Aims: Several designs are available to the surgeon for internal fixation with plates. This study compares the mechanical behaviour of three different designs for screw-plate locking: threaded screw head (Type1), conical joint with titanium insert (Type2) and spherical 3-point wedge-locking (Type3).

Methods: 3D-CAD and FEM models were used to simulate the behaviour of each device component. Two typical loading conditions were considered in order to characterize joint mechanics: screw tension and bending.

Results: The screws performances were compared in terms of stress concentration factors (SCF) with reference to the screw nominal diameter. In particular, Type3 device exhibits a strong influence of screw tightening on SCF. Results can be summarized as follows:

Tension: SCF_T-Type1=4.8; SCF_T-Type2=3.2; SCF_ T-Type3=11.7;

Conclusions: With respect to classic Type1 screw, Type2 device provides a better load distribution while Type3 system offers pivoting capabilities at the expenses of higher stresses acting on the joint.