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Hayashi Kozaburo
09-22-1995, 12:34 PM
>Date: Fri, 22 Sep 1995 14:16:08 +0100
>Reply-To: Marco Viceconti
>From: Marco Viceconti
>Subject: ACL reconstr. mech prop (summary)
>To: Multiple recipients of list BIOMCH-L
>
>Quite a long ago I posted a question about tensile properties of ACL
>reconstruction. A few colleagues replied and we discussed a little. I
>held this summary because it seemed that nobody had any conclusive evidence
>to support or to refuse my hypothesis. But the time did not help, so I am
>posting it now.
>As Joseph Crisco pointed out, "At least I have never seen any discussion
>stating that the viscoelastic properties of thick [fibrils] were different
>from thin". However, the idea was that fibrils thickness distribution
>could influence not the viscoelastic properties but the strength and the
>failure mode of the ACL. Another point is that we were referring to the
>failure LOAD not to the failure STRESS, thus we can have also structural
>effects. If somebody else can say something about it, we start up again
>the discussion!
>
>Since the question was cross-posted to BIOMCH-L and BIOMAT-L also the
>summary will be cross-posted; sorry for those signed to both.
>
>Marco Viceconti
>
>
>*************************ORIGINAL POSTING*************************
>To: biomech-l_forum, biomat-l_forum
>From: lk1boq74@icineca.cineca.it (Marco Viceconti)
>Subject: ACL reconstruction mech props
>Cc:
>Bcc:
>X-Attachments:
>
>Dear Colleagues,
> we've just completed a study on tensile strength of sheep ACL
>reconstruction done using the central third of the patellar tendon, at
>different stages of healing.
>Our methods were very similar to those used in other studies (i.e. Amendola
>et al, Am J sports Med 20-3 1992, pp:336-346) but with one substantial
>difference; the load rate. In fact our test were quasi-static (100 N/min)
>were the results obtained in literature are usually obtained at high load
>rate.
>
>The results we found tend to support the hypothesis of almost complete
>recover on mechanical strength after about 12 months; this finding seems to
>be in contrast with other studies; the same paper of Amendola reports an
>identical study on sheep where after 12 months the max. tensile load was
>still 44% of that of the intact ACL. Again, these finding are based to
>tests done at a much higher load rate than ours.
>
>How should we read these results? Can the load rate explain the difference
>between our and other data?
>
>Any opinion or comment will be welcome.
>*************************END OF ORIGINAL POSTING*************************
>
>*************************************************
>X-Sender: Joseph_Crisco_III@postoffice.brown.edu
>Mime-Version: 1.0
>Date: Thu, 22 Jun 1995 07:48:04 -0500
>To: Marco Viceconti
>From: Joseph_Crisco_III@brown.edu (Trey Crisco)
>Subject: Re: ACL reconstruction mech props
>
>Marco,
> Very interesting. I do not have Amendola's paper, but I would be
>very suprised if their rate of loading was "high". To the best of my
>knowledge there have been no studies on ligaments at rates that we would
>expect to occur during in vivo injury production. The reason for this is
>the history of testing. Material testers have been adopted by
>biomechanical engineers, and most of these testers are slow. The fastest a
>ligament has been pulled to failure is about 1 meter / second. Note that
>most previous work has been displacement rate controlled rather than force
>rate controlled, as in your work.
> Regardless, ligaments may not be that sensitive to rate; the
>material properties are more affected by age. I would doubt that the
>difference you measured is due to rate, since all the rates are all quite
>slow.
> Is there a difference in the age of your sheep vs. others?
> What about activity restrictions after surgery?
>
>Trey Crisco, Ph.D.
>josep_crisco_iii@brown.edu
>
>To: Joseph_Crisco_III@brown.edu (Trey Crisco)
>From: lk1boq74@icineca.cineca.it (Marco Viceconti)
>Subject: Re: ACL reconstruction mech props
>Cc:
>Bcc:
>X-Attachments:
>
>Joseph,
> thanks for your notes. No, the average age of the sheep is
>comparable to that of similar studies. Also the post-surgery mobility
>program was quite similar.
>
>Probably you're right but consider that 1 m/s is 1000 mm/s Vs the 100 N/min
>(0.0167 mm/s considering a stiffness of 100 N/mm in the linear portion);
>thus my rate is many order of magnitude lower than those you 're referring
>to.
>
>Let me know what do you think.
>
>ciao
>
>Marco
>X-Sender: Joseph_Crisco_III@postoffice.brown.edu
>Mime-Version: 1.0
>Date: Thu, 22 Jun 1995 08:27:25 -0500
>To: lk1boq74@icineca.cineca.it (Marco Viceconti)
>From: Joseph_Crisco_III@brown.edu (Trey Crisco)
>Subject: Re: ACL reconstruction mech props
>
>Marco,
>
>>Probably you're right but cosider that 1 m/s is 1000 mm/s Vs the 100
>>N/min (0.0167 mm/sec considering a stiffness of 100 N/mm in the linear
>>portion); thus my rate is many order of magnitude lower than those you 're
>>referring to.
>
>Personally, I am very interested in (and supportive of) rate dependence and
>we are actually studying the effects of "impact" loading (neither force nor
>displacement control) on ligament properties.
>
>Consider the following from Woo et al. J Ortho Res 1990 (8):712-721.
>Their displacement rates ranged from 0.008 mm/s to 113 mm/s. With this
>increase in displacement rate, failure load increased from 54 N to 124 N
>and stiffness increased from 24 N/mm to 38 N/mm.
>
>So clearly rates in this range have some effect (note that this range is
>still very slow compared to would we would expect in vivo). BUT. I am
>assuming that you have normalized your results to the controlateral intact
>tendon. If so, the effect of rate should be normalized.
>
>There is however, one assumption that may not be valid. That assumption is:
>scar tissue and normal tendon have the same response to changes in rate.
>If scar tissue was orders of magnitude more sensitive to changes in rate
>than normal tendon, than this might explain your findings. However, I
>think this is a new concept and clearly needs further investigation.
>
>Cheers, Trey
>
>Trey Crisco, Ph.D.
>joseph_crisco_iii@brown.edu
>
>To: Joseph_Crisco_III@brown.edu (Trey Crisco)
>From: lk1boq74@icineca.cineca.it (Marco Viceconti)
>Subject: Re: ACL reconstruction mech props
>
>>assuming that you have normalized your results to the controlateral intact
>>tendon. If so, the effect of rate should be normalized.
>
>Yes we have normal tendon data; however, we've normalised with respect to
>the intact ACL (this is a quite clinically oriented study, thus we car
>about how much weaker is the reconstruction with respect to the normal ACL.
>
>>There is however, one assumption that may not be valid. That assumption is:
>>scar tissue and normal tendon have the same response to changes in rate.
>>If scar tissue was orders of magnitude more sensitive to changes in rate
>>than normal tendon, than this might explain your findings. However, I
>>think this is a new concept and clearly needs further investigation.
>
>That is my problem actually; using TEM we found that there is a substantial
>difference between a normal sheep ACL and a reconstruction with tendon
>after one year of healing: the second has much less thick collagen fibrils.
>
>"In a normal tendon we found a bimodal distribution with two peaks at 64
>and 130 nm of diameter. For the normal ACL we found a three modal
>distrib., with peaks at 52, 120, and 187 nm.
>For the grafts at 12 months we found a unimodal distrib. with the mean at
>66 nm. It seems like the thicker fibre just disappeared; however, consider
>that, cross section and fibrils organisation is approximately unchanged.
>Now, if I do a static test, I let each fibre to elongate during the test,
>and the effective cross section is quite close to the nominal one. But if
>a go faster usually I get failure of a few bundles before the others; thus
>in the first case, the cross section is the control factor, is the second
>the chance of having thick collagen fibrils is driving the result."
>Do you think the reasoning makes some sense? Before writing this in a
>paper I'd like to have colleagues feedback on it!
>
>Thanks for your attention.
>
>X-Sender: Joseph_Crisco_III@postoffice.brown.edu
>Mime-Version: 1.0
>Date: Thu, 29 Jun 1995 07:42:00 -0500
>To: lk1boq74@icineca.cineca.it (Marco Viceconti)
>From: Joseph_Crisco_III@brown.edu (Trey Crisco)
>Subject: Re: ACL reconstruction mech props
>
>Marco,
>The above variance in distribution may explain some differences in
>stress-strain, but I do not see how it relates to the original difference
>you presented which was a rate dependent difference. At least I have never
>seen any discussion stating that the viscoelastic properties of thick were
>different from thin.
>
>I hope this is of some help, Trey
>*************************************************
>
>From: Lisa Bellincampi
>Subject: ACL reconstruction mech props
>To: lk1boq74@icineca.cineca.it
>Date: Thu, 22 Jun 1995 12:38:43 -0400 (EDT)
>Mime-Version: 1.0
>
>Hello. I received your question on the ACL mechanical properties through
>the Biomaterials Mailing List. You're results are interesting. But
>before we comment, may I ask you:
> What were your controls in this experiment? Did you also test
> a bone-ACL-bone complex at this low strain rate, or are you
> relying completely on the literature for this comparison?
>
> and
>
> What was your reason for testing at this lower rate?
>
>I would be very interested in comments from other colleagues on this
>matter. If you do not plan to post other comments to the list, would you
>drop me a line? Thank you.
>
>Lisa D. Bellincampi (bellinld@umdnj.edu)
>University of Medicine and Dentistry of New Jersey
>Department of Orthopaedic Surgery
>Date: Fri, 23 Jun 95 09:41:20 SOL
>
>To: Lisa Bellincampi
>From: lk1boq74@icineca.cineca.it (Marco Viceconti)
>Subject: Re: ACL reconstruction mech props
>Cc:
>Bcc:
>X-Attachments:
>
>Lisa,
> of course, as far I'll get a few answer I'll post the usual summary.
>No, we did test intact BACLB and reconstructed ones; the changes I was
>referring are with respect of the normal BACLB of the sheep we measured.
>
>> What was your reason for testing at this lower rate?
>
>That's a good question. Two reasons: as a material engineer I do prefer to
>know static properties before furthering the study. But most important:
>after an operation of ACL reconstruction, in non-professional sportsmen
>usually you don't have another trauma in the first year (except you're
>really unlucky!!); thus having info on the effect of healing on static
>properties could be a one boundary scenario (the other one is that given by
>data collected using dynamic loads).
>
>Hope is clear enough;
>
>Ciao
>
>Marco
>*************************************************
>
>From: "Frieder Grieshaber"
>Organization: University Stuttgart / Germany
>To: lk1boq74@ICINECA.CINECA.IT, fg@bmt.uni-stuttgart.de
>Date: Mon, 26 Jun 1995 17:33:25 CET+100
>Subject: Re: ACL reconstruction mech props
>Priority: normal
>
>
>Marco,
>
>we have researched not only the tendons of lower leg but
>also the nervous, venal, arterial tibialis and other
>tissues. With muscles, we performed quasi-static tests and
>dynamic tests with rates of deformation up to 12 m/s. We
>have found that the max strength strongly depends on the
>rate of deformation. So, at a rate of 9 m/s, muscles have a
>max strength which is 4 times higher than with quasi-static
>loads. These results will be published in a few months. So
>long.
>
>Best wishes
>frieder
>*************************************************
>
>Date: Tue, 27 Jun 1995 11:38:37 -0400 (EDT)
>From: COLLEEN1@vms.cis.pitt.edu
>Subject: Re: your posted question
>To: lk1boq74@icineca.cineca.it
>MIME-version: 1.0
>
>Mr. Viceconti,
>
>One of my co-workers alerted me to your posted question concerning ACL
>reconstruction in sheep. There was a paper published by our laboratory which
>may help you try to work this out. It is M.I. Danto and S.L-Y. Woo, "The
>Mechanical Properties of Skeletally Mature Rabbit Anterior Cruciate Ligament
>and Patellar Tendon over a Range of Strain Rates" published in Journal of
>Orthopaedic Research, 11:58-67. Central thirds of rabbit PTs were tested at
>various strain rates, the slowest of which may be more or less comparable to
>your strain (or loading) rate. However, the results of this study were that
>slower strain rates led to decreased modulus. Although the numbers are not
>specified in the paper, the stress strain curve tends to indicate that the slow
>rate also resulted in higher strains. Little could be said about ultimate
>tensile strength as all but 1 PT specimen failed by avulsion.
>
>Colleen Weaver
>*************************************************
>
>From: T.J.Lawes@bristol.ac.uk (TJ. Lawes)
>Subject: Re: ACL reconstruction mech props
>To: lk1boq74@ICINECA.CINECA.IT
>Date: Tue, 27 Jun 1995 17:18:36 +0100 (BST)
>MIME-Version: 1.0
>
>Marco, Its very evident that all collagenous tissues (including bone,
>tendons and ligaments) are not pure springs. They exhibit both hysteretic
>behaviour and, more importantly, have a large component of internal
>damping in their material properties. Hence their load, stress and strain
>behaviour is very dependant on the rate of any mechanical test.
>
>The faster loading occurs, the less the material is able to deform and as
>is well known in fractures of bone, the more energy is stored in the bone
>before breaking. In other words, as the loading rate increases, then
>the higher the breaking stress (or applied force) in BONE.
>
>In ligamentous tissue, whose damping properties are dominant, then the
>tissue will be more rigid at higher loading rates and therefore it is
>likely that problems such as equalisation of stress throughout the
>material will occur. The result is that there are regional starins higher
>than the bulk material strain and therefore the material may fail at a
>lower maximum. I am not familar with the particulars of the paper you
>refer to, but the problem can be described as strain rate dependant
>embrittlement. In other words, the material becomes more brittle at
>higher rates. This can be due to either sliding of fibres over one
>another during the loading process being inhibitted or soley to the
>material properties of the fibrous, ground substance and cellular
>components of the matrix.
>
>I hope that this ("little bit") is of some help to the list !!!!!!!
>
>Tim Lawes
>University of Bristol
>Dept of Anatomy EMail: t.j.lawes@bristol.ac.uk
>*************************************************
>
>
>-------------------------------------------------------------------
>MARCO VICECONTI
>(lk1boq74@icineca.cineca.it)
>Laboratorio di Tecnologia dei Materiali tel. 39-51-6366865
>Istituti Ortopedici Rizzoli fax.
>39-51-6366863
>via di barbiano 1/10, 40136 - Bologna, Italy
>
>Tiger! Tiger! Burning bright in the forest of the night,
>what immortal hand or eye could frame thy fearful symmetry?
>------------------------------------------------------------------
>Opinions expressed here do not necessarly reflect those of my employer
>
************************************************** ****************
Marco

Marco

Very interesting discussion.
Recently we compared stress relaxation bahavior of central thir
d rabbit PTs and fascicles (200 to 300 micrometer in diameter) obt
ained from the PTs. The stress relaxation was significantly smal
ler in the fascicles than in the bulk PTs, which indicates the imp
oratnce of intrafascicular and intrafibrillur substances. In add
ition to stress relaxation behavior, tensile stress-strain propert
ies were also much different between them.
Separately, we studied strain rate effects of the rabbit centra
l third PT on the tensile properties. Specimen deformation was m
aesured very accyrately at midsubstance with a high speed video di
emsion analyzer. The increase of strain rate from 0.57%/s to 125
0%/s increased tensile strength by approximately 50% and elongatio
n to failure by 70%. 60% and 40% of specimens failed at midsubst
ance and at patellar insertion site, respectively, for the lower s
train rate, while 100% of specimens failed at midsubstance for the
higher strain rate.
These data have been reported in Conference Abstracts (Japanese),
and will be published in English before long.

I hope this is of some useful information.
.................................................. .................
Kozaburo Hayashi, Ph.D.
Professor of Biomechanics
Department of Mechanical Engineering
Faculty of Engineering Science
Osaka University
Toyonaka, Osaka 560, Japan
Phone: +81-6-850-6170 Fax:+81-6-850-6171
E-mail: hayashi@me.es.osaka-u.ac.jp
.................................................. .................