Newsletter Volume 8 - 4th Quarter 2005
Human Hip Muscle Attachment Point Location Changes Load Distribution.
CONTENTS
Case Study: Human Hip Muscle Attachment Point Location Changes Load Distribution
Software: BRG.LifeMOD™ v2006 New Product Release!
Publications: Journal Papers, Magazine Articles and Book Chapters
This issue presents a study on how, by using human simulation tools, surgeons can gain better knowledge of the surgical outcome of muscle attachment relocation surgery, reducing the need for further revisions. This study presented in this newsletter is a simplified version of the work done in conjunction with UCLA's David Geffen School of Medicine.
The staff at BRG would like to take this opportunity to sincerely thank our customers, distributors and partners for making 2005 a record year for BRG in earnings and by increasing the BRG.LifeMOD™ user base to several thousand at more than 500 individual corporations and institutions. This achievement deepens our dedication to continue with the level of quality of our products and services and to drive the technology into new areas for the enrichment of human life.
Additionally, we are pleased to announce the release of BRG.LifeMOD™ Version 2006 with many new functions and features including a new muscle wrapping feature for each muscle and new library structure including motion libraries derived from motion capture data, object and environment libraries. These libraries will continue to grow with the product. We invite you to download a free trial version of the software; try out one of our 17 easy-to-follow tutorials and begin building physics-based human models today.
CASE STUDY: HUMAN HIP MUSCLE ATTACHMENT POINT
LOCATION CHANGES LOAD
DISTRIBUTION
Introduction
Abnormal walking patterns or gait caused by skeletal deformities and cerebral palsy are often treated by surgical intervention. By changing the location where a muscle attaches to the bone, the surgeon changes the way a muscle works across the joint, in turn changing the patient's gait or joint function. However, since it is a 3-dimensional system with many muscles spanning the joint, it is difficult to understand the mechanical dynamics and predict an attachment point that will benefit a patient, leading to multiple revisions. Revision surgeries are difficult and painful, especially for children, who make up a plurality of these patients.
Knowledge of muscle-tendon lengths and moment arms is important for planning interventions aimed at the correction of walking abnormalities because tight muscles that restrict movement are often surgically lengthened or released. For example, lengthening of the medial hamstrings and psoas muscles can improve the posture and limb alignment of patients with cerebral palsy with a wearisome, crouched gait. However, lengthening of these muscles can leave patients with weak, malfunctioning legs.
To gain insight to the function of the human mechanical system, investigators have relied on tests conducted with cadaver specimens, which cannot provide repeatable results and may not provide accurate information because of tissue damage. Clinical studies of patients with similar conditions are limiting because of the widely varying physical parameters and conditions.
Currently with the advances in human simulation technologies, such as BRG.LifeMOD™, mechanical engineers can build a human model based on the tools and skill sets they have developed modeling general mechanical systems. Many similarities exist between a biological system and mechanical systems. Like a car, for example, a human model has parts, joints, forces and a controller; or in biological terms - bone, human joints, muscles and a brain.
Model Development
Human model creation is an engineering rich activity. To begin the process of generating a human model, BRG.LifeMOD uses data from anthropometric databases which provide three levels of accuracy. The first level requires height, weight and sex. The second level requires 64 specific measurements. The third level allows the use of an MRI data scan of the patient's bones for the precise representation geometry of the patient's bones. The third level is best suited for personalized models where the patient has a substantial deformity or a significant deviation from the anthropometric norms.
Mechanical joints are created using kinematic joint elements and passive torque elements. The passive torque elements represent the frictional resistance in each joint.
Next, the muscles and associated forces on the leg are created (figure 1). BRG.LifeMOD includes a library of muscles for the entire body. The leg has enough muscles to simulate many activities. Additional muscle groups may be added as necessary. The muscles are idealizations which include data on the physiological cross sectional area which is scaled based on the size of the patient (figure 2) and act between two bone attachment points.
Figure 1. Three-dimensional musculoskeletal foot-shank-thigh-pelvis model front view (left), side view (right).
Figure 2. The BRG.LifeMOD muscle table for the leg. The table includes the scaled physiological cross sectional areas of each muscle group scaled by the anthropometric database. Further, the user may alter the output of each muscle group using the Force Output % Sliders.
When the muscle set is first created, the muscles exist as passive, "training" elements and do not produce tension forces. With this configuration, the next step is to teach or train the muscles to move the leg in a designated pattern. The pattern to be studied in this publication will be a simple hip flexion. To train the muscles, the pelvis is fixed to ground and a BRG.LifeMOD motion agent (figure 3) is attached to the foot to move the leg in a designated pattern. During the training process, the training elements in the muscle formulations record the contraction patterns for every muscle in the leg.
Figure 3. Process of training the muscles, by moving the leg in a user-specified motion pattern via a motion agent.
In a subsequent simulation, the muscles are upgraded to "trained" elements to include drivers to create the necessary forces to match the recorded contraction pattern. In this forward-dynamics simulation, the motion agent is removed and the muscles then drive the motion to replicate the recorded activity. During this forward-dynamics simulation, forces are continually monitored and never exceed the physiological properties of each muscle group. At this stage optimization techniques may be introduced to regulate the muscle behavior. Further, the muscle outputs may be altered by using the sliders in the panel in figure 2 to further satisfy available EMG data.
Simulation Trials
With completion of the forward-dynamics model, the practical application is a simulation study to investigate surgical intervention for changing muscle attachment point positions. For this simplified presentation, the anterior pelvic attachment of the gluteus medius muscle will be altered to observe how the surrounding muscles compensate for the change in force transmission (figure 4).
Figure 4. Changing the location of the pelvic attachment of the anterior gluteus medius muscle group.
The simulations are repeated and the muscle tension force for the anterior and the medial muscles groups are reported in figure 5 for the two cases.
Figure 5. Results from two successive trials. Case-1 is the original pelvic attachment of the anterior gluteus medius muscle group. Case-2 is the new position (adjusted anteriorly) of the pelvic attachment of the anterior gluteus medius muscle group. Results are reported for the anterior group and the adjacent medial groups of the medial gluteus medius muscle set.
The results presented for this simple case in figure 5 display change in force magnitudes for the relocated muscle and the compensation changes in the adjacent muscle group. When the force is reduced in the relocated muscle, the forces of the adjacent muscles must increase tension to complete the hip flexion event. Successive iterations of this type of simulation with different pelvic attachment positions can provide a better understanding of joint physics and potential surgical strategies.
The simple example presented in this issue of the newsletter is presented to serve as an outline of the procedure for the actual work being conducted in the pre-surgical setting. The actual work involves the simulation of many different activities including walking, stair climbing, sitting, etc. The models used are patient-specific, developed with solid models of the bones generated from MRI scan data and many more muscle groups. In addition, the process is automated by developing a results matrix based on design of experiments (DOE) techniques.
These simulation capabilities and techniques provide the surgeon with a working model to explore the complicated force environment of each joint in the body. The knowledge gained leads to more effective surgical procedures, fewer revisions, higher patient satisfaction and ultimately improve the quality of life.
SOFTWARE
The BRG is pleased to announce the release of BRG.LifeMOD™ version 2006. This new release makes state-of-the-art human modeling accessible to every investigator interested in the physics behind human motion.
The release includes a new library structure consisting of 13 motion capture data sets, human model libraries, posture libraries, anthropometric libraries and physical environment libraries. The libraries will grow in content as new versions of BRG.LifeMOD are released.
A convenient tissue wrapping tool is offered which automatically discretizes any existing tissue and creates contact forces between the tissue and any bone or surface in the model. This capability together with the BRG.LifeMOD generalized surface contact now allows the user to investigate phenomena such as patellar tracking in the trochlear groove.
Due to the tremendous response from users on the automated tutorial system in BRG.LifeMOD, the tutorial system has been expanded to include a new tennis swing tutorial. This tutorial imports a tennis racket from the environment library into a full-body human model. The human model proceeds to hit a tennis ball. The racket-ball contact is modeled, and the force transmission of the contact through the racket, hands, elbow, shoulder, back is displayed.
Due to the enthusiastic response we received from our users for our "trainable" muscles, we have introduced several more muscle groups to ensure LifeMOD's position as the most powerful, versatile and ease-to-use full-body human modeling package available today.
This new version is a direct result from an ongoing and rigorous user dialogue, partnerships with our research community, and the inclusion of much functionality developed by our professional staff to solve the world's most demanding biomechanics issues. View Examples...
SERVICES
The Biomechanics Research Group Inc. is a service-based organization chartered to
empower our customers to capture a level of ROI from their technology investment in
ways they've never imagined. We are committed to customer service, product excellence
and continuous quality improvement in all we do. We provide training, modeling and
simulation expertise. Contact us for more Information.
OTHER NEWS
2005 was a record year for the Biomechanics Research Group, Inc. with record earnings and attaining the 500th commercial customer for BRG.LifeMOD™. See Press Release. To support this large customer base and in anticipation of an even more successful 2006, BRG will be expanding our team to include several new professionals. Current job openings include software developers, biomechanics scientists, marketing communications personnel and application engineers. See Careers.
New book chapter: "Chapter 24: The Virtual Knee" in Total Knee Arthoplasty, Springer 2005. See PDF
New Publication: "Modeling Alpine Skiing using BRG.LifeMOD" INSA Toulouse Presentation (in French) See PDF
New Publication: "Localization and Inverse Dynamic Simulation in Determining Joint Moments" Virginia Tech Research Symposium. See PDF
Check out our new model repository! We would like to sincerely thank those who have contributed to the LifeMOD™ body of knowledge. We pledge to do our best to increase the technical capabilities of LifeMOD while developing new ways to educate the community.
If you would like further information on our software and services, please contact us.
Copyright© 2005 LifeModeler, Inc.