Bone and Fracture Repair

Question 1

What is the name of the process to lengthen long bones?

Answer 1

Endochondrial ossification

Question 2

How do most flat bones develop?

Answer 2

Intra-membranous ossification

Question 3

Name some flat bones that develop by intra-membranous ossification:

Answer 3

Skull, clavicle, scapula, pelvic bones

Question 4

Stages of intra-membranous ossification:

Answer 4

• Small cluster of mesenchymal stem cells form a cluster of cells (nidus)
• MSCs become osteoprogenitor cells
• Osteoprogenitor cells become osteoblasts and lay down an extracellular matrix (osteoid)
• Osteoid mineralises to form rudimentary bone tissue spicules
• The spicules join to form trabeculae
• These merge to form woven bone and is replaced by lamellae of nature compact bone

Question 5

Which cells develop into osteoprogenitor cells?

Answer 5

Mesenchymal stem cells

Question 6

Which cells become osteoblasts?

Answer 6

Osteoprogenitor cells

Question 7

Which cells lay down the extracellular matrix (osteoid)?

Answer 7

Osteoblasts

Question 8

Which type of collagen did in the osteoid?

Answer 8

Type I

Question 9

Which cells remodel the bony spicule once it has formed?

Answer 9

Osteoblasts, osteocytes, osteoclasts

Question 10

Describe cancellous bone:

Answer 10

Network of fine bony columns, spaces filled with marrow.

Question 11

Which canals carry blood vessels in bone?

Answer 11

Haversian (vertical) and Volkmann’s canals (horizontal)

Question 12

How are osteocytes arranged in immature bone?

Answer 12

Randomly

Question 13

How are osteocytes arranged in mature bone?

Answer 13

In the concentric lamellae of osteons

Question 14

How does a cutting cone work?

Answer 14

Osteoclasts release H ions and lysosomal enzymes to tunnel through bone.

Question 15

What factors allow bone to resist fracture?

Answer 15

High tensile strength and compressive strength.

Degree of flexibility

Question 16

Four stages of bone repair overview:

Answer 16

• Blood clot forms
• Procallus of granulation tissue replaced by fibrocartilagenous callus
• Endochondrial and intramembranous ossifications make bony callus of spongy bone
• Cancellous bone replaced by compact cortical bone

Question 17

Haematoma formation steps:

Answer 17

Blood vessels in bone break

Clotted blood (Haematoma) forms

Swelling occurs

Phagocytic and osteoclasts removed damaged tissue

Macrophages remove clot

Question 18

Fibrocartilaginous callus formation steps:

Answer 18

New blood vessels infiltrate the haematoma

Procallus of granulation tissue forms

Fibroblasts make collagen fibres that span the break

Fibrocartilaginous matrix splints the bone

Osteoblasts form spongy/trabecular bone

Question 19

Bony callus formation steps:

Answer 19

Trabeculae develop as former fibrocartilaginous callus is converted to hard bony callus

Endochondrial ossification replaces all cartilage with cancellous bone

Question 20

Bone remodelling steps:

Answer 20

Material bulging is removed by osteoclasts

Final shape is same as pervious due to the same mechanical stressors

Question 21

What is osteoporosis?

Answer 21

A metabolic bone disease in which mineralised bone is decreased in mass

Question 22

At what age range does bone mass peak?

Answer 22

25-35

Question 23

What are the most common forms of osteoporosis?

Answer 23

Primary (type 1 and 2)

Question 24

When does type I osteoporosis occur?

Answer 24

Postmenopausal women. Increase in osteoclast number due to oestrogen withdrawal

Question 25

When does type II osteoporosis occur?

Answer 25

Elderly people of both sexes. Attenuated osteoblast function.

Question 26

Osteoporosis risk factors

Answer 26

Genetic (bone mass higher in black people) Insufficient calcium intake Insufficient calcium absorption and vitamin D Low exercise Cigarette smoking