FINITE-ELEMENT ANALYSIS OF HUMAN KNEE-JOINT IN VARUS-VALGUS

Objective. The overall response, load transmission, role of ligaments, and state of stress in various components under varus-valgus moments in the intact and collateral-deficient tibiofemoral joint are investig ated. Design. A non-linear finite element model consisting of bony str uctures (tibia and femur), their articular cartilage layers, medial an d lateral menisci and four primary ligaments (cruciates and collateral s) is utilized. Background. Valgus and varus stresses are among the pr imary mechanisms of injury to knee ligaments. Several in vitro studies have investigated the role of ligaments in resisting such loads and o n the way deficiency in either collateral may affect the response. Met hods. Cartilage layers are isotropic while menisci are non-homogeneous composite. The articulation of cartilage layers with each other and w ith the intervening menisci and the wrapping of the medial collateral ligament around the tibial edge are treated as large displacement fric tionless contact problems. The non-linear elastostatic response of the joint at full extension is computed under varus-valgus moments applie d to the femur with the tibia fixed. Cases simulating deficiency in co llaterals and constraint on femoral axial rotation are also studied. R esults. The response is non-linear with large coupled axial rotations, internal in varus and external in valgus. In intact and collateral-de ficient states, the joint shows varus or valgus openings so that the a rticulation occurs at one plateau only, medial in varus and lateral in valgus. Large tensile forces in cruciates in collateral-cut models ge nerate higher compression penalty on the loaded plateau. Conclusions. Collaterals are the primary load-bearing structures; their absence wou ld substantially increase primary laxities, coupled axial rotations, f orces in cruciates, and articular contact forces. Good agreement with measurements is found. Relevance Detailed knowledge of joint biomechan ics is essential in the diagnosis, prevention and treatment of observe d disorders. Absence of collateral ligaments increases the loads in cr uciates and contact stresses transmitted through cartilage layers and menisci, and thus places the affected components at more risk, especia lly when varus-valgus is accompanied by other modes of loading as well . (C) 1997 Elsevier Science Ltd.