Biomedical Engineering Reference
In-Depth Information
kinematic quantification is of limited clinical value. Markers must either be placed directly
over palpable bony landmarks on the segment or at convenient (i.e., visible to the measure-
ment cameras) locations on the segment that are referenced to the underlying bones. An
examination of the pelvic and thigh segments illustrates these two alternatives.
Pelvic Anatomical Coordinate System
For the pelvis, markers placed over the right and left anterior-superior-iliac-spine (ASIS)
and either the right or left posterior-superior-iliac-spine (PSIS) will allow for the computa-
tion of an anatomically aligned coordinate system, as described in Example Problem 4.10.
EXAMPLE PROBLEM 4.10
Given the following three-dimensional locations in meters for a set of pelvic markers expressed
relative to an inertially fixed laboratory coordinate system (Figure 4.29),
Right ASIS
:
RASIS
¼
0
:
850
i
0
:
802
j
þ
0
:
652
k
Left ASIS
:
LASIS
¼
0
:
831
i
0
:
651
j
þ
0
:
652
k
PSIS
¼
1
:
015
i
0
:
704
j
þ
0
:
686
k
compute an anatomical coordinate system for the pelvis.
r
3
PSIS
LASIS
e
paz
PSIS
r
1
RASIS
e
pay
LASIS
r
2
H
RASIS
e
pax
H
TW
MK
LK
K
r
4
r
7
TW
e
taz
r
8
e
ttz
MK
r
5
e
tay
K
LK
e
tty
e
tax
r
6
e
ttx
r
9
FIGURE 4.29
Kinematic markers used to define pelvis and thigh coordinate systems. For the pelvis, PSIS
denotes posterior-superior-iliac-spine, H is hip center, and RASIS and LASIS denote right and left anterior-
superior-iliac-spine markers, respectively. For the thigh, TW is thigh wand, K is knee center, and MK and
LK are medial and lateral knee (femoral condyle) markers, respectively.
Continued
