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Christopher.johnston@ah.slu.se
01-30-1995, 08:37 PM
Dear Biomech:ers
Earlier (950124) I had posted a series of questions concerning injury types
and loading in joints and tendons. I have received many responses that were
interested in the results of the responses (13) and two that may serve as
sources of information. Accordingly, I send the two responses and perhaps
initiate a discussion.

The general question is: assuming that certain injuries have a biomechanical
etiology, is it loading or loading rate that is the injury-causing factor to
a biomaterial? Motivation of this question is obvious for many, we wish to
identify those conditions that may be harmful to our subjects (horses in my
case).

Let us begin with a discussion, which I do not claim to be complete or
correct but a synopsis of my subjective perception of the knowledge in this
area. Criticism is encouraged along with contribution.

In the literature I have found many statements as to the effect of
"increased popularity of running has resulted in an increase in
injuries......degeneration of articular cartilage is SUPPOSED to be result
of repetitive impulsive loading." This is potentially a very powerfull
statement as there is a cause-effect relationship supposed. Based on this
supposition, one need not search long to find articles on impact/impulse
loading in various sporting events, surfaces, shoes and other variables
considered important in impact. Much of this supposition is based on what I
believe to be excellent experimental work of Dr. Radin and coworkers. The
general hypothesis is that joint damage is brought upon by repetitive
loading and oscillary movement. This is appealling and a strong
cause-effect relationship is suggested in the animal studies of this group
and many others. Yet, at which frequency or loading rate is injury
induction, 40-70 Hz at relatively low joint moments or 7-10 Hz at higher
joint moments?

Another question which I find interesting is the direction of the loading,
that is many experiments look at longitudinal loading or vertical and
horizontal loading. If we assume the stiffness of the distal limb to be
greatest in the longitudinal direction (column of bone), then one may
continue to assume that this is sufficiently stiff to withstand the loads
imposed upon it. However, the transversal direction of the system may not
be as stiff and thus limb geometry and direction of loading may be of
consequence. Recently, O'Connor and Johnston (not me!) ISB Congress Paris
1993 suggested that compression (impulsive loading) and friction may be
needed to approach the physiological limits of articular cartilage. Does
impulsive loading have to occur in at least two directions to induce
pathological changes or does the enviroment in the joint have to change to
increase friction to then induce changes?

In response to this area of interest, I received an E-Mail from Howard J.
Dananberg, DPM (howiedbpg@aol.com). The response is within quotations.

>"I read your posting today and would like to contribute to the discussion. I
>am a podiatrist who has spent many years in gait analysis. While injuries
>(eg. falling from a height) occur regularly, the more interesting subject is
>the overuse type complaint (osteoarthritis). While my expertise is in feet,
>I am involved in seeing many lower extremity complaints which appear related
>to style of gait rather than direct injury. In other words, the degeneration
>occurs slowly over time. One of the most common arthridities is in the great
>toe joint (hallux limitus). The shock at forefoot strike does not appear to
>be vectored correctly to provide the type of degenerative changes which are
>visible. Instead, I believe that the process of injury is related to the
>following. As the heel lifts from the ground (a motion created by the pull
>of the opposite swing limb rather than the calf), there exists a momentary
>failure of the MTP joint to immediately flex. Compression then occurs across
>the joint, and eventual DJD type changes occur (after millions of cycles).
> This would seem true in the hip as well, considering the lack of motion
>which occurs in DJD is extension, a motion which occurs in the 2nd half of
>the gait cycle and unrelated to heel strike impact loads. Even knee
>arthritis, which is predominately (95%) in the medial aspect, fits this
>paradigm. The lateral knee is loading initially at heel strike. The medial
>compartment, (which does take 60% of the total load by midstance) is loaded
>later in the step.

I have written several papers on this subject and would be happy to send them
to you. I would also be happy to discuss this in more detail if you wish."

I think a more indepth discussion would be very interesting for all and
please do give the references.

The next question was that on loading and loading rates of ligaments and
tendons. The information here is scant to say the least. Strain rate has
been suggested as the determining factor of injury type in ligaments
according to two articles I have found ( Noyes et al. Biomechanics of
Anterior Cruciate ligament Failure:... J. Bone Jt. Surg. 56 (A-2) 1974;
Crowninshield and Pope The strength and failure characteristics of rat
medial collateral ligaments. Journal of Trauma 16 (2) 1976). The general
opinion is that low rates of strain result in bone-ligament interface
failure while higher rates result in mid-substance failure. My question
was if there is a differential length change in ligaments (tendons) as
related to loading rate?

Response to this came from Sharon Dixon (s.j.dixon@uk.ac.lut). Response is
in quotations.

>I was very interested to read your posting on the Biomech listing. I am at
>present in my second year of a PhD studying Achilles tendon loading during
>running. I have used a two-dimensional rigid body representation to estimate
>maximum Achilles tendon force, and have found that maximum force occurs during
>the midstance phase.
>Investigation into the influence of heel lifts on the max. force has suggested
>that max. force may not be the most important factor when considering injury
>occurrence.
>The next stage of my work will be to examine the loading at impact, looking in
>particular at the loading rate. Modelling techniques will be used for this.
>I would be very interested in any evidence you come across on the cause of
>tendon injury, specifically with reference to tendon loading rate.

I hope these comments are of interest, please feel free to comment and
contribute to the discussion.

I can compilate the discussion at a later date

Regards

Chris Johnston, DVM
Equine Biomechanics Lab.
School of Veterinary Medicine
Uppsala, Sweden
Christopher.Johnston@ah.slu.se
Chris Johnston, DVM
Equine Biomechanics Lab.
School of Veterinary Medicine
Uppsala, Sweden
Christopher.Johnston@ah.slu.se