Abstract: BACKGROUND: Patellar tendonitis can present as tendon degeneration that fails to heal due to tissue overload and incomplete recovery. Patellar tendonitis is a predisposition to high jumping and its pathogenesis has not been clearly defined.
OBJECTIVE: To explore the stress-strain relationship of patellar tendon in the take-off technique of high jump through the finite element model with accurate human anatomical structure, so as to provide ideas for the prevention and rehabilitation of patellar tendinitis.
METHODS: Based on the CT and MRI imaging data of the lower extremity (including the knee and ankle) of one subject (22 years old, 183 cm height, 70 kg body mass), a three-dimensional finite element model of the lower extremity was reconstructed using medical imaging software, reverse engineering software and modeling software. The plantar pressure of the take-off leg was collected in eight subjects by gait testing system, and the technical action of high jump take-off was collected by motion capture system. The captured data were imported into human sports biomechanics software for analysis, and kinematic and kinetic data were obtained as the boundary conditions of finite element model for finite element simulation analysis.
RESULTS AND CONCLUSION: The force borne by the patellar tendon reached 3.29 times of its own body mass when the subjects took off. In the take-off stage, the peak values of normal equivalent stress, strain and shear stress of the patellar tendon were 127.76 MPa, 0.81 and 37.69 MPa, respectively, which were in the nonlinear region of the stress-strain curve, and the peak values were distributed in the proximal and posterior parts of patellar tendon. To conclude, the high patellar tendon force, strain and shear stress caused by the load of 3.29 times its own body mass during take-off are related to the induction of patellar tendinitis.

Key words: sports biomechanics, high jump, patellar tendinitis, finite element analysis, sports injury, take off, knee joint, mechanism