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gjohnson89
11-11-1994, 09:01 PM
I was interested to see marks note about ligaments and proprioception.
Also as an engineer, I have been worried by the now almost accepted
wisdom that this is a major role of the ACL. As I understand it, while
the ligament as a whole is isometric, the indiviual fibres attach to the
bones over a relatively wide site so that not all fibres are isometric.
The result of this is that some strains accompany knee flexion
extension. However, I am still not happy. In particular, if these
strains do assist in proprioception, we would expect the infromation to
be infuenced by AP loading which would increase or decrease the tensile
strains in proportion to the applied stress (assuming they are
approximaetly linear elastic). If I were the engineer dsigning a knee
this potential for cross talk would worry me! After all, it would seem
to be much easirer to derive position information from muscles which, it
is well known, can feedback both length and force information.

I hope this stirs up a bit more discussion!

Garth Johnson
Centre for Rehabilitation and Engineering Studies
University of Newcastle
g.r.johnson@newcastle.ac.uk
tel:+44-191-222-6196
fax:+44-191-222-8600


On Wed, 9 Nov 1994, Mark Pearcy wrote:

> Dear All
>
> Recently I had a discussion with a group of medical students about the
> function of ligaments. Coming from a mechanical engineering backgound I
> expected the answer to the question,"What is the primary function of a
> ligament?", to be ,"to hold two bones together". The answer I got from a
> student who's background was in biology was that the primary function of a
> ligament was proprioception. A discussion followed as to what we each meant
> by function and what the definition of primary was!
>
> We were talking about the anterior cruciate ligament in particular and I
> started thinking afterwards about how this ligament could give
> proprioceptive signals. I believe the ACL is reasonably isometric during
> the full range of knee flexion. If this is the case it can't give
> information as to the position of the Tibia relative to the Femur. Other
> ligaments don't actually stretch much during normal activities either, or
> the muscles would be working against their resistance all the time.
>
> In conversation with anatomists and physiologists I have been told that the
> small muscles around joints tend to have more stretch receptors than the
> large motor muscles and the suggestion is that these small muscles are in
> fact the joint position transducers. At the extremes of joint motion
> signals from the ligaments might augment the muscle signals to provide a
> safety mechanism to prevent injury.
>
> What is the current thinking of those involved in this area?
>
> As I've only just been connected to the world I'm sorry if this subject has
> been done to death already but I'd appreciate your thoughts.
>
> I'll compile and post the replies as is usual.
>
> Regards
>
> Mark Pearcy
>
>
> ************************************************** **************************
> ***********
> Mark Pearcy
> Associate Professor of Biomedical Engineering
>
> Email egmjp@cc.flinders.edu.au
>
> School of Engineering
> Flinders University of South Australia
> GPO Box 2100
> Adelaide
> South Australia 5001
> Australia
>
> Phone: (+61) 8 201 3612
> Fax: (+61) 8 201 3618
>