6/4/93

Dear Biomech-l Colleagues,

I am currently conducting research in kinematically defining leg motion

in chiropractic patients who have exhibited symptoms of leg length inequality

(LLI). This LLI is physiological in nature, hypothesized to be caused by

musculature imbalance somewhere in the back. It has been reported that

chiropractic adjustment results in alleviation in pain related to the LLI

phenomenon. My research partners and I are in the process of quantitatively

assessing apparent LLI cases. Since the LLI is not a structural problem,

adjustments which cause realligment of the legs should result in one of 3

cases:

1) One leg moves inferior while the other remains stationary

2) One leg moves superior while the other remains stationary

3) One leg moves superior while the other moves inferior

Regardless of which case is occuring, there must exist some translation, and

probably rotation, of one leg with respct to the other. This probably means

that some sort of pelvic rotation is involved. Nevertheless, we are

interested in determining the location of the center of rotation of one leg

with respect to the other. This is where my question arises.

I have conducted a literature review concerning the calculation of the

Instantaneous Helical Axis of rotation. Description of this variable lies in

the equation:

v = w X r

where v is the linear velocity of a point, w is the angular velocity of that

point, and r is the radius of rotation. McFayden et al. (1988) show how this

equation may be used to find the hip and ankle joint centers. There work was

conducted in 2D. Woltring expands upon this in a complex manner to find IHAs

in 3D. It seems, however, that the previous equation could be used, since

all are vector quantities. If a reference frame attached to one of the legs

is considered to be the global reference frame and the reference frame

attached to the other leg is the local reference frame, then the point of the

ICR should be able to be determined using information from both reference

frames.

My question concerns the determination of w. If a vector is constructed

from the origin of frame 1 to frame 2, movement of frame 2 wrt frame 1 will

result in some w. But frame 2 might also be "spinning" about itself. Does

this "spinning" come into play when determining w? If it does not, the the

previous equation can be utilized. If it does, then how do I calculate w?

Any responses or thoughts would be greatly appreciated.

Thanks,

John DeWitt

Graduate Assistant

Exercise and Sport Research Institute

Arizona State University

Tempe, Arizona USA 85287-0404

(602) 965-7528

email: dewitt@espe1.la.asu.edu

Dear Biomech-l Colleagues,

I am currently conducting research in kinematically defining leg motion

in chiropractic patients who have exhibited symptoms of leg length inequality

(LLI). This LLI is physiological in nature, hypothesized to be caused by

musculature imbalance somewhere in the back. It has been reported that

chiropractic adjustment results in alleviation in pain related to the LLI

phenomenon. My research partners and I are in the process of quantitatively

assessing apparent LLI cases. Since the LLI is not a structural problem,

adjustments which cause realligment of the legs should result in one of 3

cases:

1) One leg moves inferior while the other remains stationary

2) One leg moves superior while the other remains stationary

3) One leg moves superior while the other moves inferior

Regardless of which case is occuring, there must exist some translation, and

probably rotation, of one leg with respct to the other. This probably means

that some sort of pelvic rotation is involved. Nevertheless, we are

interested in determining the location of the center of rotation of one leg

with respect to the other. This is where my question arises.

I have conducted a literature review concerning the calculation of the

Instantaneous Helical Axis of rotation. Description of this variable lies in

the equation:

v = w X r

where v is the linear velocity of a point, w is the angular velocity of that

point, and r is the radius of rotation. McFayden et al. (1988) show how this

equation may be used to find the hip and ankle joint centers. There work was

conducted in 2D. Woltring expands upon this in a complex manner to find IHAs

in 3D. It seems, however, that the previous equation could be used, since

all are vector quantities. If a reference frame attached to one of the legs

is considered to be the global reference frame and the reference frame

attached to the other leg is the local reference frame, then the point of the

ICR should be able to be determined using information from both reference

frames.

My question concerns the determination of w. If a vector is constructed

from the origin of frame 1 to frame 2, movement of frame 2 wrt frame 1 will

result in some w. But frame 2 might also be "spinning" about itself. Does

this "spinning" come into play when determining w? If it does not, the the

previous equation can be utilized. If it does, then how do I calculate w?

Any responses or thoughts would be greatly appreciated.

Thanks,

John DeWitt

Graduate Assistant

Exercise and Sport Research Institute

Arizona State University

Tempe, Arizona USA 85287-0404

(602) 965-7528

email: dewitt@espe1.la.asu.edu