2. Bone Properties/Variables
Bone is a two component system consisting of minerals (increases the yield and
ultimate strength of bone) and collagen (mostly Type II).
Variables:
1. Porosity. Increased porosity leads to increased compressive strength of bone.
Cortical bone has <15% porosity and cancellous bone has ~70% porosity.
2. Strength. Strength is defined as the amount of force a material can handle before
failure. Bone can handle a 2% increase in length before failure. Bone is has the
greatest strength in compression, followed by tension and is weakest in shear. Strength
is affected by collagen fiber orientation, trabecular orientation, age, presence of
defects and osteoporosis.
3. Stiffness. Cortical bone has 5-10 times the stiffness of cancellous bone.
3. ystem consisting of
d and ultimate strength
stly Type II).
porosity leads to
ive strength of bone.
15% porosity and
~70% porosity.
s defined as the amount
an handle before failure.
% increase in length
is has the greatest
sion, followed by tension
ear. Strength is affected
entation, trabecular
sence of defects and
4. Vascular Supply to Bone
• Blood supply to bone comes from two sources. A nutrient
artery feeds the endosteal and medullary vessels and
supplies the inner 2/3 - 3/4 of bone. The periosteal vessels
supply the outer 1/3 of bone from muscle and tendon
attachments.
• The amount of vascular disruption following a fracture
depends on the force/displacement of the fracture and
which vascular systems are disrupted.
5. Phases of Bone Healing
• Inflammation (10%)
• Reparative/Regenerative (40%)
• Remodeling (70%)
6. Inflammation (10%)
Inflammatory Phase (4-5 days)
• Hemorrhage from osseous and periosteal vessels.
• Hematoma invades fracture site.
• Macrophages invade to remove necrotic tissue.
• Anything that slows or inhibits inflammatory phase may delay bone healing.
7. Reparative/Regenerative (40%)
Reparative Stage (Proliferative)
• Resorption of necrotic bone
• Capillary growth within periosteal vessels.
• Increasing oxygen tension
• Mesenchymal and Periosteal fibroblast begin deposition of collagen fibrils and
fibrocartilage (3-4 weeks).
• Fibrocartilaginous plug
Soft callus = Vascularization of maturing hematoma or pro-callus
• Capillaries from endosteal and periosteal tissues
• Vascular invasion from Haversian System
Hard callus = Callus Formation
• 4-6 weeks post trauma
• Stimulation of chondroclasts causing a breakdown of cartilage matrix in favor of
hardening of the mineralized lattice.
8. Remodeling (70%)
• Callus completely replaced by bone
• Vascular network is normalized
• Remodels according to Wolff’s Law
• Piezoelectric Effect: appearance of electrical potentials
within bone in response to the application of an external
force
• Compression side: electronegative leading to bone
production
• Tension side: electropositive leading to bone resorption
9. Types of Bone Healing
Primary Bone Healing - Direct Osseous Repair
(Primary Intention, Direct Healing)
1. No callus formation; no motion
2. Cutting cone: Osteoclasts in the front, osteoblasts in the back. Travels
across the fx line (Schenk and Willinegger).
3. Gap Healing: Bone deposition at 90° to the orientation of bone fragments
Two Requirements:
• Intact vascular supply
• Stable rigid fixation with compression
10. Secondary Bone Healing
Indirect Osseous Repair
“Callus formation”
• “Gap healing”
• Occurs when bone is not rigidly immobilized
• Increase motion, increase callus
• Indirect or Endochondral bone healing
• Nature’s own internal fixation device
• Scaffold for bony remodeling
Radiographic Characteristics
• Callus formation
• Temporary widening
• Osteoclastic resorption
• Slow disappearance of radiolucent fracture line
11. The literature has
demonstrated that cyclic
loading and dynamization
have resulted in decreased
healing times, decreased
stiffness, increased torque
and increased energy
absorption in rabbit and dog
bones. A practical means to
accomplish this in human
subjects hasn’t been
perfected yet.
15. Malunion Slow Union Delayed Union Nonunion Pseudoarthrosis
Timeline Any 2-4 weeks 4-6 months 6-9 months > 9 Months
Key Finding Deviation in any
plane other than
intended from the
original procedure
Fracture line visible
still however no
gapping or callus
formation seen on x-
ray
Gapping increases in
the fracture line due
to granulation tissue
Must show three
months without any
sign of healing on
radiographs
End-stage, requires
surgery
