Stem cells are useful because they can divide and develop into any type of cell in the body (including bone or cartilage). Stem cells from the person’s own bone marrow have two major advantages: the patient does not experience cell rejection and this source of stem cells avoids the controversy over the use of embryonic stem cells.
Surgeons can remove or aspirate stem cells from the sternum (breast bone), vertebrae (spinal bones), and iliac crest (top of the pelvic bones). These are places where the bone is close to the skin. A collecting needle punctures through the skin and can be inserted down into the bone to withdraw bone marrow cells. The needle can be withdrawn and other areas nearby can be punctured for a second or third collection of cells.
The cells are then taken to a lab and processed. The cells are prepared in such a way to allow them to replicate (grow and multiply) over a period of days to weeks. For example, to create more bone cells (osteoblasts), the stem cells are placed in a culture that contains bone material. in this way, the stem cells are induced (persuaded or influenced) to differentiate into osteoblasts (bone building bone cells).
Likewise, to encourage stem cells to become cartilage, fat cells (adipose), or connective tissue, specific culture mediums are used that aid the stem cells in expanding. More research is focused now on tissue regeneration for soft tissue and bone repair in humans. One type called connective-tissue progenitor cells are especially useful for repair of connective tissue.
Connective-tissue progenitor cells are somewhat limited in bone marrow tissue. And usually the number of stem cells used in tissue repair is in the millions. So finding the site with the best yield will be helpful. Studies are underway to compare yield from the different harvest sites. And, there are many, many different factors that can affect the total yield of these cells. Site of harvest in only one. The age and sex of the patient may make a difference. These are additional points of interest being investigated.