Joints I

Question 1

Joint

Answer 1

• Union or junction between 2 or more bones
• Classify based on degree of movement
  o Extensive
  o Stabilize with limited movement
  o Untie and stabilize w/o movement

Question 2

Synovial joints

Answer 2

• Designed to provide extensive movement between bones
• *articular cavity (joint cavity or joint space)
• Bones help by ligaments and fibrous tissue capsule
• Ends of bone covered in articular cartilage
  o Lubricated by synovial fluid produced by synovium
• Ex. limbs

Question 3

Joint capsule

Answer 3

• Thick outer fibrous layer
• Delicate inner synovial tissue layer

Question 4

Outer fibrous layer of joint capsule

Answer 4

• Heavy sheath=contributes to joint stability
• Well vascularized and innervated
• Contains may ligaments
• Attaches or inserts into bones which defines the margins of the joint

Question 5

Ligaments of the outer fibrous layer of the joint capsule

Answer 5

• Bands of dense fibrous tissue
• Collateral ligaments=intracapsular
• Intra-articular ligaments (ex. cruciate ligaments of stifle joint)

Question 6

What is desmitis?

Answer 6

• Inflammation of ligament

Question 7

What is an enthesis?

Answer 7

• The site where a joint capsule, ligament or tendon inserts into a bone

Question 8

Synovium (synovial membrane)

Answer 8

• Covers all inner surfaces of joint except articular cartilage
• Synovial villi
• Synovial folds

Question 9

Synoviocytes may appear as (3)

Answer 9

• Plump macrophage-like cells (A cells)
• Spindle-spindle fibroblast-like cells (B cells)
• Intermediate cells

Question 10

Synovial fluid

Answer 10

• Transudate of plasma that is altered by synoviocytes
  o Add glycosaminoglycans (GAGs) (ex. hyaluronate)
• Normally: small amount that is transparent, colourless to pale yellow, viscous, small number of WBCs (90% monocytes, 10% neutrophils), no erythrocytes

Question 11

GAGs

Answer 11

• Long, linear complex polysaccharides and AA

Question 12

Hyaluronate

Answer 12

• High molecular weight GAG that gives rise to hyaluronic acid
  o Viscoelastic properties (viscous=resist shear forces, elastic=return material to original state after stress)

Question 13

Articular cartilage

Answer 13

• Hyaline cartilage
  o Cells (chondroblasts and chondrocytes)
  o ECM
• *NO blood vessels, lymph vessels and nerves
• Proteoglycan aggregates can bind a high proportion of water=giving it hydrodynamic properties
  o *reversibly resistant to compression

Question 14

What is articular cartilages function?

Answer 14

• Maximize contact area between bones while minimizing friction created by movement and transmit forces to underlying bone

Question 15

What is responsible for centrifugal growth of an epiphysis (‘length’ of bone)?

Answer 15

• Endochondral ossification directly beneath the articular cartilage

Question 16

‘articular-endochondral cartilage complex’ (AE-complex)

Answer 16

• Dual roles of articular cartilage in growing people and animals
• *minimal mitotic activity of mature animals
• *MINIMAL replacement of chondrocytes and collage

Question 17

Subchondral bone

Answer 17

• Provides structural support to overlying articular cartilage
• Stiff of bone enables it to support relatively high loads w/o substantial deformation and transfer the load through the bone

Question 18

What are the 2 functions of synovial fluid?

Answer 18

• Provide lubrication between moving surfaces
• Provide nutrition to articular cartilage

Question 19

Cartilaginous joints

Answer 19

• Provide limited movement between bones
• Hyaline cartilage, fibrocartilage or BOTH between bones
• Ex. intervertebral disks, symphyses of pelvis and mandible

Question 20

Fibrous joints

Answer 20

• Stabilize bones without movement
• Ex. sutures between flat bones of skull
• Ex. interosseous ligaments, fibrous union between teeth

Question 21

What can trauma (included repeated trauma of relatively less intensity) lead to in the joint capsule?

Answer 21

• Degeneration and inflammation of components of joint capsule
• Joint instability
• Eventually arthritis
• *inflammation

Question 22

Synovitis

Answer 22

• Inflammation of synovium
• Characterized by presence of inflammatory cells, hypertrophy and hyperplasia of synoviocytes and villus hyperplasia

Question 23

Articular cartilage response to injury

Answer 23

• Limited as it is avascular and had minimal mitotic activity
• Superficial: persist for long periods of time with little change
• Deep: ulcers, if extend into subchondral bone=become filled with vascular fibrous tissue that may undergo metaplasia to form fibrocartilage

Question 24

Fibrocartilage

Answer 24

• Intermediate between cartilage and dense connective tissue
• Chondrocytes within cartilage matrix and thick layers of dense collagen fibers

Question 25

Cartilage ECM normally contains inactive enzymes called matrix metalloproteinases

Answer 25

• Can be activated by chemicals liberated by injured chondrocytes and inflammatory cells
  o Degrade proteoglycans and collagen=decrease in hydrodynamic properties and tensile strength=soft cartilage susceptible to mechanical injury

Question 26

What is softening of articular cartilage referred to as?

Answer 26

• Chondromalacia

Question 27

What does the loss of cartilage and fraying of collagen fibers due to mechanical injury result in?

Answer 27

• Cleft formation OR fibrillation
• *if continues to subchonral bone=ulceration

Question 28

What is eburnation?

Answer 28

• Chronic rubbing of subchondral bone causing it to become dense and smooth

Question 29

What are chondrones?

Answer 29

• Clusters of chondrocytes
  o Trying to divide and are surrounded by ECM=can’t move

Question 30

What are degenerative changes in articular cartilage often associated with?

Answer 30

• Formation of periarticular osteophytes at or near the junction of articular cartilage and periosteum

Question 31

What can also develop secondary to the stretching or tearing of sties of insertion of the joint capsule, ligaments and tendons?

Answer 31

• Small exostoses
  o Entheses=called enthesophytes

Question 32

Subchondral bone and Wolff’s law

Answer 32

• Responds in relation to physiologic demands
• If greater or more frequent loading=increases in thickness, density and stiffness
• *subchondral bone that is increased or decreased in stiffness=may contribute to articular cartilage injury

Question 33

What is pannus?

Answer 33

• Fibrovascular and histiocytic tissue that arises from insertion of synovium
• Spreads over adjacent articular cartilage as a VELVETY MEMBRANE
• *associated with certain types of chronic synovitis

Question 34

How does pannus progress?

Answer 34

• Destroys underlying cartilage
• *if both surfaces of articular cartilage become involved, the 2 layers of fibrous tissue can fuse and cause FIBROUS ANKYLOSIS of the join

Question 35

Ankylosis

Answer 35

• Immobility and fusion of joint due to disease, injury or surgical procedure