Stability characteristics of medial meniscus tear in mild varus knee: a finite element analysis.

Background: Recent studies have pointed out that varus alignment is a potential risk factor for medial overload and the development of osteoarthritis, which may influence the healing of meniscus tears. This study aimed to analyze the stress distribution of radial and longitudinal meniscal tears in mild varus knee and use it to explore the effects of varus alignment, tear type and length on the healing potential of medial meniscal tears.

Methods: A healthy volunteer was recruited, and computed tomography (CT) and magnetic resonance imaging (MRI) scans of the right knee were performed to develop a subject-specific three-dimensional finite element model at a neutral position of 0° and with tibial varus angles of 3°, 6°, and 9°. The model contained bone structures (femur, tibia, fibula) and soft tissues (menisci, cartilage, ligaments). Stable and unstable radial tears and stable and unstable longitudinal tears (located in the white, red-white, or red zones) were introduced in the posterior medial meniscus, followed by finite element analysis.

Results: The peak contact pressure in the medial compartment increased linearly with increasing varus angle (Slope = 1.3599, R² = 0.99223). When the varus increases by 1°, the corresponding peak contact pressure increased by an average of 0.46 MPa. In the case of varus knee, the maximum stress in radial tears was localized at the tear apex. Additionally, the stress of unstable radial tears was higher than that of stable radial tears. The stress distribution on the inner and outer surfaces of longitudinal tears depended on the varus alignment and the tear position. With increasing varus angle, stable longitudinal tears in the red-white and white zones showed a gradual decrease in favourable stress differences(White zone: 0.39 MPa→0.20 MPa; Red-white zone: 0.53 MPa→0.36 MPa), while unfavourable stress differences emerged (White zone: 0.20 MPa→-0.40 MPa, while unfavourable stress differences emerged (White zone: 0.20 MPa→-0.40 MPa; Red-white zone: 0.36 MPa→-0.43 MPa). Unstable longitudinal tears in the white zone exhibited increased unfavourable stress differences(-0.18 MPa→-0.52 MPa). Notably, unstable longitudinal tears consistently demonstrated unfavourable stress differences even under mild varus conditions.

Conclusion: To our knowledge, this study is among the first to investigate the influence of varus alignment on stress distribution in meniscal tears using finite element analysis. This study investigates two types of radial tears and two types of longitudinal tear prototypes in three zones simultaneously. This study provides novel insights into how varus alignment influences stress distribution in meniscal tears, suggesting its potential role in guiding treatment decisions. Future studies incorporating clinical data are warranted to validate these findings.