University of Delaware Human Performance Laboratory A Tutorial on the Measurement of Joint Motion with Application to the Shoulder

University of Delaware Human Performance Laboratory

A Tutorial on the Measurement of Joint Motionwith Application to the Shoulder


The Challenge

The challenge associated with measuring upper extremity motion is to provide clinicians with:

1) anatomically meaningful descriptions of position, and

2) a clinically relevant sense of motion


Motion of the Shoulder

• Scapula/clavicle relative to the trunk• Humerus relative to the scapula• Humerus relative to the trunk


Marker Set Options

• Marker set similar to those used on lower extremities

• Sparse marker sets (1 shoulder, 1 elbow, 1 or 2 wrist

markers, 1 hand marker)

• More robust marker sets such as the one

recommended by the International Shoulder Group


Considerations for Marker Placement


ISG Recommended Marker Locations

Trunk Markers (Dorsal Side)• C7• T8

Scapula Markers (Dorsal Side)

• Acromioclavicular joint

• Angulus Acromialis

• Trigonum Spinae Scapulae

• Inferior Angle of Scapula

Humerus Markers

• Glenohumeral center of rotation• Medial and lateral epicondyles



Trunk (Ventral Side)

• Suprasternal Notch

• Xiphoid Process

Scapula Markers (Ventral Side)

• Ventral point of Coracoid

• Process

Clavicle Markers

• Acromioclavicular joint

• Sternoclavicular joint



Humerus Markers

• Glenohumeral center of rotation

•Medial and lateral epicondyles

Wrist & Hand

• Radial Styloid

• Ulnar Styloid

• 2nd Metacarpal Head


Determination of Glenohumeral Center of Rotation

Translation from Acromioclavicular marker• Determine shoulder coordinate system

• Translate AC marker a fixed distance along the shoulder’s Y-axis

Spherical (or Helical) fitting• Measure motion of the elbow joint center (or epicondyle

marker) relative to the shoulder coordinate system using the AC marker as the point of origin

• Sphere centroid relative to AC marker in the shoulder coordinate system approximates glenohumeral center of rotation


ISG Recommended Coordinate Systems

Trunk

• Y-vector from midpoint of T8-Xiphoid to midpoint of C7-Suprasternal Notch

• X-vector from Y crossed onto vector from Xiphoid to T8

• Z-vector from X crossed onto Y



Scapula

• X-vector follows Scapular Spine

• Vector from Scapular Spine marker to Inferior Angle marker crossed onto the X-vector creates the Z-vector

• Y-vector from Z crossed onto X-vector



Upper Arm

• Y-vector from midpoint of medial and lateral epicondyles to the center of rotation of the Glenohumeral head

• Z-vector from medial to lateral epicondyle vector crossed onto Y-vector

• X-vector from Y-vector crossed onto Z-vector


Distal Arm Segment Coordinate Systems

Forearm (Proximal)

• Y-vector from wrist center to elbow center

• Z-vector from upper arm X-vector crossed onto forearm Y-vector


Forearm (Distal)

• Y-vector from wrist center to elbow center

• Z-vector from Ulnar to Radial Styloid vector crossed onto Y-vector



Distal Arm Segment Coordinate Systems

Hand

• Y-vector from hand marker (2nd met head) to wrist center

• Z-vector from Ulnar to Radial Styloid vector crossed onto Y-vector



Modifications to ISG Marker Locations

Remove the following markers from the Dorsal side:• Angulus Acromialis• Trigonum Spinae

Scapulae• Inferior Angle of

Scapula


Modifications to ISG Marker Locations

Remove the following markers from the ventral side:

• Sternoclavicular joint

• Ventral point of Coracoid Process


Modification to ISG Coordinate Systems

Scapula (Shoulder)

• X-vector from midpoint of C7 and Suprasternal Notch to the Acromion Process marker

• Z-vector from shoulder X-vector crossed onto trunk Y-vector

• Y-vector from shoulder Z-vector crossed onto shoulder X-vector


Methods of Measuring Arm Orientation Relative to the Trunk or Shoulder

• Joint Coordinate Angles (Grood & Suntay)

• Euler or Cardan Angles

• Helical Axis Decomposition (described by Woltring)

• Instantaneous Helical and Euler Angles

• Rotation Matrices

• Quaternions, Angle-axis, Rodriguez vectors


Representative Coordinate Systems

R = XG = YB = Z


Review of Cross-Products

Review of Analysis Methods


Grood and Suntay Approach

• Select 1 vector from the trunk

• Select 1 vector from the upper arm

• The angle formed by the two vectors represents one of the anatomical angles

• Cross the vector from the trunk onto the vector from the upper arm

• The resulting intermediate vector provides remaining orientation information depending on the segment to which it is referenced



The angle between Yarm and Ytrunk represents the amount of shoulder abduction

• Select 1 vector from the trunk

• Select 1 vector from the upper arm

• The angle formed by the two vectors represents one of the anatomical angles

Review of Analysis Methods: Grood & Suntay


Yarm crossed onto Ytrunk results in an orthogonal Intermediate Vector

Cross the vertical vector from the trunk onto the vector representing the long axis of the upper arm to create the intermediate vector

Review of Analysis Methods : Grood & Suntay


Intermediate Vector with Respect to the Trunk’s Coordinate System

The intermediate vector indicates the amount of horizontal flexion/extension when viewed in the trunk’s coordinate system.



Intermediate Vector with Respect to the Arm’s Coordinate System

The intermediate vector indicates the amount of internal and external rotation when viewed in the arm’s coordinate system.



Other Combinations of Vectors

Other combinations of vectors can be used to determine angles using Grood and Suntay’s method. For example, we could use the trunk’s Z vector and the arm’s Y vector to calculate shoulder angles as well. Each combination of vectors will give you different results for one or more of the joint angles.



Euler Angles


A second approach to describing joint orientation involves the use of Euler angles. Euler angles are easily interpreted but are prone to discontinuities at 90 degree and 180 degree crossings, depending on the rotation order that is being used. For the legs, the order of rotation is:

1) Flexion/Extension, 2) Ab/Adduction, and 3) Int/Ext Rotation


Euler Angles


There are 12 different rotation sequences that can be used in this approach. They are:

XYZ XZY XYX XZX

YXZ YZX YXY YZY

ZXY ZYX ZXZ ZYZ


Calculation of Euler Angles

• Use YZY order of rotation as recommended by the International Shoulder Group

• Start with an intermediate coordinate system aligned with the trunk coordinate system

• Rotate the intermediate coordinate system about the trunk’s Y axis (angle = horiz flex/ext)

• Rotate the intermediate coordinate system about its own Z axis (angle = ab/adduction)

• Rotate the intermediate coordinate system about the arm’s Y-axis (angle = int/ext rotation)



Y-Z-Y Euler Rotation Sequence

3) Rotate the intermediate coordinate system about the trunk’s Y axis (angle = horiz flex/ext

2) Rotate the intermediate coordinate system about the intermediate Z-axis (angle = ab/adduction)

1) Rotate the intermediate coordinate system about the arm’s Y-axis (angle = int/ext rotation

Review of Analysis Methods: Euler Rotations


YZY Euler Sequence (ISG Recommendation)


ZXY Euler Sequence (Adduction/Abduction Priority)


XZY Euler Sequence (Flexion/Extension Priority)


Angles from Helical Axis Decomposition

• Find the axis about which the trunk coordinate system can be rotated to match the orientation of the arm coordinate system

• Unitize the axis, and multiply it by the magnitude of rotation

• Resolve the resulting vector into the appropriate coordinate system



Angles from Helical Axis Decomposition

Find the axis about which the trunk coordinate system can be rotated to match the orientation of the arm coordinate system

Review of Analysis Methods: Helical Axis Decomposition


Alternative Approaches to Measuring Shoulder Orientation

Quaternions, Angle-Axis representation, and Rodriguez vectors

• All in the family of helical axis

• Do not relate directly to anatomical conventions

• Can be converted into Euler angles

Rotation Matrices

• Used in all other methods of calculating joint angles

• By themselves, cannot be interpreted into meaningful anatomical angles



Alternative Approaches to Measuring Shoulder Orientation

Instantaneous Helical and Euler Angles

• Determine starting orientation of limb segment

• Calculate joint angle change between frames

• Integrate results

Advantages

• Provides excellent sense of motion

Drawbacks

• Resultant orientations aren’t exact

• Need accurate reference orientation


Angle Measures at the Elbow

• Segments on either side of the elbow share a common flexion/extension axis

• No measure of internal/external rotation

• Euler approach using same rotation order as

the legs will work fine (F/E, Ab/Add)


Angle Measures at the Wrist

• Segments on either side of the wrist share a common flexion/extension axis

• No measure of internal/external rotation

• Euler approach using same rotation order as the

legs will work fine (F/E, Ab/Add)

• Calculating the angle between the proximal

and distal forearm coordinate systems provides

the pronation/supination angle


Application of Methods at the Shoulder

Given:• Clearly defined marker sets• Well defined segment coordinate systems• Several methods of measuring orientationsWe could easily believe that:

Describing orientation of the upper arm relative to the scapula or trunk should pose a simple problem


Shoulder Orientation Measured during Walking


Shoulder Orientation Measured during Abduction/Adduction


Shoulder Orientation Measured during Flexion/Extension


Shoulder Orientation Measured during Int/Ext Rotation(Adducted)


Shoulder Orientation Measured during Int/Ext Rotation(Abducted)


Shoulder Orientation Measured during Horizontal Flex/Ext


Shoulder Orientation Measured during Codman’s Motion


Shoulder Orientation Measured during Circumduction


Shoulder Orientation Measured during Overhand Throw


Summary of Analysis Methods

XXXWalk

XThrow

X-Codman

XCircumduction

XXXIE Adducted

XXIE Abducted

XH. Flexion

XXFlexion

XX-Abduction

HelicalXZY (F/E)ZXY (Ab/Ad)YZY (ISG)


Using Instantaneous Approaches

• Instantaneous Helical or Euler angles

• Both provide excellent sense of motion

• Both require an initialization point

• Neither provide accurate orientation angles


Other Approaches to Getting Better Results

• Change the arm’s reference position to what would normally be considered 90 degrees of abduction

• Cut out sections of the curve where discontinuities in motion occur, and then interpolate for the missing data

• Splice results from different rotation sequences together depending on the arm’s location relative to the trunk


Final Recommendations for Measurement of the Shoulder

• View the results using each of the measurement approaches, giving greater weight to the approach that best measures the dominant arm motion

• Select the approach that makes the most sense

clinically

• Report the method used


Acknowledgements

• Scott Coleman, for his help with the graphics and animations

• John Henley, for his willingness to serve as a sounding board for numerous unusual measurement strategies

• Dave Hudson, for letting me use pictures of him shot in profile

The End

Documents

University of Delaware Human Performance Laboratory A Tutorial on the Measurement of Joint Motion with Application to the Shoulder