| Summary: | The failure of anterior cruciate ligament (ACL) produces abnormal kinematics of the knee joint and leads to knee instability. Graft fixation is the critical issue in the ACL reconstruction especially during the primary post operative period. Interference screw has become as one of the most common used fixation methods for ACL reconstruction. The objectives of this research are to develop the mechanical concept and finite element model of interference screw fixation in ACL reconstruction. Also, to investigate the fundamental mechanical factors that contribute to the primary stability of the fixation such as material properties of screws, screws geometry and screw positioning and alignment. Finite element analysis are conducted and discussed with respect of stress distribution and total displacement. Results show that all investigated factors do influenced the primary stability of the ACL reconstruction. Proper stress distribution and total displacement at the interference screw fixation will enhance the primary stability of the ACL reconstruction. Interference screws with different materials will reflect the graft fixation in the tunnels. Screws with dedicated bio-absorbable materials are believed to represent the best choice in terms of displacement and stress development. In the second case study, the root of the thread of the interference screw is found out to develop more stress under loading compared to other regions. The results obtained show that the more thread the interference screw posses; the stronger the fixation will be and also, the fixation improved with a larger diameter of screw size. Finally, the 3rd study represent the effects of different positioning during the ACL reconstruction procedure. The maximum tunnel and screw deformation occur in 90 degree knee flexion fixation. Minimum tunnel and screw deformation was observed in 60 degree knee flexion fixation. The maximum tunnel and screw stress has been found in 90 degree knee flexion fixation and decreases proportionally to the load and angle of fixation to 60 degree. Outcomes of the study shows that the mechanical factors are important to predict the primary stability of the interference screw fixation of ACL reconstruction.
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