8 Fat Grafting in Breast Reconstruction: The Data
This chapter reviews the current data on autologous fat grafting including fat harvest techniques, preparation, injection, and specific indications with their complication rates.
Key Teaching Points
Autologous fat grafting is becoming increasingly popular in breast reconstruction.
Centrifugation appears to retard the success of fat graft take.
Fat grafting should deposit the smallest possible aliquots of fat to achieve rapid revascularization.
Fat grafting is associated with varying degrees of fat necrosis or oil cyst formation but is no worse than that seen with standard breast reductions.
Fat necrosis may increase the need for unnecessary biopsies of mammographically suspicious calcifications.
Multiple grafting sessions may be necessary.
Autologous fat grafting does not appear to increase locoregional recurrence following either mastectomy or breast conservation therapy.
Breast reconstruction has undergone nothing short of a revolution over the past 15 years. Gone are the days of “you’ll look good in clothing” as the final comment in a reconstructive consult. The expectations that patients have of their surgeons, and that plastic surgeons have of themselves, have increased dramatically.
Technology is responsible for these changes in large part. Regarding surgical techniques the advent of perforator flaps, computed tomography angiography, acellular dermal matrices, form-stable implants, and more restrained mastectomy techniques have all contributed to better results.
Technology in the form of the Internet and social media have also contributed. Many patients do not sit in isolation lamenting a bad result or wishing they had a more natural breast reconstruction. They frequently take to social media outlets or the Internet to seek information on better techniques, engage with other breast reconstruction patients, evaluate potential surgeons, and complain about poor results. All these have pushed the bar higher.
Mastectomy reconstruction remains the main focus for most plastic surgeons. However, partial breast reconstruction and the delayed reconstruction of breast conservation deformities is an increasing part of breast reconstruction–focused practices around the world.
Autologous fat grafting plays an important role in all of these areas. The safety and efficacy of autologous fat grafting continues to be carefully studied and has gained increasing acceptance. We are in an era where the results of fat grafting techniques in an increasing variety of clinical scenarios are being evaluated, and the indications for those techniques are expanding. Autologous fat grafting has become a key adjunct in both flap and implant-based mastectomy reconstruction, the reconstruction of breast conservation deformities, and in rare cases total breast reconstruction with fat grafting alone.
8.2 Overview of Fat Harvest Techniques
A great deal of attention has been given to the process of harvesting fat and to the optimization of the techniques and instrumentation involved. The majority of studies comparing various techniques of fat harvest rely on in vitro cell viability assays or a histological examination of adipocytes for structural integrity as their endpoints rather than the in vivo assessment of fat graft viability. These types of studies can certainly answer whether a particular harvest technique damages adipocytes immediately upon harvest, but they do not answer what the impact of those techniques might be on graft viability after reinjection.
In 2000, Rohrich et al compared the impact of a variety of liposuction methods on the structural integrity and in vitro viability of human adipocytes.
Shiffman and colleagues evaluated the impact of increasing suction pressure on adipocytes in 2001. That study looked at the histological appearance of adipocytes and found that if aspiration pressures were kept below 700 mm Hg, damage to adipocytes could be avoided.
Ozsoy compared a variety of cannula sizes on in vitro adipocyte viability in 2006.
This study found that the larger the size of the cannula used to harvest fat, the better the viability of the adipocytes harvested.
This seems like a logical conclusion given the reduced shear stress on cells being aspirated through larger aperture cannulas. However, one needs to consider the impact of large particle size on the viability of fat once grafted. Larger globules of fat will certainly protect the adipocytes at the center of the globule from shear stress and direct trauma. However, they will also insulate those same adipocytes from the nutrition and neovascularization needed to maintain longterm viability. On the other end of the spectrum, a very small cannula aperture will induce significant shear on adipocytes at a given suction pressure.
8.3 Fat Preparation Techniques—An Overview
Centrifugation has long been an integral part of preparing fat grafts for reinjection. Many of the studies looking at the impact of centrifugation have used the speed of the centrifuge, or revolutions per minute as a variable data point. This ignores the impact of the centrifuge’s moment arm on the amount of G forces being applied to the fat. Kurita et al addressed this in 2008 when they looked at the impact of varying G forces on the in vivo viability of human fat injected into athymic mice.
That study found that the greatest graft retention was seen when the aspirated fat was reinjected without any centrifugation at all.
The authors did find that when the goal was to isolate stem cells, a moderate centrifugation was superior to no centrifugation.
The widespread adoption of large-volume fat grafting was originally slow in part due to efficiency issues. Many surgeons considered the time and effort involved in harvesting more than 100 cc of fat in small aliquots, draining that fat on absorbent pads or centrifuging it, and placing it back into syringes for reinjection to not be worth the trouble. Gabriel and colleagues looked at the use of a commercial filtration system, the Revolve system (Allergan), and whether that system could help expedite the harvest and preparation of fat grafts. They found that with the use of the Revolve system, and more likely with the elimination of centrifugation and the multiple transfers it requires, they could harvest more fat in less time. They found that with the Revolve system they could more than double their fat harvest yield in about one-third of the time it took using centrifugation.
There will always be a great deal of variety in how surgeons choose to pursue different operations. However, there is a growing body of literature that can point surgeons in the right direction and at least help avoid techniques that at best waste time by adding steps that don’t demonstrate a benefit or at worst are directly damaging to adipocytes. Ultimately, the harvest technique has to be reproducible, minimize morbidity for patient, harvest adipocytes, and involve procedures that can be performed efficiently.
8.4 Approaches to Reinjection
The fundamental principle of reinjection is gentle handling of the tissue and the avoidance of creating large pools of fat. Gentle pressure on the syringe during reinjection is a first step. Pressure is typically steady and slow enough that the fat is released in a string and not as a depot. The proper selection of cannulas for reinjection is also important. As with harvesting fat, cannulas that are too narrow may lead to shear forces on the fat that harm viability. However, if the speed of reinjection remains well controlled, this is probably less of an issue than it is with harvest using a liposuction machine. The concept of depositing the fat one adipocyte at a time, so that every grafted adipocyte is surrounded by the native tissue in the recipient bed, has been put forward by Rigotti and others. While this may not be technically feasible, it illustrates the importance of maximizing contact of the grafted fat with the recipient bed to improve the odds of successful revascularization.
8.5 Patient Safety
Two of the greatest risks to patients undergoing large-volume fat grafting include hypothermia and thromboembolism. It can be challenging to expose both recipient sites and adequate donor sites in these patients. The surgical can sometimes extend from the sternal notch to the patella. With alcohol-based prep solutions, this creates an ideal environment for heat loss. Prewarming patients prior to their entry to the operating room, maintaining reasonable ambient temperatures in the operating room, and employing perioperative warming strategies are all useful in avoiding hypothermia. We have found the use of circulating warm fluid warming pads and sterile forced air warming blankets to be useful.
The application of sequential compression devices can also be a challenge when the operative field is broad. We have found the use of sterile towels and sterile elastic bandages to be helpful in allowing the application and maintenance of sequential compression devices throughout these procedures.