Knee biomechanics in the deep squatting state after unicompartmental knee arthroplasty versus high tibial osteotomy: A 3-dimensional finite element study

Objective: Knee osteoarthritis (KOA) often necessitates surgical interventions like unicompartmental knee arthroplasty (UKA) and high tibial osteotomy (HTO), but their biomechanical responses during deep squatting. This three-dimensional finite element analysis (FEA) aimed to compare the mechanical behaviors of knees treated with UKA and open-wedge HTO (OW-HTO) during 120° squatting, providing insights for postoperative mechanical evaluations and patient management. Methods: Laser 3D scanning/MRI/CT data were used to construct 3D finite element models of the healthy knee, KOA knee, UKA knee and OW-HTO knee in 120° flexion conditions, and mechanical loads in the deep squat condition were applied to assess the stresses on the meniscus, cartilage, bone, ligaments, and implants under deep squat conditions. Results: The results showed that in the normal knee during deep squatting, the menisci had a symmetrical stress distribution. In KOA knees, there were significant stress increases and concentrations in the menisci, cartilage, and subchondral bone. UKA effectively reduced lateral meniscus stress, lateral femoral cartilage stress, and ligament stresses, restoring a more normal mechanical environment. In contrast, OW-HTO knees still had high meniscal, cartilage, and bone stresses, similar to the KOA state. The maximum stresses in the implants of both UKA and OW-HTO approached the fatigue limits of their materials, and high stresses at the bone-implant interfaces might lead to complications such as aseptic loosening. Conclusion: This study tentatively suggests that UKA is suitable for patients with high-frequency flexion demands, but there is a risk of aseptic loosening and fragmentation of the prosthesis, whereas HTO is suitable for young, well-boned patients with predominantly extra-articular deformities. Regardless of the procedure, prolonged knee flexion at large angles should be avoided to improve the prognosis.