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Chapter 8 JOINTS (ARTICULATIONS)

Joints AKA articulations Sites where two bones meet Provide mobility and protection Weakest part of skeleton “Arthros”= Greek word for joint

Classification of Joints Functional--defined by degree of movement Structural--defined by material binding bones or presence of joint cavity

Functional Joints Synarthroses-immovable Amphiarthroses--slightly moveable Diarthroses--freely moveable

Structural Joints Fibrous--bones connected by fibrous  (collagen) tissue Cartilaginous--bones united by cartilage Synovial--bones separated by fluid-filled cavity

Fibrous joints Fibrous tissue connections of varied length Movement depends on fiber length Sutures--short fibers ossify (skull) Syndesmoses--ligament or sheath (tib-fib and rad-ulna) Gomphoses--peg in socket (teeth)

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Cartilaginous joints United by cartilage, no cavity Synchondrosis--bar or plate of hyaline cartilage (epiphyseal); no movement Symphysis--articular cartilage fused to fibrocartilage pad (intervertebral joints, pubis); limited movement

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Synovial joints All diarthrotic All have the following features articular cartilage joint cavity double layer capsule synovial fluid reinforcing ligaments

Other synovial features Fat pads between capsule and synovial membrane or bone Articular discs (menisci) of fibrocartilage; improve bone fit and stability Bursae--sacs of fluid (ballbearings) Tendon sheaths around tendons

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Stabilizing factors Articular surfaces fit Ligaments restrict bones movement Muscle tone keep tendons which cross joints tight, hold bones in place

Diarthrotic movements Gliding--tarsals and carpals Angular--limb flexion, extension, abduction, adduction, circumduction Rotation--medial and lateral Special--pronation, supination, inversion, eversion, protraction, retraction, elevation, depression, opposition

Types of Synovial Joints Plane--articular surfaces flat, non-axial (carpals, tarsals, vertebrae) Hinge--uniaxial (elbow) Pivot--uniaxial rotation (C-1 & C-2) Condyloid--biaxial complementary ovals Saddle--saddle and rider fit (thumb) Ball and socket--spherical head in socket; multi-axial (hip, shoulder)

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Homeostatic imbalances Common joint injuries Sprains--stretch ligament, loose joint Cartilage tears--fragments freeze joint Dislocations (luxation)--bones out of normal alignment

Homeostatic imbalances Inflammatory and degenerative Bursitis and tendonitis Arthritis--over 100 types Osteoarthritis (OA) Rheumatoid arthritis (RA) Gout

Joint Health Uninjured, OK until middle age Ligaments/tendons short, stiff Intervertebral discs thin, rupture Most in 70’s have OA Careful exercise, stretching helps maintain joint mobility