Muscoskeletal 3: Joints 1

Question 1

What are the 3 types of structural classification of joints and what is their major distinguishing features

Answer 1

• Fibrous joints: bones held together by dense irregular CT rich in collagen. no synovial cavity.
• Cartilaginous joints: bones held together by cartilage, no s cavity.
• Synovial joints: bones forming joint have synovial cavity and united by dense irregular CT of articular capsule + acessory ligaments.

Question 2

What is the definition of a joint and what is its aka. What are the 3 primary functions of a joint

Answer 2

Joint is any point where two or more bones interconnect. aka articulation. 3 functions:

1. Movement
2. Force transmission
3. Allowing spaces for growth

Question 3

What are the 3 functional classifications of a joint and their definitions

Answer 3

1. Synarthrosis : immovable (wanting to fuse)
2. Amphiarthrosis : slightly movable
3. Diarthrosis: freely movable

Question 4

Compare the stability, movement and therefore common location of the 3 functional classification of joints

Answer 4

1. Synarthrosis has high stability and very little movement.
2. Amphiarthrosis has a little less stability and a little more movement.
   However both are limited by the tissue types holding them together. and are prob closer to Axial skeleton. But not
3. Diarthrosis has a low stability and high movement: Appendicular skeleton

Question 5

What are the 4 defining features of synovial joints

Answer 5

1. Articular cartilage
2. Articular capsule made of fibrous layer and synovial membrane containing bv and nerves
3. Synovial Cavity
4. Synovial fluid

Question 6

Explain simply how synovial joint structure means that its a diarthrosis

Answer 6

They are not restricted by the properties of the specific tissue which hold the bones together. Actually the ends of the articulating bones are mostly free apart from its attachment to the articular capsule, permitting wide mobility

Question 7

What is the type of CT and 4 functions of articular cartilage and what does its degradation cause

Answer 7

A specialised type of hyaline cartilage, forming thin layer on top of bone. 
Function: 
1. protect ends of bones 
2. absorb microshock
3. support heavy loads for long periods 
4. provide smooth frictionless surface. 

degradation= arthritis

Question 8

What makes up the cell component of articular cartilage and what is its function and location

Answer 8

Chondrocytes: live in lacunae and can occur by themselves or groups depending on zone
Function: build, repair and maintain cartilage

Question 9

What makes up the fibre component of articular cartilage and what is its function and location

Answer 9

Type 2 collagen which is thinner and supple. It has specific patterns in different zones.
Function: Provides structural integrity by linking surface zone to osteochondral junction.

Question 10

What makes up the ground substance component of articular cartilage and what is its function and location

Answer 10

Water and soluble ions
Function: hydrate transport nutrients and wastes
+ Glycosaminoglycans + Proteoglycans.
Function: Hydrophillic so provides swelling and hydrating mechanism for the proper function of cartilage

Question 11

What are the solid component and fluid component of articular cartilage and what is the dry weight/ wet weights

Answer 11

Fluid (can move in and out) water and soluble ions (Ca2+, Na+, K+): 75% WW
Solid (fixed inside): GAGs, PG: 25% DW
Collagen: 75% DW

Question 12

What is the PG content, arrangement of fibres and appearance of chondrocytes in Surface zone

Answer 12

1. There is low PG content, only to lubricate
2. The dense arrangement of fine fibres is parallel to the surface to resist shear forces.
3. The chondrocytes are small and flattened in their lacunae.

Question 13

What is the PG content, arrangement of fibres and appearance of chondrocytes in middle zone

Answer 13

1. PG content is increasing
2. Fibres are thicker and less densely packed. Orientated at 45 degrees to the surface
3. Chrondrocytes are fatter and have a round lacunae

Question 14

What is the PG content, arrangement of fibres and appearance of chondrocytes in deep zone

Answer 14

1. Has highest PG content
2. Collagen fibres are orientated perpendicular to the surface
3. Chondrocytes are stuck in vertical columns called nests because they are mitotically dividing. They secrete ECM between them to ‘move up’ to the surface

Question 15

What is the PG content, arrangement of fibres at the tide mark and what two functional zones does it separate

Answer 15

1. PG content has been replaced by hydroxyapatite (calcified) so low PG
2. Fibres continue straight perpendicular
3. Separates deformable + functional from calcified

Question 16

What is the PG content, arrangement of fibres and appearance of chondrocytes in calcified cartilage

Answer 16

1. Low PG content, high in hydroxyapatite from chondrocyte
2. Fibres continue straight perpendicular
3. chondrocytes in calcified lacunae

Question 17

What is the PG content, arrangement of fibres at the Osteochondral junction and what two functional zones does it separate

Answer 17

1. PG content high as it is cement line and PG= glue

2. The fibres are attached to convoluted osteochondral junction perpendicular to surface.

Question 18

How is delamination (cracking into layers) of bone prevented by the structure of articular cartilage

Answer 18

Having a layer of calcified cartilage provides a transitory area that provides more SA for the shear forces on cartilage to be distributed rather than just on the osteochondral junction.

Question 19

Does cartilage contain BV, nerves and lymphatics? How are chondrocytes nourished

Answer 19

No. Chondrocytes are nourished by diffusion only .

Question 20

Describe the structure of a PG complex

Answer 20

These are PGs attached to a long hyaluronic acid chain. (GAG) and these attach to collagen fibres

Question 21

Describe the structure of a PG and give eg

Answer 21

Many GAGs (sans hyaluronic acid) attached to a protein core. They stand out from each other because of the repulsion from their negative charges. eg. Aggrecan

Question 22

Describe the structure of a GAG and give eg

Answer 22

Repeating disaccharide (2 sugars) unit (carrying a negative charge). Eg. Chondroitin sulphate and keratin sulphate

Question 23

Describe the 6 steps of loading cycle of articular cartilage from recently unloaded cartilage

Answer 23

1. Ion conc in the matrix increases because negative charges on disaccharide units attract positive ions into the cartilage from the joint space
2. Osmotic gradient is created by moving of ions causing water to move into the matrix and the cartilage to swell.
3. The cartilage swells until the swelling force = the tension force placed on collagen. At this point : unloaded equilibrium and the volume of cartilage doesn’t change
4. When a load is introduced the fluid component is squeezed out of the cartilage back to the joint space synovial fluid or other parts of uncompressed cartilage.
5. The volume of the cartilage decreases because the loss of fluid = creep.
6. Eventually the compressive load will be supported by solid component and the repulsion of negative charges and will stop shrinking= loaded equilibrium.

Question 24

What are the main purposes of the loading cycle of articular cartilage

Answer 24

1. allow nutrients and O2 to enter with the fluid phase and then waste products + CO2 to be removed when the load is placed on it
2. To self lubricate the surfaces of the joint with the fluid phase

Question 25

What is structure and function of the joint capsule

Answer 25

Comprised of fibrous outer layer and inner synovial membrane, perforated by nerves and bv and may be reinforced by ligaments.
Function:
1. Connection between two bones.
- is loose to allow movement at the joint but
2. Protection: becomes tight at the extreme limits of range of motion

Question 26

What is the CT, structure, and function of the Fibrous layer of articular capsule

Answer 26

CT: irregular+ regular dense CT
Structure: parallel, interlacing bundles of white collagen fibres that are continuous with periosteum of bone. transitory bv but richly innervated.
Function:
-resist tensional forces and check abnormal joint movement.
-support and protect the synovial membrane + whole joint

Question 27

What is the CT, structure, and function of the synovial membrane layer of articular capsule

Answer 27

CT: loose CT of variable thickness
Structure: 2 layers. Can form villi which increase SA and reduce volume of synovial cavity. Lines all non articular surfaces inside the joint cavity up to the edge of articular cartilage.

Synovial subintima: highly vascularised, containing macrophages, fat cells and fibroblasts.
F: maintains and protect articular capsule during normal movement, reduces volume of joint cavity to cushion

Synovial intima: 1-3 cells thick, contains synoviocytes that F: secrete lubricating features of synovial fluid

Question 28

What is the structure and function of Joint cavity

Answer 28

Small area between articulating surfaces with peripheral margins filled with villi (in foldings of the synovial membrane).
F contains small amount of synovial fluid

Question 29

What is the make up and function of synovial fluid

Answer 29

Made of
1. ultrafiltrate of blood plasma from bv in the subintima + 2. secretions of lubricating proteins eg. Hyaluronic acid from synoviocytes .
3. free cells: monocytes, lymphocytes, macrophages and synoviocytes
Function: joint lubrication, shock absorption, chondrocyte metabolism and overall joint maintenance