Bone marrow is rich in stem cells. These cells are typcially obtained by a technique referred to as a bone marrow aspirate where a needle is placed into the iliac crest and cells are withdrawn through a syringe. 
Withdrawing cells in this fashion is called aspiration. Bone marrow aspiration is a common practice for obtaining stem cells. A popular technique is to take the bone marrow aspirate ( the cells obained from the bone marrow aspiration) and spin it down in a centrifuge thereby creating a concentrate of bone marrow nucleated cells. This technique is called BMAC: Bone Marrow Aspirate Concentration. The concentrated bone marrow aspirate contains stem cells and has been termed and advertised as ‘stem cell concentrate.” There are several units commercially-available.
There are many different types of stem cells in bone marrow. Stem cells that are crticial for regeneration of cartilage, tendon and ligament are very specific and are called mesenchymal stem cells.
A crtical question which has recently been studied is what is the concentration of mesenchymal stem cells from commerically available units. Equally important, is the question of whether or not the concentration of stem cells from BMAC can made a difference clinically.XXXX demonstrated that bedside bone marrow concentrate machines utilizing a 60cc bone marrow aspirate can produce between 70,000-90,000 mesenchymal stem cells. What does this mean? Animal research and data collected at Regenexx suggests that millions of mesenchyml stem cells are required to repair cartilage, tendon and muscle injuries. Furthermore unlike the BMAC units, Regenexx expands the number of mesenchymal stems stem to approximately 100-1,000 times the number obtained from BMAC. So in considering stem cell therapy it is essential to understand both the type and absolute number of stem cells injected since both will play a critical role in the success of a procedure.