Embryology

Question 1

When do the early stages of development of the musculoskeletal system start and what initiates this process?

Answer 1

The end of the fourth week due to activation of the mesenchymal cells in the somatic lateral mesoderm

Question 2

What genes regulate patterning of the musculoskeletal development?

Answer 2

Homeobox genes

Question 3

When do the upper and lower limb buds appear?

Answer 3

Upper limb bud appears at day 26

Lower limb bud follows 1/2 days later

Question 4

Through what process do the limb buds elongate?

Answer 4

Proliferation of the mesenchyme

Question 5

Where do the limb buds originate?

Answer 5

The upper limb buds develop opposite the caudal cervical segments
The lower limb buds develop opposite the lumbar and sacral segments

Question 6

What is the AER, where does it develop and what does it develop from?

Answer 6

Apical ectodermal ridge

Forms at the apex of each bud due to ectodermal thickening

Question 7

What kind of cells are found proximal and adjacent to the AER?

Answer 7

Proximal mesenchyme- differentiates into blood vessels and cartilage bone models
Adjacent mesenchyme- undifferentiated, rapidly proliferating cells

Question 8

How do the hands and feet develop?

Answer 8

The distal ends of the limb buds flatten into paddle-like hand plates and flipper-like foot plates
Digital rays are formed through condensation of mesenchymal tissues in week six in the hands and the seventh week in the feet

Question 9

How is the tissue in the interdigital regions broken down?

Answer 9

Apoptosis mediated by bone morphogenic proteins

Question 10

How are cartilaginous precursors of the limb bones developed?

Answer 10

Chondrification of the mesoderm in the sixth week

Primary centres of ossification appear in weeks 8-12 in response to growth factors

Question 11

When are dermatomes formed?

Answer 11

During the fifth week, when peripheral nerves grow from the developing limb plexus into the mesenchyme of the limbs

Question 12

What bones go under endochondral ossification?

Answer 12

All limb bones except the clavicle

Question 13

How do the upper and lower limbs rotate?

Answer 13

They both rotate by 90 degrees
The upper limbs do so laterally
The lower limbs do so medially

Question 14

What is amelia?

Answer 14

Total absence of a limb

Question 15

What is meromelia?

Answer 15

Partial absence of a limb

Question 16

What is phocomelia?

Answer 16

Some long bone absence

Question 17

What is micromelia?

Answer 17

All parts are present except small bones

Question 18

What is polydactyly?

Answer 18

The presence of more than five digits on the hands or feet
The extra digit is incompletely formed and lacks muscular development
It can be inherited or teratogenic

Question 19

What is syndactyly?

Answer 19

Common birth defect of the hand or foot

Question 20

What is the difference between cutaneous and osseous syndactyly?

Answer 20

Cutaneous syndactyly- simple webbing between the digits, more common in feet than hands
Osseous syndactyly- fusion of the bones occurs when notches between the digital rays fail to develop

Question 21

What birth defects are associated with thalidomide?

Answer 21

Absence or deformity of long bones and intestinal and cardiac abnormalities

Question 22

Describe the characteristics of congenital clubfoot

Answer 22

Relatively common birth defect

Sole of the foot inverted so foot is turned medially

Question 23

What are the possible causes of congenital clubfoot?

Answer 23

Can be multifactorial (genetic and environmental factors)

Abnormal positioning of the foetus causing restricted movement

Question 24

What are the causes of developmental dysplasia of the hip?

Answer 24

Abnormal development of the acetabulum, which is common after breech deliveries
General joint laxity