Biomechanical prerequisites for patellar tendinopathy after knee arthroscopy

Background. Patellar tendinopathy is a common problem in patients after arthroscopic surgery, accompanied by chronic pain and limitations in knee joint function. The purpose of the study was to conduct a comprehensive biomechanical analysis of the effect of quadriceps hypotrophy on the biomechanics of the knee joint and the mechanisms of patellar tendinopathy development using mathe-matical modelling. Materials and methods. Modelling of bones, li­gaments, and cartilages was performed using SolidWorks 2023 (Dassault Systmes, France) and 3ds Max 2025 (Autodesk Inc, USA). Finite element method research was performed using SimSolid 2023 (Altair Engineering, USA). Results and conclusions. A numerical mathematical model of the knee joint was developed and successfully applied, which made it possible to evaluate the distribution of stresses and contact pressures in the knee joint under controlled load. This model considers the morphometric parameters, physical and mechanical properties of tissues, and also allows modelling scenarios with quadriceps hypotrophy. Modelling the biomechanics of a healthy knee joint at flexion angles of 30, 60 and 90° showed a regular increase in local stress peaks and contact forces with an increase in flexion angle. The maximum stresses were concentrated in the areas of contact between the patella and the femur and near the geo­metry transitions. At 90° flexion, the шpatellofemoral contact force was 2058 N, and the ligament stress reached 3.28 MPa. It was found that quadriceps hypotrophy leads to a significant redistribution of loads in the patellofemoral joint and patellar tendon. There are a pronounced lateralisation of the contact zone and an increase in local stress peaks in the patellofemoral segment. At 30° flexion with hypotrophy, the la­teral force (621.4 N) prevailed over the medial force (221 N), and the stress in the ligament was 2.4 MPa. With quadriceps hypotrophy, there is an increase in stress in the areas of attachment of the tendon and ligamentous apparatus. In particular, at 60° flexion with hypotrophy, the stress in the ligament was 6.8 MPa, and local peaks in the patellofemoral region reached 13.116 MPa. This indicates an increased risk of overload of the lateral structures and tendon. Quadriceps hypotrophy creates conditions for an increase in moments that form an eccentric load (for example, 9.4 Nm at 30° flexion). These moments indicate the formation of a rotational and flexion effect that can increase local stresses and contribute to microtrauma of the ligament.