There is some evidence stem cells work injected into knees and to a much lesser degree in the shoulders. For the spine, there is very little evidence. There was one Spanish study of 10 patients with intradiscal injections and a pilot study of 15 patients (
https://www.ncbi.nlm.nih.gov/pubmed/28086781) using autologous fat stromal fraction with improvement in pain. Another study of 26 patients using autologous bone marrow showed some improvement over a year with 8/20 demonstrating MRI improvement. (
https://www.ncbi.nlm.nih.gov/pubmed/26156727). However there is another series of 10 patients that received zero improvement from intradiscal stem cells (
https://www.ncbi.nlm.nih.gov/pubmed/16522171) There are no controlled studies of intradiscal stem cell therapy, yet this is frequently offered much in the way DC electricity was offered as a treatment in the late 19th and early 20th century. There are also cowboys injecting intrathecally stromal fractions from fat or bone marrow, sometimes with disastrous results. Some inject both into the disc or both plus PRP and there have been severe discitis cases due to the fact you cannot sterilize the cells obtained by penetrating the skin with needles to obtain them. There is also a case report of epidural abscess with cauda equina syndrome after intradiscal stem cells (
https://www.ncbi.nlm.nih.gov/pubmed/23131581) Perhaps in the future we will have better capabilities to understand why stem cells (or the other 98% of stromal fractions) may work, but it would be prudent in intradiscal injections to wait for controlled studies, while completely avoiding injection of cellular debris and other undesirable cells into the intrathecal or epidural areas until we can purify and sterilize the injectates.