Department of Orthopaedic Surgery, New York University-Hospital for Joint Diseases, New York, NY, USA,
Clin Orthop Relat Res. 2014 Jan;472(1):238-47. doi: 10.1007/s11999-013-3088-2.
In different posterior-stabilized (PS) total knees, there are considerable variations in condylar surface radii and cam-post geometry. To what extent these variations affect kinematics is not known. Furthermore, there are no clearly defined ideal kinematics for a total knee.
QUESTIONS/PURPOSES: The purposes of this study were to determine (1) what the kinematic differences are caused by geometrical variations between PS total knee designs in use today; and (2) what design characteristics will produce kinematics that closely resemble that of the normal anatomic knee.
Four current PS designs with different geometries and one experimental asymmetric PS design, with a relatively conforming medial side, were tested in a purpose-built machine. The machine applied combinations of compressive, shear, and torque forces at a sequence of flexion angles to represent a range of everyday activities, consistent with the ASTM standard test for measuring constraint. The femorotibial contact points, the neutral path of motion, and the AP and internal-external laxities were used as the kinematic indicators.
The PS designs showed major differences in motion characteristics among themselves and with motion data from anatomic knees determined in a previous study. Abnormalities in the current designs included symmetric mediolateral motion, susceptibility to excessive AP medial laxity, and reduced laxity in high flexion. The asymmetric-guided motion design alleviated some but not all of the abnormalities.
Current PS designs showed kinematic abnormalities to a greater or lesser extent. An asymmetric design may provide a path to achieving a closer match to anatomic kinematics.
One criterion for the evaluation of PS total knees is how closely the kinematics of the prosthesis resemble that of the anatomic knee, because this is likely to affect the quality of function.
在不同的后稳定型（PS）全膝关节中，髁面半径和凸轮-后柱几何形状存在很大差异。这些差异在多大程度上影响运动学尚不清楚。此外，对于全膝关节，目前还没有明确界定的理想运动学。
问题/目的：本研究的目的是确定（1）当今使用的 PS 全膝关节设计之间的几何差异导致了哪些运动学差异；（2）哪些设计特征将产生与正常解剖膝关节非常相似的运动学。
在专门设计的机器中测试了四种具有不同几何形状的当前 PS 设计和一种具有相对一致的内侧的实验性非对称 PS 设计。机器在一系列弯曲角度施加压缩、剪切和扭矩力的组合，以代表日常活动的范围，符合 ASTM 测量约束的标准测试。股胫接触点、运动中性路径以及前后和内外松弛度被用作运动学指标。
PS 设计在彼此之间以及与之前研究中确定的解剖膝关节运动数据之间表现出主要的运动特征差异。当前设计中的异常包括对称的内外侧运动、易发生过度前后内侧松弛以及在高屈曲时松弛度降低。非对称导向运动设计缓解了一些但不是所有的异常。
当前的 PS 设计在不同程度上表现出运动学异常。非对称设计可能为更接近解剖运动学提供一种途径。
PS 全膝关节评估的一个标准是假体的运动学与解剖膝关节的相似程度，因为这可能会影响功能质量。
