Download Tissue Mechanics II – Soft Tissue Cartilage Muscle Ligaments

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Tissue Mechanics II – Soft Tissue
Cartilage
Muscle
Ligaments
Tendons
Meniscus
All connective tissue (including bone and adipose) is
characterized by distinctive cells surrounded by an
extracellular matrix within a ground substance. The
tissue is classified based upon this ECM. Blood is
also a specialized form of connective tissue.
Cartilage Types
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Cartilage is a dense connective tissue, collagen fibers
arranged within a ground substance, chondrocytes
Hyaline
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Most widespread, forms articular cartilage in adults,
among other jobs
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Smooth appearance
Fibrocartilage
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Intervertebral Disc, other
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Transitions in tendon and ligament
Elastic Cartilage
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Mostly elastic fiber, rigid, found in outer ear
Cartilage Structure
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Articular Cartilage is the load-bearing cartilage in
diarthroidal joints
Structure is a large ECM (proteoglycans, collagens, water)
with a sparse population of cells (chondrocytes)
Superficial, Middle (Transitional) and Deep Zones leading
to calcified cartilage and the bony tissue underneath:
Articular Cartilage Tissue
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Type II Collagen (primarily) provides tensile properties,
immobilizes proteoglycan “gel” within ECM
Water + PG provide compressive capabilities
–
PG aggregate molecules are made up of many
aggrecans together along Hyaluronic Acid core
–
60-85% water weight (water content increase with
diseased state)
Biomechanics of Articular Cartilage
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Static, Cyclic, Repetitive High Loads
Matrix compacts due to load, causing water flow, treat
cartilage as biphasic (solid & fluid)
Fluid Pressurization is the dominant physiologic load
support mechanism
Viscoelasticity
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Flow dependent and flow independent
Creep
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Under constant load support transferred fluid to solid
phase
Ligament and Tendon
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Tendon Function: tough fibrous bands of tissue that
connect bone to muscle.
Ligament Function: short, tough bands of fibrous tissue
connecting bones or supporting various organs.
http://health.allrefer.com/pictures-images/tendon-vs-ligament.html
Ligament and Tendon : Tissue Structure
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Dense connective tissue, grossly and microscopically
similar
Collagen (I) molecules combine:
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Microfibril -> subfibril -> fibril
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Fibrils are arranged in parallel bundles, longitudinal
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Embedded in proteoglycan, water, other proteins
Fibroblasts contained in above ECM (rod-shaped)
Picture from Simon, Orthopaedic Basic Science
Ligament and Tendon : Tissue Structure
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Ligament collagen more randomly oriented, lower collagen
(fibril) content, higher ground substance
Fascicles are bound by endotendon (loose ct) which
supports vascularity and innervation and permits
longitudinal movement
Ligaments exhibit heterogenous properties (ACL different
from LCL, etc)
Ligament and Tendon : Biomechanics
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Largely tensile, tendon experiences compression around
articular surface of joint (Poisson's effect)
More purely elastic due to higher collagen content (as
compared to other ST)
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Viscoelastic material properties **Note fascicle crimp**
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Testing difficulties
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Rat Tail Tendon
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Bone-Ligament-Bone complex, Bone-Tendon-Muscle complex
Affecting factors include age, anatomic location, preloading, handling
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Effects of immobilization/exercise is inconclusive
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Tissue thought to adapt to mechanical demands, more
slowly than in bone due to lower vascularity
Skeletal Muscle : Tissue Structure
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Bundles of individual fibers, muscle cells, compose a
muscle fasciculi. Fascicles, group of fasciculi, make up a
muscle.
Connective Tissue continuous throughout, tendon at
muscle/bone interface, periosteum of bone
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Endomysium
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Perimysium
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Epimysium
Seeley et.al
Skeletal Muscle : Tissue Function
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Movement is achieved through a series of events starting
with an electrical signal from the nerve cell axon that is
delivered to the muscle at the motor end plate by means of
the muscle fiber membrane.
Seeley et.al
Skeletal Muscle : Biomechanics
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Nonlinear, time-dependent viscoelastic material, tied into
tendon biomechanics
Force/Pull (P) /Fulcrum (F) /Weight (W) scenarios:
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Class I (W - F - P)
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Class II (P - W - F)
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Class III (W - P – F)