Biomechanical impact of progressive meniscal extrusion on the knee joint: a finite element analysis

Abstract

Background: While measuring meniscal extrusion quantitatively is an early risk factor for knee osteoarthritis (KOA), the biomechanics involved in this process are not well understood. This study aimed to investigate the effects of varying degrees of medial and lateral meniscal extrusion and their material softening on knee osteoarthritis progression.

Methods: Finite element analysis (FEA) was utilized to simulate varying degrees of meniscal extrusion (1-5 mm) in 72 knee joint models, representing progressive meniscal degeneration and material softening due to injury. Changes in von Mises stress of the cartilage and menisci and the load distribution on the tibial plateau's meniscus and cartilage were studied under balanced standing posture in both healthy and injured knees, and statistical analysis was performed using Spearman correlation.

Results: Compared to healthy knees, peak stress in medial compartment tissues increased by over 40% with 4 mm of medial meniscus extrusion, and in lateral compartment tissues with 2 mm of lateral meniscus extrusion. Meniscus extrusion reduced the contact load between the meniscus and femoral cartilage but increased it between the tibial and femoral cartilages, with a maximum increase up to fivefold. Spearman correlation analysis indicated that meniscal extrusion significantly affected peak stress and contact loads in the respective knee compartment (p < 0.001), with a lesser impact on the opposite compartment. Notably, medial meniscal extrusion also significantly increased peak stress in the lateral tibial cartilage (p < 0.05).

Conclusions: The quantitative analysis revealed that meniscal extrusion significantly affected the biomechanics of soft tissues within the same compartment, with limited impact on the opposite side. Specifically, Medial extrusion beyond 4 mm significantly affected the biomechanics of the medial compartment, while lateral extrusion over 2 mm had a similar impact on the lateral compartment. Meniscal softening, without altering joint contact characteristics, primarily affected the biomechanics of the meniscus itself, with minimal impact on other soft tissues.

Keywords: Correlation analysis; Finite element analysis; Load distribution; Meniscal extrusion; Von-Mises stress.

Fig. 1

A Clinical radiological data of the knee joint of a 44-year-old female volunteer; B Bone and soft tissue reconstruction of the knee joint; C Meniscal extrusion in clinical radiology and definition of meniscal extrusion model; D Mesh model of the knee and load boundary conditions of the knee joint. PT: Patellar tendon; MCL: Medial Collateral Ligament; LCL: Lateral Collateral Ligament; ACL: Anterior Cruciate Ligament; PCL: Posterior Cruciate Ligament; MFC: Medial femoral cartilage; LFC: Lateral femoral cartilage; MTC: Medial tibial cartilage; LTC: Lateral tibial cartilage; MM: Medial meniscus; LM: Lateral meniscus

Fig. 2

A Comparison of contact area as meniscal extrusion increases. Reproduced with permission from Debieux P et al. (2020). Copyright 2020 Springer Nature. B Comparison of peak von Mises stress in the soft tissues of healthy knee joints. Reproduced with permission from Gokkus et al. (2016). Copyright 2016 Elsevier BV. C Comparison of peak compressive stress in the soft tissues of healthy knee joints. Reproduced with permission from Zhang K et al. (2019) and Li L et al. (2020). Copyright 2019 and 2020 Elsevier BV

Fig. 3

Von Mises Stress contour of soft tissue of knee joint with medial meniscal extrusion. A, C, E respectively represent the stress contour of menisci, tibial cartilage and femoral cartilage under normal meniscus material conditions; B, D, F respectively represent the stress contour of menisci, tibial cartilage and femoral cartilage under softened meniscus material conditions

Fig. 4

Peak stress and its increasing ratio of soft tissue of knee joint. A The peak von Mises stress in the soft tissue of the knee joint with meniscal extrusion; B Proportional increase in peak von Mises stress in knee soft tissues due to lateral and medial meniscal extrusion compared to healthy knees in static standing simulations. Positive values on the horizontal axis indicate medial meniscus extrusion, and negative values indicate lateral meniscus extrusion. -N: with Normal meniscus material; -S: with Softened meniscus material

Fig. 5

Von Mises Stress contour of soft tissue of knee joint with lateral meniscal extrusion. A, C, E respectively represent the stress contour of menisci, tibial cartilage and femoral cartilage under normal meniscus material conditions; B, D, F respectively represent the stress contour of menisci, tibial cartilage and femoral cartilage under softened meniscus material conditions

Fig. 6

The load distribution on the tibial plateau soft tissues as the meniscus extruded. A Percentage change of each load relative to the total load with medial and lateral meniscus extrusion. B Percentage change of each load relative to the total load with meniscus extrusion; C Proportional increase of each load compared to a healthy knee. Positive values on the horizontal axis indicate medial meniscal extrusion, and negative values indicate lateral meniscal extrusion

Fig. 7

A-F The peak stress histogram of meniscus and cartilage as the extrusion of lateral and lateral menisci. Positive values on the horizontal axis indicate medial meniscus extrusion, and negative values indicate lateral meniscus extrusion