3D Kinematics Methods and Instrumentation Santiago De Grau and Jess Valic October 28, 2014

Overview Introduction to Kinematics Kinematic Data Collection Coordinate Systems Marker Placement Kinematic Data Application to Neurotrauma Impact Science Laboratory

Introduction to Kinematics Describes the motion of points or bodies without consideration of the causes of motion What is measured? Not measured? Linear and angular –Body landmarks and segments –Joint angles Can be either 2D (planar) or 3D (spatial)

Evolution of 3D Kinematics

Applications in Biomechanics Athlete performance –Analysis of golf/tennis swing Injury rehabilitation (pre vs post) –Joint range of motion differences Injured/non-injured –Flexion/extension during stair climb Head Impact Reconstructions –Acceleration

Kinematic Data Collection 1)Magnetic 2)Mechanical 3)Optical –Passive (reflective markers – VICON) –Active (IRED – Optotrak) –Sample rates; Capture space –Marker ID; Positional data only

Additional Data Collection Tools Accelerometer –Measures acceleration directly  velocity, displacement Electrogoniometer –Measures joint angles immediately; cheaper than imaging systems –Encumbers movement; best for hinge joints; ONLY measures joint angles

Motion Capture Data Collection Record motion of markers affixed to a moving subject Digitize the data  marker coordinates Process coordinates  kinematic variables –Segmental/joint movements Multi-camera system –Minimum 2; consider occlusion and rotation

Data Collection Calibration necessary –Ensures correct image scaling Static Calibration –Control points affixed to a structure in field of view –Orients 3D workspace (GCS) –Establishes origin  forceplate often used Dynamic Calibration –Relative positions and orientations of cameras

Data Collection Cameras capture coordinates in 2D –Need to use a transformation process to convert to spatial (3D) coordinates Direct Linear Transformation (DLT) –A set of equations computed to scale digitized coordinates into metric units –Also corrects errors associated with camera tilting Distance distortions

Coordinate Systems Cartesian coordinate system –Position vector defines point in space (X,Y,Z) –Stationary orthogonal axes –Origin (0,0,0) –Commonly right handed (counterclockwise +ve) Two coordinate systems for 3D analysis –Global Coordinates System (GCS) –Local Coordinate System (LCS)

Global Coordinate System Internal reference system – Fixed system Determined when object space is defined –Origin from static calibration Point of interest (marker) described by position (X,Y,Z) Right handed orthogonal

Local Coordinate System Fixed within and moves with body or segment –Describes position of body or segment Right handed and orthogonal; origin at COM or proximal joint center Origin and axes attached to and moves within the body Segment volume and shape finite –Orientation described wrt GCS

Local Coordinate System Orientation changes as body moves through 3D space –Calculate orientation of LCS to GCS Static calibration to align LCS with GCS is useful Used to determine joint angles –LCS of two segments –Rotational matrix –Cardan Euler, JCS, Helical Axis Neurotrauma Impact Science Laboratory

Markers Need minimum of 3 non-collinear markers per segment Four general configurations 1) Markers mounted on bone bins 2) Skin mounted markers 3) Arrays of markers on rigid surface 4) Combination of (2) & (3) Each have own pros and cons

Marker Placement Guidelines 1. Sufficient measurements of each marker should be available. The light reflected from the markers should be visible to sufficient cameras for identification 2. The number of markers associated with each bone must be more than or equal to three 3. The relative movement between markers and the underlying bone should be minimal 4. Mounting the markers on the subject should be quick and easy Cappello et al. (1997)

Femoral and Tibial wands as a reference for other markers Markers secured at anatomical landmarks that determine embedded axes for segments Use of anthropometric measurements ‘Improved Helen Hayes Model’ – medial anatomical markers included, static trial performed, and markers are not placed on wands Vaughan et al Helen Hayes Marker Placement

Pros: Markers are easy to track in three-dimensional space with video based kinematic systems Easy to apply to a subject Subjects movements are minimally impaired Cons: Jerky movement causes wands to vibrate which is picked up by the cameras Skin movement relative to the underlying bone Both create error of marker coordinate reconstruction. Modeling procedures often do not accommodate these artefacts and assume the marker is rigid with the bone Vaughan et al. 1999

Femoral and Tibial clusters Used to reduce skin movement artifact for more accurate measurement ‘A local reference frame can be defined starting with the co- ordinates of three non- collinear markers’ Define joint centers Clusters used as a technical system along with the anatomical marker placement Static trial must be performed Cappello et al Cluster Marker Placement

Pros: Markers are easy to track in three-dimensional space with video based kinematic systems Relative skin movement error is reduced through marker clustering Easy to apply to a subject Cons: Movement of subject might be impaired or unnatural due to clusters being placed on large muscles MARKER PLACEMENT Cappello et al. 1997

Kinematic Measurements Consists of two parts: 3D Translation & 3D Rotation (6 degrees of freedom) Inverse Kinematics: Take motion of markers to determine angles and position of segments in relation to another

Linear Kinematics

Angular Kinematics

Application - NISL

Maximum Linear Magnitudes AxisBlockAcceleration, gVelocity, m/s XC S T YC F T ZC F S Resultant

Maximum Angluar Magnitudes AxisAcceleration, rad/s 2 Velocty, rad/s X Y Z R

Lesion typeThresholdMeasurement methodReference mTBI82 g for 50% chanceLaboratory reconstructionZhang et al. (2004) mTBI81 gInstrumented helmetsDuma et al. (2005) mTBI103 gInstrumented helmetsBrolinson et al. (2006) mTBI82–146 gInstrumented helmetsSchnebel et al. (2007) mTBI103 gDynamic modelingFrechede and McIntosh (2009) mTBI90 gPrimate impactsGurdjian et al. (1966) Subdural hematoma130 gLaboratory reconstructionWillinger and Baumgartner (2003a) Lesion typeThresholdMeasurement methodReference mTBI 5900 rad/s 2 for 50% chance Laboratory reconstructionZhang et al. (2004) mTBI3000–4000 rad/s 2 Laboratory reconstruction Willinger and Baumgartner (2003a) mTBI8020 rad/s 2 Dynamic modelingFrechede and McIntosh (2009) Subdural hematoma4500 rad/s 2 Cadaver impactsLowenhielm (1974a) mTBI1800 rad/s 2 Primate impactsOmmaya et al. (1967) DAI16,000 rad/s 2 Primate, physical and numerical model impacts Ommaya et al. (1967) Thresholds of Injury

Brain Mapping

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