Bone/Joint development

Question 1

What is the name of the process that precedes bone development

Answer 1

Mesenchymal consendation

Question 2

What is mesenchymal condensation

Answer 2

When previously dispersed mesenchymal cells gather together to differentiate into a single tissue type
In the case of bone, they differentiate into chondroblasts/osteoblasts

Question 3

What initiates the formation of a joint

Answer 3

Appearance of the interzone & tri-laminar structure

Question 4

What is the interzone

Answer 4

An intermediate layer of flattened mesenchymal cells

Separates the 2 cartilaginous templates previously formed via mesenchymal condensation

Question 5

What protein do the interzone cells express

Answer 5

Collagen type I

Question 6

What is the theory via which joint cavitation occurs

Answer 6

Small tears form in the structurally weak interzone

These are propagated via movement of the joint in utero

Question 7

What joint factors does mechanical loading in utero affect?

Answer 7

Shape of joint

Cavitation

Question 8

What is not affected by mechanical loading in utero?

Answer 8

Interzone formation

Question 9

What 2 types of ossification occur during the development of bone?

Answer 9

Intramembranous ossification

Endochondral ossification

Question 10

How does the MoA of intramembranous & endochondral ossification differ

Answer 10

Intramembranous: direct differentiation of MSCs into osteoblasts
Endochondral: mineralisation of pre-formed cartilage template

Question 11

Outline the process of intramembranous ossification

Answer 11

MSCs aggregate and differentiate into osteoblasts

Osteoblasts secrete osteoid matrix which is subsequently calcified

Question 12

What are the 2 types of intramembranous ossification

Answer 12

Dermal

Perichondral

Question 13

What type of bones are produced in dermal intramembranous ossification (3)

Answer 13

Skull
Mandible (& most facial bones)
Clavicle

Question 14

What type of bones are produced in perichondral intramembranous ossification

Answer 14

Periosteal bone collar of long limbs (CORTICAL BONE)

This aids endochondral ossification

Question 15

Outline the process of endochondral ossification

Answer 15

1. Chondrocytes in the centre of the diaphysis become hypertrophied forming 1ry ossification centre
2. They release a collagenous matrix which is mineralised
3. The calcification causes chondrocytes to die via apoptosis creating a cavity
4. Vessels penetrate bringing osteoblasts and osteoclasts to the site
5. Osteoblasts produce and mineralise osteoid, osteoclasts remodel to form the medullary cavity
6. Chondrocytes at the epiphyses become hypertrophied, forming 2ry ossification centre
7. Vessels penetrate the cavity left by dead chondrocytes bringing osteoblasts leading to ossification of the epiphyses

Question 16

What type of bones are produced in endochondral ossification

Answer 16

Appendicular bones (limbs)
Axial bones (those not produced by IO)

Question 17

Do vertebral bodies contain growth plates

Answer 17

No

Question 18

How do the VERTEBRAE develop

Answer 18

After endochondral ossification, they are left with cartilaginous plates on their inferior and superior surfaces
Once they are fully grown they reduce the cartilaginous plates to thin layers

Question 19

Which spinal curvatures are primary and which are secondary

Answer 19

Primary: Thoracic and Sacral (concave/kyphotic)
Secondary: Cervical and Lumbar (convex/lordotic)

Question 20

When does the cervical and lumbar curves appear

Answer 20

Cervical: When babies begin sitting
Lumbar: When babies begin standing

Question 21

What type of collagen is produced in intramembranous ossification

Answer 21

Type 1 collagen produced by osteoblasts

Question 22

What type of collagen is produced in endochondral ossification

Answer 22

Type X collagen matrix produced by the hypertrophic chondrocytes

Question 23

What is an osteogenic bone graft

Answer 23

A bone graft that contains all the cellular components, growth factors and scaffold necessary to FORM new bone

Question 24

What is an autogeneous osteogenic bone graft

Answer 24

Bone sample from an individual (usually from iliac crest)

Question 25

What is an osteoconductive bone graft

Answer 25

This is an acellular graft that serves as a scaffold that can host/support the cells necessary for bone formation

Question 26

Pathophysiology of Achondroplasia

Answer 26

• Mutation in FGFR-3 gene

* Chondrocytes undergo premature hypertrophy and they fuse before growth can occur

Question 27

Pathophysiology of Rickets

Answer 27

• Results from a lack of Vitamin D
• Leads to insufficient/delayed mineralisation of growth plates
• Results in reduced compressive strength
• With weightbearing, this results in the distinctive bowing of bones

Question 28

Pathophysiology of Arthrogryposis

Answer 28

Multiple stiff joints

There is fibrosis of the muscles resulting in restricted movement in utero

Question 29

Pathophysiology of Developmental Dysplasia of the Hip

Answer 29

Femoral head is not located in acetabular space

More commonly affects left hip

Question 30

Risk factors of DDH

Answer 30

Family history

Female sex

Question 31

Mechanical risk factors for DDH (4): All lead to reduced in utero movement

Answer 31

Ligament laxity
Breech presentation
Lack of in utero fluid
Larger baby