Biomechanics Laboratory

Laboratory Personnel

  • Zbigniew Gugala, MD, PhD
  • William L. Buford, Jr., PhD, PE
  • Randal P. Morris, BS - Lab Manager

The UTMB Orthopaedic Biomechanics Laboratory is devoted to the advancement of clinical care by continuously seeking improved knowledge of musculoskeletal function. The research goals of the lab include enhanced clinical methods through the design and use of new measurement tools for analysis of in vivo biomechanics function. Laboratory research projects focus upon the time honored study of fresh cadaver mechanics augmented with correlative studies using improved structures derived from medical imaging. Results of clinical methods and laboratory studies provide the requisite analytical detail to develop mathematical and computer simulation of the musculoskeletal system. This simulation is a major effort which has culminated in a real time, interactive, 3-dimensional computer graphics model of the human body. The simulation has direct research, educational, and clinical applications in all orthopaedic specialties.

The strengths of the Orthopaedic Biomechanics Laboratory are best understood when looking at the personnel and what they have accomplished with available resources. While individuals have demonstrated significant success, the success came as a result of a genuine team approach to collaborative research. This group effort is enhanced and augmented by the pervading cooperative ambiance of UTMB and by the thrust of the Orthopaedic leadership.

Laboratory Facilities

The Orthopaedic Biomechanics Laboratory facilities are located within the Rebecca Sealy Hospital at UTMB, in close proximity to the main orthopaedics department. The workspace consists of several laboratories, an electronics shop, and the accompanying staff offices and student workstations.

The "wet" lab is primarily for anatomy and physiology studies using fresh frozen and embalmed cadaver specimens. The lab includes a walk-in -4 degree C freezer with an adjoining cold room. Thus, we can perform anatomy studies on many specimens and are equipped to measure many physiological functions and variables such as joint pressure, range of motion, moment arms, tendon force and tendon excursion, to name a few.

The materials testing and biomechanics lab is equipped with an MTSĀ® 858 Mini-Bionix biaxial materials testing machine. The Mini-Bionix is a computer controlled, servohydraulic system capable of measuring axial forces up to 10,000N and torsional forces up to 100Nm. Axial and rotational displacement can also be measured and there are attachments for measuring strain, as well. This system gives us the ability to test some of the smallest tissues such as interosseous membranes, tendons and ligaments, joint systems, and large bones like the femur and spine.

The lab also maintains motion analysis equipment for kinematic studies, both in cadaver specimens and living subjects. The system, from Motion Analysis Corp., consists of 6 CCD analog cameras, monitor bank, 4 calibration analogs and the most up to date kinematic analysis software. With this setup we can record motion in cadaver specimens at the joint level, physiologic movement in live subjects, and simple gait analysis. An important addition to our motion study capabilities is an 8-channel portable EMG (electromyography) system and a 4-channel research EMG system. We also employ a portable 2 camera video motion system for studies in sports medicine and physiology. Other equipment includes a 6 degree of freedom Microscribe for detailed surface mapping, a FLIR thermal imaging camera system, and a machine shop housing a milling machine, lathe, drill press, band saw, and other fabrication equipment essential to biomechanics research support.

Research from the Orthopaedic Biomechanics Laboratory has been presented in many peer-reviewed journals, proceedings, and research presentations at local, national, and international conferences.

Current Projects

Research in the Biomechanics lab can be loosely organized into three categories. Naturally, many projects tend encompass aspects from more than one area.

Functional Anatomy and Measurement

Includes studies of joint mechanics and physiologic systems and evaluation of surgical techniques and practices. Projects include comparative anatomy using human cadaver specimens, direct measurements of orthopaedic patients, motion analysis of joint systems in cadaver specimens and in vivo.

Examples:

  • Ankle Torque Range of Motion
  • Photoelastic Stress Analysis
  • Muscle-Tendon Pathway Definitions
  • Direct 3-d Mapping of Joint Surfaces

Biomechanics and Mechanical Testing

Biomechanics testing involves all forms of mechanical testing of physiologic systems (soft tissue, bone, tendons, cartilaginous structures, muscle systems) and the prosthetic and/or implant devices that enhance, correct, or rehabilitate these systems.

Examples:

  • Muscle Mechanics of the Knee
  • Achilles Tendon Rupture Repair Techniques
  • Ankle Fracture Management
  • Ligament Reconstruction Mechanics

Computer Simulation, Animation, and Image Analysis

Projects combine the multidisciplinary studies of computer simulation, image analysis, animation and mathematical modeling. By combining the mechanical testing of joint systems with the dynamics of motion analysis and the power of computer reconstruction, we develop detailed, high resolution accurate, 3-D simulations of kinematic structures and their movement.

Examples:

  • Motion Analysis and Computer Graphic Simulation of the Extremities
  • Computational Biomechanics
  • Knee Kinematics in Sports
  • Specimen-Specific Modeling

Simulation Development
Introduction

In order to obtain a visual and quantitative verification of the appropriateness of one, two, and three degree of freedom models for motion, we have developed an interactive system for the independent adjustment and definition of multiple degree-of-freedom linkage systems representative of human leg and arm motion. The system is built so that, once the kinematic structure is defined, control points for interactive definition of muscle-tendon and ligament paths may be manually adjusted and refined, providing a tool for interactive musculoskeletal modeling and simulation.

All kinematic transformation nodes are built as linkages within an openGL hierarchical structure. The structure for independent adjustment of each axis of motion required tracking the inverse of all transformations applied to the axis during visualization and adjustment. The inverse is applied to all structures below the axis of interest so that only the axis is effected during 3D adjustment.

The system allows for the visual adjustment and verification of the placement of an axis or axes. This interactive task is carried out through control of point of view of the observer, the position and orientation of the view, and the position and orientation of each axis. These dynamic view and control commands are carried out simultaneously with rotational control of distal joint segments about their defined axis or axes. With such immediate and interactive flexibility, the user is able to rapidly iterate upon appropriate axis placement based upon a 3D visual verification of joint congruence throughout joint range-of-motion.

Methods

The current development environment is a dual processor 700 Mhz Pentium III Windows 2000 system using Visual C++ v6.0, and OpenGL with the GLUT Library. The graphics driver is the Evans & Sutherland Tornado using Realimage technology. In addition to mouse and keyboard interactive methods, this system utilizes pop-up menus with control widgets and 6 DOF control using a Spaceball (Spaceball model 3003, Spacetec IMC Corp., Lowell, MA).

Structures for this kinematic model are derived from axial computerized tomography (CT) slices of fresh-frozen cadaver specimens. One mm thick slices spaced at 1 mm are used for the joint areas which require the greatest resolution. One mm thick slices spaced 5 mm apart are used for the mid shaft areas of bones. This approach helps to maintain highest detail in critical areas and save on structure size where such detail is not needed.

The limbs used in the model were scanned on a General Electric Computerized Tomography scanner (GE Model 9800). The images are processed with Mimics software to yield standard stereolithography files describing each individual bone as a triangulated surface.

The simulation software is then used to read in each stereolithography according to a kinematic hierarchy. Axes (up to three per diarthroidal joint) positions and orientations must initially be manually adjusted per literature references when available, or visual approximation when they are not. Various display modes (shading, wireframe, 3D stereo) and control methods ranging from keyboard to GUI to spaceball are available.

Muscle-tendon and ligament paths may be described in terms of a sequence of manually positioned control points, some in a fixed position relative to a particular bone, others designed to slide smoothly over the surface of the bone. Once a path has been defined, it may be modeled as either a line segment or one of a variety of spline curves, and the moment arm as a function of joint angle may be viewed in real-time or recorded.



Acknowledgments

This project was supported by a grant provided by the Texas Advanced Technology Program (Project Number: 004952-0011-1999), with additional support from Sulzer Orthopedics, Inc., Austin, TX.