Minimally Invasive Bone Grafting

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.