BBL risks: what methods are used to prevent the doctors from injecting fat into the muscle or the main vein?

Thank you for your question.It is important to stay above the muscle, in a safe plane. The experience of the surgeon in performing this procedure is very important. The cannula type and size that are used, is also important. In general, very sharp and thin cannulas are more likely to cause problems. You should discuss your concerns with a Board Certified Plastic Surgeon who is experienced in this procedure. All The Best !

The fat is injected above the gluteus muscles and superficially under the skin into the fat and surrounding tissue of the buttocks.  I do not inject fat into the muscle to all but eliminate the risk for fat embolus and death (although this rate is most probably not zero).  Precise placement of the fat is necessary to help reduce the risk for fat pooling and resulting fat necrosis and/or infection. 
 

The greatest tool is experience and caution. While some use US guidance to find the plane, the vast majority depend on experience and technique to guide them. Generally speaking, maintain control of the cannula (rigid) and understanding where the tip is at all times is usually enough to stay superficial.With regards to your specific question, an experienced practitioner should have a sense of where they are at all times. That being said, inadvertent intramuscular injection is being considered as a root cause for problems. In all of the serious complications which have been explored, the surgeons claim to have been superficial. Thus there is the possibility of migration from superficial to deep causing inadvertent issues.
In summary, the procedure can be safely performed, however, they should be performed by a board certified (ABPS) plastic surgeon with experience. These risks should be discussed as well as the strategies being employed to avoid them.