Abstract: BACKGROUND: The kinematic and kinetic characteristics of the knee joint during the different movements of patients undergoing anterior cruciate ligament reconstruction have been analyzed. Herein, it is assumed that patients undergoing anterior cruciate ligament reconstruction have higher von Mises stress in the anterior cruciate ligament on the unaffected side than on the affected side and lower von Mises stress in the meniscus and femoral cartilage on the unaffected side than on the affected side during stop-jump maneuvers.
OBJECTIVE: To investigate the stress response characteristics of the soft tissue of the knee on the unaffected and affected sides of patients undergoing anterior cruciate ligament reconstruction in order to provide a reference for reducing secondary injuries such as secondary anterior cruciate ligament injuries and chronic knee osteoarthritis in this population.  
METHODS: Kinematic and kinetic parameters of the knee joint were acquired during the stop-jump maneuvers in patients with anterior cruciate ligament reconstruction using an infrared spot motion capture system (Nokov) and a force measuring platform (Bertec). The three-dimensional angle and torque parameters of the knee joint were obtained by the Euler angle calculation method and inverse dynamics. The three-dimensional angle and torque, used as boundary and loading conditions, were then loaded into the finite element model of the knee joint, and numerical simulations were subsequently performed to compare the stress distribution of the internal structure of the knee joint on the unaffected and affected sides under actual motion loads.
RESULTS AND CONCLUSION: At the peak of the first horizontal posterior ground reaction force, the flexion and adduction angles of the affected knee were significantly greater than those of the unaffected side, and the vertical ground reaction force was higher on the unaffected side than on the affected side. In addition, the peak vertical ground reaction force of the unaffected side appeared when the stop-jump maneuver was performed by 4%-6%, and that of the affected side appeared when the stop-jump maneuver was performed by 15%-17%, showing the unaffected leg lands earlier than the affected side. Finite element analysis results showed that the peak value of anterior cruciate ligament von Mises stress on the unaffected side was higher than that on the affected side (28.47 MPa vs. 13.18 MPa). The maximum stress on the unaffected side occurred at the posterior tract of the anterior cruciate ligament, while that on the affected side was mainly distributed in the anterior femoral end of the anterior cruciate ligament. In addition, the von Mises stress peak values of the affected femoral cartilage (12.16 MPa vs. 5.342 MPa) and meniscus (17.35 MPa vs. 16.18 MPa) were greater than those of the unaffected side. The corresponding maximum stress peaks were located at the edge of the lateral condyle of the distal femoral articular cartilage and the edge of the anterior horn of the lateral meniscus, respectively. Finite element simulation indicated that the risk of anterior cruciate ligament injury on the unaffected side might be greater than that on the affected side. Furthermore, knee osteoarthritis could be aggravated by a higher stress on the affected femoral cartilage and meniscus. Overall, the rehabilitation training programs for patients undergoing anterior cruciate ligament reconstruction should not only pay attention to the rehabilitation training of the affected knee, but also focus on the abnormal movement pattern and compensation mechanism of the unaffected knee.

Key words: anterior cruciate ligament reconstruction, stop-jump, femoral cartilage, meniscus, stress, finite element analysis