anatomy. The piriformis muscle is landmarked by drawing a line connecting the posterior-superior ischial spine (PSIS) and the coccyx. Piriformis courses from the midpoint of this line to the greater trochanter in a transverse/oblique direction. The clinical relevance of piriformis is that it passes through and divides the greater sciatic foramen transversely and provides a useful clinical landmark for key neurovascular structures within the buttock region such as the superior and inferior gluteal vessels. These lie superior and inferior to the muscle, respectively. The buttock extends from the posterior iliac crest superiorly to the infragluteal fold inferiorly. It comprises of a number of layers from superficial to deep. These are the skin, subcutaneous fat, Scarpa’s fascia, deep muscle fascia, superficial and deep muscles, periosteum, and bone. The subcutaneous fat, as in other places has multiple layers with superficial, intermediate, and deep components. The muscles of the buttock may be divided into superficial and deep; those within the superficial layer are the gluteus maximus, medius and minimus, as well as the tensor fascia lata. Those in the deep layer are the piriformis, obturator externus, gemelli, and quadratus femoris. The gluteal muscles form the bulk of the buttock volume and shape. The underlying bony structures provide supporting framework for this and are formed by the ilium, ischium, sacrum, and coccyx. The buttocks receive blood supply primarily from the superior and inferior gluteal vessels. Innervation of the buttock musculature mainly arises from the superior and inferior gluteal nerves as well as the nerve to piriformis, obturator nerve and nerve to obturator internus. Skin sensation to the buttocks is provided by perforating cutaneous cluneal nerves from the posterior branches of T12–TS3.1–3
2. Nahai F, ed. The Art of Aesthetic Surgery: Principles and Techniques. 2nd ed. St Louis, MO: Quality Medical Publishing;
3. Da Rocha RP. Surgical anatomy of the gluteal region’s subcutaneous screen and its use in plastic surgery. Aesthetic Plast Surg 2001;25(2):140–144 NERVE ANATOMY OF THE BUTTOCK 2. Which one of the following structures passes through the greater sciatic foramen above the piriformis muscle? The greater sciatic foramen is an opening in the pelvis through which pass a number of key neurovascular structures. The greater sciatic foramen is formed by the sacroiliac, sacrotuberous, and sacrospinous ligaments along with the greater sciatic notch and ischial spine. The nerves which exit the pelvis through this foramen include the inferior gluteal, pudendal, sciatic, posterior femoral cutaneous, nerve to obturator internus, and nerve to quadratus femoris. However, these all pass below the level of piriformis and the only nerve passing above this muscle is the superior gluteal nerve. The superior gluteal nerve (L4–S1) is a motor-only nerve that innervates gluteus medius, gluteus minimus, and tensor fascia lata, but does not supply gluteus maximus. It travels with the superior gluteal vessels. The inferior gluteal nerve (L5–S2) supplies the gluteus maximus and the hip capsule. It travels with the inferior gluteal vessels. The sciatic nerve (L4–S3) supplies the hamstring muscles in the thigh. It then divides at the knee to form the common peroneal and tibial nerves which supply both motor and sensory innervation to the leg. The pudendal nerve (S2–S4) is the main nerve of the perineum. It innervates the external Fig. 123.1 Nerve anatomy in relation to piriformis muscle. Superior gluteal nerve and artery Inferior gluteal nerve and artery Piriformis muscle Sacrotuberous ligament Sciatic nerve Posterior femoral cutaneous nerve Nerve to obturator internus Internal pudendal artery Pudendal nerve 1104 Part VII ■ Aesthetic Surgery genitalia and skin around the anus and perineum. It also innervates some of the pelvic muscles and urethral and anal sphincters. It runs with the internal pudendal artery and vein. The obturator nerve (L2–L4) innervates the adductor muscles of the medial thigh including obturator externus, adductor longus, brevis and magnus, as well as gracilis. It also provides sensory innervation to the skin of the medial thigh. It does not pass through the greater sciatic foramen. In contrast, the nerve to obturator internus (L5–S2) does and this supplies the obturator internus and superior gemelli (Fig. 123.1).1–3
Gluteal implants can be used to restore volume and projection to the medial two-thirds of the buttock with a similar concept to breast augmentation. It is a useful technique to adopt in patients with insufficient fat for autologous fat graft augmentation who are prepared to accept the long-term implications of implants and the access scars created. However, this patient is likely to be disappointed as the implants will not improve her lateral buttock emptiness. To address the lateral deficiency, buttock implants can be combined with gluteal fat grafting as a hybrid augmentation in some patients. This can provide predictable volume augmentation of the medial two-thirds of the buttock (implant) with correction of the lateral one-third and the waist-to-hip ratio (liposuction and fat grafting).1 However given this woman is slim, this may not be a feasible option. The limitations of using implants alone must be explained preoperatively to set realistic expectations, otherwise with this patient’s remit there will be disappointment. Patient selection is important when considering implant-based buttock augmentation and patients must have a stable weight, sufficient soft tissue to accommodate a gluteal implant, and realistic expectations. Buttock implants are either round or oval. A round implant would probably suit this patient best as she has a short, rounded buttock. Oval implants are better suited to patients with taller buttocks, but as with anatomic breast implants, malrotation can be a problem. Buttock implants can be gel filled with silicone shells as per current breast implants, or solid silicone devices. At present, only soft-solid silicone implants are FDA-approved for buttock augmentation in the United States. Silicone gel implants are widely used elsewhere, for example, in Central and South America. Implants are available with smooth or textured external surfaces. Buttock implants may be placed through a single midline incision, or two separate parasacral incisions placed within the gluteal cleft. Separate incisions reduce tension across the wound and so may reduce the risk of wound dehiscence. Buttock implants can be placed subcutaneously, subfascially, intramuscularly, or submuscularly (between gluteus maximus and medius). However, subcutaneous or submuscular placement is no longer recommended due to high complications rates. Intramuscular placement gives low implant visibility and palpability, so may be well suited to this patient. However, it is a more challenging pocket dissection and risks sciatic nerve injury. In contrast, subfascial placement provides an easier plane of dissection and can help projection, especially in the lower pole. However, it may be more palpable and visible; so, it would be less preferable in this slim patient.1–3 Fig. 123.3 (A, B) Characteristics of ideal female buttock shape. Note the waist-to-hip ratio of 0.7 in both the posterior and lateral views. Short infragluteal fold A B 1106 Part VII ■ Aesthetic Surgery
Gluteal fat grafting (a.k.a. Brazilian buttock lift) allows for volume augmentation and reshaping of the buttock. It is obviously combined with liposuction for fat harvest, but enhancement of shape can be more dramatic when additional targeted liposuction to the waist, lower back, and flanks is performed. This can help narrow down the waist and improve the waist-to-hip ratio. Fat grafting provides superior precision for buttock reshaping than implant-based augmentation alone and is particularly useful for the lateral one-third that cannot be addressed with implant-based augmentation. It is an ideal technique for patients with mild to moderate lipodystrophy. Patients with minimal excess body fat (body mass index [BMI] < 20) and obese patients (BMI > 30) are not ideal candidates for gluteal fat graft augmentation. Graft volume maintenance in gluteal fat grafting depends on the ability of the fat to revascularize within the recipient bed. The amount of fat that the recipient site can tolerate depends on soft-tissue compliance and characteristics including vascularity. Significant overfilling of the recipient site increases pressure and reduces oxygen diffusion capabilities, which can decrease percentage volume maintenance. Therefore, is should be avoided.1 Expansion vibration lipofilling is a technique that allows for large volume fat grafting by expanding the recipient bed while simultaneously back-filling the recipient site.2
In recent years, there has been a major focus on the risks of developing a life-threatening pulmonary fat embolism (PFE) during or following fat augmentation to the buttocks. This is a situation where macroembolism of fat into the venous circulation occurs, such that fat globules are transported to the heart and lungs, causing obstructive cardiopulmonary dysfunction.1 PFE in gluteal fat grafting (macroembolism) is a different clinical entity to fat embolism syndrome (microembolism) and the signs and symptoms differ greatly. Traditionally, PFE was attributed to direct cannulation of gluteal vessels during fat injection. However, PFE has been observed in cases where deep intramuscular injection was not reported. Given this fact, the “Deep intramuscular migration” theory of PFE has been described.2,3 In this theory, gluteus maximus muscle fascia acts as a barrier to prevent deep intramuscular migration of fat. However, when fat is injected deep to superficial gluteal fascia, it migrates along a path of least resistance, through gluteus maximus muscle fibers. A lack of deep fascia of the gluteus maximus muscle allows fat to collect in the submuscular space. Increased pressure in the submuscular space places traction on the gluteal veins. Traction-induced tears of the gluteal veins create a siphon effect, drawing fat into the venous circulation. Deep intramuscular migration theory explains how PFE might occur even in cases where no injections were performed in the deep intramuscular plane. The estimated risk of death in buttock fat transfer due to PFE is between 1 in 2,351 and 1 in 6,241.4 Death is rapid in onset, typically occurring intraoperatively or < 24 hours postoperatively. There does not seem to be an association with PFE and the volume of fat injected. However, gluteal fat grafting is associated with the highest risk of mortality in aesthetic surgery; so, care must be taken when considering whether to perform this surgery and make steps to minimize risk of PFE occurring.4–7
7. Alvarez-Alvarez FA, González-Gutiérrez HO, Ploneda-Valencia CF. Safe gluteal fat graft avoiding a vascular or nervous injury: an anatomical study in cadavers. Aesthet Surg J 2019;39(2):174–184 When injecting fat into the buttock, placement must always be superficial to the gluteal muscles and muscle fascia. This is because deeper injections have been associated with fatal fat embolic events. Intraoperative measures to reduce the risk of this occurring commence with the surgeon having awareness of this eventuality and ensuring they have maintained an up-to-date knowledge of the buttock soft tissue and vascular anatomy. At all times, the operator should know exactly where the cannula tip is located in terms of depth and advancement and this can be achieved by palpation, proprioceptive feedback, visualization, and maintaining a three-dimensional awareness. Further measures to reduce risk include using a single-hole injection cannula at least 4 mm diameter, avoiding downward angulation of the cannula and positioning the patient in such a way to limit deep injection. Fat may be injected antegrade or retrograde, but the key point is to only inject while in motion so that large deliveries of fat to a single spot are avoided. There is no specific limit to the amount of fat that can be safely injected per side during buttock augmentation. However, common sense should prevail and volumes adjusted on a case-by-case basis. A good indicator of reaching the maximum fill is where there is a loss of resistance during injection and fat begins to drain from the injection-site incision. There is no standardized protocol for fat preparation and there are a number of accepted ways of doing this such as centrifugation, washing, sieving, and custom-made devices which filter the fat automatically. Postoperatively patients must be advised to refrain from sitting or lying supine for at least 2 weeks to avoid causing compression and ischemia to the transferred fat.1–5
There are a number of potential complications that must be discussed with patients prior to undergoing fat grafting to the buttock area. The most commonly recorded complication is seroma formation and this occurs in around 2.5 to 3.5% of cases. It is usually self-limiting unless it becomes complicated by infection. Fat necrosis is a complication that one may expect to be common after this procedure, yet this seems to occur in less than 1% of cases. It may be that fat necrosis occurs much more commonly, but at a subclinical level, and so goes unnoticed. Venous thromboembolism occurs in less than 1% of cases. This can be minimized with chemoprophylaxis and 1108 Part VII ■ Aesthetic Surgery calf compression devices/TED hose. As with all aesthetic procedures, realistic expectations must be in place and an acceptance that there will be only modest improvements as well as asymmetry and imperfections. Under- correction and infection each occur in around 2% of cases; pain and or sciatic nerve problems occur in less than 2% of cases. It would be extremely unlikely (though not impossible) that a significant neuropraxia affecting lower limb function could occur. Contour irregularities and asymmetry occur in less than 1% of cases, which again seems lower than might be expected. Death can occur following fat augmentation to the buttocks. The estimated risk of this is 1 in 2,351 to 6,241, which is, of course, extremely high for an elective cosmetic procedure. The cause of this high risk is fatal fat embolism. Patients must be counseled on this risk and the evidence, which supports it.1–7
Following massive weight loss, patients are often left with significant buttock ptosis, deflation, and a lack of buttock projection. To a degree, traditional techniques such as a circumferential body lift will improve the buttock area, but may still leave flattening and further loss of projection.1 Therefore, in this patient cohort, local autoaugmentation flaps may be useful to restore gluteal volume and projection. These would normally be performed at the same time as the body lift itself and are based on similar principles to those used to revolumize the breast in this same patient group, where medial and lateral flaps are transposed more centrally to revolumize the middle part of the breast. Examples of local flaps described for gluteal autoaugmentation include dermal fat flaps, superior gluteal artery perforator flaps, split gluteal muscle flaps, and purse string gluteoplasty.2–5 Gluteal autoaugmentation does not significantly influence complication rates in circumferential lower body contouring, although wound dehiscence is the most common complication associated with these procedures. Following pregnancy, most patients with residual soft-tissue excess would tend to have this located in the central lower abdomen rather than the buttock. Patients with a BMI of less than 30 tend to be deficient in soft tissue to augment with more generally. Diabetic patients are best discouraged from having aesthetic buttock surgery unless their glucose control is especially good. Female patients who have undergone massive weight loss may be good candidates for autoaugmentation, but not male patients, per se.
Injection of soft-tissue fillers into the subcutaneous tissues of the buttock can be used to achieve temporary nonsurgical buttock augmentation. The two most likely products that would be used are stabilized hyaluronic acid (HA) gel such as Macrolane and poly-L-lactic acid such as Sculptra.1 The main issue with this treatment is the volume that needs to be injected and the financial implications of doing this. Typically, in facial rejuvenation, products for injection such as HA are marketed in syringes of 2 mL. In order to achieve a meaningful volume enhancement in a buttock, 200 to 300 mL would normally be required, and the cost implication of doing so with current prices would be prohibitive. In addition, this is something that would need to be repeated on an annual basis thereby compounding the financial limitations of this technique. The other issue is that while it is accepted that small volumes can safely be injected into the face, which is well vascularized, should the product to native tissue ratio be changed dramatically, the risk of complications including infection, allergic reaction, or soft-tissue swelling could be markedly elevated. There has been one study which looked at the results of injecting large volumes of stabilized HA into the buttock. This prospective multicenter study involved 61 patients with a mean age of 41. Each patient had injection of HA to the subcutaneous area of the buttock with an average of 340 mL in total. They were then followed up for 2 years at regular intervals. The authors reported a low complication rate and high levels of patient satisfaction. Moreover, the results were maintained for more than 1 year in many cases.1 Based on this study, it would seem that the concept may be reasonable as an alternative to other invasive procedures such as fat grafting or implants. However, this is not approved for such use by the FDA; so, it would be off label in the United States. The use of a permanent filler should be avoided, as this risks irreversible changes which may be unwanted. Permanent fillers are associated with a high risk of complications including infection, ulceration, granuloma formation, asymmetry, and permanent deformity of the buttocks.2–6