Dear All

Here is a summary of the responses to my query which I have added at the top
of the replies for completeness.

Thanks for all the replies. This is obviously an area that isn't fully
defined. There is evidence that the soft tissues in and around the joints
provide some information but how this relates to other sensory information
is unclear. Certainly food for thought and more years of research!

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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?

From: Dan Baker

Check out the following paper for some information. I'd agree w/ you that
the crux of the conversation is in what the definition of primary is, but
there is support for the idea that some of the ligaments may be involved in

Brand, R. A., 1986, "Knee Ligaments: A New View," Journal of
Biomechanical Engineering, Vol. 108, No. May, pg. 106-109.


From: Joel Vilensky

A recent review especially pertaining to the ACL is entitled:
Neurogenic factors in the etiopathogenesis of osteoarthritis, by
O'Connor and Brandt- Rheumatic Disease Clinics of North American 19:
581-605, 1993.


From: Howard J. Dananberg, DPM

I believe that the roleof ligaments are multifaceted.
Not only do they "connect one bone to the
other" and act proprioceptively, but they also store and return significant
amounts of energy during movement. When viewed in this light, the incapacity
rendered by a "simple" ankle sprain makes far more sense. There is a group
in the United States, the American Academy of Orthopedic Medicine (AAOM)
which is predominately MD's and DO's who treat many orthopedic pain syndromes
via a treatment process known as prolotherapy. This involves injecting
ligaments with proliferent solutions which create fibroblastic activity and
thus increase the integrity of it. The published results, particular as
regarding chronic lower back pain are quite excellent, especially when this
is viewed long term.

Much of what we have viewed in medicine, particularly in the field of
orthopedics and musculoskeletal entities, eg. arthritis, chronic joint and
muscle pain, etc. have been based on treatment which have proven themselves
to be less than optimal. Prehaps, the AAOM is correct in their thinking and
that we should examine ligaments in a different light.

From: Joseph E. Hale

I suggest you check the literature for articles by R. A.
Brand and colleagues or try contacting Dr. Brand directly
( Good luck!


From: Serge van sint Jan

I do not know the "state of the art" opinion about
the ligament function, but I think their basic function
is joint coherence. It is true that ligaments have proprioceptive
mechanisms, but for ligaments located in the neighboorhood of
big joints these mechanisms are not very efficient. At the
opposite of their colleagues close to smaller joints (e,g, fingers).
Also, some ligaments seems to act like a guide during a motion. Their
would assist the geometry of the surface to lead the moving segment.

I hope my boss will send your his meaning. He's on the list too
but he so busy that maybe he'll forget to do it.

Anyway here is his name:

Professor M. Rooze.
Department for Functional Anatomy
University of Brussels

Also the address of a neurophysiologist that has been involved
in proprioception research.

Professor K. Hainaut.
Department of Neurophysiology
Institute of Physiotherapy
University of Brussels
1050, Av. F. Roosevelt
1050 Brussels
phone: 32 2 650 21 05


From: Neil Glossop

Few fibres of the acl are isometric during normal knee motion. During
normal flexion, bands go from tension to compression (relaxation) depending
on their location and amount of flexion.



Grigg P. Peripheral neural mechanisms in proprioception. Journal of Sport
Rehabilitation. 1994, 3, 2-17.

"...While ligament afferents have been suggested to serve a role in proprio-
ception, I feel it is unlikely that they serve major proprioceptive roles, for
the following reasons:
1. There is a paucity of nerve endings. While there are relatively
large numbers of afferent neurons having endings in the joint capsule, there
appear to be no more than a few ligament afferents that originate in the ACL.
2. Ligament afferents would function as nonspecific limit sensors.
ACL afferents are not active whe the knee is in a neutral position, defined as
30 degrees from full extension. They have been shown to respond to stimuli
that would cause tensile loading of the ACL: rotations into the limit of
flexion, extension, and internal or external rotation. Since ligament tension
can be caused by a number of different types of rotations, the
mechanoreceptors in them are poor candidates to subserve proprioceptive
sensations of movements
in specific directions. While neurons innervating the collateral ligaments
are less well documented, they also appear to be tension sensitive, and thus
to be subject to the same reservations as stated for ACL..."

Also from DeCarlo MS & Talbot RW. Evaluation of ankle joint proprioception
following injection of the anterior talofibular ligament. Journal of
Orthopaedic and Sports Physical Therapy. 1986, 8, 70-76.

"...The anesthetic injection had no effect on joint proprioception..." The
investigators injected the ligament with Xylocaine and came to the above

Hope this helps with the ligament proprioception question.


From: Tom Buchanan

In response to your request on BIOMCH-L, here are a few observations from
literature on ligaments afferents. As you will see, there is considerable
controversy about the nature and importance of the neural role of
ligaments. This is by no way a complete list, but merely an intoduction to
some of the issues.


Three types of nerve endings have been found in the human knee: free nerve
endings (FNE), Ruffini corpuscles and Pacini corpuscles (Halata, Rettig &
Schulze; 1985). Ruffini corpuscles resemble Golgi tendon organs when the
perineural capsule is well-developed, generally found when collagenous
fibrils are orientated in parallel fashion.

In cat, Golgi-type receptors are innervated by the medial articular nerve
(MAN) and lie along the inside surface of the capsule (Grigg, Hoffman &
Fogarty; 1982). Also in cat, Ruffini-type receptors are innervated by the
posterior articular nerve (PAN) and lie along the posterior region of the
capsule (Grigg & Hoffman; 1982).

Human finger studies reveal that although articular mechanoreceptors can
signal joint movement in the absence of other sensory input, they do not
make significant contributions to proprioception (Clark, Grigg & Chapin;
1989). This agrees with earlier human studies (Clark et al., 1979). It is
believed by these investigators that muscle and skin are largely
responsible for proprioception.

On the other hand, Ferrell (1977) argues that there are adequate articular
mid-range units to provide useful information about joint angle.

Also, locomotion studies following injection of an anesthetic into the knee
capsule showed obvious abnormalities including a reduction of motor
activity (Ferrell, Baxendale, Charnachan & Hart; 1985). This has been
explained as being a result of reduced proprioceptive acuity.

Activation of a small number of PAN afferents can significantly influence
the behavior (i.e., result in entrainment) of quadriceps motor units
(Baxendale, Ferrell & Wood; 1987, 1988). However, only some PAN neurons
have this effect, whereas others do nothing or have inhibitory effects.

The excitability of flexion reflexes are influenced by the initial angle of
the limb (Baxendale & Ferrell; 1981). Specifically, the excitability of
flexion reflex pathways decrease as the knee is progressively flexed whilst
the excitability of the crossed extensor reflex decreases as the knee is

Sjolander (1989) has argued that the cruciates play a sensory role via
reflexes onto the gamma muscle spindle system.

Studies that we have done (Kim et al., in review) indicate that direct
electrical stimulation of medial and lateral collateral ligaments will
result in reflex activity of the medial and lateral muscles which could
offer protection to the joint. The same was also found following rapidly
applied varus and valgus movements (Kim et al., also in review). These
studies imply that afferant signals from joint meechanoreceptors, be they
from ligaments or joint capsule, can provide important information about
joint stability.


Baxendale, R.H., Ferrell, W.R., and Wood, L. The responses of quadriceps
motor units to mechanical stimulation of knee joint receptors in the
decerebrate cat. Brain Res. 453: 150-156, 1988.

Baxendale, R.H., Ferrell, W.R., and Wood, L. The effect of mechanical
stimulation of knee joint afferents on quadriceps motor unit activity in
the decerebrate cat. Brain Res. 415: 353-356, 1987.

Baxendale, R.H. and Ferrell, W.R. The effect of knee joint afferent
discharge on transmission in flexion reflex pathways in decerebrate cats.
J. Physiol. 315: 231-242, 1981.

Clark, F.J., Grigg, P., and Chapin, W. The contribution of articular
receptors to proprioception with the fingers in humans. J. Neurophysiol.
61: 186-193, 1989.

Clark, F.J., Horch, K.W., Nach, S.M., and Larson, G.F. Contributions of
cutaneous and joint receptors to static knee-position sense in man. J.
Neurophysiol. 42: 877-888, 1979.

Ferrell, W.R., Baxendale, R.H., Carnachan, C., and Hart, I.K. The influence
of joint afferent discharge on locomotion proprioception and activity in
conscious cats. Brain Res. 347: 41-48, 1985.

Ferrell, W.R. The discharge of mechanoreceptors in the cat knee joint at
intermediate angles. Proc. Physiol. Soc. Feb: 23P-24P, 1977.

Grigg, P., Hoffman, A.H., and Fogarty, K.E. Properties of Golgi-Mazzoni
afferents in cat knee joint capsule, as revealed by mechanical studies of
isolated joint capsule. J. Neurophysiol. 47: 31-40, 1982.

Grigg, P. and Hoffman, A.H. Properties of Ruffini afferents in cat knee
joint capsule, as revealed by stress analysis of isolated sections of cat
knee capsule. J. Neurophysiol. 47: 41-54, 1882.

Halata, Z., Rettig, T., and Schulze, W. The ultrastructure of sensory nerve
endings in the human knee capsule. Anat. Embryol. 172: 265-275, 1985.

Sjolander, P. A Sensory Role for the Cruciate Ligaments. Ph.D. Thesis,
University of Umea, Sweden, 1989.


You maybe interested to look at a paper

Gandevia, S.C. and Burke, D.(1992) Does the nervous system depend on
kinethestic information to control natural limb movement. Behavioral
and Brain Sciences, 15,4,614-632

From: Chris Kirtley

How's it going, old marrow?!

You've opened a can of worms with your question on proprioception (which
was the subject of my PhD at Strathclyde). Basically, this is still a
controversial topic. Most neurophysiologists would say that the primary
proprioceptive afferents are the spindles and skin organs. As you say, the
spray endings in the joint capsule seems to be more important at the
extremes of joint motion.

Two very notable heretics however, are Ron Baxendale & Bill Ferrel of
Glasgow University, who still claim that the spray endings are primarily
important. I read a review some months ago which seemed to be putting the
case for discounting the Glasgow school and reaching a final consensus (the
issue has been debated for a frustratingly long time) about the relative
unimportance of the spray endings.

Hope this clarifies things a bit!


From: Allen Goodship

With respect to your request for info on ligaments I think the role in
relation to proprioception and mechanoreceptors is important and poorly
addressed. Dick Brand has done some work to show the presence of
mechanoreceptors in the cranial cruciate ligament of the cat, including
muscle response to stimulation of these receptors.
We have recorded strains in the cruciate of sheep during locomotion, there
are changes in deformation during the gait cycle, David Pickles is my
post-doc who has been doing this work. So I am not sure how you define
isometric, I beleive ligaments are not operating in an isometric mode in
the pure sense.

From: Trey Crisco

There is lots on this issue. I would recommend starting with Dick Brand's
article: Brand RA, "Knee ligaments: A new view", J. Biomechanical
Engineering, 108:106-110, 1986.

From: Peter Bower

There is good EMG data to support the notion that ligamentous structures
and small muscles surrounding spinal joints both influence muscular tone.
The encoded neural info from stretch receptors is complex in its
interaction at a spinal cord level, but load application into many
ligamentous structures can produce demonstrable changes in the tone of
quite distant muscles. The proprioceptive function of both ligaments and
fascial structures seems well established.

From: Julie Steele

I am just completing the literature
review for my thesis on ACL deficiency which includes a section on the
role of the ACL in proprioception.

From: "G.R.Johnson"

I was interested to see Mark's 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 information to
be infuenced by AP loading which would increase or decrease the tensile
strains in proportion to the applied stress (assuming they are
approximately 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 easier 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!


From: Peter Sinclair

I had never heard ACL suggested as a proprioceptive organ before your
posting last week and on first glance it does seem hard to believe.


From: Per Sjolander

It is true that it seems very likely that sensory endings within
ligaments provide cues for movement and position sense. The
proprioceptive function of the ligaments does not, of course,
imply that the mechanical functions of the ligaments are of less
importance. Regarding proprioception it seems safe to
conclude that the ability to perceive movements and joint
positions are, in general, derived from sensory information
emanating from both muscles and joints (and perhaps skin).
The relative contribution from different sources is probably
not the same for different joint, and is quite certainly
dependent on whether position sense or movement sense are
considered. For extensive discussions on these topics I can
recommend the following reviews:

Johansson H. et al.; Receptors in the knee joint ligaments and
their role in the biomechanics of the joint. Critical Reviews in
Biomedical Engineering 18, 1991, 341-368.

Johansson H. & Sjolander P.; The neurophysiology of joints.
In: Mechanics of Human Joints - Physiology, Pathophysiology,
and Treatment. Eds: V Wright & EL Radin. Marcel Dekker,
New York, 1993, pp 243-290.


From: Robert Day

As to proprioception, most of the recent work I have seen tends
to show the joint capsules as being much more important in this than
previously thought.

And of course, the primary function of ligaments is mechanical
constraint. Beware of asking medical students philosphical questions!


From: Marwan Sati
(On behalf of Prof. Hocine Yahia)

We believe that the ligament's function is both mechanical and
neurological. Through gold chloride staining and immunohistochemical
studies, we have found, as have others using different techniques,
mechanoreceptors in the body of the canine ligament (see refs below).
Surprisingly these receptors were mostly in the body of the ligament
not at the attachment sites.

The mechanoreceptors probably play a protective role, since mechanically
speaking, ligaments have a low security factor compared to bone. The
security factor of the ligament is of the order of 1 compared to the
bone's security factor which is of the order of 4 to 6.

Some references from our institute on this work include:

Yahia L.H., Newman N. St-Georges M."Innervation of the Canine Cruciate
Ligaments", Anat. Histol. Embryol., 21:1-8, 1992.

Yahia L.H., Newman N. "Mechanoreceptors in the Canine Anterior Cruciate
Ligament" Anat. Anzeiger Jena. 173:223-238, 1991.


Mark Pearcy
Associate Professor of Biomedical Engineering

School of Engineering
Flinders University of South Australia
GPO Box 2100
South Australia 5001

Phone: (+61) 8 201 3612
Fax: (+61) 8 201 3618