Abstract: BACKGROUND: The medial patellofemoral ligament reconstruction is the most commonly used method for the treatment of lateral dislocation of patella at present. The ultimate goal is to adjust the patella to the normal anatomical position and restore the patella track. Currently, the main core problem of medial patellofemoral ligament reconstruction is the selection of its femoral end fixation point.  
OBJECTIVE: Finite element method was used to analyze the limiting effect of the reconstructed medial patellofemoral ligament on the patella at different flexion angles of the knee joint, and to simulate the limiting effect of medial patellofemoral ligament reconstruction at different fixation points of the femoral end on the patellofemoral end, so as to provide help for the selection of fixation points of the femoral end during the reconstruction of the medial patellofemoral ligament.
METHODS: A finite element model of knee including bone and soft tissue was established according to the extracted CT and MRI data of knee joint. When the knee flexion angle of 30° and 60° was simulated, the medial patellofemoral ligament was constructed by selecting different fixation points of femur end. The contact stress and contact area between patellofemoral joints at different points were compared, as well as the transverse binding force on patella. The equilength of the medial patellofemoral ligament constructed from the same fixation point of the femoral end at different flexion angles was verified to study the effect of various reconstruction positions of the medial patellofemoral ligament.  
RESULTS AND CONCLUSION: (1) A three-dimensional finite element model of the knee joint at 30° and 60° flexion angles was established to construct the medial patellofemoral ligament at different fixation points of the femur end. The medial patellofemoral ligament constructed at the same position of the femur end had usable isometric length at different flexion angles. (2) After the lateral displacement of the patella, in the transverse direction, the medial patellofemoral ligament constructed at different fixed points of the femur end produced different transverse binding force on the patella, and the transverse binding force was maximum at the anterior 10 mm and minimum at the proximal 5 mm. In the longitudinal direction, the location and size of stress concentration points on the patella cartilage were roughly the same, and the contact pressure did not change much. However, the contact area between the patella cartilage and the femoral cartilage was significantly different, with the maximum contact area at 10 mm at the front end and the minimum contact area at 5 mm at the proximal end. (3) The medial patellofemoral ligament constructed at the center of the saddle region has a good lateral restriction on the patella, but does not cause excessive restriction on the patella in the longitudinal restriction, and can achieve a good restriction on the patella.

Key words: medial patellofemoral ligament reconstruction, medial patellofemoral ligament, knee joint, finite element, fixation point of femur end, saddle area