Bone healing

Question 1

What is an osteoblast

Answer 1

only cell capable of bone production. Osteoblasts are derived from precursors located in the walls of blood vessels (mesenchymal cells)

An adequate blood supply must be present for the cells to reach areas of fracture, osteotomy, or growth.

Question 2

What is an osteoclast

Answer 2

• large multinucleated cells located in the tip of the cutting cones
• dissolve bone matrix by forming canals through existing bone.
• Responsible for bone reformation

Question 3

What is an osteoid

Answer 3

• it is a noncalcified organic matrix formed by osteoblasts.
• Contains 95% collagen and 5% proteoglycans

Question 4

What is mineralization

Answer 4

• it is the process by which osteoid becomes deposited with calcium phospate
• In mature bone, mineralization occurs 8-10 days after osteoid is formed.
• Normal mineralization in lamellar bone occurs at a rate of 1 uM per day

Question 5

What is woven bone

Answer 5

Type of bone which forms in healing bone callous.

• The intercellular substance contains a disordered three dimensional array of collagen fibrils.
• Woven bone rapidly mineralizes following formation.
• Eventually remodels into lamellar bone.

Question 6

What is lamellar bone

Answer 6

• highly organized bone laid down in congruent layers with parallel collagen fibers which change direction from one lamella to the next
• Requires a flat smooth substrate in order to be synthesized

Question 7

Stages of bone healing (just the 5 stages)

Answer 7

1-Inflammation: hematoma formation
2-Induction
3-Soft callus 
4-Hard callus
5-Remodeling

Question 8

Inflammation stage

Answer 8

from day 1 until day 3/4

• initial hematoma formation around site followed by necrosis of bone margins
• macrophages invade area to remove dead bone and tissue

Question 9

Induction

Answer 9

from day 1 -?

osteoblasts or chondroblasts form depending on the vascular supply and stability

—(if bad blood supply and stability then this will result in chondrocyte formation)

— (if good blood supply and stability then this will result in osteoblast formations)

***pro-callus develops from the maturing hematoma

Question 10

Soft callus

Answer 10

Day 4-4 weeks

• clinical union noted with elimination of motion across site
• formation of the callus can be noted at this point

Question 11

Hard callus

Answer 11

4 weeks to 4 months

-callous converted to mature lamellar bone

Question 12

Remodeling phase

Answer 12

4 months to 2 years

Question 13

Type of bone healing

Answer 13

Primary (direct)

Secondary (indirect)

Question 14

Primary bone healing (4 points)

Answer 14

1) occurs when bone fragments are rigidly immobilized
2) stages of bone healing undifferentiated and callus formation is absent
3) with rigid immobilization, framework provided by callus not necessary
4) due to the rigid immobilization, the fixation device assumes partial load applied to the bone. The result is bone resorption due to reduced biomechanical demand

Question 15

Types of primary bone healing

Answer 15

1) gap healing: hematoma fills the microscopic gaps
- –area is infiltrated by capillaries and osteoblastic cells then filled with woven bone
- –remodeled osteoblasts initially form lamella oriented 90 degrees to the long axis of the fracture site and are then replaced by axially oriented lamella

2) contact healing: surfaces in direct contact
- – cutting cones cross interface, producing concentric pattern of new lamella bone
- –cutting cone advances approximately 70-100 um per day

Question 16

Secondary bone healing (4 points)

Answer 16

1) occurs when bone is not rigidly immobilized
2) motion/instability allow for additional hemmorhage which favors fibrocartilage formation and ultimately callus
3) bone callus creates a framework so that bone healing may occur. A layer of high tensile strength connective tissue is laid down between fragments followed by granulation tissue.
- this framework is then replaced by fibrous cartilage. Eventually chondroclasts remove the cartilage. Osteoblasts then take over to begin woven bone production.

4) bone remodels in accordance to Wolff’s law wherevy bone deposition takes place on the concave side and resorption on the convex side