R epairing b ro ken b o n e s • Figure 5.6
The healing process takes place in four stages and can take up to several months.
I Formation of
fracture
hematoma (several
weeks)
• Broken blood vessel leaks blood, which clots
• Nearby bone cells die
• Phagocytes and osteoclasts digest dead cells,
debris, and bone tissue in and around
hematoma
Phagocyte
Fracture
hematoma
Red blood
cell
Bone
Fibrocartilaginous callus
formation (3 weeks)
• Fibroblasts from
periosteum invade site
and produce collagen
fibers
• Chondroblasts from
periosteum produce
fibrocartilage
• These events produce
fibrocartilaginous callus
that bridges the broken
ends of bone
Fibroblast
Phagocyte
Fibrocartilaginous
callus
Osteoblast
Collagen fiber
Chondroblast
Cartilage
I Bony callus formation
(3 - 4 months)
• In areas close to
healthy bone,
osteogenic cells
become osteoblasts
• Osteoblasts produce
spongy bone
trabeculae, which joins
living bone and dead
bone fragments
• Fibrocartilage
becomes spongy bone
(bony callus)
Which of the following sequences correctly describes
the steps in the bone healing process after a fracture?
a. Fibrocartilaginous callus; bony callus; remodeling;
hematoma
b. Hematoma; bony callus; fibrocartilaginous callus;
remodeling
c. Remodeling; fibrocartilaginous callus; bony callus;
hematoma
d. Hematoma; fibrocartilaginous callus; bony callus;
remodeling
>
Bone remodeling
• Osteoclasts resorb
dead fragments of
original bone
• Compact bone replaces
spongy bone around
the fracture periphery
• Healed fracture line
may be visible in X-ray;
if not, a thickened area
on the surface remains
where fracture
occurred.
Osteocyte
New compact
bone
Osteoclast
CONCEPT CHECK
1.
What
are the functions of bone tissue and the
skeletal system?
2.
How
does compact bone differ from spongy
bone?
3.
What
are the stages of intramembranous os-
sification?
4.
How
does an open, complete fracture differ
from a closed, comminuted one?
The Structure of Bone Controls Function and Growth
121
p r o c e ss
diagram
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