Inherent laxity in total knee prostheses.
The anterior-posterior and rotatory laxities of 14 total knee prosthesis designs were measured in a loading rig with compressive, shear, and torque loads representative of physiologic loads. The measured laxities covered a wide range, both greater and smaller than that of the anatomic knee. This range was mainly due to the curvature or flatness of the plastic tibial surface and conformity with the femoral component. Pressure patterns showed the corresponding contact track and area on the tibial surfaces. It is proposed that for normal function, the laxity of the device should complement the remaining anatomic structures to produce a combined laxity resembling that of the normal knee. Excessive prosthetic laxity will lead to the risk of instability, soft tissue attenuation, edge-loading on components, and high contact stresses on the plastic. Inadequate prosthetic laxity may lead to altered kinematics and excessive stresses at the interface, running the risk of long-term loosening. The authors show the laxities of many currently used devices, providing important background information for assessing the role intrinsic prosthetic constraint might play in total joint performance in clinical analyses.
Thatcher
J C
JC
Department of Orthopedic Surgery, University of Massachusetts Medical Center, Worcester.
Zhou
X M
XM
Walker
P S
PS
D001696:Biomechanical Phenomena; D006801:Humans; D007720:Knee Prosthesis; D009068:Movement; D011474:Prosthesis Design; D012399:Rotation