Page 113 - Anatomy and Physiology of Farm Animals, 8th Edition

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(A) (B) (C)
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Figure 5-6. Types of fractures. (A) Greenstick. (B) Complete. (C) Comminuted.

cavity, forming an internal (endosteal) callus. As soon as the bone is put to use,
callus. Along the periosteum, there is addi- functional orientation of the callus begins,
tional proliferation and an external callus with a tendency to straighten imperfections
completely encircles the broken ends of in the alignment of the bone. The callus will
the bone, forming an effective splint that increase in size on the concave side, where
usually prevents movement between the stress is greatest, and tend to erode on the
segments. However, that rapid prolifera- convex side, thus tending to correct any
tion of the osteogenic cells of the perios- deformity. The amount of spontaneous
teum rapidly outpaces the vascular supply correction that is possible in fractures
and a cartilaginous matrix begins to form depends on a number of factors, including
adjacent to the fracture gap. The internal age of the animal, blood supply to the bone,
portion of the callus will undergo minerali- degree of correction necessary, presence or
zation with the formation of true bone absence of infection, and amount of damage
without a cartilaginous intermediary; as a to surrounding tissues. Excessive separation
result, it is the internal callus through of fragments, which may be caused by too
which the repair of the fracture is achieved much traction or incomplete immobiliza-
and remodeling of the internal callus to tion of a fracture, may result in nonunion,
form a typical bone shaft with a marrow with fibrous tissue filling the gap between
cavity will be necessary to complete the fragments. Lack of vascular supply to the site
internal healing process. Final resolution may also result in nonhealing and a devital-
of the external callus will require replace- ized piece of bone called a sequestrum.
ment of the cartilage with woven bone, Rapid fracture healing occurs in young
similar to endochondral ossification. animals, particularly if the fracture site has
Misalignment of the fractured bone is a good blood supply and is completely
corrected to some extent by the action of immobilized with the ends of the frag-
osteocytes and osteoclasts, which also ments in apposition. In humans, a fracture
remove excessive internal and external may heal completely within a month in an