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The term "Minimally Invasive Bone Grafting" refers to new techniques of bone
grafting in which the grafting procedure can be done using injection through
a needle, avoiding the need for a surgical incision.
The goals and principles of bone grafting is the same, in the conventional
bone grafting procedures, and these new minimally invasive procedures. Only
the way in which the graft is delivered to the site differs. There are currently
only three injectable graft materials available: bone marrow, setting calcium
phosphate cements, and processes allograft bone matrix gel.
Bone Marrow
Bone marrow has been shown to be an effective graft material in many animal
studies, and an increasing amount of human clinical experience. The effectiveness
of bone marrow as a graft is thought to be due to the immature bone forming
cells that are contained in a bone marrow sample. Other cells, in bone marrow
may also play a role.
Bone marrow grafting can be very effective. This is particularly true in stiff
well-aligned fractures that have failed to fully heal. This includes fractures
which have had open surgery and fixation, but have failed to progress satisfactorily.
Bone marrow cells can also be used to supplement the healing in a new fresh
fracture.
Bone Matrix Gel
Injectable grafts made from human bone are available and approved for clinical
use. This type of graft is a highly purified gel of osteoconductive human bone
matrix. It is made thin enough to be injected through a large needle. Small
clinical reports support the use of bone matrix gels in many settings. This
matrix can also be combined with bone marrow to provide an "osteoconductive
scaffold" on which bone marrow cells can attach and grow.
Setting Calcium Phosphate Cements
Several formulations of injectable pastes of calcium and phosphate are now available.
After injection, these pastes will set firmly, like a cast, but inside the body.
The calcium and phosphate in the paste form a hard mass of calcium phosphate
ceramic, which is very similar to the mineral found in bone, called "hydroxyapatite."
Once set, the graft does three things:
1) The hard ceramic serves as an internal splint, holding the fracture in
the position maintained which the cement set,
2) The ceramic is "osteoconductive," allowing bone forming cells to grow
over its surface and form new bone, and
3) The ceramic slowly dissolves, over the course of several months. This
rate of dissolution is intended to allow new bone to grow into the graft site
replacing the graft without weakening the bone.
Setting cements have been used in a variety of locations and specific settings
including wrist fractures and in correcting or preventing some deformities caused
by osteoporosis.
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