Referenced as one of the most frequently performed aesthetic operations in the world, liposuction has become extremely popular with various modifications of equipment and technique.  External ultrasound-assisted liposuction (UAL) is a technique that requires transcutaneous application of high-frequency ultrasonic fields delivered into wetted tissue, followed by traditional aspirative liposuction, with the goal of improving the mechanical removal of adipose cells. [2, 3]
The use of high-intensity, high-frequency external ultrasound before liposuction has been reported to enhance the ability to extract fat, increase the amount of fat extracted, and decrease patient discomfort during and after liposuction. External UAL, during which the ultrasonic energy is applied through the skin, must be differentiated from internal UAL, during which the ultrasonic energy is applied through a specialized cannula. External UAL is a good option for removal of localized fat in patients with moderate obesity. [4, 5] Recently, external UAL at frequencies of 2-3 MHz and a potency of 3 W has been associated with complete fat tissue disruption, including both adipose cells and collagen networks, making it useful for body contouring, especially in patients with fibrous and inveterate cellulitis. [5, 6]
In 2003, Rohrich et al noted that ultrasound-assisted liposuction (UAL) is a safe and effective method for the treatment of gynecomastia.  The technique is particularly efficient in removing dense, fibrous breast tissue in men and produces minimal external scarring. Rohrich and colleagues proposed a new system of classification and graduated treatment, based on glandular versus fibrous hypertrophy and the degree of breast ptosis.
Rohrich's series of 61 patients with gynecomastia demonstrated an overall success rate of 86.9%.  In this series of patients, suction-assisted lipectomy was used from 1987-1997 and UAL was used from 1997-2000. UAL was found to be effective in treating most grades of gynecomastia. External UAL is effective in this setting because of its effect not only on fatty tissue but also on fibrous connective tissue, as external UAL leads to loosened cell–to-cell interactions and an altered structure of collagen, allowing for easy of removal of adipose cells. 
Other means of liposuction include the following:
Suction-assisted liposuction is the traditional method. In this type of liposuction, the surgeon removes fat by inserting a cannula that is connected to a vacuum pressure unit and directing the cannula through tiny incisions into areas to be suctioned.
In power-assisted liposuction, a cannula (see the image below) with a back-and-forth motion of the tip passes through tissue to suction out fat and fibrous or scarred tissue with reduced effort.Surgeon Vishal Kapoor, MD and a power-assisted liposuction cannula. © James C. Mutter / Vishal Kapoor, MD. Image courtesy of Wikimedia Commons.
The Vibration Amplification of Sound Energy at Resonance (VASER) System (Sound Surgical Technologies LLC, Louisville, Colo) is another method of liposuction. In VASER-assisted liposuction, intermittent or continuous bursts of ultrasonic energy can be used to break up fat cells, which are then removed by suction. See the images below.VASER probes with grooved tips.VASER ultrasonic liposuction machine including tumescent infiltrator, ultrasound generator, and suction with some aspirate in container.
A study by Milanese et al involving 28 young, normal-weight females found that 10-weeks of low-intensity, low-frequency, localized treatment with external ultrasound decreased subcutaneous adipose tissue thickness. The study, in which the women underwent two 48-minute sessions per week, reported that subcutaneous adipose tissue thickness was significantly reduced bilaterally in the gluteus and thigh areas, with fat mass in the trunk and lower limbs also decreasing. 
History of the Procedure
The use of liposuction was first described in 1976 by Georgio and Arpand Fischer.  Tumescent liposuction is also called standard liposuction, liposuction, lipoplasty, liposculpture, liposculption, and suction-assisted lipoplasty. This type of liposuction has been performed in the United States since 1982. First, the surgeon instills the fat with tumescent fluid (a solution that contains saline and local anesthetic with epinephrine). Following instillation of tumescent fluid, the fat is aspirated with long thin rods called cannulas. The suction can now be performed through a few small incisions, which can be hidden within natural skin creases. The tumescent technique may reduce blood loss and alleviate pain. The local anesthesia is frequently supplemented with intravenous sedation or general anesthesia. This type of liposuction is frequently performed as an outpatient procedure.
The use of ultrasonic technology has been on rise in all areas of medicine. In 1987, Scuderi et al introduced the use of ultrasound as an emulsifying modality for adipose tissue. [10, 2] In 1992, Zocchi outlined the technique of ultrasonic liposculpturing, which involved 3 fundamental steps: (1) preparation of the areas to be treated with a large infiltration of a special solution, (2) treatment of the areas with ultrasonic energy through special titanium probes, and (3) manual remodeling of the treated areas to eliminate the fluid from the burst adipocytes (fatty acids). 
In 1998, Silberg elaborated on the technique of ultrasound-assisted liposuction as the transmission of a high-frequency ultrasonic field sent through the skin.  Since then, several reports, including those by Lawrence and Coleman in 1999 and Lawrence and Cox in 2000, have discussed the procedure. [13, 14] In 2008, Ferraro et al demonstrated that increased intensity of ultrasonic energy of 2-3 MHz with external UAL demonstrated complete adipose cellular destruction confirmed by histologic analysis. 
Soft tissue injuries, orthopedic trauma, and pain relief for chronic pain conditions all can be treated with external ultrasound. The action of manual liposuction can be time-consuming and physically taxing. In this regard, ultrasound appears to offer the advantage of breaking up adipose tissue to facilitate liposuction and decrease postoperative pain.
With internal UAL, areas of skin necrosis and seroma formation can occur. Therefore, interest has been garnered in the application of external ultrasound prior to liposuction. Theoretically, external ultrasound should soften or disrupt adipose tissue and (1) facilitate the task of suctioning adipose tissue, (2) make the patient more comfortable during and after the procedure, and (3) improve the quality of the aspirate by decreasing the amount of blood.
External UAL is not widely used, and the evidence of its effectiveness is conflicting. [13, 14, 15, 1, 5] External UAL at lower intensity appears to be fibrinolytic and facilitates the loosening of cell-to-cell interactions; at higher intensities, it leads to destruction of adipose cell structure.
External UAL is a type of UAL in which the ultrasonic energy is applied from outside the body, through the skin, making the specialized cannula of the internal UAL procedure unnecessary. While internal UAL can result in skin necrosis and seromas, external UAL can, in theory, avoid this potential complication by applying the ultrasound externally.
External UAL is also potentially useful because (1) the external location of the ultrasound device can lead to less discomfort for the patient during and after the procedure; (2) the external location of the device means the probe does not physically touch internal tissue (blood loss can, therefore, be decreased); (3) it allows superior access through scar tissue; and (4) it is not constrained by internal structures and can, therefore, be used to treat larger areas.
Ultrasound causes tissue destruction via 3 mechanisms: (1) cavitation, (2) micromechanical disruption, and (3) thermal damage. Articles on internal UAL largely attribute the destruction to unstable or transient cavitation. Reports on ultrasound suggest that the disruptive biologic effects of external ultrasound are due to micromechanical disruption or tissue heating. Other reports postulate that external UAL loosens adipose cell attachments, facilitating aspiration.
The ultrastructure of cells is affected by ultrasound. It disrupts membranes and affects calcium influx, which can stimulate mast cell degranulation. Ultrasound can induce fibroblast activity and enhance collagen production. It can stimulate endothelial cell activity and new capillary formation in chronically ischemic tissue. These effects make ultrasound useful for the care of chronic wounds, as well. In addition, the manifestations of effects of external ultrasound appear to be directly proportional to the intensity delivered, with simple cellular detachment at 1 MHz to complete adipose cellular destruction at 2-3 MHz. 
Patients with localized increased adipose tissue benefit from liposuction. This condition is termed lipodystrophy, and, even if the patient is at or below his or her ideal weight, fatty tissue can be present in excess in specific areas. Overweight patients may also have lipodystrophy, but diet and exercise, rather than large-volume liposuction, are the mainstays of treatment for generalized obesity. The best liposuction results involve healthy patients with good skin elasticity and localized deposits of excessive fat.  Good candidates for liposuction should have realistic expectations and should not be obese. Some patients must have multiple procedures if they have more fat than can safely be removed in one operative setting. In rare cases, patients can experience problems with the anesthesia.
Ultrasonic liposuction appears most useful for treating larger or more fibrous areas that would be otherwise difficult with liposuction alone. External UAL allows much easier access through scar tissue. External UAL is especially appropriate for treatment of male breasts and retraction of the skin on the neck. In addition, high-frequency treatment of 2-3 MHz is recommended for treatment of fibrous and inveterate cellulitis.
In 2004, Shi and colleagues reported external UAL performed on 500 patients (595 sites).  The volume of anesthetic drugs, the volume of aspirated pure fat, and the body contour variations of every area were recorded at 1-3 months postoperatively. Both volumes were greatest in the waist-abdomen and thigh. The decreased postoperative dimensions at different body sites were then compared and analyzed; all dimensions were decreased to certain degrees. The most obvious decreases were in the severity of obesity and in the waist-abdomen; the decreases in the umbilical circumference and the minimum and maximum waist circumferences tended to be less. However, when the minimum waist circumference was >111 cm (50.45 in), obvious changes occurred in the umbilical region. The upper middle part of the thigh and the upper part of the arm showed larger variations than lower on either limb.
UAL reduced blood loss and pain and resulted in smooth skin without severe complications. Shi and colleagues therefore noted that external UAL is a safe, effective, and easily acceptable procedure for body contouring.  They noted that “the body circumference variation may have its intrinsic rule, which, to some extent, is meaningful for conducting clinical inquiry and forecasting the operation results.” 
In 2004, Zhang demonstrated that external UAL is a safe, effective, and simple method for liposuction in the upper legs.  In this series, 32 patients underwent external ultrasound-assisted tumescent liposuction in the upper legs with local anesthesia. All patients had satisfactory weight reduction and leg shaping. No obvious complications occurred in these cases; all patients recovered smoothly and promptly.
In a study by Gadsen et al, the use of high-intensity focused ultrasound (HIFA) was used to treat and ablate subcutaneous adipose tissue prior to abdominoplasty cases with histologically proven success. This represents a new potential use for external ultrasound technology as a pretreatment regimen for ablating and remodeling subcutaneous deposits. 
Adipose tissue is the tissue removed during liposuction procedures. The most common areas involved are the abdomen and thighs in women and the abdomen and flanks in men.
See the list below:
Patients who are extremely obese or in poor health, especially those with cardiac problems, should not undergo external UAL.
Only a limited amount of fat should be removed at each session, as very high volume lipectomy has been associated with development of pulmonary embolus and death.
Some warn against performing liposuction around the neck and upper chest because of the possibility of creating depressions or noticeable cavities.
Ultrasonic energy can theoretically cause air emboli; this possibility should be considered when selecting sites for the procedure. To date, this injury has not been reported.
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