Bone Healing

What are the parts of the bone?

Epiphysis, metaphysis, diaphysis

Physis in growing bones

How does blood supply work in the bone?

It is unidirectional inside to outside

What is the diameter of Haversian systems?

70-100um

What is against the epiphysis?

Resting or dividing cells

Where is calcification occuring?

Closer to the metaphysis

Where is a SALTER 1 fracture?

Along physis

What happens at places where muscle attaches?

Vessels from the muscle will provide blood to segment of the bone providing centripetal blood supply

What happens do blood supply when a fracture occurs?

Normal medullary to cortex flow is interrupted and bone in the area is devascularized

Periosteal arterioles at soft tissue attachment sites will hypertrophy and revascularize bone

This will be reversed after healing is over

What causes aseptic necrosis?

Insufficient blood supply tot he head

The head revascularized and replaces the dead bone

As dead bone is resorbed, the articular cartilage loses support and collapses when weight bearing occurs

What is really importent to prevent long term damage with aseptic necrosis?

Keep the leg non-weight bearing

What are the phases on bone healing?

Inflammatory phase

Debridement phase

Repair phase

Remodeling phase

What is the inflammatory and debridement phase?

hematoma forms at fracture site

Osteocytes die back from fracture edges dead bone is resorbed by macrophages

Soft tissues responds to revascularize via extraosseous temporary supply

Why should you not remove a hematoma during a fracture repair?

Platelets are releasing cytokines to help with healing in the hematoma

What happens to fracture lines at first?

They get bigger because osteocytes die at edges and bone is resorbed

What happens in the reparative phase of bone healing?

Hematoma organizes and proliferation of periosteal and endosteal stem cells lead to formation of a mixture of chondrocytes and osteocytes creating a callus

What is the law of transformation of bone?

Form follows function

What happens in the remodeling phase of bone healing?

It resorbes the callus to form new haversian systems

How long does the remodeling last?

years

What mechanicals concepts rule bone fracture and healing?

Stress = force/unit area

Strain = change in length related to the original length (deltaL/L)

What determines the kind of tissue the body can lay into a fracture gap?

Strain on the fracture gap

With a 2% strain what is laid down into the fracture gap?

Bone

With a 10% strain what is laid down into the fracture gap?

Fibrocartilage

With a 30% strain what is laid down into the fracture gap?

Fibrous tissue

What are the types of bone healing?

Primary (direct)

Secondary (callus and remodeling)

What is required for primary bone healing?

Strain on the fracture gap must be <2% (must be a very small fracture)

What is seen on a radiograph of most fractures?

Callus and remodeling (secondary bone healing)

What is the cutting cone of primary bone healing?

Osteoclasts eat bone followed by a capillary loop followed by a line of osteoblasts depositing bone

This creates a cutting cone forming a longitudinal haversian system

When do the phases of bone healing occur?

Secondary bone healing

What happens at each stage of secondary bone healing?

Less flexibility so less strain until bone is made

How does a callus change over time?

1. Hematoma

2. Granulation tissue

3. Connective tissue

4. Cancellous bone

5. Bone

6. Haversian remodeling

What is the size of the callus related to?

Rigidity of fixation. The more movement the larger the callus

T/F a callus tells you better or worse?

False, it just tells you it healed by secondary bone healing