2012 IR&D Annual Report

Dynamic Modeling of Knee Mechanics, 18-R8167

Principal Investigators
Daniel P. Nicolella
W. Loren Francis
Travis Eliason
Baron Bichon

Inclusive Dates:  07/01/11 – Current

Background — Osteoarthritis (OA) is the most common form of arthritis and, as the major cause of activity limitation and physical disability in older people, is a tremendous public health concern. Arthritis causes pain, swelling, and reduced motion in joints caused by the breakdown or degradation of the articular cartilage covering the joint surfaces. While it is generally accepted that differences in knee mechanics or alterations in knee mechanics due to certain risk factors lead to knee OA, the precise dynamic mechanical environment of the knee and its anatomical structures during routine physical movements is largely unknown. Thus, a remaining unmet, technically difficult challenge in musculoskeletal research, and the focus of this project, is determining the detailed dynamic mechanical environment of the healthy knee joint and understanding alterations in knee mechanics caused by injury, aging or disease.

Figure 1. Initial and final muscle activations. The optimally determined muscle activations 
			required to perform a leg extension compared to the initial muscle activations.
Figure 1. Initial and final muscle activations. The optimally determined muscle activations required to perform a leg extension compared to the initial muscle activations.

Approach — The primary objectives of this project are:

  1. Develop a dynamic, finite element model of the lower human body driven by neuromuscular control and active contraction of the major muscle groups of the lower body.

  2. Determine the dynamic neuromuscular control parameters for: i) leg extension, ii) standing squat, iii) single gait cycle and simultaneously determine the mechanical environment within the knee.

  3. Determine the changes in knee mechanics resulting from known OA risk factors.

Accomplishments — In this project, SwRI researchers have used multibody dynamics, active muscle modeling, and detailed finite element modeling to generate a high fidelity dynamic model of the human lower body. Researchers explicitly modeled the lower limbs (pelvis down to the foot), including a detailed representation of the knee, using finite elements. Motion at the knee joint is controlled explicitly via deformable surface contact at each articular surface (rather than idealized as simple revolute or ball and socket joints). The major muscles activating the lower limb are explicitly modeled using anatomical muscle insertion points and geometric wrapping. The dynamic muscle forces, joint kinematics, contact forces, and detailed (e.g., continuum) stresses and strains within the knee (cartilage, meniscus, ligaments and bone) were simultaneously determined for a neuromuscularly controlled seated leg extension with a weight of 30 pounds added to the ankle. The simultaneous prediction of multibody dynamics and detailed continuum mechanics of the knee (or any other biological structure) under self-actuation (e.g., muscle activation) has not been previously performed.

Figure 2. The lower limb dynamic finite element model (left) was used to simulate a standing 
			squat (right). Active time varying muscle forces were applied using a Hill-type muscle model for the quadriceps muscles 
			(vastus lateralis, vastus medialis, rectus femoris, and vastus intermedius), tibialis anterior, gastrocnemius  and soleous 
			muscles.
Figure 2. The lower limb dynamic finite element model (left) was used to simulate a standing squat (right). Active time varying muscle forces were applied using a Hill-type muscle model for the quadriceps muscles (vastus lateralis, vastus medialis, rectus femoris, and vastus intermedius), tibialis anterior, gastrocnemius and soleous muscles.
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Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 10 technical divisions.
04/15/14