## 4 Discussion  
Fractures of the tibia are common injuries of the lower extremities occurring both in young and old age people. In particular, proximal fractures are approximately 11% of all fractures of the tibia [40] and, among these, plateau fractures are the most common representing about 9% of all tibial fractures [4; 41]. If these fractures are not suitably treated to restore the articular surface or the limb alignment, and to allow early knee motion, both a marked decrease in the range of motion and joint  
Figure 11: FEM analysis results: pressure maps at the screw/tibia interfaces. Figure 12: Position of screw n.7. instability can occur [8]. To avoid the above-mentioned complications, a surgical approach is needed to reduce the fracture, restore joint anatomy and mobility, as well as axial alignment of the limb and to allow early mobilization [42; 43; 44]. Thus far, the clinical treatment of complex tibial plateau fractures is still a challenge. Regarding Schatzker type I fractures, one of the most common surgical approaches is plate fixation with locking screws to achieve a very stable construct [2], thereby ensuring a good osteosynthesis. Locking compression plates in fact minimize local damage to soft tissue and blood supply of the periosteum, and show a low incidence of non-union and infection, hence giving very good results in terms of functional rehabilitation and clinical therapeutic effects [41; 45; 46]. Unfortunately, this kind of fixation technique requires, post-operatively, a non-weight-bearing period of up to eight weeks [2]. This long period of inactivity can impair the patient's functionality and can also affect the articular cartilage [27]. For this reason, it would be very interesting to understand how various design parameters (e.g., screw orientation, plate positioning, etc.) affect the stability of the construct. A more stable fixation system could in fact allow reduction of the non-weight-bearing time, thus reducing the negative effects on a patient's functionality and speeding up the healing process. Several studies have been performed on this topic, focusing mainly on how the stability of the construct is influenced by the type and number of screws [17; 47], or by the shape or positioning of the plate [8; 18; 39; 48; 49]. This study investigates how the position of the screws affects the stability of proximal tibial fractures treated with locking compression plates. A numerical approach was used and four different screw configurations were analysed. The stability of the different configurations was measured in terms of the reaction force, which is directly proportional to the force necessary to cause the mobilization of the fractured bone fragment, and to the maximum value of pressure at the screw/tibia interfaces which can cause bone damage and consequently screw-loosening and implant instability. Therefore, more stable configurations can be characterised as having a high reaction force and a low pressure at the screw/tibia interface. From the analysis of the obtained results it emerged that the orientation of the screws does not affect the reaction force. As a matter of fact, the reaction force variation was almost negligible for all configurations. Instead, when it comes to the maximum contact pressure at the screw/bone interfaces (Figure 13), a remarkable influence of the orientation of the screws was detected. Configuration N.2 has the lowest value, equal to 384.05 MPa, which is about 38% less than the highest value (563.48 MPa) calculated for configuration N.4. This means that for the specific type of fracture analysed (Schatzker type I), configuration N.2, among those analysed, ensures the highest level of stability of the construct. Of course, even if the obtained result is valid only for the specific case analysed, the adopted approach can be used to study other different types of fractures in order to find the best configuration on a case-by-case basis.