The influence of a change in the meniscus cross-sectional shape on the medio-lateral translation of the knee joint and meniscal extrusion.

The purpose of this study was to evaluate the influence of a change in the meniscus cross sectional shape on its position and on the biomechanics of a knee joint.One main finite element model of a left knee joint was created on the basis of MRI images. The model consisted of bones, articular cartilages, menisci and ligaments. Eight variants of this model with an increased or decreased meniscus height were then prepared. Nonlinear static analyses with a fixed flexion/extension movement for a compressive load of 1000 N were performed. The additional analyses for those models with a constrained medio-lateral relative bone translation allowed for an evaluation of the influence of this translation on a meniscus external shift.It was observed that a decrease in the meniscus height caused a decrease in the contact area, together with a decrease in the contact force between the flattened meniscus and the cartilage. For the models with an increased meniscus height, a maximal value of force acting on the meniscus in a medio-lateral direction was obtained. The results have shown that the meniscus external shift was approximately proportional to the meniscus slope angle, but that relationship was modified by a medio-lateral relative bone translation. It was found that the translation of the femur relative to the tibia may be dependent on the geometry of the menisci.The results have suggested that a change in the meniscus geometry in the cross sectional plane can considerably affect not only the meniscal external shift, but also the medio-lateral translation of the knee joint as well as the congruency of the knee joint

The influence of a change in the meniscus cross-sectional shape on the medio-lateral translation of the knee joint and meniscal extrusion - Fig 4

<p>The influence of a change in the lateral meniscus height (red line) or in the medial meniscus height (blue line) on the congruence measurement <i>CM</i> in: a) the lateral compartment, b) the medial compartment and the total contact area in: c) the lateral compartment, d) the medial compartment.</p

Ligament material parameters.

<p>Ligament material parameters.</p

The influence of a change in the meniscus cross-sectional shape on the medio-lateral translation of the knee joint and meniscal extrusion - Fig 8

<p>The influence of the relative bone motion <i>u</i> on the medio-lateral components of the contact forces acting on the femur condyle in: a) model MMH↓↓ with a decreased height of the medial meniscus; and b) model LMH↑↑ with an increased height of the lateral meniscus; CM-L–models with a constrained medio-lateral relative bone motion.</p

A comparison of the average menisci angles and , forces FM-L and relative medio-lateral bone translation u.

<p>The medio-lateral constraint forces <i>F</i>_M-L were calculated for the models with a constrained medio-lateral relative bone motion. A positive value of <i>u</i> denoted the medial relative translation of the femur with respect to the tibia. Intact model with the original geometry of the menisci; models MMH↑, MMH↑↑ with an increased height of the medial meniscus; models MMH↓, MMH↓↓ with a decreased height of the medial meniscus; models LMH↑, LMH↑↑ with an increased height of the lateral meniscus; models LMH↓, LMH↓↓ with a decreased height of the lateral meniscus.</p

The influence of a change in the meniscus cross-sectional shape on the medio-lateral translation of the knee joint and meniscal extrusion - Fig 9

<p>The extrusion forces: a) <i>F</i>_L acting on the lateral meniscus; and b) <i>F</i>_M on the medial meniscus, in a function of the compressive force. Intact model with the original geometry of the menisci; models MMH↑, MMH↑↑ with an increased height of the medial meniscus; models MMH↓, MMH↓↓ with a decreased height of the medial meniscus; models LMH↑, LMH↑↑ with an increased height of the lateral meniscus; models LMH↓, LMH↓↓ with a decreased height of the lateral meniscus; CM-L–models with a constrained medio-lateral relative bone motion.</p

The influence of a change in the meniscus cross-sectional shape on the medio-lateral translation of the knee joint and meniscal extrusion - Fig 3

<p>The influence of a change in the lateral meniscus height (red line) or the medial meniscus height (blue line) on the resultant contact forces between the articular cartilages in: a) the lateral compartment, b) the medial compartment and the resultant contact forces between the meniscus and the tibial cartilage in: c) the lateral compartment, d) the medial compartment.</p

A comparison of the contours of the contact pressures on the tibial articular cartilages for the different knee models: Intact model with the original geometry of the menisci; model MMH↑↑ with an increased height of the medial meniscus; model MMH↓↓ with a decreased height of the medial meniscus; model LMH↑↑ with an increased height of the lateral meniscus; model LMH↓↓ with a decreased height of the lateral meniscus; Δ<i>h</i>_M = ±1.8 mm, Δ<i>h</i>_L = ±2.0 mm.

<p>A comparison of the contours of the contact pressures on the tibial articular cartilages for the different knee models: Intact model with the original geometry of the menisci; model MMH↑↑ with an increased height of the medial meniscus; model MMH↓↓ with a decreased height of the medial meniscus; model LMH↑↑ with an increased height of the lateral meniscus; model LMH↓↓ with a decreased height of the lateral meniscus; Δ<i>h</i>_M = ±1.8 mm, Δ<i>h</i>_L = ±2.0 mm.</p