Dear BIOMECH-L'ers,
Recently, our group has been doing some dynamic modeling on the full
body motions, and are interested in simple mechanical models of the
lumbar/sacral joint. We have two main questions:
(1) We are looking for reasonable estimates of the moment arms of intra-
abdominal pressure acting about the L5/S1 joint. We are aware of a
reference in an article by Chaffin:
Chaffin (1975) "On the validity of biomechanical models
of the low back for weightlifting analysis," ASME
Proceedings, 75-WA-bio-1.
This is also cited in Chaffin and Andersson's book:
Chaffin and Andersson, Occupational Biomechanics,
Wiley, New York, 1991.
Are there any other approaches we can take in modeling intra-abdominal
pressure? We are particularly interested in subject-specific models
based on scaling schemes based on bony landmark measurements. We are
hoping to obtain a simple relation between TORSO ANGLE and the L5/S1
intra-abdominal pressure MOMENT ARM.
(2) We also are trying to find a subject-specific scaling scheme (based
on bony landmarks, hopefully) for the distance from the skin surface to
L5/S1 joint center of rotation. Is there a database or study out there
that relates to this estimate in some way? We are aware of the work of
McNeill et al:
McNeill, T, Warwick, D, Andersson, GBJ, Schultz (1980)
"Trunk Strengths in attempted flexion, extension and
lateral bending in healthy subjects with low back
disorders," Spine 5: 529-538
This study places the L5/S1 joint center 34% from posterior on the
anteroposterior diameter. Is there any other related information out
there?
As always, we will post a summary of responses. Thanks in advance,
Hsin-I Chang, B.S.
Wynne Lee, Ph.D.
Jim Patton, M.S.
Aileen Russo, M.S.
Julie Steege, B.S.
Motor control and learning group
Programs in Physical Therapy and Biomedical Engineering
Northwestern University
Chicago, Illinois, USA