This region may be subdivided into gluteal and adductor portions, and region of Scarpa's triangle.
The gluteal region is bounded above by the iliac crest, and below by the gluteal fold ; internally by the intergluteal sulcus, and externally by a line from the anterior superior spine to the tip of the great trochanter. The anterior superior spine is generally visible as a landmark, and can be easily palpated. The crest of the ilium may be obvious, or may be overhung by flesh, and terminates posteriorly in the posterior superior spine, which is frequently marked by a dimple, and is on a level with the second sacral spine, and just behind the centre of the sacroiliac articulation. The gluteal fold does not correspond to the lower border of the gluteus maximus muscle, but lies considerably above it. It extends horizontally outwards, and is most distinct when the thigh is extended, becoming obliterated when it is flexed to a right angle. Thus, in hip disease, where the limb is flexed, loss of the gluteal fold is an early sign, and, later, this symptom becomes more marked from atrophy of the muscles.
The great trochanter is an obvious landmark, although in a fat person its position may be indicated by a depression. It is covered by the fascial insertion of the gluteus maximus, and the tendon of the gluteus medius passes over its upper border. It becomes very prominent when the gluteal muscles atrophy, and on abduction of the thigh these muscles are relaxed, and thus the tip of the trochanter is more readily palpated. Normally it should occupy a position midway between the anterior superior spine and the tuber ischii, and should just touch a line drawn between these two points (Nelaton's line) when the thigh is very slightly flexed. As it is frequently of importance in suspected hip affections to test whether the head of the femur is in its position by carefully noting that of the great trochanter, another method has been devised by Bryant (Bryant's triangle). With the patient lying on his back, a vertical line is dropped from the anterior superior spine, and a second line drawn from the same point to the tip of the great trochanter. A third line, at right angles to the vertical line, is now dropped from the trochanteric tip, and this third line, which completes the triangle, is compared in length with its neighbour of the other side. A line drawn from the posterior superior spine to the tip of the trochanter indicates the interspace between the gluteus medius and the pyriformis, and the point of emergence of the gluteal artery from the pelvis is at the junction of its inner and middle one-third. A line drawn from the posterior superior spine to a point midway between the tuber ischii and great trochanter crosses the gluteal artery at the junction of its upper and middle one-third, while the junction of its middle and lower one-third indicates the point of emergence of the great sciatic nerve from the sacro-sciatic foramen. A line drawn from the posterior superior spine to the outer part of the tuber ischii crosses the posterior inferior spine 2 inches down, and the ischial spine 4 inches down. The pudic artery crosses over the ischial spine in passing from the great to the small sacro-sciatic foramen, and the sciatic artery reaches the gluteal region at the junction of the middle and lower one-third of this line.
The trochanteric fossa is the depression behind the trochanter into which the fingers can be pushed deeply normally, but which is frequently obliterated in extracapsular fracture of the neck. The tuber ischii is covered by the gluteus maxi-mus when the limb is extended, but is exposed when the limb is flexed to a right angle, and is then easily palpable.
The skin over the gluteal region is thick, and contains numerous sebaceous glands, and is a frequent seat of boils. The subcutaneous tissue is very fat, and is directly continuous with the fatty tissue which occupies the ischio-rectal fossa, and with a layer lying under the gluteus maxim us.
This layer under the gluteus maximus communicates through the sacro-sciatic foramina with the intrapelvic connective tissue, atfid that of the ischio-rectal fossa and that descending the back of the thigh along the sciatic nerve. The laxity of this tissue favours the formation of large collections of pus or blood, and lipomata are frequently found in this region. The fascia lata in this region is strong and tense. Attached above to the outer lip of the iliac crest and to the sacrum and coccyx behind, it splits in front to enclose the tensor fasciae fern oris ; and, again, lying on the gluteus medius, splits to enclose the gluteus maximus. Effusions of blood, or abscesses, occurring beneath this layer, are much circumscribed, and frequently give rise to much pain. They may travel down the thigh, or even farther, before reaching the surface, or may enter the pelvis through the sciatic foramina ; while, conversely, a pelvic abscess may find its way below the gluteus maximus, as may also pus from the hip-joint by perforation of the posterior aspect of the capsule. A thickened band of the fascia-the ilio-tibial band-into which the tensor fasciae femoris is inserted, runs from the iliac crest to the outer tuberosity of the tibia and head of the fibula. A tense portion of this band runs between the iliac crest and the great trochanter, which becomes relaxed in fractures of the neck of the femur.
The gluteus maximus is the most massive layer of muscle in the body, and is inserted below into the fascia lata overlying the great trochanter, and into the back of the femur. Its lower margin is oblique, and lies well below the gluteal fold. It has been ruptured by muscular violence. The gluteus maximus is separated from the outer surface of the great trochanter, the tuber ischii, and the outer tendinous surface of the vastus externus by bursae. The bursa over the great trochanter is occasionally affected by chronic inflammatory processes, causing the limb to be kept flexed and adducted, and when it bursts it generally gives rise to a sinus difficult to heal on account of the constant movement of the gluteus maximus, while, on the other hand, the disease may spread to the bone.