A Multibody Knee Model Corroborates Subject-Specific Experimental Measurements of Low Ligament Forces and Kinematic Coupling During Passive Flexion

Abstract

A multibody model of the knee was developed and the predicted ligament forces and kinematics during passive flexion corroborated subject-specific measurements obtained from a human cadaveric knee that was tested using a robotic manipulator. The model incorporated a novel strategy to estimate the slack length of ligament fibers based on experimentally measured ligament forces at full extension and included multifiber representations for the cruciates. The model captured experimentally measured ligament forces (≤ 5.7 N root mean square (RMS) difference), coupled internal rotation (≤ 1.6 deg RMS difference), and coupled anterior translation (≤ 0.4 mm RMS difference) through 130 deg of passive flexion. This integrated framework of model and experiment improves our understanding of how passive structures, such as ligaments and articular geometries, interact to generate knee kinematics and ligament forces.

A geometric ratio to predict the flexion gap in total knee arthroplasty

“…The ability of the proposed MCL ratio to predict medial and lateral flexion gaps was evaluated using six computational models of the tibiofemoral joint following TKA. A previously published modeling framework that has been used to predict kinematics, contact forces, and ligament forces of the tibiofemoral joint in its native state and following TKA was utilized 18‐21 . Intraoperative clinical exams were simulated to evaluate the medial and lateral gaps in flexion, and the new geometric ratio was measured and related to these gaps.…”

“…Laterally, the anterolateral (ALL), fabellofibular (FFL), and the lateral collateral ligaments (LCL) were each modeled using one fiber (Figure 2B). Medially, the MCL consisted of three proximal and three distal fibers and two transverse fibers wrapping around the medial aspect of the proximal tibia 21,26 . The posterior oblique ligament (POL) consisted of three fibers (Figure 2C).…”

“…The ligament slack length, or the length at which the ligament fibers became taut, was standardized. Specifically, ligament slack length was defined using a previously developed optimization algorithm to produce in situ ligament pretensions measured experimentally in the native knee at full extension 21 . In this algorithm, the slack length is calculated as a percentage of the inter‐insertional distance of each ligament fiber at full extension.…”

Fixed‐bearing medial unicompartmental knee arthroplasty restores neither the medial pivoting behavior nor the ligament forces of the intact knee in passive flexion

“…A previously developed multibody computational model of an intact tibiofemoral joint was adapted for the current study and used in two main phases to address our research questions. First, the AP translations of the medial and lateral femoral condyles relative to the tibia were compared to a corresponding cadaveric experiment; and second, a fixed bearing UKA was virtually installed and the effect of implant thickness on tibiofemoral kinematics and ligament forces was assessed.…”

“…Mean structural properties were employed to describe the force‐elongation response of the fibers including toe and subsequent linear regions . The slack length of each fiber was determined using a previously described algorithm . The MCL was represented with anterior, central, and posterior fibers: each divided into distal and proximal pairs .…”