The Effects of Freezing The Effects of Freezing on the Properties of on the Properties of

Bovine MeniscusBovine Meniscus

Scott MorganScott Morgan

What Is Meniscus?What Is Meniscus?

Semi-lunar Semi-lunar fibrocartilagefibrocartilage• LateralLateral• MedialMedial

Importance?Importance?

Provide smooth, low friction Provide smooth, low friction articulating surfacesarticulating surfaces

Serve as shock absorbers and Serve as shock absorbers and stabilizersstabilizers

When injured and/or removedWhen injured and/or removed• Degeneration leading to osteoarthritisDegeneration leading to osteoarthritis• Knee movement becomes more difficultKnee movement becomes more difficult

Why freezing?Why freezing?

Literature review Literature review (Proctor et al, J of Ortho R, 1989)(Proctor et al, J of Ortho R, 1989)

• Experimental menisci described as freshExperimental menisci described as fresh• Frozen to microtome twice during slicingFrozen to microtome twice during slicing

Menisci are roughly 70% waterMenisci are roughly 70% water• No studies to determine effect of No studies to determine effect of

freezing on material propertiesfreezing on material properties

Materials & MethodsMaterials & Methods

Bovine menisciBovine menisci• Obtained from local slaughterhouseObtained from local slaughterhouse• Medial meniscus only Medial meniscus only to reduce variability to reduce variability

MedialLateral

MethodsMethods

Treatment Groups Treatment Groups 5 5 • Control (Fresh)Control (Fresh)• 4 Freeze/Thaw Cycle (FTC) Group4 Freeze/Thaw Cycle (FTC) Group

1 FTC = 5 days frozen, 2 days thawed1 FTC = 5 days frozen, 2 days thawed 2 FTC2 FTC 3 FTC3 FTC 4 FTC4 FTC

MethodsMethods

MethodsMethods

12 Menisci per treatment12 Menisci per treatment• Minimum of 5 slicesMinimum of 5 slices• Maximum of 15 slicesMaximum of 15 slices

Thickness measuredThickness measured• Dial caliperDial caliper

Sandpaper glued to endsSandpaper glued to ends• Facilitated gripping in fixtureFacilitated gripping in fixture• Provided gage lengthProvided gage length

MethodsMethods

MTS servohydraulic MTS servohydraulic mechanical testing systemmechanical testing system• Computerized data Computerized data

acquisitionacquisition• Custom gripping jigCustom gripping jig

Performed tensile testPerformed tensile test

MethodsMethods

Tensile testTensile test• 1 N preload1 N preload• Photograph for later Photograph for later

digital analysis for digital analysis for specimen specimen dimensionsdimensions

• 0.5 mm/min 0.5 mm/min crosshead speedcrosshead speed

• Tensile tested until Tensile tested until failurefailure

MethodsMethods

Data analysisData analysis• Digital image analysis Digital image analysis

Specimen dimensions from photosSpecimen dimensions from photos

• Calculate stress & strain Calculate stress & strain Plot stress-strain curvePlot stress-strain curve

twF

AF

0ll

(Wainwright, 1976)

Statistical AnalysisStatistical Analysis

Compared menisci within each Compared menisci within each treatmenttreatment• Look for individual variabilityLook for individual variability

Compared treatment groupsCompared treatment groups ANOVAANOVA

• Multiple comparisons – Tukey-KramerMultiple comparisons – Tukey-Kramer

Maximum Stress

0

5

10

15

20

25

Control 1 FTC 2 FTC 3 FTC 4 FTC

Treatments

Max

Str

ess

(MP

a)

Modulus

0

20

40

60

80

100

120

140

160

Control 1 FTC 2 FTC 3 FTC 4 FTC

Treatments

Mo

du

lus

(MP

a)

ConclusionsConclusions

Large variability between specimensLarge variability between specimens• Increasing FTC’s lead to increasing Increasing FTC’s lead to increasing

variabilitityvariabilitity

There appears to be little to no effect There appears to be little to no effect of multiple FTCs on the tensile of multiple FTCs on the tensile strength of the circumferential strength of the circumferential collagen fiberscollagen fibers

CurrentCurrent

Changes in the specimensChanges in the specimens• TextureTexture• Ease of slicingEase of slicing

Creep & Relaxation TestingCreep & Relaxation Testing Design of new apparatusDesign of new apparatus

• Compression indenterCompression indenter New experimental procedureNew experimental procedure Meniscus from other speciesMeniscus from other species

• OvineOvine• PorcinePorcine

AcknowledgmentsAcknowledgments

Dr. Carolyn SkurlaDr. Carolyn Skurla

Daniel BlandDaniel Bland Zachary KelmZachary Kelm Erik SchaeferErik Schaefer Christopher ToweChristopher Towe David WebsterDavid Webster