Lecture 8 Bone injury guest

Question 1

Sometimes bones crack or break

Answer 1

• Traumatic fracture (e.g., accidents and sports)
• Pathological fracture (e.g., osteoporosis and cancer)
• Fatigue fracture (e.g., stress fracture and atypical femoral fracture)

Question 2

Lamellar bone

Answer 2

– Slowly formed, highly organized
– Parallel layers of anisotropic matrix of mineral crystals and collagen fibers

Question 3

Woven bone

Answer 3

– Quickly formed, poorly organized
– Randomly arranged mineral and
collagen fibers
– Sites of fracture healing, tendon/ligament attachments

Question 4

Form follows function

Answer 4

• Bone is a dynamic tissue
• Constantly remodelling in response to its mechanical environment
• Adapts to best resist the loads experienced during habitual activity
• Mechanical stimuli = bone strain
  (or some consequence thereof)

Question 5

Three rules for bone adaption

Answer 5

1. Driven by dynamic, rather than static, loading
2. Only a short duration of loading is necessary; extended loading durations have diminishing adaptive returns
3. Bone cells accommodate to customary loading making them less responsive to routine loading signals

Question 6

Fracture classification

Answer 6

• Traumatic fracture – caused by acute high energy trauma
• Pathologic fracture – caused by minimal trauma in a weak, diseased, or fragile bone
• Fatigue fracture – caused by accumulation of microtrauma associated with repetitive loads

Question 7

Pathophysiology of fracture

Answer 7

• Fractures are biomechanical events
• Traumatic and pathological fracture when the applied load exceeds the bone’s strength
• Fatigue fracture when number of repetitive loads exceeds the bone’s fatigue life

Question 8

Soft-tissue involvement

Answer 8

• Closed fracture – bone does not break
  through skin
• Open fracture/Compound fracture – bone breaks through skin. These carry high risk of infection

Question 9

Fatigue fracture

Answer 9

Fluctuating loads are more detrimental than monotonic loads
* Human cortical bone
– Monotonic load failure = 190 MPa
– Cyclic load failure = <30 MPa (107 cycles)

Question 10

S-N Curve

Answer 10

For biological materials such as cartilage, tendon, and bone the relationship
between peak stress magnitude (S) and the number of cycles to failure (Nf ) is
well described by an inverse power law:

Question 11

Three stages of fracture healing

Answer 11

1. Inflammatory phase
2. reparative phase
3. remodelling phase

Question 12

Inflammatory phase

Answer 12

• Immobilizes the fractured bone and activates cells for repair
• Hematoma formation
• Vasodilation and serum exudation
• Infiltration of inflammatory cells
• 3-7 days

Question 13

Reparative phase- soft callus

Answer 13

• Primary callus response
• Inflammation triggers cell division and growth of new blood vessels
• Chondrocytes secrete collagen and proteoglycans to form fibrocartilage
• 2 weeks

Question 14

Reparative phase- hard callus

Answer 14

• Endochondral ossification
• Direct bone formation by osteoblasts
• Soft callus turns to hard callus made of woven bone
• 2 weeks

Question 15

Remodeling phase

Answer 15

• Modeling and remodeling of fracture site
• Gradually restores original shape and internal structure
• Woven bone replaced by secondary lamellar bone
• Can last for many year

Question 16

Spotting the signs

Answer 16

• Pain and tenderness
• Swelling and bruising
• Deformity and loss of motion/function
• Protruding bone

Question 17

Conservative treatment

Answer 17

Reduction and Immobilization
* Splinting and bracing
* Plaster or fiberglass casting
* Bandages and orthoses

Question 18

Surgery

Answer 18

When conservative treatment fails or fracture is highly displaced or unstable
– Intramedullary rods
– Locking and stabilizing plates

Question 19

Speeding up or improving repair

Answer 19

• Bone grafts
• Stem cell therapy
• Mechanical stimulation
  – Ultrasound
  – Electricity and magnetic fields