6_KINE426_Joints

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Texas A&M University *

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426

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Health Science

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Oct 30, 2023

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1 Andrew Nordin, PhD Assistant Professor, Department of Health & Kinesiology KINE 426 Exercise Biomechanics Chapter 2 Skeletal Considerations for Movement Cartilage • Properties – Firm, flexible tissue • Made of chondrocytes surrounded by extracellular matrix – No blood supply (avascular) or nerves – Nourished by fluid within joint • Function – ↑ joint stability – Distributes load in joint • ↓ contact stress • Types of Cartilage – Articular – Fibrocartilage ace-pt.org

2 Cartilage • Articular Cartilage (hyaline) – Articulating ends of bones covered with connective tissue – 60-80% water, 1-7mm thick • ↑ thickness with contact pressure – Collagen: protein providing stiffness & strength – Proteoglycan: highly hydrated gel – Anisotropic & viscoelastic – Function • Transmit compressive forces across joint • ↓ friction • Spread stress over > area • Protect bone ace-pt.org Cartilage • Fibrocartilage – Where articular cartilage meets a tendon or ligament (intermediary) – Functions • ↓ friction • Spread stress over > area • Improves fit between bones • Structure – Fibrocartilage structure: meniscus, articular disc – Example: intervertebral discs, jaw, knee ace-pt.org

3 Ligaments • Properties – Connect bone to bone – Short band of fibrous connective tissue • Consist of collagen, elastin, reticulin – Maximum stress related to cross-sectional area – Viscoelastic : time-dependent, nonlinear stress-strain response – Tensile loading → ↑ strength & stiffness • Function – Guide normal joint function – Restrict abnormal movement knee.in Ligaments • Types of ligaments – Capsular : thickenings in the wall of the capsule (shoulder) – Extracapsular : outside joint, collateral ligaments (fibular collateral ligament of the knee) – Intra-articular : inside joint (cruciate ligaments of knee) • Injury – Sprain – 3 grades (1-partial tear, 2- tear with loss of stability, 3- complete tear with loss of stability knee.in

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4 Joint Types • Diarthrodial (synovial) – Characteristics • Articular end plate (bone end) • Articular cartilage→ thin cortical bone→ cancellous bone – ↑ load transmission, ↑ stability, ↑ fit, protection, lubrication – Low friction – High resistance to wear & tear – Capsule • Connective tissue made of collagen • Interarticular space inside joint – ↓ pressure • Synovial membrane : secretes synovial fluid lubricating joint + nutrition • Viscoelastic : time-dependent, nonlinear stress-strain response Joint Types • Joint Stability – Ligaments • Tendons spanning joint – Gravity • Load – Vacuum • Capsule & negative pressure

5 Joint Types • Contact area varies with joint position • Close-packed – Maximum contact area between surfaces – Maximum compression • Full knee extension – ↑ joint stability, ↑ risk of injury • Loose-packed – All other joint positions – ↓ contact area Joint Types • Types of diarthrodial joints (7) – Plane/gliding : nonaxial, 2 flat surfaces translate (tarsals) – Hinge : uniaxial, one plane (elbow) – Pivot : uniaxial, one plane (radio- ulnar joint) – Condylar : primary movement in one plane (knee) – Ellipsoid : biaxial, two planes (phalanges) – Saddle : similar to ellipsoid (thumb) – Ball & socket : triaxial, three planes (hip)

6 Joint Types • Other types of joints – Synarthrodial/fibrous • Bones held together by fibrous articulations • Allows for little or no movement – Example: sutures in skull – Amphiarthrodial/cartilaginous • Hyaline cartilage or fibrocartilage holds joints together • Little movement – Intervertebral discs Joint Types

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7 Joint Degeneration • High repetitive loading erodes cartilage – Osteoarthritis: degenerative joint disease • Degeneration of articular cartilage → fissures → disappearance of cartilage • ACL injury → ↑ risk of OA dreamstime.com Summary • Stress & Strain – Elastic modulus – Yield point – Failure – Elastic – Plastic – Residual strain – Mechanical energy storage – Viscoelastic

8 Summary • Skeletal System Components – Bones – Joints – Cartilage – Ligaments • Skeletal Functions – Leverage – Support – Protection – Storage – Blood cell formation Summary • Bones – Types • Long, short, flat, irregular • Cortical vs. Cancellous Bone – Bone remodelling • Wolff’s Law : response to stress – Resorption: osteclasts – Deposition: osteoblasts – Strength (energy storage) vs. Stiffness (elastic modulus) – Anisotropic – Viscoelastic

9 Summary – Types of Loading • Compression, tension, shear, bending, torsion – Injury • Acute vs. Overuse – Cartilage • Articular : bone ends, stability, load distribution, ↓ friction • Fibrocartilage : fit & structure – Ligaments • Structure & stability – Joint types • Diarthrodial : load, stability, fit, protection, friction – Stability : ligaments, gravity, vacuum (capsule) • Other types • Close-packed vs. Loose-packed

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