Although they are studied in many tissues of the body, stem cells used to treat musculoskeletal conditions are most commonly obtained from bone marrow. In addition, stem cells are obtained from tissues such as muscle, adipose tissue, and the synovial lining of the knee. Since about one out of every hundred thousand cells in these tissues is a stem cell, these cells need to be multiplied in order to be effective. It takes two forms. Tissue samples and cell culture can be obtained by multiplying stem cells by means of a special centrifugal pump or by concentrating stem cells.