1. Tissue structure of the buttocks.
The shape of the buttocks is mainly determined by the following four factors: skin, subcutaneous fat (superficial fascia) distribution, gluteus maximus and bony structure.
(1) Skin: The skin of the buttocks is thicker and has abundant sebaceous glands and sweat glands, which are more obvious in the upper part.
(2) Superficial fascia: The superficial fascia is well developed and is a fatty tissue rich in fibers, which can be considered to be composed of subcutaneous fat and subcutaneous fascia intervals. It is generally thicker near the iliac crest, thinner in the middle, and especially thick in the lower part of the buttocks, where the weight of the entire trunk is pressed on the “fat pad” when a person is sitting. The superficial fascia of the buttocks migrates above the superficial fascia of the lumbar back, and the lower and lateral parts of the superficial fascia of the femur, while the inner part is very thin near the posterior sacrum and the posterior superior iliac spine, and some individuals lack fat, which makes it easy to form bedsores when under long-term pressure. Women have more subcutaneous fat than men, infants have more than adults, and certain races have more. The superficial fascia of the buttocks has a great influence on the aesthetics of the buttocks, firstly, it plays the role of a “fascia shield”, and its relaxation and tension have an impact on the shape of the buttocks. Secondly, the thick “fascia hood” also makes the buttock shape moist and the deep muscular structures are not easily visible. Although the protrusion of the buttocks mainly comes from the capacity of the gluteus maximus muscle and the lumbar spine protrusion, the amount of subcutaneous fat is also crucial to the protrusion, and it is the rich superficial fascia that constitutes the full garden-shaped buttocks.
(3) Deep fascia (also called gluteal fascia): the deep fascia of the buttocks is closely attached to the iliac crest and divided into two layers at the upper edge of the gluteus maximus muscle to wrap around the gluteus maximus muscle, and many small fiber compartments are issued between the muscle bundles of the gluteus maximus muscle from the deep side of the fascia to separate each muscle bundle, thus the fascia is very firmly combined with the muscle. The lower part of the gluteal fascia is merged with the tendon fibers of the vastus medialis and the superficial layer of the gluteus maximus outside the greater trochanter to form the iliotibial bundle, and the gluteal fascia continues downward to the vastus medialis behind the femur. The fascia wrapping the gluteus maximus acts as a supportive structure to accommodate the placement of the implant below and as an anchor point for the augmentation of the buttocks with autologous tissue. The superficial fascial shield and the gluteal fascia are closely fused together below to form the subgluteal groove, which serves as the lower boundary of the buttocks, but it is difficult to reconstruct in a surgical manner.
(4), gluteal muscles: hierarchically, they can be divided into three layers, the superficial gluteus maximus and the broad fascial tensor, the middle gluteus medius, the pear-shaped muscles, the internal closed-hole muscles and the femoral square muscles, and the deep gluteus minimus and the external closed-hole muscles. The vascular nerves adjacent to them are: the superior gluteal artery and the superior gluteal nerve through the superior foramen of the pear muscle; the sciatic nerve, the posterior femoral cutaneous nerve, the inferior gluteal artery, the inferior gluteal nerve, the internal pubic artery, and the pubic nerve through the inferior foramen of the pear muscle. The gluteal cutaneous nerves include the superior gluteal cutaneous nerve, the middle gluteal cutaneous nerve, the inferior gluteal cutaneous nerve and the inferior iliac abdominal nerve.
(5) There are three myofascial compartments in the gluteal region, which have relatively fixed and inelastic wall boundaries.
The gluteus maximus compartment consists of the gluteus maximus muscle and the deep gluteal fascia in its superficial and deeper layers, which is continuous with the broad fascia of the thigh. Above this compartment is the iliac crest, laterally is the iliotibial bundle, and medially is the superficial and deep gluteal fascia anchored to the sacrum, coccyx, and sacral tuberosity ligaments.
(ii) Gluteus medius¸minimus fascial compartment (gluteus medius-minimus compartment): separated above by the deep gluteal fascia and the broad fascial gap, with the iliotibial bundle on the lateral side and the iliac crest on the deep side.
(iii) Broad fascia lata compartment (tensor fascia lata compartment): it is composed of broad fascia and iliotibial bundle.
The most important vascular nerve bundles are located within the gluteus medius, gluteus minimus fascial compartment. Knowledge of the structure of this intrafascial compartment is essential, as well as for the possible rescue of rare fascial compartment syndromes. The increased volume of implanted material within the fascial compartment, bleeding and hematoma formation may increase intra-fascial pressure beyond the safe range. Sporadic data show that intrafascial intraventricular pressure greater than 30 mmHg can lead to intramuscular necrosis in as little as 4 to 6 hours and induce neuro-Wahrenheit degeneration in more than 8 hours.
2.Applied anatomy of gluteus maximus muscle.
(1), gluteus maximus major is the thickest muscle in the human body, a quadrilateral powerful flat thick muscle, is an important muscle to maintain the human body upright and posterior extension of the hip joint, it is also an important part of the composition of the hip form. This muscle has an extensive start, and the medial edge starts from the posterior iliac hip line and its bony surface, the back of the lower sacrum and the back of the coccyx, as well as the sacral tubercle ligament and the thoracolumbar fascia with a wide short tendon from above. The upper edge of the muscle is about 10.9 cm long, with a thickness of about 1.2 cm at the midpoint of the upper edge, and the lower edge is about 12.6 cm long, with a thickness of about 2.4 cm at the midpoint of the lower edge, starting and ending at a width of about 11 cm. The muscle fibers run obliquely outward and downward, and are divided into an upper 3/4 muscle fiber bundle and a lower 1/4 muscle fiber bundle. The upper half of the muscle fiber bundle crosses the greater trochanter and is continuous with the tendon membrane in the iliotibial bundle, resulting in a significant thickening of the iliotibial bundle here; the lower half of the muscle fiber bundle ends at the gluteus medius and the lateral femoral septum with a thick tendon between the biceps femoris and the lateral femoral muscle.
(2) The main trophoblastic vessels of the gluteus maximus are the superior gluteal artery and the inferior gluteal artery. The superior gluteal vascular nerve penetration point: from the posterior superior iliac spine to the greater trochanter for a line, its upper, middle 1/3 junction point, for the superior gluteal vascular nerve out of the pelvis point. The superior gluteal artery exits the superior foramen of the pear muscle and divides into deep and superficial branches, with the deep branch branching in the deep surface of the gluteus medius muscle to feed the gluteus medius and gluteus minimus; the superficial branch is superficial between the superior edge of the pear muscle and the posterior edge of the gluteus medius muscle, and branches into the muscle in the deep surface of the gluteus maximus muscle, mainly feeding the upper and middle gluteus maximus muscles, the posterior iliac crest and the adjacent skin, with a branch anastomosing with the inferior gluteal artery. The superficial branch of the artery exits the superior foramen of the pear muscle with an external diameter of 3 mm and is accompanied by 1 to 2 veins with an external diameter slightly thicker than that of the artery. The inferior gluteal artery is one of the terminal branches of the anterior trunk of the internal iliac artery, which exits the inferior foramen of the pear muscle and travels outward and downward, sending branches to the middle and lower gluteus maximus. The surface projection of the inferior gluteal artery is medial to the intersection of the lower 1/3 and middle 1/3 of the vertical line between the iliac crest and the sciatic tuberosity. The outer diameter of the arterial puncture is 3.5 mm, and the accompanying veins are mostly two in number, with a thicker outer diameter than the artery. The gluteus maximus is innervated by the inferior gluteal nerve, which exits the foramen magnum medial to the inferior gluteal artery, then travels with the inferior gluteal artery and enters the muscle through the inferior foramen of the pear-shaped muscle with accompanying vessels.
(3), the projection contour of the gluteus maximus on the body surface: the upper inner gluteus junction with the sacrum; the inner lower gluteus crease formation; the lower lateral gluteus junction with the thigh; the middle lateral gluteus junction with the hip. As can be clearly seen from the superficial surface, the superior medial gluteus muscle junction with the sacrum is actually also the two sides of the triangular V of the sacrum. The lower inner part is the inferior gluteal crease, which originates at the upper end in the intergluteal sulcus and is the beginning of the separation of the hip from the midline, which should be at 2/3 or 3/4 of the gluteal muscle. This line is 45ºoff from the midline and terminates at the midline or slightly lateral to the hip. The above two boundaries should be clear, while the latter two should be smooth. The lower lateral hip transitions to the thigh, while the mid-lateral hip and hip shift should be more natural, although there can be a lateral concavity present.
3. Body surface features.
(1), Lateral depression of the hip (Lateral depression): the lowest point is the greater trochanter of the femur, the upper edge is the gluteus medius muscle belly and stop, the lower edge is the stop of vastus lateralis, and the deep posterior edge is the stop of the femur square and the superficial layer is the gluteus maximus muscle belly. This surface feature appears more clearly in athletes with good gluteal tone, but some races such as those of African and South American descent do not like this depression, and some even ask for filling to eliminate it.
(2) Infragluteal fold: It starts from the lower end of the intergluteal sulcus and transitions to the posterior femur through a natural curvature, showing the tension and fullness of the medial gluteal area from above to below. When viewed from behind, the gluteal sulcus should not be too long and should not exceed 1/2 the width of the base of the thigh, and when viewed from the side, it is best not to see a sagging subgluteal fold. In terms of internal composition, this is a shallow sulcus close to the level of the sciatic tuberosity, with the lower edge of the sulcus being the start of the semitendinosus, semimembranosus, and biceps longus on the sciatic tuberosity, and the supragluteal eminence consisting of the lower edge of the gluteus maximus, so that its lateral aspect should not extend beyond the connection between the deep semitendinosus and biceps femoris. Excessive skin and superficial fascial laxity will result in a change in the arc of the subgluteal crease. An excessively long, deep and distorted subgluteal crease is characteristic of an aging, sagging and flat buttock, while a shorter subgluteal crease arc reveals a full, tense and youthful buttock.
(3), supragluteal fossa, also known as lumbar fossa (Supragluteal fossettes , sacral dimples): in the supragluteal position, there is a shallow fossa on each side of the lumbar region, the lowest point is the posterior superior iliac spine, the medial side is the sacral spine and sacral spine muscle multifidus muscle, the lower and lateral side is the beginning of the gluteus maximus muscle, and the superficial side is the lumbodorsal fascia. The lumbar fossa often becomes difficult to identify in men, with probably only 18% to 25% of men having a recognizable lumbar fossa. The supragluteal fossa is usually visible in most women, which is related to the distribution of more subcutaneous fat and is not easily seen in overly lean women.
(4), Sacral triangle, or sacral V-shaped shallow fossa (Sacral triangle, V-shaped crease): two arms of the V-shape starting from the proximal end of the intergluteal sulcus and extending to the supragluteal fossa, to the sides equivalent to the posterior superior iliac spine. This arm is formed by the beginning of the gluteus maximus on the lumbodorsal fascia, and the tip of the triangle is where the gluteal edges on both sides touch each other toward the midline, corresponding to the sacrococcygeal joint. the rising height of the V-shape should be 1/3-1/4 of the length of the entire intergluteal sulcus. The blurring of the boundaries of the sacral triangle may be due to fat accumulation in the sacral area or to the underfilling of the gluteal muscles. If it is the former, it can be improved by liposuction, and if it is the latter, it can be solved by prosthesis or fat filling. There is also the “Michaelis’ diamond”, which refers to the diamond-shaped area between the two lumbar fossae. The upper corner of the diamond is equivalent to the position of the waist point, where the 5th lumbar spine is located.
4. Aesthetic impression of the buttocks.
Although the protrusion of the human buttocks may be the evolutionary process of adapting to the physiological need for the human body to stand upright and walk with both lower limbs, its shape also inevitably gives the human body aesthetic significance.
Women have a wider pelvis than men, and a wide buttock usually becomes an important feature that reflects the differences between men and women. Specifically, the average width of an adult female’s buttocks is 39 cm, while the average width of an adult male is only 36 cm.
Full hips are an integral part of the Hourglass figure. The concept of the hourglass figure has been promoted since ancient times, not only in modern society but also in ancient paintings and sculptures. The feminine shape has long been ingrained in the human mind as a biological sign of youth, health and fertility.
The posterior protrusion of the buttocks is an important feature that constitutes the aesthetics of the buttocks. It consists of the following three factors.
1. It is mainly determined by the anterior projection of the lumbosacral spine and the angle of inclination of the pelvis.
2.The amount of muscle and subcutaneous tissue possessed by the buttocks.
3. The degree of tension of the soft tissues. The hyperextended lumbosacral spine protrusion is a distinctive feature of races of African descent, and forced training during childhood can produce an average sacral tilt of 5º~7º. In lateral view, the posterior expansion of the buttocks can be seen prominently, but it is not determined solely by the shape of the buttocks, but rather by the natural excess and derivation of the lumbar region and thighs. Fat accumulation and tissue laxity in the waist and thighs can conceal the degree of posterior protrusion of the buttocks.
The appearance and tactility of the buttocks should have a greater tension in the buttock tissue than that of the female breast. The buttocks are a part of the body that harbors personal passion and motivation, and it is an important feature of a woman’s buttocks to be full, moist and full of elasticity.
The texture of the skin of the buttocks is important and should not be too delicate. Usually the skin of the buttocks is thicker and rich in sebaceous glands and sweat glands, so the appearance should be slightly rougher than the skin of other parts of the body.
From behind the standing position, there is an almost rhombus-shaped gap between the inner and lower edges of both buttocks and between the two inner thighs, through which you can vaguely glimpse the part of the labia majora and the opening toward the bottom.
5.Aesthetic ratio of the buttocks.
(1) Waist-to-hip ratio (WHR, Waist-to-hip ratio): Waist circumference refers to the circumference of the smallest part of the waist from the rib cage to the iliac crest. Hip circumference refers to the circumference of the most prominent part of the hip. The most aesthetically pleasing waist-to-hip ratio for adult women is 7:10, while for men it is 9:10. It is important to note that the difference between women and men in terms of waist-to-hip ratio is a fairly constant ratio that does not change with social and cultural changes. Whether in a society where fat is beautiful or a society where “bones” are prized, men’s waists are always thicker and stronger than women’s. This characteristic of the human body has a long history. This feature of the human body has a long history and a very basic utility. The ratio of pre-pubescent girls and post-menopausal women is close to that of men, and it is believed that this is mainly due to the different distribution of fat under the action of sex hormones.
(2), posterior protrusion ratio of the buttocks: the degree of posterior protrusion of the buttocks is an important factor in determining local attractiveness. Visually from the side of the human body, or by palpation, several markers can be identified: point A the greater trochanter , point B the most prominent part in front of the pubic symphysis; point C the most obvious point of the posterior protrusion of the buttocks; point D the anterior superior iliac spine; through these fixed points are made plumb lines, point D and point B two plumb lines should basically overlap, with the plumb line leading from point D representing the point B plumb line. After analysis, it is found that the hip of women with beautiful hips is characterized by the following: the distance between AC should be twice the distance between AB, which is called the ratio of the posterior protrusion of the hip 2:1.
6. Partitioning and typing of the buttocks.
(1) From the back, the buttocks and adjacent parts can be divided into 8 areas: one each for the lumbar back area (fland units), one each for the sacral triangle, one each for the surface area of the buttocks (buttock units), one each for the diamond-shaped area below the buttocks, and one each for the posterior thigh area (thigh units, one on each side. From the posterior side, the buttocks and adjacent areas are divided into 8 blocks: 1 and 2 are the dorsal lumbar area on the left and right sides, 3 areas are the sacral triangle, 4 and 5 are the buttocks on the left and right sides, 6 areas are the diamond areas between the lower buttocks on both sides, and 7 and 8 areas are the two symmetrical femoral areas.
(2), from the side, the outline from the back of the waist to the lower part of the buttocks should be distributed in an S-shaped curve, showing the front concavity of the lumbosacral part, connecting the full posterior protrusion of the buttocks with the arousal, and then down to the transition of the thighs. Divide the part of the posterior eminence of the buttocks into three zones from top to bottom, and the height of the most protruding point in the middle zone towards the back should be flush with the level of the pubic bone.
(3) The most prominent point of the lateral iliac is designated as point A, the most prominent point of the lateral thigh is designated as point B, and the lateral point of the middle part of the buttocks is C. Connecting the above points, the lateral contour of the buttocks is formed. Looking at this contour from the back, the shape of the buttocks can be divided into the following four basic forms: square, garden, A-shaped (pear-shaped), V-shaped (apple-shaped), and some between the above four basic types. From the side, the presence or absence of loose hip tissue moving down to the subgluteal crease is used as a criterion to classify the two types with or without hip sagging. The buttocks without sagging can be divided into types A, B, and C. Type A is a full buttock and a clear subgluteal crease, type B is a less than full subgluteal pole area, and type C is a subgluteal crease that is not visible due to insufficient buttock augmentation. Sagging buttocks are also divided into A, B and C types according to their degree.
(4) The shape of the buttocks is divided into five categories according to the difference in the posterior protrusion ratio, combined with the presence or absence of fat accumulation on the upper and lower buttocks and the presence or absence of sagging buttocks, to guide the formulation of clinical treatment plans. type I: good posterior protrusion of the buttocks with sufficient volume, but too much fat in the upper, parietal and lower buttock areas; type II: insufficient posterior protrusion of the buttocks with a posterior protrusion ratio of less than 2:1, but too much width on both sides. The appearance of broad and relatively flat buttocks is usually due to excessive fat in the upper and lower buttocks; Type III: the lumbosacral spine is too anterior, making the sacrum tend to be horizontal, with a posterior protrusion ratio of less than 2:1 and a lack of volume in the buttocks; Type IV: an athlete-like body shape with ideal weight, lack of fat and therefore insufficient volume, and women tend to resemble male buttocks with a posterior protrusion ratio of less than 2:1; Type V. It is a type of aging hip change, characterized by atrophy and sagging of skin, fat and muscles.
(5), Bubuccu et al. investigated 115 randomly selected women (aged 17-48 years) for anthropometric and radiographic examinations and found that fat changes in the buttocks were associated with age and weight. Increasing body weight caused an increase in both height and width of the buttocks, a lengthening of the intergluteal sulcus, and a shortening of the subgluteal crease. If weight remains constant, the height of the buttocks increases with age, and the intergluteal sulcus and subgluteal crease lengthen. If both body weight and age increase, the droop in the subgluteal crease increases, while weight alone increases only the width of the buttocks, and the width increases less with age. Changes in subcutaneous fat content and laxity of the gluteal skin and fascia are thought to be associated with these changes.