# In vivo kinematics of knee joint cartilage and meniscus contact areas under load application: a biomechanical MRI study

## TL;DR

This study uses MRI to track how knee cartilage and meniscus move under load, revealing how the meniscus stays stable in healthy knees.

## Contribution

The study provides a physiological baseline for in vivo knee joint mechanics and meniscus behavior under load.

## Key findings

- Axial loading increased cartilage-to-cartilage contact more in the medial than lateral compartment.
- Meniscus-to-cartilage contact decreased with loading, but tibial-meniscal contact remained stable.
- The meniscotibial ligament likely prevents excessive meniscus extrusion at the tibial interface.

## Abstract

Distinguishing physiological meniscus mobility from pathological extrusion remains a clinical challenge, particularly regarding the prevention of osteoarthritis. While cadaveric studies suggest that meniscectomy increases contact stress, the in vivo dynamics of the healthy meniscus under load—specifically the role of the meniscotibial (coronary) ligament—remain poorly defined. This study aimed to establish a physiological reference standard for load transmission and contact area kinematics in the healthy knee.

In a biomechanical MRI study, nine healthy male subjects underwent high-resolution 3T MRI with prospective motion correction. Knee joints were scanned in an unloaded state and under a physiological axial load of 400 N. We performed 3D segmentation to quantify changes in cartilage-to-cartilage and cartilage-to-meniscus contact areas, differentiating between femoral and tibial interfaces.

Axial loading significantly increased the direct cartilage-to-cartilage contact area, with a predominant increase in the medial compartment (+ 15.0%) compared to the lateral compartment (+ 6.7%), reflecting the physiological adduction moment. Conversely, the overall meniscus-to-cartilage contact area decreased. A detailed compartmental analysis revealed a distinct kinematic pattern: while the femoral-meniscal contact area significantly decreased due to relative motion, the tibial-meniscal contact area remained stable.

This study defines the in vivo healthy baseline of knee contact mechanics. The results demonstrate that under physiological load, the healthy meniscus undergoes controlled radial displacement to facilitate direct cartilage contact. Crucially, the stability of the tibial contact area supports the hypothesis that the meniscotibial (coronary) ligament acts as a primary anchor, preventing excessive extrusion at the tibial interface. These data serve as a vital benchmark for evaluating meniscus repair techniques and differentiating physiological mobility from pathological failure.