Abstract: BACKGROUND: Recovery of knee joint function and muscle strength is a key focus of rehabilitation after anterior cruciate ligament reconstruction. However, abnormal inter-joint mechanical patterns of the lower limbs may alter lower limb biomechanics during movement and increase the risk of anterior cruciate ligament injury. 
OBJECTIVE: To explore the lower limb biomechanical characteristics of anterior cruciate ligament reconstruction patients during single-leg landing 2 years after surgery, and their correlation with hip joint muscle strength. 
METHODS: Totally 23 subjects who underwent anterior cruciate ligament reconstruction were randomly recruited. The Qualisys three-dimensional motion capture system and AMTI three-dimensional force platforms were used to capture kinematic and kinetic data of both lower limbs during single-leg landing. The Biodex isokinetic muscle testing system was used to measure muscle strength of both hip and knee joints at an angular velocity of 60°/s. Paired sample t-tests were used to compare the biomechanical characteristics of bilateral lower limb joints and the isokinetic muscle strength of the hip and knee joints at 60°/s. Pearson correlation analysis was employed to examine the correlation between kinetic data from the single-leg landing test and the isokinetic muscle strength of the hip and knee. 
RESULTS AND CONCLUSION: (1) At the moment of single-leg landing, patients who had undergone anterior cruciate ligament reconstruction on the affected side showed smaller knee extension angles, smaller ranges of knee flexion/extension motion, smaller vertical ground reaction forces, smaller peak moments of hip extension, hip abduction, and knee extension, and larger hip extension angles and larger ranges of hip flexion/extension motion at the time of contact. (2) During angular movement at 60°/s, the muscle strength of the operated side for hip abduction, hip extension, knee flexion, and knee extension was significantly lower. (3) During single-leg landing, the peak vertical ground reaction force on the operated side was significantly related to the peak hip extension torque and hip abduction strength, while the peak knee extension torque on the operated side was significantly related to the strength of hip abduction, flexion, and extension. (4) The results showed that two years post-anterior cruciate ligament reconstruction, patients fail to regain equal strength on the operated side, possibly due to neural inhibition induced by surgery. To reduce vertical ground reaction force during single-leg landing, they use a hip-muscle-powered buffering strategy. Yet, the operated side's lower hip abduction torque peak also compromises coronal-plane knee stability. Therefore, it is recommended that after anterior cruciate ligament reconstruction, patients continue to do hip and knee strengthening exercises for 2 years, focusing on hip abduction, extension, and knee flexion and extension while specifically including neuromuscular training and sport-specific technique guidance. This will enhance neuromuscular control during movement and prevent negative impacts from faulty movement patterns.

Key words: "> , anterior cruciate ligament reconstruction, single-leg landing, biomechanical characteristics, muscle strength, correlation