag screw reduced fracture motion dramatically. The stress was greatest at the screw closest to the fracture site.

Conclusions: In order to achieve a dynamic plate OS with callus formation a long plate with a minimal amount of screws and no lag screws should be used. To adjust the flexibility of the OS, the distance of the first screw to the fracture site is the most crucial parameter. Additional screws do not influence the stiffness. The stress is highest at the screw head close to the fracture site. This screw is endangered for fatigue failure. To reduce the stress on this screw it must not be placed oblique and also not eccentric. However, the last screw has little stress and should be placed oblique to increase the pull out strength.