MSK L3 Joint structure and function Flashcards
Classification of Joints:
According to structure
According to function
Classification of Joints: According to structure
- Fibrous
- Cartilaginous
- Synovial
Classification of Joints:
According to function
Synarthroses
Amphiarthroses
Diarthroses
- Synarthroses
no/little movement (fibrous and some cartilaginous joints
- Amphiarthroses
– some movement (cartilaginous joints)
- Diarthroses
free movement (always synovial joints)
Fibrous
no joint cavity and dense fibrous connective tissue joining articulating surface.
Cartilaginous joints
no cavity and two bones are joined y pad of cartilage – fibrous or hyaline.
Synovial –
cavity between ends of articulating bones – ends covered with fibrous or hyauline for protection.
Fibrous Joints: 3 sub classifications:
- Sutures
- Syndesmoses
- Gomphoses
Sutures
Found only in the skull,
Form at 18mths of age when they replace fontanels
Fibrous tissue covered by periosteum
Several types of sutures
- Serrate (between frontal and parietal bones)
- Lap or squamous - overlap (between parietal and temporal bones
- Plane or butt (between paired maxillary bones forming hard palate).
Synostosis sutures
Sutures may become totally ossified in adults forming a synostosis (e.g. between frontal bones)
Syndesmoses:Definition
Bones joined by interosseous ligament or dense aponeurotic membrane
Syndesmoses: Example
Interosseous membrane between radius and ulna
Syndesmoses: Movement
Flexibility of collagen fibres in ligament may allow limited movement
Gomphoses: Definition
Pegs and sockets, held in place by bundles of regular collagenous connective tissue
Gomphoses: Example
Found between teeth and bones of jaw – periodontal ligaments
Gomphoses:Movement
Allow sight movement of teeth during mastication as collagen fibres are orientated in different planes.
Cartilaginous joints: types
- Synchondroses (primary)
2. Symphyses (secondary)
Syncondroses (primary) Definition
Advancing centres of ossification separated by hyaline cartilage
Syncondroses (primary) Temporary types
Most are temporary (e.g. epiphyseal growth plates (and fuse in adults
Syncondroses (primary) Permanent types
Some persist throughout life e.g. costal cartilages, which allow some flexibility of rib cage during inspiration.
Symphyses (secondary) Definition
Fibro-cartilage pads between a.c. of adjacenet bones
Symphyses (secondary) Movement
Allow for slight movement: Symphysis pubis allows expansion of pelvis in childbirth.
Symphyses (secondary)Examples
Symphysis pubis – childbirth
Intervertebral discs allow limied motion between vertebrae
Symphyses (secondary)Examples that fuse
Some symphses fuse during growth (e.g. sacral and coccygeal discs)
Synovial Joints: Definition
Articulating bones separated by synovial cavity filled with synovial fluid
Synovial Joints: Movement
Cavity gives synovial joints wide range of movement compared to other joints
Synovial Joints: Examples of movement in different planes
Plane (or gliding) Hinge Pivot Ellipsode(or condyloid) Saddle Ball and socket
Plane (gliding) joints: Definition
Opposing surfaces almost flat or slightly convex and concave
Plane (gliding) joints: Allow
Small side0to-side or back-and-forth movements and small amount of rotation
Plane (gliding) joints: Examples
- Sacroiliac joints
- Apopphyseal joints of spine
• Allow thoracic sine ribs to movement upwards and outwards during inspiration
Hinge joints → Definition
Convex and of one bone articulates with concave end of another.
Hinge joints → Allow
Hinge-type movement about a single axis such as flexion and extension.
Hinge joints →Examples
Interphalangeal joints of fingers, and tibio-femoral joint of knee.
Pivot joints:Definition
Conical or rounded surface of one bone fits into depression on another.
Pivot joints: Allows
Rotation about a single axis
Pivot joints: v
- Joint between head of radius and ulnar allows rotation of forearm.
- Atlanto-axial joint between atlas and axis allows rotation of head.
Ellipsoid:Definition
Oval convex surface articulates with ellipsoid concavity.
Ellipsoid:Allows
Bi-axial movement in 2 planes but no rotation.
Ellipsoid:Examples
- Atlanto-occipital joint in neck
- Meta-carpophalangeal (MCP) joints in hands
Radiocarpal joint of wrist
Saddle joints: Definition
Two saddle-shaped surfaces articulate at right angles to one another
Saddle joints: Allows
Modified condyloid joint, allows wide range of movement about 2 axes
Saddle joints:Examples
Found in carpometacarpal (CMC) joint of thumb, and in ankle.
Ball and Socket Joints: Definition
Almost spherical head (ball) articulates with almost spherical cup (socket)
Ball and Socket Joints:Movement
Allow for greatest range of movement of al joints, allow multi-axial movement in all planes
Ball and Socket Joints: Examples
Hip and shoulder joints
- All synovial joints are surround by
joint capsule which fully encloses articulating surfaces.
- Joint capsule is lined by
synovium/synovial membrame – lines inner surface of joint capsule except where there is articular cartilage
- Joint cavity – filled with
synovial fluid.
Capsule
Outer fibrous capsule
Inner synovial membrane (synovium
Outer fibrous capsule
Blends with periosteum
Outer fibrous capsule composed of
Dense irregular connective
Function of outer
Type 1 collagen – resists tensile loads as it is an irregular orientation – allows resistance of a range of mvoements
Innervation of capsule
Highly innervated – site of joint pain rather than articular cartilage which has non blood supply or innervation.
Inner capsule (syovium) Definition
Lines joint cavity except for articular surfaces
Inner capsule (syovium) Functions
Produces constiuents of synovial fluid
Ligaments: (within capsule) Formed from
Localised thickening of fibrous capsule
Ligaments: (within capsule) Composed of
Denses REGULAR CT comprising parallel collagen fibres (mainly type 1)
Function of collagen arrangement
Gives ligaments great tensile strength along their length
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.
2 main layers of synovium
- Supporting layer or stroma (sub0intima)
2. Lining of synovial cells in contact with synovial fluid
2 types of synovial cell in inner lining
- Type A
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
Type B cells
→Cell type
→ Function
Type of fibroblasts
Role in synthesis of hyaluronic acid (HA) and proteins → important for maintenance of viscosity (lubrication).
Synovitis
Inflammation of synovium – symptom of RA
Articular Cartilage: Contains
Cells, fibres and matrix arranged in zones
Articular Cartilage: Zones
- Tangential zone
- Transitional zone
- Radial zone – column arrangement
- Calcified cartilage (by ossified bone)
Articular Cartilage: Cartilage cells
Chondrocytes; density varies with age, morphology changes in different zones.
Articular Cartilage: Fibres of Articular collagen
Fibres are collagen, mostly type II – resist stress
Small amount so type VI,IX,XI
Articular Cartilage: Matrix composed of
Large aggregated proteoglycans (aggrecan) some smaller PGs (decorin and biglycan).
Articular Cartilage: GAG side changed important for
Hydrophillic and therefore attract water into the cartilage – allows it to resist pressure and forces.
Articular Cartilage: Surface of articular cartilage
Lamina splendens – covers articular surface
Provides a low friction surface
Articular cartilage sits on
Subchondral bone
Subchondral bone Definition
Cortical bone plate supported by trabecular bone
Subchondral bone:In children
Perforated by blood vessels where it provides route for nutrient exchange, in adults it gathers nutrients from synovial fluid.
Subchondral bone: In disease
Shows biochemical and structure changes in some joint diseases.
Menisci: Definition
Articular discs or pads composed of fibro-cartilage
Menisci: Located
Within capsule, provide extra strength and support
Menisci: Greater contact area action
Increases stability and decreases stress on joint.
Bursae: Definition
Flattened sacs filled with synovial fluid
Bursae: Location
Often found where tendon passes over bone
Bursae:Modified bursae
Form tendon sheaths that surround tendons
Bursae: Inflammation
Bursitis can occur with overuse
Synovial Fluid: Definition
Fills joint cavity and any bursae
Synovial Fluid: Components
Similar to interstial fluid but contained high concentratinos of Hyalornic acid.
Synovial Fluid: Hyalornic acid
Forms structure (longitudinal molelcus) GAG attach to to form aggregates. Provides viscosity properties – helps with lubrication
Synovial Fluid:Role
- Lubrication
2. Cartilage nutrition
Mechanical Function of synovial joints:
- Synovial joints allow movement whilst providing stability
- Shape of articulating surfaces influences type and range of movement
- Increased mobility associated with reduced stability
Improving stability:
- Bones enlarge at ends to provide large contact are (increased stability and reduced stress).
- Deformed cartilage and menisci also increase contact area
- 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.
Mechanical function of cartilage:
- To protect bone from high stresses by distributing load evenly on to subchondral bone
- To provide low-friction low-wear surfaces (helped by presence of joint lubricants
Role of mechanical factors in joint disorder: Shear causes friction leading to
- Loss of energy
- Increase in temperature
- Wear and tear at bearing surface
Role of mechanical factors in joint disorder: Lubrication reduces
Damaging effects of friction
Role of mechanical factors in joint disorder:In synovial joints, two main types of lubrication
Fluid-film
Boundary
Fluid Film lubrication: Static compressive loading
- Load acting in centre
- Film of synovial fluid between two joint surfaces which acts to separate the surfaces
- Fluid will try to move laterally but because cartilage is deformable and permeable it spreads the load over a larger area leaving the film
- Fluid is also added
Fluid Film lubrication: Dynamic loading e.g. walking
Hydrodynamic lubrication
- Fluid filled is dragged between the surfaces.
- At leading edge where cartilage is being loaded
- The fluid gets dragged between the two joint surfaces
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
Lubrication Failure:
- Failure of lubrication mechanisms can lead to increased friction and fibrillation of cartilage surface
- Roughened fibrillated surface results in increased friction and wear and may lead to further cartilage damage.
Effects of sustained or repetitive loading:
- Mechanical loading causes fluid changes in cartilage, which are usually reversible
- Sustained compression squeezes fluid out, reducing cartilage thickness and ability to equalise stress on underlying bone.
- Repetitive cyclic loading can cause proteoglycan loss at cartilage surface and distortion of collagen network
Effects of mechanical overload:
- High levels of mechanical loading can:
a. Damage cartilage surface
b. Kill chondrocytes
