Buttock augmentation advanced with the advent of autologous fat grafting, first reported by Chajchir and colleagues in 1990.¹ Since then, there has been an increase in the literature documenting that there is one female body shape that is universally found to be most attractive, with the buttocks as one of the two most important determinants of beauty of the female torso. This attractiveness is directly related to the proportion of the waist to the buttocks, or the waist-to-hip ratio.^2,³

Patient and physician interest gradually escalated during the late 1990s and through to today.⁴^–⁶ Over that time, there has been an evolution in gluteal augmentation, with modifications in the approach, understanding of the various anatomical planes for implant insertion, and improvement of the surgical technique for implant-based augmentation.⁷^–¹² The implants themselves have evolved with different silicone elastomers, shapes, sizes and projection, making it possible to individualize the implant for each patient. Likewise, there has been refinement of the autologous fat grafting technique to improve fat survival, minimize complications and optimize outcomes for patients.¹³^–¹⁶

Basic science

Gluteal aesthetic ideals

The attractiveness of the buttocks is not judged in isolation, but in proportion to the waist. According to Singh,² there is one female body shape that men universally find most attractive (full buttocks, narrow waist). These ideal female proportions are summarized as a waist-to-hip ratio of 0.7 (measuring the waist at its narrowest and the buttock at the level of maximum circumference). In addition to this overall proportional relationship, there are various characteristics associated with attractive youthful buttocks. These include: (1) A smooth inward sweep of the lumbosacral area and waist; (2) a very feminine cleavage as the buttocks separate superiorly and inferiorly; (3) maximum prominence on the vertical axis at the level of the mid to upper buttock, and on the transverse axis, at the junction of the medial and central thirds of the buttocks; (4) minimal infragluteal crease; and (5) no ptosis.¹³

Topographical anatomy

A thorough grounding in anatomy and aesthetics is essential when dealing with the gluteal aesthetic unit.¹⁷ We can all recognize attractive buttocks, but translating these aesthetics into words becomes a challenge. Dr Ralph Millard¹⁸ emphasized in his book, Principalization of Plastic Surgery, that in order to be successful in our surgical design, approach and ultimate results, we must first understand the beautiful – in this case, the ideal buttock.

The gluteus maximus muscle originates primarily along the lateral margin of the sacrum and, to a lesser extent, from the coccyx and sacrotuberous ligament. The origin continues in an upward curvilinear fashion to the posterior iliac spine (identified as bilateral dimples in the parasacral zone); traditional teaching tells us that the muscle attaches all along the superior iliac crest, but in reality it only follows the crest for one-third of its initial distance. The superior limit of the gluteus maximus muscle is the posterior iliac spine. The gluteus maximus inserts into the iliotibial tract, and to a lesser degree, the greater trochanter (Fig. 28.1).

Fig. 28.1 Anatomy of the gluteus maximus muscle.

Knowledge of the superior aspect of the gluteus maximus origin is essential in describing the ideal buttock. However, buttocks aesthetics are not solely dependent on the gluteus muscles; the overall buttock shape is also influenced by bony pelvic anatomy, fat distribution, and to a lesser degree the tightness of skin. The skin will influence the appearance if there is laxity or ptosis, as is the case in massive weight loss patients. In fact, the attractiveness of the female buttock is primarily dependant on the thickness and distribution of the fatty layer, which is usually 50–60% of the volume of the buttock. Confirmation of this can be easily obtained by looking at the shape of the buttocks in a woman’s fitness magazine. The women who exercise and diet competitively to make their muscles maximally full and visible accomplish this also by losing body fat. This loss of fat makes the buttocks look gaunt and unfeminine.

Aesthetic analysis

To evaluate the buttock, it is helpful to divide it into quadrants by drawing an imaginary line down the center of the buttock. The ideal buttock has equal volumes on either side of this line and has the shape of a football.

To further assess volume distribution, a horizontal mid-buttock line is added to divide the buttocks into four quadrants (Fig. 28.2). The ideal buttock also has equal volumes above and below this horizontal line. If we evaluate each quadrant individually, then the lower quadrants, three and four are equal, but tend to be slightly wider than one and two. In determining the best procedure for a particular patient, all four quadrants are evaluated as either sufficient or deficient.

Fig. 28.2 Ideal gluteal aesthetics based on quadrant analysis.

Once volume has been assessed, there are three other zones that surround the buttock, which become important in our evaluation: the upper inner gluteal/sacral junction, the lower inner gluteal fold/leg junction, and mid-lateral gluteal/hip junction.

Upper inner gluteal/sacral junction: ideal presacral space shape

The inner gluteal/sacral space should be well defined so that a V-shape is apparent; this lower presacral space is appropriately called the “V” zone (Fig. 28.3). As the “V” zone becomes more visible, the buttock has greater aesthetic appeal. In the ideal buttock, the gluteal muscle edge should be well defined and have a semicircular upward turn. If this space is not well defined, the buttock becomes blunt and appears flat, especially on the lateral view.

Fig. 28.3 The “V” zone. Visible muscle fullness versus loss of definition from excess fat and back of muscle volume.

Lower inner gluteal fold/leg junction

To describe this relationship, the intergluteal crease will be referred to as the midline. The upper aspect of the crease is easily identified; however, the inferior aspect is defined at the point where the buttock begins to separate from this midline. In the ideal buttock this occurs at about the bottom two-thirds to three-quarters of the muscle. The separation widens until it meets the inner leg junction. At this point the lower gluteal fold has a 45° take-off from the center intergluteal crease line and the inner gluteal fold/leg junction should create a diamond shape space (see Fig. 28.4). This is a key point in gluteal aesthetics.

Fig. 28.4 Red lines indicate how the fullness increases at the lower inner gluteal fold and the diamond zone turns from a 45° into a straight line. (A) Downward slope; (B) horizontal line; (C) upward slope.

As the lower inner gluteal fold and inner leg become fuller, it changes the 45° sloping line to a more horizontal position, which causes the diamond shape space to turn into a straight line, losing its aesthetic appeal (Fig. 28.4). As the fullness increases, it develops an inverse relationship creating an upward slope (negative angle) (Fig. 28.4). Improvement of this zone will depend on the severity of the fullness.

Lateral mid-buttock/hip contour

In the aesthetic buttock, the lateral mid-buttock is an area without any depression. This zone is categorized as having; no depression, mild depression, moderate or severe depression (Fig. 28.5).

Fig. 28.5 Variation in lateral mid-buttock depression. (A) None to mild; (B) moderate; (C) severe.

Lateral view aesthetics

On lateral view, the presacral area should have a sweeping curve that has a lazy S shape (from the back to the bottom of the gluteus) (Fig. 28.6). Most of the gluteal volume is central and has equal distribution in the upper and lower gluteal zones, giving a C-shape curve. It has been suggested that the peak of the central mound should be at the level of the pubic bone (Fig. 28.7).

Fig. 28.6 Aesthetics of the gluteal region – lateral view.

Fig. 28.7 Variation in volume distribution on lateral view.

Determining where most of the volume lies (upper, central or lower buttock) will be important in deciding what procedure is best used to augment the buttock (Fig. 28.8).

Fig. 28.8 Ideal gluteal aesthetics. One can see that the upper aesthetic unit of the gluteus follows its origin; it begins at the midsacral line, continues as a semicircular line that connects to the posterior iliac spine (identified as bilateral dimples in the parasacral zone) and peaks at 2–3 cm above this point. In a well-developed buttock with very little lower presacral fat, a visible “V” zone is apparent, which further accentuates the upper inner muscle anatomy; the muscle has a football shape with nearly equal volumes in all four quadrants (quadrants three and four tend to be slightly wider than quadrants one and two). The gluteal unit is marked superiorly by its attachment to the iliac ridge (easily palpated) and inferiorly by the inferior gluteal crease. Without a doubt, the most important contributor to gluteal aesthetics is the volume of distribution in all four quadrants. When this volume is adequate, all other aesthetic points can be overlooked and still render an attractive buttock. The inferior gluteal aesthetics is defined by a diamond shape at the intergluteal/leg junction, the medial buttock cheeks have a 45° take-off from the intergluteal line and flows into the inferior gluteal crease which terminates at or just beyond the mid-buttock line. On lateral view there is an S-shaped curve from the lower back as it comes into contact with the buttock and most of the gluteal volume is located in the central zone.

Diagnosis/patient presentation

Patients present with a desire to improve their body contour/proportions, due to aging or general soft tissue deficiency. Specific patient desires can be affected by ethnic background and social relationships. There are six zones where augmentation is requested: upper medial buttocks, mid medial buttocks, lower medial buttocks, lateral hollow/trochanteric depression, lateral thigh, and various localized depressions.

Ethnic ideals need to be taken into consideration regarding patient desires (Table 28.1).¹³ Some Caucasian patients may desire full, but not overly large buttocks which are rounded laterally (Fig. 28.9) or a trim, athletic appearance with hollow lateral buttocks. Some Asian patients may desire buttocks that are relatively small, whereas some Hispanic patients may prefer buttocks that are full and rounded medially and laterally, with lateral buttocks that are relatively full (Fig. 28.10). Some African-American and Caribbeans of African descent (Fig. 28.11) may desire larger buttock size, with fullness in the lateral buttocks and lateral thighs (“hips”).

Table 28.1 Ethnic ideals of beautiful buttocks

Fig. 28.9 A 22-year-old Caucasian patient desiring full buttocks throughout. After buttock augmentation with 900 cc of fat grafted per side.

Fig. 28.10 A 25-year-old Hispanic patient desiring more fullness to the lateral buttocks. After 780 cc of fat grafted per side.

Fig. 28.11 A 36-year-old African-American female status post-buttocks augmentation with 890 cc of fat grafted per side.

Gluteal augmentation is not just about making the buttock bigger, but rather accentuating, contouring, and reshaping. The focus becomes volume redistribution; shifting volume from an unattractive zone to a more desirable position. With this perspective, even the full-figured woman becomes a candidate since, on closer examination, the large buttock has maldistributed adiposity, with deficient volume in pertinent aesthetic zones (Fig. 28.12). The question is no longer who is a candidate, but rather, what reshaping method is best for each particular patient? Liposuction is for sculpting, while fat transfers and/or implants are used for volume expansion.

Fig. 28.12 Improvement of the gluteal region with overall volume redistribution.

Patient selection

The ideal patients for implant-based augmentation are young, with an athletic build with little or no ptosis. Morbidly obese patients are not candidates for this surgery unless they lose weight, after which the laxity of tissues converts them into good candidates if they undergo excisional procedures to correct the back and gluteal regions.

Early series on implant-based augmentation documented unacceptably high rates of would dehiscence and implant exposure. As patients requested greater augmentations, larger implants were used, resulting in higher complication rates. Patients were retrospectively stratified into various groups of body frames, based on size/BMI (Figs 28.13–28.16).⁹ The larger the body frame, the greater the risk of wound dehiscence and implant exposure

Fig. 28.13 Small frame BMI <20.

Fig. 28.14 Medium frame BMI 21–27.

Fig. 28.15 Large frame BMI 28–31.

Fig. 28.16 Extra large frame BMI >32.

How do we distinguish the frames?

As surgeons, we would like some sort of scientific method to help guide and standardize these four body frames. While the approach used was very subjective, in an attempt to cement a standard tool, several evaluation methods were examined: percentage body fat, body mass index, dress size, and presacral fat measurements. The small frame is usually a BMI of ≤20 (US dress size 0–2); the medium frame is a BMI of 21–27 (US dress size 3–9); the large framed patient is a BMI of 28–31 (US dress size 10–14) and finally, the extra large frame usually has a BMI of ≥32 (US dress size >15).

Conclusion

If the BMI is ≤20, the patient will usually not have enough fat for augmentation and implants are the volume enhancer of choice. Patients with a BMI of ≥28, usually have abundant lipodystrophy and are best augmented with fat.

What has been most helpful in patient selection has been “presacral fat measurements”; anyone with 6–7 cm presacral thickness will usually have the body type that has sufficient fat for transfers. There is an excess layer of fat over the sacrum which makes these patients a set up for wound dehiscence if implants are used. There is no foolproof system that will individualize each patient, given all the variables discussed. As a general rule, we should start considering fat transfer as the preferred choice for augmentation in patients that have a BMI of ≥24, a US dress size above 8, or a 5–6 cm presacral fat thickness. However, physicians’ judgment and experience remain the standard.

Aesthetic goals

Research by Singh, as well as other authors, has documented the importance of an ideal waist-to-hip ratio of 0.7.² There is a tremendous synergistic effect of liposuction of the lower back, waist and flanks in conjunction with buttock augmentation to achieve this ideal waist-to-hip ratio. This is clearly evidenced by the fact that fuller, more shapely buttocks appear more attractive when the waist is slender rather than fuller.

In attractive female buttocks, there is beautiful cleavage as the buttocks separate superiorly. Furthermore, there is an inward sweep of the lower back, lumbar and sacral area, which accentuates this cleavage. It is also important to make the buttocks shorter vertically, than one would think. A short full buttock is attractive. A vertically long buttock simply appears big. (For a detailed summary of advantages and disadvantages of the various techniques for buttock augmentation see Table 28.2.)

Table 28.2 Advantages and disadvantages of various techniques of buttocks augmentation^a