I love fat grafting. But fat grafting to the buttock, also known as the Brazilian Butt Lift, has been found to be risky. There are reports that the mortality rate is 5%. See the report HERE. This has prompted a huge interest in researching the topic by the Society of Plastic Surgeons. Above all, we value safety. If something has risks, we need to evaluate it more.
The typical teaching has been to try to stay superficial when injecting the fat, as this layer is “safe.” But when doing large amounts of fat grafting, conventional thought was it was okay to inject in the superficial muscle too, as long as you don’t go deep. In some of the deaths, the surgeons had thought they were superficial, but autopsy showed there had been fat injected deep.
A new study published in the Plastic and Reconstructive Surgery Journal, “Clinical Implications of Gluteal Fat Graft Migration: A Dynamic Anatomical Study,” looked at BBL (Brazilian Butt Lift).
Background: The intraoperative mortality and overall complication rate for BBL is unacceptably high. This study was done to see if under pressure, fat injected into the gluteal muscle can migrate out of the muscle and into a deeper plane. They estimate the intraoperative death rate is 1 in 2351. In addition to these issues, nonfatal complications like microfat embolism and sciatic nerve injury are also high. All of these focus of the depth of fat insertion.
Methods:
They used 8 dissections in cadavers. They injected fat intramuscularly, and then dissected the buttock to see where the fat went by visual inspection and endoscopic evaluation. They used standard 4mm cannula to inject, and used applesauce which was dyed blue to simulate fat. They used a 60cc syringe to inject, taking care to not go deeper than 2 cm and keeping the tip visibly up in the superficial muscle throughout the injection. With each progressive syringe injection, they looked at the intramuscular site pressures. Volumes of 540 to 720 were injected, with a visual inspection after each 60cc was injected.
When inspected, they found the blue “fat” came out from an area far medial and deep to the original cannula insertion.
They found it migrated under the muscle to other areas, going all the way up to the greater trochanteric insertion.
There was no deep fascia around the gluteus muscle. (why does this matter? It would keep the fat “in” the muscle and not let it migrate as far. With no wall there, the fat can go wherever). The gluteus does have fascial in the lining above it. This prevents the fat from migrating into the superficial “safe” space between the skin and muscle. So you have a system where you have a roof preventing the fat from going in the safe direction, and no floor to keep it from migrating in the dangerous direction. As you inject more, the pressure rises, and the force to push the fat in a bad direction goes up.
Discussion:
Why do surgeons inject into the muscle? It allows for more fat to be transferred. You can only inject so much into the superficial space. Many had argued if you stay in the “superficial muscle” it was okay to inject in the muscle.
They found whether you insert the fat into the deep or superficial muscle, when given enough volume, it WILL NOT REMAIN IN THE MUSCLE.
When injecting fat into other muscles, they don’t see this phenomenon. The most other cited muscle is the pectoral muscle (in the chest.) Why no emboli from there? The authors postulate the numbers are smaller- the maximum fat volume into the pec is usually 100-150, which is much less than the gluteus. The thought is without the high volume, you don’t get the high pressures, so it is less likely to migrate. Second, the pec area doesn’t have the large fragile deep veins the buttock area does.
BOTTOM LINE:
Yes, these are cadavers. Yes, they used applesauce. Yes, they used a 4mm cannula, and maybe you would use a smaller cannula. They did big volumes, and maybe you would use smaller volumes. But the anatomy was clear.
You can’t inject into the muscle.
This will limit the amount of fat you can transfer. The safe way to get big changes may be doing serial surgeries, thus increasing the fat small amounts at a time and only injecting into the space above (not in) the muscle.
The authors conclude, “The intramuscular insertion of fat, which up to this point has been considered reasonable to perform in the superficial muscle and even recommended in articles and textbooks is now deemed to be an inexact and potentially dangerous technique.”