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Flashcards in MSK L3 Joint structure and function Deck (102):
1

Classification of Joints:

According to structure
According to function

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Classification of Joints: According to structure

1. Fibrous
2. Cartilaginous
3. Synovial

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Classification of Joints:
According to function

Synarthroses
Amphiarthroses
Diarthroses

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1. Synarthroses

no/little movement (fibrous and some cartilaginous joints

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2. Amphiarthroses

– some movement (cartilaginous joints)

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3. Diarthroses

free movement (always synovial joints)

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Fibrous

no joint cavity and dense fibrous connective tissue joining articulating surface.

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Cartilaginous joints

no cavity and two bones are joined y pad of cartilage – fibrous or hyaline.

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Synovial –

cavity between ends of articulating bones – ends covered with fibrous or hyauline for protection.

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Fibrous Joints: 3 sub classifications:

1. Sutures
2. Syndesmoses
3. Gomphoses

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Sutures


Found only in the skull,
Form at 18mths of age when they replace fontanels
Fibrous tissue covered by periosteum

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Several types of sutures

1. Serrate (between frontal and parietal bones)
2. Lap or squamous - overlap (between parietal and temporal bones
3. Plane or butt (between paired maxillary bones forming hard palate).

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Synostosis sutures

Sutures may become totally ossified in adults forming a synostosis (e.g. between frontal bones)

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Syndesmoses:Definition

Bones joined by interosseous ligament or dense aponeurotic membrane

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Syndesmoses: Example

Interosseous membrane between radius and ulna

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Syndesmoses: Movement

Flexibility of collagen fibres in ligament may allow limited movement

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Gomphoses: Definition

Pegs and sockets, held in place by bundles of regular collagenous connective tissue

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Gomphoses: Example

Found between teeth and bones of jaw – periodontal ligaments

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Gomphoses:Movement

Allow sight movement of teeth during mastication as collagen fibres are orientated in different planes.

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Cartilaginous joints: types

1. Synchondroses (primary)
2. Symphyses (secondary)

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Syncondroses (primary) Definition

Advancing centres of ossification separated by hyaline cartilage

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Syncondroses (primary) Temporary types

Most are temporary (e.g. epiphyseal growth plates (and fuse in adults

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Syncondroses (primary) Permanent types

Some persist throughout life e.g. costal cartilages, which allow some flexibility of rib cage during inspiration.

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Symphyses (secondary) Definition

Fibro-cartilage pads between a.c. of adjacenet bones

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Symphyses (secondary) Movement

Allow for slight movement: Symphysis pubis allows expansion of pelvis in childbirth.

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Symphyses (secondary)Examples

Symphysis pubis – childbirth
Intervertebral discs allow limied motion between vertebrae

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Symphyses (secondary)Examples that fuse

Some symphses fuse during growth (e.g. sacral and coccygeal discs)

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Synovial Joints: Definition

Articulating bones separated by synovial cavity filled with synovial fluid

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Synovial Joints: Movement

Cavity gives synovial joints wide range of movement compared to other joints

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Synovial Joints: Examples of movement in different planes

Plane (or gliding)
Hinge
Pivot
Ellipsode(or condyloid)
Saddle
Ball and socket

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Plane (gliding) joints: Definition

Opposing surfaces almost flat or slightly convex and concave

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Plane (gliding) joints: Allow

Small side0to-side or back-and-forth movements and small amount of rotation

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Plane (gliding) joints: Examples

1. Sacroiliac joints
2. Apopphyseal joints of spine
• Allow thoracic sine ribs to movement upwards and outwards during inspiration

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Hinge joints → Definition

Convex and of one bone articulates with concave end of another.

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Hinge joints → Allow

Hinge-type movement about a single axis such as flexion and extension.

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Hinge joints →Examples

Interphalangeal joints of fingers, and tibio-femoral joint of knee.

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Pivot joints:Definition

Conical or rounded surface of one bone fits into depression on another.

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Pivot joints: Allows

Rotation about a single axis

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Pivot joints: v

1. Joint between head of radius and ulnar allows rotation of forearm.
2. Atlanto-axial joint between atlas and axis allows rotation of head.

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Ellipsoid:Definition

Oval convex surface articulates with ellipsoid concavity.

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Ellipsoid:Allows

Bi-axial movement in 2 planes but no rotation.

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Ellipsoid:Examples

1. Atlanto-occipital joint in neck
2. Meta-carpophalangeal (MCP) joints in hands
Radiocarpal joint of wrist

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Saddle joints: Definition

Two saddle-shaped surfaces articulate at right angles to one another

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Saddle joints: Allows

Modified condyloid joint, allows wide range of movement about 2 axes

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Saddle joints:Examples

Found in carpometacarpal (CMC) joint of thumb, and in ankle.

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Ball and Socket Joints: Definition

Almost spherical head (ball) articulates with almost spherical cup (socket)

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Ball and Socket Joints:Movement

Allow for greatest range of movement of al joints, allow multi-axial movement in all planes

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Ball and Socket Joints: Examples

Hip and shoulder joints

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1. All synovial joints are surround by

joint capsule which fully encloses articulating surfaces.

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2. Joint capsule is lined by

synovium/synovial membrame – lines inner surface of joint capsule except where there is articular cartilage

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3. Joint cavity – filled with

synovial fluid.

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Capsule

Outer fibrous capsule
Inner synovial membrane (synovium

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Outer fibrous capsule

Blends with periosteum

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Outer fibrous capsule composed of

Dense irregular connective

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Function of outer

Type 1 collagen – resists tensile loads as it is an irregular orientation – allows resistance of a range of mvoements

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Innervation of capsule

Highly innervated – site of joint pain rather than articular cartilage which has non blood supply or innervation.

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Inner capsule (syovium) Definition

Lines joint cavity except for articular surfaces

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Inner capsule (syovium) Functions

Produces constiuents of synovial fluid

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Ligaments: (within capsule) Formed from

Localised thickening of fibrous capsule

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Ligaments: (within capsule) Composed of

Denses REGULAR CT comprising parallel collagen fibres (mainly type 1)

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Function of collagen arrangement

Gives ligaments great tensile strength along their length

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Where synovium meets articular cartilage

Lots of infolding and villi
Villi → have many capillaries to ensure constituents e.g. oxygen and nutrients can transfer into the synovial fluid. Articualar (avascular) relies on this.

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2 main layers of synovium

1. Supporting layer or stroma (sub0intima)
2. Lining of synovial cells in contact with synovial fluid

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2 types of synovial cell in inner lining

3. Type A

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Type A cells
→ Derived from
→ Function

Derived form bone marrow (macrophages)
Secretory and phagocytic functions → high density of mito and golgi.
→ Remove cell debris from synovial fluid

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Type B cells
→Cell type
→ Function

Type of fibroblasts
Role in synthesis of hyaluronic acid (HA) and proteins → important for maintenance of viscosity (lubrication).

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Synovitis

Inflammation of synovium – symptom of RA

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Articular Cartilage: Contains

Cells, fibres and matrix arranged in zones

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Articular Cartilage: Zones

1. Tangential zone
2. Transitional zone
3. Radial zone – column arrangement
4. Calcified cartilage (by ossified bone)

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Articular Cartilage: Cartilage cells

Chondrocytes; density varies with age, morphology changes in different zones.

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Articular Cartilage: Fibres of Articular collagen

Fibres are collagen, mostly type II – resist stress
Small amount so type VI,IX,XI

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Articular Cartilage: Matrix composed of

Large aggregated proteoglycans (aggrecan) some smaller PGs (decorin and biglycan).

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Articular Cartilage: GAG side changed important for

Hydrophillic and therefore attract water into the cartilage – allows it to resist pressure and forces.

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Articular Cartilage: Surface of articular cartilage

Lamina splendens – covers articular surface
Provides a low friction surface

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Articular cartilage sits on

Subchondral bone

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Subchondral bone Definition

Cortical bone plate supported by trabecular bone

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Subchondral bone:In children

Perforated by blood vessels where it provides route for nutrient exchange, in adults it gathers nutrients from synovial fluid.

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Subchondral bone: In disease

Shows biochemical and structure changes in some joint diseases.

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Menisci: Definition

Articular discs or pads composed of fibro-cartilage

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Menisci: Located

Within capsule, provide extra strength and support

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Menisci: Greater contact area action

Increases stability and decreases stress on joint.

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Bursae: Definition

Flattened sacs filled with synovial fluid

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Bursae: Location

Often found where tendon passes over bone

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Bursae:Modified bursae

Form tendon sheaths that surround tendons

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Bursae: Inflammation

Bursitis can occur with overuse

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Synovial Fluid: Definition

Fills joint cavity and any bursae

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Synovial Fluid: Components

Similar to interstial fluid but contained high concentratinos of Hyalornic acid.

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Synovial Fluid: Hyalornic acid

Forms structure (longitudinal molelcus) GAG attach to to form aggregates.
Provides viscosity properties – helps with lubrication

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Synovial Fluid:Role

1. Lubrication
2. Cartilage nutrition

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Mechanical Function of synovial joints:

1. Synovial joints allow movement whilst providing stability
2. Shape of articulating surfaces influences type and range of movement
3. Increased mobility associated with reduced stability

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Improving stability:

1. Bones enlarge at ends to provide large contact are (increased stability and reduced stress).
2. Deformed cartilage and menisci also increase contact area

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3. Stability further increased by:

a. Capsule and ligaments surrounding joint
b. Internal ligaments e.g. cruciates in knee – prevent forward and backward sliding
c. Attachment of muscles and tendons across joint.


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Mechanical function of cartilage:

1. To protect bone from high stresses by distributing load evenly on to subchondral bone
2. To provide low-friction low-wear surfaces (helped by presence of joint lubricants

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Role of mechanical factors in joint disorder: Shear causes friction leading to

1. Loss of energy
2. Increase in temperature
3. Wear and tear at bearing surface

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Role of mechanical factors in joint disorder: Lubrication reduces

Damaging effects of friction

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Role of mechanical factors in joint disorder:In synovial joints, two main types of lubrication

Fluid-film
Boundary

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Fluid Film lubrication: Static compressive loading



1. Load acting in centre
2. Film of synovial fluid between two joint surfaces which acts to separate the surfaces
3. Fluid will try to move laterally but because cartilage is deformable and permeable it spreads the load over a larger area leaving the film
4. Fluid is also added

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Fluid Film lubrication: Dynamic loading e.g. walking

Hydrodynamic lubrication
1. Fluid filled is dragged between the surfaces.
2. At leading edge where cartilage is being loaded
3. The fluid gets dragged between the two joint surfaces

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Fluid Film lubrication: Boundary lubrication

Lubricin – bound tightly to articular surface.
Charged molecules – like charged particles will repel eachother maintain a distance between the two surface

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Lubrication Failure:

1. Failure of lubrication mechanisms can lead to increased friction and fibrillation of cartilage surface
2. Roughened fibrillated surface results in increased friction and wear and may lead to further cartilage damage.


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Effects of sustained or repetitive loading:

1. Mechanical loading causes fluid changes in cartilage, which are usually reversible
2. Sustained compression squeezes fluid out, reducing cartilage thickness and ability to equalise stress on underlying bone.
3. Repetitive cyclic loading can cause proteoglycan loss at cartilage surface and distortion of collagen network

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Effects of mechanical overload:

2. High levels of mechanical loading can:
a. Damage cartilage surface
b. Kill chondrocytes

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