Joints

Classification of JointsFunctional classification

Synarthroses Amphiarthroses Diarthroses

Synarthroses

• bones are in almost direct contact

• no appreciable motion

• Sutura

• Schindylesis

• Gomphosis

• Synchondrosis

Sutures• margins of the bones are

united by a thin layer of fibrous tissue

• Only between bones of skull

• Fibrous tissue continuous with periosteum

Gomphoses

“peg-in-socket” Insertion of a

conical process into a socket

Only example is tooth with its socket

Schindylesis

• a thin plate of bone is received into a cleft or fissure

• rostrum of the sphenoid• perpendicular plate of the ethmoid with the vomer

Synchondroses• Bones are joined by hyaline cartilage

– rib attachment to sternum by – epiphyseal plate in children binds epiphysis and

diaphysis

Amphiarthroses

• slightly movable articulations• bony surfaces are either connected

by• Symphysis : broad flattened disks of

fibrocartilage, of a more or less complex structure

• Syndesmosis : united by an interosseous ligament

Symphysis

Fibrocartilage unites the bones Slightly movable Resilient shock absorber Provide strength and flexibility

Hyaline cartilage on articular surfaces of bones to reduce friction

Examples Intervertebral discs Pubic symphysis of the pelvis

11

• Two bones bound by ligament– interosseus

membrane

• Interosseus membranes

• unite radius to ulna and tibia to fibula

Syndesmosis

Diarthroses

• bony surfaces are covered with articular cartilage, and connected by ligaments lined by synovial membrane.

• The joint may be divided, completely or incompletely,by an articular disk or meniscus, the periphery of which is continuous with the fibrous capsule

• Eg Synovial joints

Structural classification

• Fibrous• Cartilaginous, • Bony or Synovial

Fibrous joints• Fibrous joints have collagen fibers

spanning the space between bones– sutures– gomphoses – syndesmoses

Cartilagenous joints

Articulating bones united by cartilage Lack a joint cavity Not highly movable Two types

Synchondroses (singular: synchondrosis) Sympheses (singular: symphesis)

Synchondroses

Hyaline cartilage unites the bones Immovable (synarthroses) Examples:

Epiphyseal plates Joint between first rib’s costal cartilage and

manubrium of the sternum

Synchondroses and sympheses

Also pubic symphsis

Synovial joints

Include most of the body’s joints

All are diarthroses (freely movable)

All contain fluid-filled joint cavity

• Uniaxial - all movements take place around one axis

• Biaxial

• polyaxial

Ginglymus(Hinge Joints)

• Articular surfaces are moulded to each other

• Permit motion only in one plane

• Direction which the distal bone takes in this motion is seldom in the same plane as that of the axis of the proximal bone

• Connected together by strong collateral ligaments

• Interphalangeal joints

• Ulna and Humerus at elbow joint

9-20

• One bone has a projection that fits into a ringlike ligament of another

• First bone rotates on its longitudinal axis relative to the other– atlantoaxial joint (dens and atlas)– proximal radioulnar joint allows the radius during

pronation and supination

9-21

Pivot Joints

• Oval convex surface on one bone fits into a similarly shaped depression on the next– radiocarpal joint of the wrist – metacarpophalangeal joints at the bases of

the fingers

• Biaxial joints

9-23

Condyloid (ellipsoid) Joints

Saddle Joints Each articular surface is

shaped like a saddle, concave in one direction and convex in the other◦ trapeziometacarpal joint at

the base of the thumb

Biaxial joint◦ more movable than a

condyloid or hinge joint forming the primate opposable thumb

9-25

• Smooth hemispherical head fits within a cuplike depression– head of humerus into glenoid cavity of

scapula– head of femur into acetabulum of hip bone

• Multiaxial joint

9-26

Ball-and-Socket Joints

Mechanism of lubrication in

synovial joints

Structure

• Hyaline Cartilage

• Ends of long bones (1-5 mm thick)

• Avascular

• Aneural

Composition

Cellular – chondrocytes (10% of volume)

Composition

Extracellular Matrix• Organic – collagen (type II) (10-30% of

weight) & proteoglycans (3-10% of weight)

• Water (most abundant component), inorganic salts, glycoproteins, lipids (60 - 87%)

Composition

• Collagen fibers offer little resistance to compressive forces

• Highly organized stiffness and tensile strength

Composition

• Isotropic – material properties of substance are same regardless of loading

• Hyaline cartilage is anisotropic:• Collagen arrangement • Cross link density• Collagen/PG interaction

Fluid Component

• Permits diffusion of gases, nutrients, wastes SYNOVIAL FLUID

• Important to the structural organization of collagen load bearing /mechanical behavior (80% surface / 65% deep)

Collagen-PG Interaction

• Plays direct role in organization of extracellular matrix

• Important to mechanical properties resists compression

AC under Compression

• constant load rapid initial deformation slow (time dependent) deformation equilibrium

• 20 to exudation of interstitial fluid

Synovial Fluid

• Lubrication

• Reduce Friction

• Nutrition

Synovial Fluid

• Plasma-like

• High in hyaluronate lubrication to reduce friction

• Lubricin – has an affinity for AC - cartilage lubrication

Synovial Fluid

• Hyaluronate (HA) – responsible for viscosity of synovial fluid

• Resistance to shear forces

Type of Lubrication

Boundary – single layer of lubricant molecules on each bearing surface (lubricin has affinity for AC)

Type of Lubrication

Fluid Film • thin fluid film provides greater surface separation • rigid bearings (stainless steel)

Fluid Film Lubrication

• Hydrodynamic – a wedge of fluid is formed when non-parallel surfaces slide over each other

Mixed Lubrication

Mixed Lubrication

Boosted

• ultrafiltration of synovial fluid thru collagen-PG matrix

• H2O & electrolytesarticular cartilage (squeeze-film)

• concentrated gel of HA protein complex coats surfaces (boundary)

Type of Lubrication

Boundary

• high loads

• low relative speeds

• long duration

Fluid-film

• low/oscillated magnitude

• high relative speeds

Synovial joints classified by shape

(of their articular surfaces)

Plane (see right) Hinge (see right) Pivot Condyloid Saddle Ball-and-socket