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Musculoskeletal Block > Joint Mechanics > Flashcards

Joint Mechanics Flashcards

1
Q

Synovial Joints

A
  • have articular cavity filled with synovial fluid
  • hyaline cartilage covers ends of bones
  • space surrounded by
    - synovial membrane secretes fluid
    • fibrous membrane structural
      Articular capsule made of fibrous capsule and synovial membrane
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2
Q

Solid Joints

A

Type Types:
1. Fibrous: suture, gomphosis, and syndesmosis (interosseous membrane between radius and ulna)

  1. Cartilagenous: synchondrosis (hyaline cartilage type II) and symphysis (fibrocartilage type I)
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3
Q

Cartilagenous Joints

A

Number of synchondroses varies with age
Increasing in number through early teens as new centers of ossification develop
Decreasing in late teens early 20’s as growth plates fuse throughout body

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4
Q

Planar, Hinge, Saddle, Condyloid, Ball and Socket, and Pivot Joint Examples

A

Planar joint: acromioclavicular joint
Hinge: ulna articulation with humerus; only one plane of motion
Saddle: trapezium and 1st metacarpal
Condyloid: metacarpal phalangeal joint in 2nd digit
Saddle and condyloid: allow flexion, extension, abduction, and adduction thus allowing circumduction, but not long axis rotation
Ball and socket: allows all the above motions + long axis
Pivot: atlantoaxial joint

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5
Q

Maintenance of Posture for the Hip, Knee, and Ankle

A

ACL: all the weight will rest and prevent hyperextending of the knee

Iliofemoral Ligament: primary limiter of hip hyperextension

Soleus: prevents dorsiflexion at the ankle

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6
Q

Articular Capsule

A

Made of:
1. Fibrous capsule (stratum fibrosum)
Dense CT, attaches/continuous with periosteum, reinforced by ligaments & tendons, may thicken to form capsular (intrinsic) ligaments
Highly innervated, poorly vascularized

  1. Synovial membrane (synovium; stratum synovium)
    Covers all the non-cartilaginous surfaces inside joint capsule
    Highly vascularized, poorly innervated
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7
Q

Synovial Membrane

A

The cruciate ligaments are intraarticular but extrasynovial

“Housemaids knee”= prepatellar bursitis (between patella and skin)

“Clergyman’s knee”= infrapatellar bursitis (superficial and deep in relation to the patellar ligament below the patella)

Suprapatellar bursa is kept taught during leg extension via the articularis genus muscle

Synovial membranes are found in the form of tendon bursae and tendon sheaths

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8
Q

Histology of Synovial Membrane

A

Intima: synoviocytes; secretes synovial fluid and macrophages keep the fluid clean; CT with stem cells and blood vessels to bring blood to synoviocytes

The deeper subintima contains relatively unspecialized counterparts such as blood vessels, macrophages, and fibroblasts; mostly collagenous; vascularized (nutrients for synovium as well as avascular cartilage)

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9
Q

Synoviocytes

A

Within the intima layer of synovial membrane
Type A = macrophage-like, debris-removal (phagocytosis of undesirable substances from synovial fluid)

Type B = fibroblast-like; synthesizes:
hyaluronic acid
lubricin (glycoprotein)

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10
Q

Synovial Fluid

A

Ultrafiltrate of blood plasma by Type B synoviocytes

Content:

  1. Hyaluronic acid – traps water in joint spaces
  2. Lubricin – lubricates joint surfaces

Normally: clear, pale yellow; small volumes

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11
Q

Articular Cartilage

A

Composed of hyaline cartilage
Devoid of nerves, blood supply and lymphatic channels (physiologically isolated)
Permeable (i.e., porous)
Lubricated by synovial fluid

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12
Q

Zones of Articular Cartilage

A

SMDCB
1. Superficial Tangential Zone – oblong chondrocytes
2. Middle Zone – round, randomly distributed
3. Deep Zone – columnar; perpendicular to tidemark
4. Calcified Cartilage Zone
5. Bone
Tide Mark – border between deep zone and calcified cartilage

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13
Q

Collagen of Articular Cartilage

A

STZ: collagen tightly woven into sheets; arranged parallel to surface with few cells

MZ: randomly arranged fibrils; less packed to accommodate PG & water

DZ: large radially-arranged bundles; cross tidemark into calcified zone to anchor articular cartilage to subchondral bone

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14
Q

Proteoglycans of Articular Cartilage

A

Proteoglycan monomer: glycosaminoglycans (GAGs) attached to protein core

GAG: chondroitin sulfate, keratin sulfate

Superficial: resists stretch to prevent cartilage detachment from bone

Aggrecans are covered with negatively charge endings that stick off and act like sponge and attracted to water

Collagen fibrils and PGs interact to form porous composite and fiber-reinforcing organic solid matrix
Swollen with water

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15
Q

Superficial Tangential Zone

A

Chondrocytes: small, oval or elongate, long axis parallel to articular surface
Collagen Fibrils: dense sheets; oriented parallel to surface
PGs: low PG
Water: most abundant in STZ and decreases linearly to concentration of about 65% in DZ

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16
Q

Middle Zone

A

Chondrocytes: round, randomly distributed
Collagen Fibrils: lower than STZ; wavier fibrils, randomly oriented
PGs: high PGs

17
Q

Deep Zone

A

Chondrocytes: large, round & in vertical columns perpendicular to tidemark; most active in synthesizing organic components of AC
Collagen Fibrils: large bundles; oriented perpendicular to subchondral bone plate
PGs: med-high PG content

18
Q

Biomechanics of Articular Cartilage

A

Mechanical response is related to fluid flow through the tissue.

General Properties:
1. Viscoelastic –
Viscous: resists flow and deformation when load is applied.
Elastic: tendency to stretch instantly and return to normal state when load is removed.
Response is time-dependent (i.e., changes with time)
Stiffness influenced by rate of applied load.

  1. Anisotropic – response to loading is direction- dependent
19
Q

Biomechanics of Articular Cartilage: Unloaded to Loaded

A

Negatively charged GAGs repel each other

Interstitial Fluid (Swelling) Pressure
Total ion concentration is higher inside tissue than in the bathing solution
Ion concentration differences creates a positive osmotic pressure causing matrix to swell.
This swelling support 90% of load for a significant period (several hundreds of seconds) following compressive loading.
Swelling reduces the load supported by the collagen-PG matrix

20
Q

Biomechanics of STZ, MZ, and DZ

A

STZ collagen resist AC spread (high tensile strength)
STZ & MZ collagen restrain swelling pressure of PG
DZ collagen fibrils resist AC detachment

21
Q

Compression Tests: Creep and Stress Relaxation Modes

A

Stiffness: The higher the stiffness when all fluid flow has ceased, the less the tissue deforms under a given load

Permeability: Indicates the resistance to fluid flow through the cartilage matrix. Highest near joint surface, lowest in deep zone. As cartilage is compressed, permeability decreases

Equilibrium displacement: if permeability is high, fluid flows out of AC easily and equilibrium (i.e., no further deformation) is reached quickly

Flow of fluid in and out of AC is critical for waste removal from and nutrition of AC

Creep Mode: Relatively linear change over time and then repulsion because running out of water
Stress Relaxation: Apply same controlling force over time = stops pushing back against force because water is more equally distributed in matrix

22
Q

Tensile Test: Direction

A

Loading results in realignment of collagen fibers

Direction Dependency:
When pulled in the direction of the orientation of the collagen fibers, AC is stiff and strong in tension.
AC is weaker when pulled at an angle to the orientation of the collagen fibers (ANISOTROPY). Collagen fibers will attempt to reorient within the matrix to align to the direction of tension

Middle layers with all the fibers in all different directions; tissue fibers will change angles from random to more lined up to resist deformation
Time dependent situation; if you do this rapidly it does a worse job of realignment of fibers, but if slowly the fiber align much better

23
Q

Tensile Test: Rate

A

Loading results in realignment of collagen fibers

Rate Dependency:
When pulled at a slow rate, the collagen network alone is responsible for the tensile strength of cartilage.
When the tissue is loaded rapidly, proteoglycans restrain the rotation of the collagen fibers and tensile strength is reduced.
When you apply shear forces (parallel to surface) find there is no fluid flow and basically little resistance due to collagen fibers and proteoglycans

24
Q

Shear Tests – Volume changes

A

No fluid flow in shear = No volume changes.

Fluid has low viscosity, therefore provides little resistance to shear.

Resistance to shear is due to solid matrix (i.e., collagen, PGs, cells, lipids)

25
Q

Boundary Lubrication

A

Involves a single monolayer of lubricin adherent to each articular surface
High loads
Low speeds or stationary
Prolonged period

26
Q

Fluid Film Lubrication

A

Film of lubricant separates bearing surfaces.
Load on bearing surfaces supported by pressure developed in fluid-film.
Dependent on the viscosity of the fluid due to hyaluronic acid
Loads varying in magnitudes
Surfaces moving quickly

27
Q

Rheumatoid Arthritis

A

SM becomes hyperplastic and infiltrated with inflammatory cells (sinovitis)

Thickens into a pannus that releases enzymes that compromise cartilage and bone integrity.

28
Q

3 Types of Wear on Articular Cartilage

A
  1. Interfacial wear – adhesion/abrasion, no separation of joint surfaces by lubricant causing AC-AC adhesion or abrasion
  2. High impact loading – excessive loads, traumatic event that does not allow sufficient time for internal fluid redistribution
  3. Fatigue wear – cyclically repeated deformation causes accumulation of microscopic damage that exceeds the repair rate; disruption of the collagen-PG solid matrix and PG washout causing the surface to fray and crack, lesions (fibrillation) that go through the full depth, and erosion
    PG washout: decreased stiffness of AC and loses its ability to resist compression
29
Q

Response to Injury

A

Repair is limited because cartilage is avascular
location of chondrocytes- nearby proliferate and produce more matrix - territorial matrix (i.e., immediately surrounding lacunae) at first

Supplements, e.g. glucosamine (repair) and chondroitin sulfate (elasticity)
Pain relief
Slow degeneration

30
Q

OA

A

Degradation of ECM by matrix degrading enzymes (matrix metalloproteanases) proceeds faster than repair resulting in net loss of collagen and PGs
Joint pain and swelling
Cartilage fibrillation followed by entrance of synovial fluid into cartilage; can cause cysts in bone
Erosion or detachment of cartilage & subchondral bone
Eburnation (exposed bone becomes dense, worn and “polished”)
Vascularization, cracks and osteophyte formation

31
Q

Components of Articular Cartilage

A

Cellular:
Chondrocytes- manufacture, secrete, and maintain organic components of ECM

ECM:
Mostly type II collagen (10-30%)
Proteoglycans
Water (60-80%)
Inorganic salts, matrix proteins, glycoproteins, and lipids

Musculoskeletal Block (29 decks)

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