Bioengineering

Question 1

Define motion capture

Answer 1

Recording movement and translating that movement into a digital model.

Question 2

What is the difference between kinematics and kinetics?

Answer 2

Kinematics is directly referring to movements.

Kinetics is referring to the forces involved in those movements.

Question 3

What is required to define a position in 3D space?

Answer 3

A reference frame. This includes an origin where all three axis meet, and all positions are recorded in relation to this.

Question 4

What are the four components of kinetics?

Answer 4

• Displacement
• Orientation
• Velocity (1st derivative of displacement)
• Acceleration (2nd derivative of displacement).

Question 5

How are velocity and acceleration recorded

Answer 5

By recording position as a function of time, it is then possible to calculate velocity (1st derivative) and acceleration (2nd derivative) too.

Question 6

Orientation:
What are the three movements?
Which planes are these movements in?
Which axis does each movement rotate around?

Answer 6

• Flexion/extension – Sagittal (YZ) plane – Rotates around the X axis.
• Abduction/adduction – Frontal (XZ) plane – Rotates around the Y axis.
• Rotation – Transverse (XY) plane – Rotates around the Z axis.

Question 7

What are the “zero” angles for each joint defined as?

Answer 7

the angles are all zero when the person is in the anatomically neutral position

Question 8

For each movement, is the angle +ve or -ve?

Answer 8

• Flexion +ve/extension -ve
• Adduction +ve, abduction -ve
• Internal rotation +ve, external rotation -ve.

Question 9

What are the five assumptions made for motion capture?

Answer 9

1) Bones are rigid.
2) Joints have fixed axes.
3) Joints are frictionless.
4) Mass distribution is unaffected by soft tissue movement.
5) Geometry is consistent between subjects.

Question 10

How can a technical reference frame be used to ensure one of the assumptions of motion capture is not broken?

Answer 10

• Technical reference frame involves placing markers onto external pieces of plastic.
• This ensures the markers remain static in relation to one another, preventing the assumption that bones are rigid bodies being broken.

Question 11

What are the 18 data variables that need recording for each segment in motion capture?

Answer 11

• Position (XYZ) of CoM of segment.
• Linear velocity (XYZ) of CoM of segment.
• Linear acceleration (XYZ) of CoM of segment.
• Angle of segment (XYZ).
• Angular velocity of segment (XYZ)
• Angular acceleration of segment (XYZ).

This totals 9 measurements for both position and angle. (3 sets of 3 for each, relating to position, velocity and acceleration).

Question 12

What is a goniometer and how does it work?

Manual vs electronic

Answer 12

Is attached to two adjacent segments of the body either side of a joint. Used to measure the angle of the joint.

Manual - used to measure static angles. Cheap but not very useful.

Electronic - Can be used to measure angles in active movement. However, difficult to align and can inhibit natural movement patterns.

Question 12

How are segments defined in relation to one another?

Answer 12

Parent segment - the segment that is static.

Child segment - the segment that rotates around the parent.

Question 12

What is an intertial measurement unit? (what components does it contain))?

Answer 12

• Accelerometer. Measures acceleration.
• Gyroscope. Measures angular acceleration.
• Magnetometer. Measures orientation in relation to gravity.

Not all IMUs contain the magnetometer, but this is required to obtain real-world measurements.

Question 13

What is important when setting up 2D imaging measurement motion capture)?

Answer 13

Ensure the camera is positioned exactly orthogonally to the plane the movement is being measured in.

Also make sure the camera is in exactly the same place for all readings being compared to one another.

Question 14

How can multiple angles be measured at the same time using 2D motion capture?

Answer 14

Set up multiple cameras at orthogonal angles to one another.

Question 15

What is 2D fluoroscopy motion capture?

Answer 15

Use fluorescence and scanners to measure angles far more precisely.

Rarely used as expensive, can only measure small, unnatural movements and often requires exposing the patient to radiation - difficult to justify.

Question 16

What are the two types of 3D motion capture? Define them

Answer 16

Passive - reflective balls are used as markers. Cameras have infrared lights and pick up on reflected infrared light. Other reflective surfaces in the FOV will result in interference.

Active – The ball markers contain LEDs and will flash. The cameras pick up on this light. Much better as the cameras can identify one marker from the other more easily.

Question 17

What is the most common issue with motion capture in the gait lab?

Answer 17

Difficult to get patient to exhibit their natural gait pattern under observation.

Use of treadmills/VR environments aims to improve this.

Question 18

What is the capture volume in relation to 3D motion capture?

Answer 18

Capture volume – Refers to the area in which the subject can be motion captured.

Question 19

How is the room calibrated for 3D motion capture?

Answer 19

Uses a calibration wand, which has lots of the LED balls attached. To calibrate:

1) Wave the wand around in the capture volume. This lets the cameras work out where they are in relation to one another.

2) Then, place the wand on the floor to calibrate where the floor is. It is important to not move the cameras after calibration, as this will mess up the data.

Question 20

How many markers are required to define a reference frame?

Answer 20

3 markers required to define a reference frame.

Question 21

How many cameras must be able to see a marker at any one time to define its position in 3D space?

Answer 21

2 cameras must be able to see the marker otherwise it will be lost.

Question 22

Where are the physical markers placed on the patient for 3D motion capture?

Answer 22

• Bony prominences.
• Anatomically significant locations.

Question 23

What extra calibration is required for passive motion capture?

Answer 23

Participant must stand still in the capture volume. Each marker is then calibrated to the relevant anatomy.

Question 24

What data processing is required for motion capture (especially for passive capture)?

Answer 24

Markers will have been dropped and/or mixed up throughout the motion capture. Software is available to assist with cleaning the data, but often it needs doing manually.

For an active system, less data cleaning is needed but still might be necessary.

Filtering is also used to remove noise - usually a low-pass filter.

Question 25

What is one gait cycle?

Answer 25

One gait cycle refers to the time in a walking pattern between one foot striking the ground, and then the same foot striking the ground again.

Question 26

What are the two main phases in the gait cycle? What percentage of each cycle does each take up?

Answer 26

Stance phase – time when the leg of interest is in contact with the floor (60%)

Swing phase – time when the leg of interest is NOT in contact with the floor (40%).

Question 27

What are virutal markers? How are they defined and what is their significance?

Answer 27

• Virtual markers are created in the model to correspond to points that are not physically accessible on the patient.
• They are defined by using two physcial markers, and placing the virtual one in relation to them.
• Useful as lots of anatomically significant points (such as joint centres) are not accessible without the use of virtual markers.

Question 28

How is the primary axis definied?

How are the secondary and tertiary axes defined?

Answer 28

Primary axis is assigned from the primary to the secondary marker.

Use the right hand rule to define the other two: pointer finger along the primary (x) axis. Middle finger is then the secondary (Y) axis, and the thumb is the tertiary (Z) axis.

Question 29

How is direction of rotation assigned to a given axis in motion capture?

Answer 29

Right hand rule - point thumb along the axis. The direction fingers are curling is +ve rotation, other direction is -ve.

Question 30

What is a hemiplegic gait? What pathology causes it?

What is the most obvious marker on the gait analysis?

Answer 30

Unilateral foot drop due to distal weakness in ankle.

Caused by stroke.

Gait analysis shows unilateral reduced flexion in ankle during the swing phase.

Question 31

What is a diplegic gait? What pathology causes it?

Answer 31

Bilateral scissoring with the patient walking on tip-toes.

Associated with cerebral palsy.

Question 32

What is a neuropathic gait? What pathology is it associated with?

What is the most obvious marker on the gait analysis?

Answer 32

Bilateral foot drop. Associated with peripheral neuropathy.

Gait analysis shows more hip and knee flexion due to compensatory high leg lift.

Question 33

What is a myopathic gait? What pathology is it associated with? What sign is it associated with?

Answer 33

Waddling gait caused by pelvic weakness. Associated with muscular dystrophy.

Trendelenburg sign +ve.