Biomechanics - Introduction to Biomedical Engineering - page 216

16. Pelvic obliquity is commonly associated with an angular displacement of the pelvis as seen
from the front of the patient and is estimated as the angle formed between the vector from
right to left anterior superior iliac spine (ASIS) and the horizon. Given the pelvic position data
below, calculate the clinician's estimate of pelvic obliquity. Note: The clinician would be
looking down the

x -axis of the global coordinate system at the pelvic data in the y-z plane.

Right ASIS ¼ 0 : 400 i þ 0 : 400 j þ 0 : 580 k m

Left ASIS ¼ 0 : 390 i þ 0 : 435 j þ 0 : 600 k m

PSIS ¼ 0 : 100 i þ 0 : 418 j þ 0 : 820 k m

z-x-y
rotation sequence, would provide a value of pelvic tilt that would best match the clinician's
estimate in this case?
17. Given the pelvis and thigh anatomical coordinate systems defined in Example Problems 4.10
and 4.11, compute the pelvis tilt, obliquity, and rotation angles using a

Which Euler angle algorithm, one based on a y-x-z rotation sequence or one based on a

z - x - y rotation sequence.

18. Repeat Problem 17 (using a rotation sequence) solving for hip flexion/extension, hip

abduction/adduction, and internal/external hip rotation. Hint:

z - x - y

f e ta g is the triple-primed

is the unprimed system in this case.
19. Using MATLAB, determine the effect that a 10 mm perturbation in each coordinate direction
would have on ankle power amplitude (Section 4.6.3). Hint: Increase the foot anatomical
coordinate system

coordinate system, and f e pa g

by 0.010 m in each direction.
20. Reflective markers placed over the anterior superior iliac spine (ASIS) and the posterior superior
iliac spine (PSIS) define the pelvic anatomical coordinate system. An easy mistake to make in the
placement of these markers on an overweight or obese subject is to place the ASIS marker(s) at
the horizontal level of the ASIS, but not in the pelvic plane, as shown in the figure below. The
same type of error can be made with the placement of the PSIS. If the actual pelvic tilt for a patient
is 34 and reflective markers are placed in the following pelvic locations relative to the fixed
laboratory coordinate system, what is the magnitude of the error in pelvic tilt, if any?

f

e fa g

PSIS

ASIS