Eine neuartige Knieendoprothese mit physiologischer Gelenkform

Abstract

The natural tibiofemoral joint (TFJ) functions according to a roll-glide mechanism. In the stance phase (0-20 degrees flexion), the femur rolls backwards over the tibia plateau, while further flexion causes increased gliding. This kinematics is based on the principle of a quadruple joint. The four morphological axes of rotation are the midpoints of the curvatures of the medial and lateral femoral condyles and the medial and lateral tibia plateau. In addition, the medial and lateral compartments are shifted a few millimetres in a sagittal direction, the medial tibia plateau being concave and the lateral plateau convex. In most knee arthroplasties, these factors are not taken into account; instead they are equipped with symmetrical medial and lateral joint surfaces. Thereby, the midpoints of the curvatures of the sagittal contours of the lateral and medial joint surfaces, on the femoral as well as on the tibial sides, create a common axis of rotation which does not allow a physiological roll-glide mechanism. The goal of this study was therefore to report on the biomechanical basis of the natural knee and to describe the development of a novel knee endoprosthesis based on a mathematical model. The design of the structurally new knee joint endoprosthesis has, on the lateral side, a convex shape of the tibial joint surface in a sagittal cross section. Furthermore, from a mathematical point of view, this knee endoprosthesis possesses essential kinematic and static properties similar to those of a physiological TFJ. Within the framework of the authorization tests, the endoprosthesis was examined according to ISO/WC 14243 in a knee simulator. The abrasion rates were, thereby, lower than or at least as good as those for conventional endoprostheses. The presented data demonstrate a novel concept in knee arthroplasty, which still has to be clinically confirmed by long term results.

Physiologically shaped knee arthroplasty induces natural roll-back

“…Both arthroplasties seem to restore the natural four-bar linkage mechanism of the human knee. Since they do not replace the total knee, the physiological anterior-postorior position for the replaced part must be found so that the natural mechanism of the human knee is set into function as it is expected by the theoretical considerations [9,16]. This procedure may be the mechanical reason for the possible physiological pattern of the unicompartmental knee arthroplasty.…”

“…The newly developed knee arthroplasty "Aequos G1" (Aequos, Germany) (Figs 1, 2 and 3) was designed to mimic the roll-gliding mechanism of the physiological knee [9,16] and thus to reduce the patellofemoral force in flexion and thus resulting pain. Compared to conventional TKRs, the "Aequos G1" has a convexly curved lateral tibial plateau and a small sagittal offset of the medial and lateral knee compartment.…”

“…Compared to conventional TKRs, the "Aequos G1" has a convexly curved lateral tibial plateau and a small sagittal offset of the medial and lateral knee compartment. Frosch et al and Nägerl et al showed analytically that these features account for the backwards motion of the femur in flexion resulting in a reduced patellofemoral force [9,16].…”

Klinische und radiologische Ergebnisse nach operativ versorgter Patellafraktur

“…Insgesamt besitzt das Kniegelenk vier Freiheitsgrade, nämlich Flexion/Extension, Ab-/Adduktion, Außen-/Innenrotaion und axiale Rotation. Aufgrund von vier anatomischen Drehachsen wird das Knie als Viergelenk bezeichnet (Nägerl et al 1993, Frosch et al 2009.…”

“…Inkongruenz der Gelenkpartner (Wirth et al 2005) und verbinden die beidseitig konvexen Femurkondylen mit dem Tibiaplateau, welches medialseitig konkav und lateralseitig konvex geformt ist (Frosch et al 2009). Außerdem führen die Menisken zu einer vergrößerten Gelenkfläche zwischen dem Femur und der Tibia, wodurch der Spitzendruck im Gelenk gemindert wird.…”