Joints and their connective tissues

Structural classification

(Based on the material binding them and presence or absence of a joint cavity) - Fibrous (presence of fibrous tissue and lack of cartilage) - Cartilagenous (cartilage is present in between the bones) - Synovial (more complex structure including a cavity and a capsule)

Functional classification

(Focuses on amount of movement) - Synarthroses (immovable joints) - Amphiarthroses (slightly movable joints) - Diarthroses (freely movable joints)

Factors Affecting Contact and Range for Motion at Synovial Joints

-Arrangement and tension of the muscles -Contact of soft parts -Hormones -Disuse

Saddle Joints

-Articular surface of one bone is saddle-shaped, and the articular surface of the other bone fits into the "saddle" (one is convex and one is concave) -Thumb

Cartilagenous Joints

-Articulating bones united by cartilage -Joint cavity: NO -Movement: not highly movable -Two types depending on the intervening cartilage Synchondrosis (plurar: synchondroses), Symphesis (plural: sympheses)

Ball-and-Socket Joints

-Ball-like surface of one bone fitting into a cuplike depression of another bone -Shoulder and hip

Fibrous joints

-Bones connected by fibrous tissue: dense regular connective tissue. Cartilage is lacking. -Joint cavity: NO -Movement: Fix or slightly movable -Types Sutures, Syndesmoses, Gomphoses

Planar (Gliding) Joints

-Flattened or slightly curved faces -Primarily permit back-and-fortand side-to-side movements -Intercarpal joints

Syndesmoses

-In Greek: σύν, syn ("with") δεσμός, desmos ("a band") -Bones connected only by ligaments . Is a truly fibrous connection -movement depends on length of the fibres (longer than in sutures)

Synchondrosis

-In Greek: σύν, syn ("with") + χόνδρος, chondros ("cartilage"). Literally: "junction of cartilage" -Non-articular hyaline cartilage -With age may tend to synostose (complete ossification)

Symphesis

-In Greek: σύν, syn ("with")+ φύσις, physis ("growing area"). Literally "growing together" -Ends of the articulating bones are covered with hyaline cartilage, but a disc of fibrocartilage connects the bones Slightly movable (amphiarthroses) Resilient shock absorber Provide strength and flexibility -Hyaline cartilage on articular surfaces of bones to reduce friction -Ligaments may extends from the periosteum across the joint to blend with hyaline and fibrocartilagineous perichondria.

Gomphoses

-Is a "peg-in-socket" -In Greek: γόμφος, gomphos ("a peg") -Only example is tooth with its socket -Ligament is a short periodontal ligament starting from periodontium to the alveolar bone

Hinge Joints

-Produce an opening and closing motion like that of a hinged door -Permit only flexion and extension -Knee and elbow

Range of motion (ROM)

-Refers to the range, measured in degrees of a circle, through which the bones of a joint can be moved

Factors contribute to keeping the articular surfaces in contact and affect range of motion

-Structure or shape of the articulating bones •Shape of bones determines how closely they fit together -Strength and tension of the joint ligaments •Ligaments are tense when the joint is in certain positions •Tense ligaments restrict the range of motion

•Pivot Joints

-Surface of one bone articulates with a ring formed partly by another bone -Joints that enable the palms to turn anteriorly and posteriorly

Condyloid Joints

-The projection of one bone fits into the oval-shaped depression of another bone -Wrist

Sutures

-Typical of the skull -Bone is covered by a layer of osteogenic cells (cambial) overlaid by a fibrous tissue continuous with the periosteum (capsular lamella) In between there is a loose connective tissue -Ossify and fuse with age: technically called "synostoses"= bony junctions

Movement of Synovial Joints

-monoaxial if the bone moves in just one plane -biaxial if the bone moves in two planes -multiaxial if the bone moves in multiple planes

General structure of synovial joints

Articular Surfaces •Irregular shape (movement+stability) •Covered by articular hyaline cartilage (5-7 mm ; 3 layers; white, smooth, glistening and compressible) -Permanent (deep coating of bony surfaces) •Deep : higly complex 3-D reticulum of fibrils •Superficial : collagen fibres + chondrocytes -Transient (superficial coating toward cavity) •Particulate or filamentous material (debris, synovial fluid and products of chondrocytic necrosis)

Classification of Synovial Joints

Classified by shape (of articular surfaces) shape sets movements!! -Planar-Gliding -Hinge -Pivot -Condyloid -Saddle -Ball-and-socket

Synovial Joints

Different from the other types of joints •Freely moveable •Articulating bony surfaces are NOT in continuity •Bones are covered by a fibrous capsule •Ligaments and tendons provide joint stability •Presence of a synovial membrane that produce a viscous fluid acting as a lubricant •Presence of other connective fibrocartilaginous structures

Epiphyseal plates

Joint between first rib's costal cartilage and manubrium of the sternum

Ligaments

Ligaments are responsible for holding joints together. They guide joint movement and prevent bones moving out of position during the stresses of physical activity. If they are pulled or twisted too far by extreme physical movements, ligaments can tear and the joint may dislocate (sprain).

Principle of Biomechanics

Principles of Biomechanics The increase in contact surface area reduces the contact stress by 50%

Classification of Joints II

Structural classification Functional classification

Principles of Biomechanics

Superficial alignement of fibrils parallel to the surface provides higher resistance to tissue splitting reducing wear due to high and repetitive loads Swelling due to water attraction by proteoglycans provides compressive turgor and load is progressivlely distributed on the different layers and underlying bones Cartilage has greater degree of deformation because is softer than bones

Tendon Sheaths

Tendon sheaths = cylinders of connective tissue lined with synovial membrane and wrapped around a tendon

Synovial membrane (III)

Two different cell lines •Type A: - macrophage-like (ruffle membrane) -Lytic enzyme and phagocitose -Immigration from bone marrow precursors •Type B: -Fibroblast-like -Hyaluronan, glycoproteins and other protecting enzymes -Divide actively "in loco" after trauma

Vascularization

Vascular plexus of synovial membrane Adjacent bone marrow spaces Vascular supply from subchondral bones

Synovial fluid

•Clear pale yellow viscous trasudate (only 2% of proteins) from synovial capillaries filling synovial spaces •Function is to reduce friction by: •lubricating the joint reducing friction •absorbing shocks •supplying oxygen and nutrients to the cartilage •removing carbon dioxide and metabolic wastes from the cartilage

Composition

•Dense connective tissue (parallel-fibers of collagen) - Sparsely vascularized •Cellular : fibroblasts(20 %) •Extracellular (80%) - 70% H2O - 30% collagen, ground substance, elastin

Fibrocartilagineous structures

•Fat Pad soft structures filling joint recesses. Changes shape according to position •Disc or Meniscus (pl.menisci) fibrocartiolagineous structures covered by layers of fat cells. Surrounded by ligaments and connected to fibrous capsula by vascularized connective tissue. •Labrum (pl. labra) thin lips attached on an articular margin increasing the area of contact between articular surfaces and spreading lubricant

Hormones

•Flexibility may also be affected by hormones •Relaxin increases the flexibility of the pubic symphysis and loosens the ligaments between the sacrum and hip bone toward the end of pregnancy

Fibrous Capsule

•Interlacing bundles of parallel fibres attached round articulating bones (vessels and nerves pass through bundles to get to the articular space) •Intrinsic (local thickening of fibrous bundles) and extrinsic (extra or intra capsular) ligaments, muscle and tendons provide joint stability. •Inner surface is completely covered by the synovial membrane (except articular surfaces and other intra-articular structures).

Synovial membrane (II): microscopic aspect

•Intima (basal lamina is lacking): granular amorphous fibre-free matrix embedding "packed"synovial cells •Subsynovial tissue: fibrovascular layer - Lamellae of collagen and elastin -Small fat lobules surrounded by highly vascularized septa - Aspecific cell types (macrophage, fibroblast, mastcell, fat cell)

Classification of Joints I

•It's not simple to find a truly efficient classification of joints because of their high variability in structure, shape and function . •A quite consistent attempt of grouping joints in classes has been made according to two different aspects: structural and functional

Joints: general characteristics

•Joints (or articulations) are the place where two bones meet and articulate. •Some Joints allow movement, others stability •Joints transmit forces between bones (weight and exercise) •Through movement, Joints facilitate bone growth and remodeling

Bursae

•Lubricating device consist of a closed fibrous sac. •Present wherever tendons rub against bones,ligaments or other tendons

Meniscus

•Meniscus is an incomplete rim of white fibrous cartilage between articular cartilages •Enhancement of congruence •Protection of edges •Weight distribution •Facilitation of movement •Shock absorber

Disuse

•Movement may be restricted if a joint has not been used for an extended period

Arrangement and tension of the muscles

•Muscle tension reinforces the restraint placed on a joint by its ligaments , and thus restricts movement

Factors affecting Mechanical Properties

•Physical Training - tendon tensile strength and ligament-bone interface strength - ligaments become stronger and stiffer, collagen fibers increase in diameter •Aging - collagen content stiffness, strength & ability to withstand deformation •Pregnancy and postpartum - tensile strength & stiffness in tendons •Immobilization - tensile strength of ligaments, more elongation, less stiff - in cross-links -After 8 weeks of immobilization 12 months to recover strength & stiffness

Synovial membrane (I): macroscopic aspect

•Pink, smooth, shining, with small villi, fringes and folds •Secrete synovial fluid •Dynamic changes of membrane shape during movements reduce friction of articular structures •May protrude through capsule fibrous bundles forming bursae and tendon sheats (reduce friction and improve slippering of the other structures)

Types of Synovial Joints

•Planar (Gliding) Joints •Hinge Joints •Pivot Joints •Condyloid Joints •Saddle Joints •Ball-and-Socket Joints

Ligament - Structure and Function

•Pliant and flexible •Strong and inextensible/inelastic Non-parallel collagen (type I) arrangement, aligned in direction of imposed stress

Factors Affecting Range for Motion and Contact at Synovial Joints

•Range of motion (ROM) •Factors contribute to keeping the articular surfaces in contact and affect range of motion

Fibrocartilagineous structures (function)

•Shock absorption •Increase fitting between surfaces •Increase area of deployment of weight •Allow combined movements •Protect articular margins •Spread of lubricant

Mobility and Stability in Joints

•Structure determines both its mobility and its stability. •Motion permitted ranges from none to various extensive motions.

Contact of soft parts

•The point at which one body surface contacts another may limit mobility •Movement be restricted by the presence of adipose tissue