Growth and development of the human skeleton

Question 1

When does limb development begin?

Answer 1

Around the 4th week of development

Question 2

What layer of the trilaminar embryo does limb development mostly occur from?

Answer 2

Most limb development arises from the mesoderm layer of the trilaminar embryo

These limbs begin as limb buds from the mesoderm layer

Question 3

What are the main 3 genes that control limb development?

Answer 3

This is controlled by 3 main genes, HOX gene (Mass and growth), ZPA (AP growth and AER) and sonic hedgehog gene

ZPA = Zone of polarising activity

Question 4

What is the AER?

Answer 4

The AER is the Apical Ectodermal Ridge, which is the edge of a limb bud formed from ectoderm surrounding the mesoderm

This surrounds the mesenchymal chondrogenic core

These mesenchymal cells differentiate to form chondrocytes to create hyaline cartilage, as the basis of bones and limbs

The AER goes onto form the hand

Apoptosis occurs within the AER layer to form the 5 digits

Question 5

When does limb bud rotation occur and what does it form?

Answer 5

Limb bud rotation at week 7 forms 3 regions, mid-axial (Middle finger), pre-axial and post-axial

Question 6

Describe the ossification of bone during development?

Answer 6

The primary ossification centre to begin ossification of the diaphysis begins at 12 weeks, with the diaphysis being completely ossified by birth

Question 7

What are the main zones of the physis?

Answer 7

Resting zone
Proliferative zone
Hypertrophic zone
Primary spongiosa

Question 8

What is the resting zone of the physis?

Answer 8

Longitudinal bone growth starts in the resting zone, containing widely spread germinal cells

Question 9

What is the structure of proliferative zone?

Answer 9

In the proliferative zone, cells form columns which are flattened and closely packed

Question 10

What occurs in the hypertrophic zone of the physis?

Answer 10

In the hypertrophic zone, cells increase in size, then undergo apoptosis to release calcium in order to begin calcifying and joining the metaphysis where bone matures

Question 11

Where does circumferential growth (Widening) of bone occur?

Answer 11

Circumferential growth occurs peripherally in the groove of Ranvier, the periosteum in the diaphysis and the perichondral ring of La Croix, providing support around the physis

Question 12

What are some conditions that affect the resting (reserve) zone of the physis?

Answer 12

Gaucher’s disease
Diastrophic dysplasia

Question 13

What are some conditions that affect the proliferative zone of the physis?

Answer 13

Achondroplasia
Gigantism
MHE

Question 14

What are some conditions that affect the hypertrophic zone?

Answer 14

SCFE
Rickets
Salter Harris syndrome

Question 15

What are some conditions that affect the primary spongiosa?

Answer 15

Corner syndrome
Scurvy

Question 16

What are some factors that are important for bone growth?

Answer 16

• Diet
• Sunshine
• Vitamins
• Growth plates
• Hormones

Question 17

What are some methods of predicting child growth?

Answer 17

• 2nd birthday height
• Menalaus
• Mosely charts
• Paley multiplier (Lower limbs)
• Greulich and Pyle (Wrist radiographs)
• Sauvegrain and Nahum

Question 18

How can 2nd birthday height predict adult height?

Answer 18

The height on the 2nd birthday is approximately half the adult height

Question 19

What are some methods used to predict spinal growth?

Answer 19

Spinal growth can be measures using menarche (Girls first period) as girls usually stop growing around 2 years after menarche

Risser grading is used to estimate how much spinal growth is remaining based on the ossification of the iliac apophysis

This can be an important measure in scoliosis

Question 20

By what age will most children develop arches in their feet?

Answer 20

Most children will develop arches in their feet by the ages of 6 or 7, however, 1 in 5 adults will have physiological flat feet in which no arch will form

This does not need management unless symptomatic