We tested the vitality of MSCs after adding them to the most commonly used anesthetics (with or without adrenalin). Within hours after the addition, most of the cells died. This implicates that injecting blood-derived MSCs immediately after intra-articular anesthesia compromises the results of the therapy. Therefore, it is strongly advised to wait for at least 3 days before injecting the previously anesthesized joint with MSCs.

Also the needle size for aspirating and injecting the MSCs is very important to prevent cell damage. We found that aspirating MSCs through a 23G needle gave a neglectable percentage of cell death. On the other hand, aspirating MSCs through a 25G needle gave a death rate of more than 20%. This indicates that the needle size can also determine whether or not stem cell therapy is successful.

The compatiblity of blood-derived MSCs with different possible carriers has been tested by means of a cytotoxicity study. Hereby, we found that carriers on the basis of hyaluronic acid and polysulfated glycosaminoglycans did not effect MSC vitality (lines above 90% vitality) and are therefore the most suitable to use in combination with MSCs for intralesional or intra-articular injections.