29. Fractures

Question 1

What happens at the site of a bone fracture at the tissue/cell level?

Answer 1

1. Bone breaks –> there is blood/hematoma
2. usually surrounded by muscle or other soft tissue which can be a source of mesenchymal stem cells (MSCs)
3. the MSCs do a few things:
   - release trophic mediators (Bone Morphogenic Proteins)
   - differentiate into osteoblasts, endothelial cells, chondrocytes. all these can become new bone.

Question 2

what kind of fracture?

Answer 2

stress fracture.

Question 3

what kind of fracture?

Answer 3

fracture through the “waist” of the scaphoid bone (on the left side of the image)

Question 4

Fracture on the left is called?

Fracture on the right is called?

Answer 4

Left: simple/hairline

Right: comminuted

Question 5

open v closed fracture: what do these words mean?

Answer 5

open = has broken the skin (either the bone has punched out, or the skin has been broken by trauma at the site of the break. skins is open either way)

closed = nothing has broken skin

Question 6

Open fractures: what are the absolutes in terms of treatment?

Answer 6

• sterile dressing using saline (not betadine: it is caustic to tissue)
• Splint (immobilize to prevent further soft tissue damage)
• tetanus prophylaxis
• IV antibiotics
• this is a surgical emergency so irrigate a lot and debride wound

Question 7

Classification of fractures by anatomic location: terms we use are

• intra v extra articular
• metaphyseal v diaphyseal
• prox, middle, or distal third

Answer 7

• remember that diaphyseal means the shaft/skinny part of the bone (diaphyseal has been on a diet).
• metaphyseal and epiphysis: see pic
• note he never used the word epiphysis, only metaphysis.

Question 8

what kind of fracture/what kind of force?

Answer 8

transverse fracture. implies a failure under tension.

direct blow, high energy

Question 9

what kind of fracture/what kind of force?

Answer 9

f him, he only said that it was due to a low skiboot.

either oblique or spiral.

Question 10

what kind of fracture/what kind of force?

Answer 10

Butterfly fracture

bending prior to breaking.

Question 11

which bone fragment do we use do describe if the displacement is medial/lateral or anterior/posterior?

Answer 11

typically use the distal fragment to describe.

ie, below would be described as anterior displacement.

Question 12

Describe this fracture

Answer 12

Skeletally immature, communited fracture. Open fracture (absence of soft tissue medially), valgus position, middle portion of bone.

Question 13

Special term to describe a fracture: what does greenstick mean? what population does this happen in?

Answer 13

in younger bones, with a bending mechanism, one cortex can fail by fracture, while the other cortex only bends (deforms plastically) and does not fracture, much like what happens when trying to break a “green” stick out in the woods.

Question 14

what is a buckle fracture?

Answer 14

once again, usually in young bones, with a compression type mechanism, one cortex fails by a forming a “wrinkle”, and the other cortex appears intact. VERY stable fractures, heal quite quickly

Question 15

name 2 types of pathologic fractures?

why are they called this?

Answer 15

osteoporosis compression fracture, metastatic fracture

term used to describe a fracture that occurs in bone that is “weakened” by another process, such that the bone “fails” with much less of an insult.

Question 16

Impacted fracture: what is this?

Answer 16

when either a piece of a joint is driven down into the softer metaphyseal bone, or in a “long” bone when the end of the bone is impaled by the shaft (example - proximal humerus)

occurs around the metaphyseal region of joint, helps indicate long term prognosis for the joint. (usually the joint will progress to OA).

Question 17

what are the three phases of bone healing?

Answer 17

• inflammatory
• reparative
• remodeling

Question 18

Inflammatory phase of fracture healing: how long does it last?

why is the hematoma important to maintain?

what happens to dead bone?

Answer 18

lasts 0-2 weeks

Hematoma is impt because it is the site of the non-differentiated cells that can promote healing

Dead bone: the edges look normal initially, but then you will see on imaging that the break site widens slightly as dead bone is removed.

Question 19

How long does the reparative phase last?

what occurs during this phase?

Answer 19

• Reparative Phase: 2-12 weeks (wide range because it depends on how much soft tissue surrounds the bone in question)
• the hematoma organizes with mesenchymal precursor cells.
• Callus forms: (=new bone at site of injury). fracture becomes “sticky”. will hold together by itself somewhat.
• increase in a few mediators, and Types I and II collagen.

Question 20

what is the difference between delayed union and non-union?

Answer 20

If a bone is taking longer the “average” amount of time to heal, the term “delayed union” is used.

Occasionally the body will abort its attempt to heal, and the bones never “unite”; this is known as a “nonunion”.

(taken from his “notes” since he couldn’t get it together to explain this in “lecture”)

Question 21

Remodeling phase of fracture healing: how long can it take?

what determines how long this take, and how well the bone re-forms?

Answer 21

• Can take 6 wks to many years.
• Depends on how young you are (younger -> faster healing)
• Wolff’s law: the bone responds to stress. putting a little weight on the bone will actually help it heal.
• Based on stress to the bone and osteoclast/blast activity, the bone may be in a process of remodeling for years.

Question 22

What are a few biologics/growth factors that enhance the bone healing process?

Answer 22

• Transforming growth factors**
• Bone morphogenetic proteins (BMPs)**
• Fibroblast growth factors**
• Platelet-derived growth factors (PDGF)**
• Insulin-like growth factors**
• Vascular endothelial Growth Factor (VEGF)
• Interleukins/cytokines**

(** means he talks more about this)

Question 23

Transforming Growth Factors: what do they do?

Answer 23

Huge family of proteins.

–Induces synthesis of cartilage-specific proteoglycans and type II collagen

Cartilage then turns to bone

Question 24

Bone Morphogenic Proteins (type of Transforming Growth Factor). what do they do?

important sub-types?

Answer 24

Promote cartilage growth

Crucial in the three steps of the healing cascade (chemotaxis and mitosis, differentiation into cartilage, replacement by bone)

-BMP 2 and BMP 7 induce endochondral bone formation in segmental defects.

Question 25

Fibroblast Growth Factors: what do they do?

Answer 25

Enhance Callus formation.

Question 26

Insulin-like Growth Factor: what does it do?

Answer 26

• Stimulates bone collagen and matrix synthesis
• stimulates replication of osteoblasts
• inhibits bone collagen degradation

Question 27

Cytokines: what is their role in bone healing?

Answer 27

Stimulate bone resorption.

IL-1 is the most potent for this.

Both IL1 and IL6 synthesis is decreased by estrogen: so in the absence of estrogen, IL1 and IL6 are more plentiful, and resorb more bone.

Question 28

bones that have more articular surfaces that others are likely to heal less well - why?

Answer 28

more articular surfaces -> less contact with soft tissue (and vasculature, blood supply, mesenchymal cells, etc).

example: scaphoid bone of the wrist - very little soft tissue contact. does not heal well.