We refer about our experience in treating of 30 Pts with periprosthetic fractures (15 involved the hip prosthesis and 15 involved knee prosthesis) from jan 2002 to june 2008 with three different kinds of locked plates. The first system used has been the L.I.S.S. based on titanium plates and screws with the screws inserted in the plate by thread holes, the second was the so-called O’Nil system with the steel plates and the titanium screws screwed in a titanium conical insert, the third hardware system was represented by steel screws and plates with the screws screwed on the thread plate hole.

The results have been good and excellent in the most part of the patients, with only one complication regarding a non-union and plate mobilisation settle using a bicortical screws series.

Moreover we present our biomechanical study based on the collaboration with the Mechanical Engineering Department of our University regarding the relationship “screw-plate” using the Finite Elements Method (FEM), outlining the specific features of the three individual system of locked plates.

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.