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Pressuredistributionsonthe medial tibial
plateau aftermedial meniscalsurgeryand tibial
plateau levellingosteotomy in dogs
A. Pozzi
1
,A.S.Litsky
3
,J.Field
4
,D.Apelt
1
,C.Meadows
2
,K.A.Johnson
1
1
DepartmentofVeterinaryClinical Sciences;
2
DepartmentofPreventiveMedicine;
3
TheOrthopaedic
BioMaterialsLaboratory,DepartmentsofOrthopaedics andBiomedical Engineering, TheOhio State
University,Columbus,Ohio,USA
4
Orthopedic Unit, Repatriation General Hospital, Flinders UniversityofSouth Australia, Australia
Summary
Objective: To evaluate theeffect of medial meniscal
release (MMR) andmedial, caudalpole hemimeniscec-
tomy (MCH)onpressure distribution in the cranial cru-
ciateligament (CCL) deficientcaninestifle, and with ti-
bial plateau levellingosteotomy (TPLO). Animals:
Twelve adultdogs. Methods: In experiment one, six
pairs of cadaveric canine stifles with an intactCCL were
axially loadedwithaservo-hydraulic material testing
machineand pressure distributionsweremappedand
quantifiedusing pressure sensitive films. Axial loading
of each joint wasthen repeated followingMMR,and
again afterMCH.Inexperimenttwo,six pairs of cada-
veric canine stifles with or without TPLOweretested be-
fore andafter CCL transection, and each MMRand MCH
procedure usingthe same methods of experiment 1.
Results: In experiment one, MMR andMCH hadsig-
nificanteffectsonthe pressure distribution resultingin
a2.5-fold increaseinthe percentage of surfacearea
with pressure higher than10MPa.Inexperimenttwo,
CCL transection resulted in asignificant change in
pressure distribution only in thestifle withoutTPLO
(P<0.05).BothMMR andMCH resulted in a1.7-fold
increaseinthe percentage of areawithpeakpressure
in the stifle with TPLO(P<0.05). Conclusions: Me-
niscal surgery results in achangeinpressure distribu-
tion andmagnitude withinthe medial compartment of
the stifle. Clinical relevance: Compromised function of
the meniscus by either MMR or MCH result in stress
concentration which may predispose to osteoarthritis.
Keywords
Canine, cruciate ligament, meniscus, release,load
transmission
VetCompOrthopTraumatol 2008; 21: 8–14
Prepublished online November 2, 2007
doi:10.3415/VCOT-06–12–0099
Introduction
Themeniscal fibrocartilageshaveimpor-
tant functionsinloadtransmission andsta-
bility in the femoro-tibialjoint in both hu-
mans andotheranimals(1–6). In the dog,
medialmeniscusdamageiscommonly
found in conjunction with cranialcruciate
ligament(CCL)ruptureorasalatecompli-
cation to the surgical management of the
CCL deficient stifle by tibialplateau level-
ling osteotomy (TPLO), andothertech-
niques (7–15). Some of the recommended
treatments formeniscal injuriesfound at the
time of surgical reconstruction of the CCL
deficientstifle in dogs arepartialortotal
meniscectomy, depending upon the type of
meniscal lesion (5, 7, 9, 11, 16). However, in
cases wherethe meniscusisfound at sur-
gery to be grosslynormal, controversy re-
mains over the best waytoprevent the devel-
opment of late meniscal injury (12, 15). Re-
lease of the medialmeniscusbyradialtrans-
ection hasbeen recommended in orderto
prevent meniscal injury following TPLO in
dogs (15). Releasing the meniscusallows
caudal retraction of the caudalpole of the
medialmeniscusawayfrom the medialfe-
moral condyle during cranialtranslation of
the tibia, andisthought to prevent the devel-
opment of late meniscal injury (15). How-
ever,medialmeniscal release probablydis-
rupts the load transmission roleofthe me-
niscibecause axialloads acrossthe femoro-
tibial joint arenormallycounteracted by
hoop tension withinthe circumferentially
orientedcollagen fibres(5, 17).
Partialorcompleteremoval of menisci in
humans andexperimentalanimalsresults in
the development of articularcartilage de-
generation andosteoarthritis (18–22). Fur-
thermore,the severity of osteoarthritisthat
followedexperimentalmedial, caudalpole
hemimeniscectomyindogswas similarto
thatarising aftercompletemedialmenis-
cectomy(22). Disruption of meniscal func-
tion of loadtransmission results in ade-
crease in jointcontactareawhich in turn
causes the jointsurfaces to be subjected to
greater loadingstresses (1, 2, 6, 23).As are-
sult, supra-physiological loadingofarticu-
larcartilage induces an upregulation in syn-
thesis anddegradation of cartilage matrix
whichultimately leadstoosteoarthritis (21,
24,25). Therefore it would be important to
determine if medialmeniscal release has
equivalent deleterious effectsonloadtrans-
mission as meniscectomyindogs, because
routine medialmeniscal release mayplaya
role in the development of osteoarthritisin
the CCL deficient canine stifle.
We hypothesizedthatboth medialmenis-
cal release andmedial, caudalpole hemime-
niscectomywould result in disruption of
normal load transmission in the medial
compartment of the femoro-tibialjoint.In
ordertotest our hypothesis, we evaluated
load transmission in the canine cadaveric
stifle jointusing pressure sensitive film and
amaterialtesting machine,similartopre-
viously describedmethodology (26, 27).
Thespecificobjectivesofour study were to
determine the effectsofmedialmeniscal re-
lease andmedial, caudalpole hemimenis-
*The paper waspresented at the Annual Confer-
ence of the European Society of VeterinaryOrtho-
paedics and Traumatology,September 10–12,
2004, Munich, Germany.
ReceivedDecember18, 2006
VetComp OrthopTraumatol1/2008 AcceptedApril 20, 2007
8Original Research
©2008 Schattauer GmbH
VetComp OrthopTraumatol1/2008
9
Pressuredistribution with meniscectomy andTPLO
cectomyonthe magnitude anddistribution
of pressure on the articularsurface of the
medialtibialcondyle in the normal canine
stifle,and the CCL deficientcanine stifle,
with andwithout TPLO.
Materials and methods
Materials
Twelve pairsofcadaveric hindlimbswere
harvested by disarticulation of the coxo-fe-
moral jointwithin twohours of deathfrom
adult male andfemaledogsthatwereeutha-
natized for reasons unrelatedtothe study.
Thedogswereofvariousbreedsand hada
body weightof25to35kg. Aftercollection,
allsoft tissues proximal to the patella were
dissected from the limbs,whilecarefully
preserving the rest of the soft tissuesdis-
tally, including allofthe periarticulartissue
of the stifle joints.Stifleswith anygrossly
evident abnormalities were excludedfrom
the study.
In vitro limb loading
Soft tissueswerekeptmoist during the ex-
periment by spraying the specimens with
isotonic saline.A2.5mmdiameterdrill hole
wasmadeinthe midportion of the patella
from medialtolateral.Braided-steel cable
(7 x7strands) of 1.6mmdiameterwas
threaded through the hole andsecuredinto a
loop using a9.5 mm-long oval compression
sleeve
a
.An8mmdiameterSteinmanpin
wasplaced transverselythrough the femur,
2–3 cm distaltothe greater trochanter, in a
lateraltomedialdirection to permit sub-
sequent loadingofthe limb.Aturn-buckle
anchoredtothe femoral neck by aloop of
cable andtothe patella by the secondloop of
cable wasused to mimic the quadriceps
mechanism, as previouslydescribed(28). A
3cmcaudo-medialarthrotomywas per-
formedjustcaudaltothe medialcollateral
ligamenttoexposethe caudalpole of the
medialmeniscustoallowfor subsequent
meniscal treatments andinsertion of pre-
scalepressure film (29).The arthrotomy
wassutured closed aftereach meniscal
treatment. Each limb wasmounted in a
servo-hydraulic materialtest machine
b
by
attaching the proximalSteinmanpin to the
actuator while the foot wasrested on anon-
slip foot-plate thatlimitedcranial, caudal
andlateral translation of the paw(Fig. 1).
Axialloading of the limbs wasperformed
with the stifle jointataninitial angle of
145°. Thejoint angle variedduring loading
from 145° to approximately105°. Thetest
machine wasprogrammedtoapplya200 N
axialload(about 50% body weightofthe
dogs from whichlimbs were harvested)ina
‘ramp up-plateau-release’ loadingpattern
beginning with a15s‘ramp up’ from 0–
200 N, followedbya15 s200 Nplateau and
thenanimmediate release of load.
Prescale pressure sensitivefilm
Pressure distributions in joints were
measuredbyusing prescale pressure sensi-
tive films thathad apressure range of 2–10
MPa
c
.Prescale films consistedofanAlayer
andaClayer thathad acombinedthickness
of 0.2mm. The Alayer containedmicrocap-
suleswhich ruptured at specificpressures
andreacted with adevelopercontainedin
the Clayer to produceared stain, the inten-
sity of whichcorrelatedwith the magnitude
of local pressure (30). The colourdensity of
the film could therefore be calibrated as a
function of the contactpressure.The film
wascut to matchapproximatelythe dimen-
sions of the articularsurface of the medial
tibial condyle. Each film hadasmalltab
protruding from the caudo-medialedge that
waspositioned adjacenttothe medialcollat-
eral ligament. The films were sealed be-
tween twosheetsofselfadhesive polyethy-
lene
d
in ordertoprevent wetting by synovial
fluid (31). This packet wascarefullyinserted
beneath themedial meniscusthrough the
caudo-medial arthrotomy. After the stifles
had been axiallyloaded, the film wasre-
moved. Twotothreefilms were stained for
each meniscal treatment. Exclusion criteria
of the films included damage of the seal pack
or of the actual film, artefacts caused by
handling anddisplacement duringloading.
Thefilms that were damaged during inser-
tion were alsoexcludedfrom the analysis,
andthe film with fewest artefacts wasused
for the analysis. All procedureswereper-
formedbyone investigator,(K. A. Johnson)
to reduce variabilitybetween subjects.
Experiment1-meniscal disruption
in normaljoints
Standard radiographic views (cranio-caudal
andmedio-lateral) were takenofsix pairs of
limbs to ensure the stifle joints were freeof
radiographic evidenceofosteoarthritis and
to measure the tibial plateau angle (TPA),
using previously describedmethods (14,
15). Thelimbs were axiallyloadedtodeter-
Fig.1 Schematic representation of limb mountedina
servo-hydraulic test machine with apin placedtransversely
throughthefemurproximallyandthefootrestingonanon-
slipfoot plate. Aturn-buckle andcablefromthe proximal
femur to the patella mimicsthe quadriceps mechanism.
b
Bionix858, MTS System Corporation, Eden
Prairie, MN,USA.
c
SPI Sensor Products Inc,East Hannover, NJ,
USA.
d
Tegaderm, 3M Health Care, St. Paul, MN,USA
a
McMaster-CarrSupply Company,Cleveland,OH,
USA.
VetComp OrthopTraumatol1/2008
10
Pozzi et al.
mine the pressure distribution in the medial
compartment of the femoro-tibialjoint to
establishcontrol baseline data.The axial
loadingofeach jointwas thenrepeated fol-
lowing medialmeniscal release andthen
againfollowing medialcaudalpole he-
mimeniscectomy.
Experiment2-meniscal disruption
and TPLOincranial cruciate
ligamentdeficient joints
Standard radiographic views (cranio-caudal
andmedio-lateral) were takenofsix pairs of
limbs to ensure thatthe stifle joints were
freeofradiographic evidenceofosteoarthri-
tis andtomeasure the tibial plateau angle
(TPA), using previously describedmethods
(14, 15). Pairedlimbs were randomlyas-
signedtothe standard TPLO group or a
shamTPLO group (SHAM).The TPLO was
performed as previouslydescribedtopro-
duceaTPAinthe range of 5° to 7° (14). In
the SHAMgroup the standard TPLO pro-
cedure wasperformedwithout alteringthe
TPA. As for experiment 1, each limb was
axiallyloadedand pressure distributions
were recordedinthe medialcompartmentof
the femoro-tibialjoint with the CCL andthe
medialmeniscusintact, andthenagain fol-
lowing CCL transection,medialmeniscal
release, andmedial, caudalpole hemime-
niscectomyrespectively. Twotothreefilms
were stainedfor each meniscal treatment.
Quantificationofprescale pressure
sensitivefilm
The stained films were digitized using are-
flectivescanner
e
.After digitalizationofthe
images an oval template wasused to define a
standard areaofinterest
f
.The oval template
waspositioned on thefilm with thelong axis
parallel to thelong axisofthe film. The tem-
platewas centred on the film andcaudally
aligned with thetab that defined the position
of the medial collateral ligament. The contact
stresses were measured as percentagesofthe
total oval area. The parameters of interest for
each imagewere extracted using computer-
ized imageanalysistechniques with commer-
ciallyavailable software
g
.Thissystem has the
capability of reading area and pressurefor all
areasofinterestaswell as providing informa-
tion about the pressure distributions. From
this informationwecalculated percentages of
area corresponding to pressure ranges of 0to
<4, 4to<6, 6to<8, 8to<10 and >10 MPa.
Calibration stains of theprescale film were
obtained using amaterial testing machine
h
usingthe method of Liggins (32).Thisin-
volved theapplicationof12differentload re-
gimes in therangefrom282 to 1131 Nover
known contact areas of 113mm
2
(12mmdi-
ameter circle). Applied pressurefor each load
wasthen calculated using theformula: press-
ure=load ÷area.The stains producedwere
then digitized,resulting in atabulation of
mean greyscale levelversus applied pressure.
Asixth-order polynomial wasthen fittothe
datatobeused as acalibration curve.The cali-
brationcurve wasthen usedtoconvert the
greyscale levels in thedigitalized contactpat-
terns to pressure units.
Statistical analysis
Experiment 1-meniscal disruption in normal
joints
Sincethe data derivedfrom pressure sensi-
tive films were organizedinto ranges, or cat-
egories, it could not be consideredtobecon-
tinuous data. As such, parametricmethods
of data analysis could not be applied.There-
fore, pressure distributions in the threedif-
ferent meniscal treatments were compared
with χ
2
test for homogeneity (33). Data from
twoofthe 12 stifleswereexcluded from the
analysis due to the presence of artefactsin
the films thathad developed during the pro-
cess of film digitization.The remaining 10
stifleswererandomlydividedinto two
groups of five limbs each (group Aand
group B). Splitting the data allowedusto
compare pressure distributions from differ-
entpopulations, thus avoiding the potential
for covariance. Thepressure distributions
samples for the ‘intactmeniscus’of groupA
were comparedwith samples for ‘meniscal
release’ of group B. Next,samples for ‘me-
niscal release’ of group Awerecompared
with samples for ‘hemimeniscectomy’ in
group B. Significancewas set at P<0.05.
Experiment 2-meniscal disruption andTPLO
in cranial cruciate ligamentdeficient joints
Using datafrom experiment 1, it waspossi-
bletoidentify the pressure range (>10 MPa)
thatlargely contributed to the non-homo-
geneity. Therefore,datafrom this pressure
range wasused as an outcome measure to
performthe analysis in experiment 2. By
using data from asingle pressure range,we
were able to useanANOVA test for experi-
ment 2. Theeffect of CCL treatment and
meniscal treatment on pressure distribution
andtheir interaction were analyzed using a
two-way repeated-measuresANOVA .The
factors that were analyzed were TPLO,me-
niscal treatment andtheir interaction.Sig-
nificantdifferences among groups were
evaluated with Bonferroni post-hoc test.
0to<4MPa
INTACT
a
19.18 ±6.92
MMR
b
23.37 ±6.98
MCH
b
22.97 ±3.31
INTACT,intact meniscus; MMR, medial meniscusrelease;MCH,medial caudal pole hemi-meniscectomy. Between groups different lettersdenotesignificant difference
(P<0.05).
4to<6MPa
32.7 ±7.72
26.05 ±7.85
21.68 ±5.89
8to<10 MPa
8.41 ±3.14
3.35 ±1.39
4.28 ±2.37
6to<8MPa
25.43 ±7.31
12.33 ±3.48
11.39 ±2.6
>10MPa
14.25 ±8.23
34.92 ±13.97
39.71 ±8.52
e
UMAX 2200, UMAX Australia, Melbourne,
Victoria, Australia.
f
AdobePhotoshop 7.0, Adobe Systems Inc,
Seattle, WA,USA.
g
Interactive Data Language, Research Systems
Inc.,Boulder,CO, USA.
h
Instron 810 Servohydraulic Testing system,
Instron, Wycombe, UK.
Table 1 Effectof medialmeniscalreleaseormedialcaudalpole hemimeniscectomyon pressuredistributions,expressedas
apercentagearea, of the medial tibialplateau of normalcanine stifle joints (mean ±SD)
VetComp OrthopTraumatol1/2008
11
Pressuredistribution with meniscectomy andTPLO
Significancefor the two-way ANOVA was
set at P<0.15,and for the post-hoc tests at
P<0.05. Data from four out of 12 legs were
lostdue to artefactsinthe films,and could
not be includedinthe analysis.
Results
Experiment1-meniscal disruption
in normaljoints
Medial meniscal release hadasignificant
effect on the pressure distribution in the
medialcompartmentofthe stifle (P<0.05)
(Table 1).Following the release a2.5-fold
increase in percentage of area with peak
pressure (>10 MPa) from the control intact
stifle wasnoted,but thisspecificcompari-
sonwas not evaluated statistically (Fig. 2,
Table1). In the control intact stiflesmuchof
the area measuredinthe mid-range of press-
ure (32% of area with 4to<6MPa), where-
as in the medialmeniscal release stifle much
of the area measuredinthe peak pressure
(35% of area with >10 MPa) (Table 1).The
differences between medialmeniscal re-
lease, andmedialcaudal-pole hemimenis-
cectomyfor the pressure distribution in the
medialcompartment, were not significant
(P>0.05). It wasapparent that alarge por-
tion of the χ
2
value wasattributabletodiffer-
ences at the >10 MParange.Following
medialmeniscal release the peak pressure
area apparentlytranslatedfrom its central
position andshifted caudally, justcranialto
the caudalmenisco-tibial ligament, al-
thoughthis change wasnot evaluated
quantitatively (Fig. 3).
Experiment2-meniscal disruption
and TPLOincranial cruciate
ligamentdeficient joints
Basedonthe information obtainedfrom ex-
periment 1, data from the >10 MPacategory
were used as the outcome measure for ex-
periment 2. Data from four out of 12 legs
were lostdue to artefactsinthe films,and
could not be includedinthe analysis. Asig-
nificantinteraction by the two-wayANOVA
(P=0.1315), with the major sourceofvari-
ation being meniscal treatment (P<0.0001).
Thepost-hoc tests found asignificantin-
crease in percentofpeak pressure (>10
MPa) after transecting the CCL in the
SHAMstifle (P<0.05) (Fig 4).Medialme-
niscal release andmedialcaudalpole he-
mimeniscectomydid nothaveany further
significant effect (P>0.05). In the TPLO
stifle asignificantincrease in percentage of
highpressure wasfound aftermedialmenis-
cal release (P<0.05) (Table 2).Performing
medialcaudal-pole hemimeniscectomyfol-
lowing medialmeniscal release did not have
anyfurther significant effect on percentof
high pressure (P>0.05) (Table 2).Acaudal
shift of the contactareawas noted as in ex-
periment 1following medialmeniscal re-
lease andmedialcaudalpole hemimenis-
cectomy(Fig. 3).
Discussion
In our study we found thatmedialmeniscal
release, medialcaudalpole hemi-meniscec-
tomyand CCL transection in vitro resulted
in significant alterationsinthe load trans-
mission function of the medialmeniscusin
the canine stifle.Afterperforming amedial
meniscal release andsimilarlyamedial,
caudalpole hemimeniscectomyinintact
andCCL deficient stifle stabilized by
TPLO,weobservedafocal area of high
pressure in the caudalregion of the medial
tibialcondyle. Cranial cruciate ligament
transection caused asimilarareaofhigh
pressure in the CCLdeficient stifle thatwas
not stabilized by TPLO.
The role of themenisci as load bearing el-
ements has been already studied in depth in
human and animals models (1–4,6,23, 34).
Fig.2
Pressure sensitivefilms
stainedbefore medial
meniscal release(A), fol-
lowing medial meniscal
release (B) andafter
medial caudal pole he-
mimeniscectomy (C).
Fig.3
Pressure sensitivefilm
stainedfollowing medial
meniscalrelease illus-
trates the caudallocation
of the areaofhighpress-
ure on the medial tibial
plateau.
VetComp OrthopTraumatol1/2008
12
Pozzi et al.
Several studies have shown that meniscec-
tomy causes an immediate, acute increase in
stiflecontactpeak pressure and that these
changes in stress distribution cause remod-
elling of bone and soft tissue (1, 2, 4, 23).
Ahmed andBurke reported that theremoval
of themedial meniscus caused areduction in
the compartment area by 50–70% and a
marked increaseinpeak pressure in the
human knee (1). Krause et al. showedthat
canine menisci transmit 65% of theweight
bearing and that atwo-fold increaseincom-
pressive deformationofcartilage and sub-
chondral bone occurred after meniscectomy
(35). Shriveetal. reported that radial trans-
ectionofthe porcine and human meniscus
wasequivalenttomeniscectomyinterms of
load-bearing, suggesting that the loss of
‘hooptension’ wasresponsible for highand
non-uniform pressuredistribution(17).In
our experimentwefound that themedial me-
niscusisalso an importantload bearingel-
ementinthe normal andCCL deficientca-
ninestifle, stabilized by TPLO.Medial me-
niscal release and medial, caudal pole he-
mimeniscectomyimpaired theload trans-
missionfunctionofthe meniscusand pro-
ducedatwo-fold increaseinpeak pressure
area and anon-uniform pressuredistribu-
tion. These results concur with findings re-
ported by other authorsafter meniscectomy
in canineand human models(2, 23, 34, 35).
As Shrive et al. suggested,the transectionof
thecircumferential fibres of themeniscus
disrupts the hoop tensionwhich is respon-
siblefor theload bearingfunction(17).
In aprevious study of load transmission
in canine stifles, it wasfound that CCL
transection caused acaudalshiftofthe stifle
contactareas, without anychange in press-
ure magnitude (36). In our study we like-
wise found acaudalshiftofthe contactarea
following CCL transection butwenoted a
significant increase in peak pressure.The
different results of the twostudiesmay be
relatedtothe different model, film sensitiv-
ity or specimen preparation. Thecaudal
shift of the area of high peak pressure prob-
ably occurred during cranialtibialtrans-
lation. One mathematical analysis of femo-
ro-meniscal loadingfound that axialload-
ing by the condyle through the centroidal
axis of symmetryofthe meniscusresulted
in generation of uniform hoop tension in the
meniscus(17). During weightbearing on an
unstable stifle,the medialfemoralcondyle
shifts caudallyand losesits normal central
position in the crescentshapedmeniscus
(13). This condylar translation maydisrupt
the normal ‘hoop tension’ by applying a
high pressure in aperipheral area of the me-
niscus,and potentiallyincreasing the risk of
injuryofthe caudalpole of the meniscus. In
our study we also found thatthe magnitude
of peak pressure diminished in the stifle
treated by TPLO,which suggeststhatthe
detrimentaleffect of CCL transection on
loadtransmission waseliminatedbyneu-
tralizing the cranialtibialthrustwith TPLO
(26).Performing aTPLOinthe presence of
an intact meniscusmay maintain the load
transmission function of the medialmenis-
cusinaCCL deficient stifle.The results of
the pressure distributions in TPLO stifles
suggested some interesting points fordis-
cussion. Despite ahomogeneous distribu-
tion,the magnitude of the pressure
measuredinthe normal stifle with TPLO
washigher thaninthe normal stifle without
anytreatment. This would suggest that
Fig. 4 Pressure sensitivefilms fromastifletreated with aSHAMTPLOstainedbefore medial meniscal releaseand CCL
transection (A), following CCL transection (B), following medial meniscalrelease (C) and aftermedial caudalpole hemime-
niscectomy (D). Pressure sensitivefilms fromastifletreated with aTPLOstainedbefore medial meniscal releaseand CCL
transection (E), following CCL transection (F), following medial meniscalrelease (G)and after medial caudal pole hemime-
niscectomy (H).
Table 2 Effectof cranialcruciateligamenttransection andmedial meniscalsurgeryonthe percentageofareaon themedi-
al tibialplateau with pressuredistributions of >10MPA (mean±SD) in stifle joints with atibialplateau levelling osteo-
tomy (TPLO) or ashamTPLO(SHAM) procedure
ICCL+IM
TPLO 20.68±11.43
a
SHAM 3.51 ±2.99
a
ICCL+IM, intact cranial cruciateligamentand intact medial meniscus; TCCL+IM,transectedcranial cruciate ligament and intact medial meniscus; TCCL+MMR, trans-
ected cranialcruciate ligament and medial meniscus release; TCCL+MMR, transected cranialcruciate ligament and medial caudal pole hemi-meniscectomy. Within
each row, differentlettersdenotesignificant difference (P <0.05).
TCCL +IM
28.08 ±7.93
a
38.13 ±11.11
b
TCCL +MMR
47.48 ±13
b
45 ±10.9
b
TCCL +MCH
55.75 ±12.17
b
52.63 ±5.45
b
VetComp OrthopTraumatol1/2008
13
Pressuredistribution with meniscectomy andTPLO
TPLO maychange the normal stifle bio-
mechanicsinvivoand mayincrease the
forces acting on the tibialplateau without
changing itsdistribution. However, the ef-
fect of TPLO on pressure distribution was
not our specific objective.
Thelink betweenmeniscal damage or me-
niscectomy andosteoarthritisispoorly
understood (25, 37–41). It hasbeen proposed
thatcompression of the cartilageatphysio-
logical strains serves as asignal to modulate
chondrocyte responses,whileprolonged
compression at higherstrains mayberespon-
siblefor tissueand cell damage (40). Radin et
al. reportedthatfailure to properlyabsorb im-
pact leadstomicrodamage in the subchon-
dralplate and cartilage which causes reacti-
vation of the secondary centreofossification
andthe development of subchondralbone
sclerosis (42, 43). This mechanical overload
can activate abiological responsethatpo-
tentiates theprogression of arthritis(42, 43).
Clements et al. reportedthatrepetitive com-
pressive loadingwith peak stress ranging be-
tween 3.5and 14 MPacausedanimmediate
dose-relatedincreaseincollagen denatu-
ration in bovine articular cartilage(44). In ad-
dition, it wasreportedthatthe application of
a15MPa impact to the femoral condyle of
dogs resulted in hypertrophic changesinthe
articular cartilageafter12weeks, which is
consistent with earlychangesofosteoarthri-
tis (45). There is alsoabody of clinical litera-
ture thatsuggeststhatthe surgicalremovalof
the medial meniscus constitutes ariskfactor
for the laterappearance of joint cartilage
changes(46–48). In our study we measureda
focalpeak pressure on the cartilageofthe
caudalmedial tibialplateau higher than 10
MPafollowing medial meniscalreleaseand
medial, caudalpole hemimeniscectomy..
Theseobservationssuggest that the caudal
regionofthe medialcompartment of stifle
could be at ahigher riskofcartilagedamage
after medial meniscal releaseand medial,
caudalpole hemimeniscectomy in dogs.This
is consistent with experimentalstudies which
foundearly cartilagedegeneration of the
medialfemoralcondyle andmedial caudalti-
bial plateaufollowing medial meniscalre-
leaseand medial, caudalpole hemimeniscec-
tomy in the dog(22).
Alimitation of the mechanical testing
apparatus used for our study wasthatites-
sentiallylimitedstifle jointmotion to
flexion-extension duringthe application of
axialloads.Use of the Oxford rigfor our
testing mayhavemore closelyapproxi-
mated in vivo loadingconditions. TheOx-
ford rigwas designedfor the biomechanical
testing of cadaveric humankneejoint speci-
mens duringsimulatedflexed-kneestance
(49).Using the Oxford rig, load is applied
through the hip,allowing the knee specimen
its natural sixdegrees-of-freedom of move-
ment.
In ourmodel, load transmission was
evaluatedbythe measurement of the magni-
tude anddistributionofpressure using
pressure sensitive films.Pressure sensitive
film hasseveral limitations, notably the
rangebetween threshold andsaturation and
the sensitivity of the film to loadingrateand
environmentalconditions. Thepeak press-
uresofthe CCL deficientjointsand that of
the stifle aftermedialmeniscal release or
medial, caudalpole hemimeniscectomy
were beyond the 10 MPathresholds. We
consideredpressureshigher than10MPa as
supraphysiologic as suggested by previous
studies (44). Theresults frompressure sen-
sitive film also areaffected by shear
stresses, the time between testing andanaly-
sis, and environmentalconditions (3). These
effectswerecertainlypresent in this study
butwerenot consideredtoaffect the results
significantly, mainlybecause the differ-
ences between paired limbs were the most
important variables. We did not measure the
contactareaorits shift. Previousstudies
suggested thatpressure is amore sensitive
indicator of meniscal function (3). We chose
to describe qualitatively the apparent shift
of contactareabecause we could not find an
objective methodtoreadilyquantify this
change.Inaddition, the position of contact
between the femur andtibia would shift
caudallyduring stifle flexion, andtherefore
introducesome additional artefact.
In conclusion, our results show that
medialmeniscal release andsimilarlymedi-
al,caudalpole hemimeniscectomysignifi-
cantlyaffect the loadtransmission function
of the meniscusand consequentlythe carti-
lage pressure.The findings of our study also
suggested thatTPLOmightneutralizethe
negative effect of CCL transection on load
transmission. Theimplication of these data,
for clinical use, is thatanintactmeniscus
should be ideallypreservedinthe CCL defi-
cientstifle stabilized by TPLO.Maintaining
the load bearing function of the medialme-
niscus mayprotect the articularcartilage
fromsupra-physiological pressure andits
potentialdetrimentaleffectsoncartilage
metabolism(50). Furtherclinical studies
areneeded to determine if medialmeniscal
release is necessaryinCCL deficient stifles
treated by TPLO.
Acknowledgements
The research wasfunded in partbygrants awarded to
ProfessorKennethJohnson by AO-Vet and the Ohio
State UniversityCanineResearch Fund Grant.The as-
sistance of TimVojt and Marc Hardman in producing
the figures is gratefully acknowledged.
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Correspondenceto:
Kenneth A. Johnson MVSc,PhD
The Ohio State University
College of VeterinaryMedicine
601 VernonL.Tharp Street
Columbus, Ohio 43210, USA
Phone: +1 614 247 6757, Fax: +1 614 292 0895
E-mail: johnson.2064@osu.edu
