DTIC ADA628102: Passive Biomechanical Properties of Sutured Mammalian Muscle Lacerations

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by  Defense Technical Information Center

JournalofInvestigativeSurgery,18:19–23,2005
Copyright(cid:1)c Taylor&FrancisInc.
ISSN:0894-1939print/1521-0553online
DOI:10.1080/08941930590905170
Original Research
Passive Biomechanical Properties of
Sutured Mammalian Muscle Lacerations
JohnF.Kragh,Jr.,MD
OrthopaedicService,BrookeArmy ABSTRACT Muscle trauma, such as laceration or transection, is a
MedicalCenterandU.S.ArmyInstitute
common occurrence, but repairing delicate tissue poses a clinical chal-
ofSurgicalResearch,FortSamHouston,
Texas,USA lenge. This is at least partially due to the lack of established muscle
repair models. The purpose of this study was to compare the biome-
StevenJ.Svoboda,MD,and
chanical properties of stitches in transected porcine and bovine mus-
JosephC.Wenke,PhD
U.S.ArmyInstituteofSurgicalResearch, cle bellies. A biomechanical protocol was designed for measuring su-
ExtremityTraumaStudyBranch,FortSam
ture performance in muscle belly lacerations. Twenty simple stitches
Houston,Texas,USA
in porcine and 21 stitches in bovine specimens were tested. Individ-
JohnA.Ward,PhD
ual stitches were placed in lacerated muscle bellies and tensioned on a
DepartmentofClinicalInvestigation,
biomechanicaltester(model8521S,InstronCorporation,Canton,MA).
BrookeArmyMedicalCenter,FortSam
Houston,Texas,USA The mean maximum load for porcine (22.0 N) and bovine (23.9 N)
stitches was not significantly different (p = .48). The difference in
ThomosJ.Walters,PhD
U.S.ArmyInstituteofSurgicalResearch, mean strains at maximum load between porcine (9.7%) and bovine
ExtremityTraumaStudyBranch,FortSam (8.0%) groups was statistically significant (p = .004). Failure mecha-
Houston,Texas,USA
nisms were similar. One porcine stitch avulsed the muscle transversely,
while 19 stitches tore out longitudinally. All 20 stitches tore out in
Received29March2004; bovine specimens. Sutured muscle was the weakest element in each
accepted3August2004.
test. The present study demonstrated that sutured muscles performed
TheauthorsthankMichaelA.Dubick,PhD,
andJillL.Sondeen,PhD,forassistancewith similarly for the two mammals regarding the parameters of maximum
specimencollection,andRobertoRiosfor
illustration.Nofundingwasreceivedforthe load and mechanism of failure. Regarding suturing of skeletal muscle
presentstudy.
lacerations,bothmammalianmodelshadsimilarbiomechanicalperfor-
Theopinionsorassertionscontainedherein
mance for maximum loads and failure mechanisms, while strain data
aretheprivateviewsoftheauthorsandare
nottobeconstruedasofficialorreflecting differed.Thestitchloadmagnitudesinthisstudyapproximatethosere-
theviewsoftheDepartmentofDefenseor
U.S.government.Theauthorsare quired to successfully repair transected muscle. Knowledge introduced
employeesoftheU.S.government.This
by this study fills a gap concerning muscle stitching relevant to clinical
workwaspreparedaspartoftheirofficial
dutiesand,assuch,thereisnocopyrightto care.
betransferred.
AddresscorrespondencetoLTC(P)Kragh,
U.S.ArmyInstituteofSurgicalResearch, KEYWORDS biomechanical testing, epimysium, laceration, load, mus-
ExtremityTraumaStudyBranch,3600 cle anatomy, muscle injuries, orthopedics, repair, stitch, surgery, suture,
RawleyE.ChambersAve.,Room292-1Bldg. trauma
3611,FortSamHouston,TX78234-6315,
USA.E-mail:[email protected]
19
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Passive biomechanical properties of sutured mammalian muscle
5b. GRANT NUMBER
lacerations
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Kragh Jr. J. F., Svoboda S. J., Wenke J. C., Ward J. A., Walters T. J.,
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Original Research
M
uscle trauma, such as laceration, transec- we determined that refrigeration of muscle did not
tion,orrupture,iscommoninmedicine, affectpassivebiomechanicalpropertiescomparedto
posing clinical challenges for surgeons to fresh specimen testing. Further, differing durations
repair disrupted delicate tissue [1, 2]. Often, severe ofrefrigeration,asusedinthecurrentstudy,didnot
muscle trauma is treated without surgery, because affectpassivebiomechanicalproperties.
historically, treatment outcomes of muscle injury A bovine steer tibialis anterior muscle was ac-
without tendon involvement were suboptimal [3, quired freshly from a commercial slaughterhouse.
4].Recently,investigatorspresenteddatasupporting One muscle from one animal was used and refriger-
◦
surgical repair over nonoperative care of complete atedat4 Cfor84h.Theporcineandbovinemuscles
muscle disruptions [5–9]. Models of muscle stitch- selectedhadhalf-belliesofsimilarsizeandshape.
ingarebeingdeveloped,butcomparisonsofmodels Thecompartmentalfasciawasremovedfromspec-
have not been reported. A better understanding of imens, and care was used to preserve epimysium.
the models and the biomechanics of muscle sutur- Muscle belly lacerations were made in areas where
ingiskeytothedevelopmentofoptimalrepairtech- no tendon was present. The laceration made with
niques. Surgical research of muscle repair is needed a surgical blade was transverse to the long axis of
to improve patient care and rehabilitation, because the muscle, and the laceration completely severed
earlymobilizationofsuturedmuscleimprovesheal- the muscle belly into two half-bellies without con-
ing [8, 9]. Early motion after repair leads to better nection. Saline was used to moisten the specimens
healing, less scar, and less atrophy, but requires no throughout testing. Sutures were placed around the
stitch failure by pullout during early loading [8, 9]. laceration edge to repair with simple stitches with
Asskeletalmusclehassimilaritiesamongmammals, metric size 2 braided polyester suture. A stitch was
mammalian muscle is often used to model human placed in the tendon using a running interlocking
clinicalsituations.Sinceporcineandbovinemuscles technique. Both stitches were secured by tightening
appear similar to human skeletal muscle, it was hy- inbothgripsbeforeloadingonabiomechanicalma-
pothesizedthatbothmammalswouldmodelmuscle chine (Figure 1). The stitch tested in each test was
bellylacerationrepairsimilarly. the stitch in the sutured portion of the muscle, and
To improve the clinical performance of stitching the stitch in the sutured tendon was used simply to
muscle, a biomechanical study was designed to test secure the specimen. In prior work with this setup,
stitches in porcine and bovine muscle belly transec- weascertainedthatnoslippageoccurredattheloads
tions, focusing on the passive traits of sutured mus- used. No rigor mortis occurred. No measured strain
cles. The purpose of the present study is to com- of the sutures or tendon occurred, and only the su-
pare maximum loads, strains, and failure mecha- tured portion of the muscle deformed. The weakest
nismsofsuturedmusclebelliesinporcineandbovine element in each test was the sutured portion of the
specimens. muscle.
A biomechanical protocol was designed for mea-
suringsutureperformanceinmusclebellylacerations
MATERIALS AND METHODS
in a porcine specimen and in a bovine specimen.
Skeletally immature female Yorkshire cross pigs, Parameters compared were maximum load, strain at
weighing approximately 40 kg, were acquired and maximumload,andmechanismoffailure.Thegauge
then attended in an accredited facility for an ap- lengthwasthelengthofthespecimen,notincluding
provedstudyotherthanthepresentstudy.Apigca- thesutures.
daverextremitywasacquiredattheendoftheother A servohydraulic materials tester (model 8521S,
study, and the institutional review board approved InstronCorporation,Canton,MA)wasusedtoapply
the present study. The porcine quadriceps femoris tension. Under position control with a 0.1-kN load
musclegroupfromoneanimalusedandwasrefriger- cell,themachineappliedtensionalongthelongaxis
◦
atedat4 Cfor40h.Inapriorstudyatourlaboratory, ofthemuscle,andthesutureswereheldingripswith
20 J.F.KRAGH,JR.ETAL.
Original Research
TABLE 1 Mean maximum load (±SD expressed in
newtons), mean strain at maximum load (±SD expressed as
mm/mminapercentage),andsignificance(pvalue)forporcine
andbovinemusclestitches
Porcine
muscle, Bovinemuscle,
mean±SD mean±SD pValue
Maximumload(N) 23.9±8.93 22.0±7.98 .48
Strain 8.0±1.79 9.7±1.83 .004
(mm/mm×100%)
eredsignificant.Clinicallysignificantloadandstrain
differencesweresetat6Nand3%basedonunpub-
lished work by us with this setup, and sample size
estimationconfirmedadequatepower.Software(ver-
sion11.5SPSS,Inc.,Chicago)wasusedforstatistical
analysis.
RESULTS
FIGURE 1 Testing setup of materials testing system with
The results of load testing are summarized in
connected specimen. The tester includes the base platform,
Table 1 and Figure 2. The mean maximum load for
two uprights, upper crossbar, and two grips. The load cell is
labeled,andgripsholdstitches.Thesimplesutureisgripped porcine repairs was 23.9 N, while that for bovine
below, and the tendon suture is gripped above. The muscle repairs was 22.0 N. The difference between groups
specimenisahalfbellytransectedinthemiddle.
was not significant (p = .48). The ranges, standard
leatherfacing.Thescientificmodeltestedthepassive deviations, and 95% confidence limits were similar
propertiesofthespecimensimilartotheclinicalsit- betweengroups.
uation [8]. The specimen was preloaded minimally TheresultsofstraintestingaredisplayedinTable1
with 5 to 8 N to remove slack immediately prior to and Figure 3. The mean strain at maximum load
testing. Stitched muscles were loaded at an elonga- for porcine repairs was 8.0%, while that for bovine
tion rate of 25 mm/min until failure. Two failure
modesweredefined.Suturetear-outoccurswhensu-
turespulloutlongitudinallyfromthemuscle.Avul-
sion is the mechanism of failure when the muscle
failstransverselyandaportionofmuscleisremoved
asthesuturecutsoutofthemuscle.
Software(SeriesIX,InstronCorporation,Canton,
MA) was used for data collection, and the system
recorded the maximum load in newtons and the
strain at maximum load in mm per mm expressed
as a percent. Further, the mechanism of failure was
observeddirectlyandrecorded.
Independent sample t-tests were used as the test
FIGURE2 Maximumloadsforsuturedbovineandporcine
statistic for loads and strains, and Levene’s test was muscle bellies. The gray box plots have the 25th and 75th
used for assessing equality of variances. For mech- percentile confidence limits as the lower and upper borders
anism of failure analysis, a 2×2 contingency test respectively.Thebarsarethe95%confidencelimits.Thedots
areoutliers.Themeanisadashedlinewithinthegraybox,and
wasusedwithFisher’sexacttestbecauseofthesmall
themedianisasolidlinewithinthegraybox.Thedifference
sample sizes. A p value of less than .05 was consid- betweengroupsinmeanmaximumloadisnotsignificant.
SUTUREDSKELETALMUSCLELACERATIONS 21
Original Research
parametersofmaximumloadandmechanismoffail-
ure. The strain parameter was statistically different
by a small amount. Both animal models approxi-
mated closely the human clinical situation and val-
idated the testing method by showing the weakest
link to be the muscle in each test. The finding that
thebovinemodelhadhigherstrainatmaximumload
wasprobablybecausethebovinemodelappearedto
have more muscular connective tissue. The epimy-
sium of the bovine tissue seemed slightly more ro-
bust than the porcine muscle, and the greater con-
nectivetissuelikelypermittedgreaterelongationand
FIGURE 3 Strain at maximum load for stitches in bovine
strainpriortofailure.Thesmallstatisticaldifference
andporcinemuscle.Strainisexpressedasmm/mmasaper-
cent. The gray box plots have the 25th and 75th percentile in strain between the two muscles is not clinically
confidencelimitsasthelowerandupperborders,respectively. significant. The two different muscles selected from
Thebarsarethe95%confidencelimits.Thedotsareoutliers.
the two species have obvious differences and may
Themeanisadashedlinewithinthegraybox,andtheme-
dianisasolidlinewithinthegraybox.Thedifferencebetween have different length–tension diagrams, but despite
groups in mean strains at maximum load is significant by a differences,themusclestestedhadmeasuredbiome-
clinicallyinsignificantamount.Thedataoverlapconsiderably
chanicalpropertiesthataresimilarordifferlittle.
betweengroups.
Thefindingsofthepresentstudyapplytohuman
repairswas9.7%.Thedifferencebetweengroupswas and veterinary surgical care of muscle disruptions.
statistically significant (p = .004). The ranges, stan- Both porcine and bovine muscle tissues handle
darddeviations,and95%confidencelimitsweresim- grossly similar to human muscle, and both mod-
ilarbetweengroups. els offer usefulness to investigators studying severe
The mechanisms of failure were not significantly muscledisruption.Bothporcineandbovinemuscles
different between groups (p = .49). One porcine canprovidecliniciansarefrigeratedpracticematerial
stitch avulsed the sutured portion of the muscle, prior to facing the clinical challenge of human or
while 19 sutures failed by tearing out longitudinally veterinarymusclelacerationrepair.Bothspeciescan
from the muscle. No bovine stitch avulsed muscle, beusedtomodelclinicalapplications,asthebiome-
while20suturestoreout(Table2).Thesuturedpor- chanicalpropertiesofinterestdifferedlittleornotall.
tionofthemusclewastheweakestlinkineachspec- The clinical relevance of the loads pertains to re-
imenandtest. habilitation of muscle injury, and the estimation of
muscleandstitchloadscanhelpexplainclinicalsuc-
DISCUSSION cessandfailure.Letusassumeabicepsbrachiimuscle
is repaired as the belly is commonly repaired [7, 8],
Thisstudydemonstratedthatsuturedmusclesper-
and the belly is architecturally simpler than many
formedsimilarlyforthetwomammals,regardingthe muscles.Forearmsupinationtorqueaverages9N·m
◦
[10]maximallyat90 ofelbowflexion.Ifthebiceps
TABLE 2 Failuremechanismsandsignificance(pvalue)of
contributes 5 times more than the supinator mus-
suturespulledfromporcineandbovinemuscles
cle, since the biceps cross sectional area is 5 times
Porcine Bovine
greaterthanitssynergist,thenthebicepscontributes
muscle muscle pValue
five-sixths;7.5N·m(9N·m×5/6),oftotalsupina-
Numberofstitches 20 21
tiontorque.Ifthebicipitaltuberosityis15mmfrom
Failuremechanisms 19/1 21/0 .49
the center of supination (longitudinal rotation axis
Tear-outs/avulsions
◦
Tear-outproportion 95% 100% of the radius) at 90 of elbow flexion, then the mo-
(Tear-outs/total)×100% mentarmis0.015m.Therefore,themaximumbiceps
22 J.F.KRAGH,JR.ETAL.
Original Research
forceis500N(7.5N·m/0.015m)[11].Ifindividual of the laboratory findings beyond the narrow scope
stitchescanbearloadsof20N,asinthecurrentstudy, of the current study may be limited. Further model
then25stitchescanbearthe500-Nrequirement.As development is needed to address the complex and
the biceps circumference is 16 cm [2π×(2.5 cm)2], poorlyunderstoodproblemofsurgicalrepairofmus-
manystitchescanbeusedclinicallytobearloadsuc- clelaceration.
cessfully [7, 8], but the difference between success
and failure is small. As rehabilitation forces are typ-
CONCLUSIONS
ically below maximum, stitches may be able to bear
estimated loads successfully, but risk of failure by
This study established that porcine and bovine
tear-outremains.Threelimitationsofthecalculation
muscle suturing performs similarly in biomechani-
are notable. First, noncompliant patients may con-
cal testing, except for strain at maximum load. The
tractrepairedmusclewithoutcontrol,andthus,risk
present study adds new knowledge to a growing un-
failure. Second, biomechanical testing was immedi-
derstandingofskeletalmusclerepair,andtechniques
atelyafterrepair,butmaximumloadsduringhealing
of repair may now be investigated with more devel-
could be less than those immediately after repair.
opedmodels.
◦
Third, positions other than 90 of flexion may de-
mand higher loads. Nonetheless, calculations offer
contexttocurrentmuscleknowledgeanddetailhow
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SUTUREDSKELETALMUSCLELACERATIONS 23