The basic procedure of obtaining minimally manipulated stem cells from a patient’s fat tissues or bone marrow and injecting them into the same patient’s arthritic joints have a very low risk of serious side effects such as infection, local anesthetic toxicity, fat embolism, and so on. The common side effects include temporary exacerbation of pain for two days to two weeks and bruising.

However, as stem cell procedures become more complex the risks start to go up. For example, expanding stem cells in culture (to let the stem cells divide and increase in number) increases the risk of contamination of these cells with viruses and bacteria from lab technicians’ hands and even from the air. If allogeneic embryonic stem cells (obtained from another person) are used for injections, there are also concerns about stimulating tumor growth.

Also, the site of injections matters. Injecting stem cells into a joint is safer than injecting them into the eyes, hearts or spinal cord. For example, there have been cases of blindness after the injection of stem cells into the eye at a stem cell clinic chain.