Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Tissue Mechanics II – Soft Tissue Cartilage Muscle Ligaments
Transcript
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 ● ● ● ● Cartilage is a dense connective tissue, collagen fibers arranged within a ground substance, chondrocytes Hyaline – Most widespread, forms articular cartilage in adults, among other jobs – Smooth appearance Fibrocartilage – Intervertebral Disc, other – Transitions in tendon and ligament Elastic Cartilage – Mostly elastic fiber, rigid, found in outer ear Cartilage Structure ● ● ● 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 ● ● 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 ● ● ● ● 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 – ● Flow dependent and flow independent Creep – Under constant load support transferred fluid to solid phase Ligament and Tendon ● ● 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 ● ● ● Dense connective tissue, grossly and microscopically similar Collagen (I) molecules combine: – Microfibril -> subfibril -> fibril – Fibrils are arranged in parallel bundles, longitudinal – Embedded in proteoglycan, water, other proteins Fibroblasts contained in above ECM (rod-shaped) Picture from Simon, Orthopaedic Basic Science Ligament and Tendon : Tissue Structure ● ● ● 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 ● ● 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) ● Viscoelastic material properties **Note fascicle crimp** ● Testing difficulties ● – Rat Tail Tendon – Bone-Ligament-Bone complex, Bone-Tendon-Muscle complex Affecting factors include age, anatomic location, preloading, handling – Effects of immobilization/exercise is inconclusive – Tissue thought to adapt to mechanical demands, more slowly than in bone due to lower vascularity Skeletal Muscle : Tissue Structure ● ● 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 – Endomysium – Perimysium – Epimysium Seeley et.al Skeletal Muscle : Tissue Function ● 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 ● ● Nonlinear, time-dependent viscoelastic material, tied into tendon biomechanics Force/Pull (P) /Fulcrum (F) /Weight (W) scenarios: – Class I (W - F - P) – Class II (P - W - F) – Class III (W - P – F)
