Gluteal Compartment Anatomy
The gluteal region or buttock forms part of the root of the limb. It overlies the dorsum of the ilium, ischium and
sacrum and is continuous proximally with the lower trunk and distally with the
posterior compartment of the thigh. Three substantial muscles (gluteus maximus,
medius and minimus), covered by deep fascia and a thick layer of subcutaneous
fat, form the bulk of the buttock and account
for its surface contour. The gluteal fold, a prominent surface feature, lies at
the junction of the buttock and thigh.
Gluteus maximus
This very large trapezoidal muscle is the most superficial in the
buttock. Its fibres slope downwards and laterally (Fig.
6.28) and its lower edge passes obliquely across the gluteal fold. Some of the
sensory nerves to the skin of the buttock penetrate the medial part of the
muscle, while others emerge around its upper and lower borders. Proximally, the
muscle has an extensive attachment: to the ilium behind the posterior gluteal
line, to the lower part of the sacrum, to the coccyx, to the sacrotuberous
ligament and to the thoracolumbar (lumbar) and gluteal fasciae. A synovial bursa
is usually present where it crosses the ischial tuberosity. Distally, some of
the deeper fibres are attached to the gluteal tuberosity of the femur (Fig.
6.29), but most of the muscle is attached through the iliotibial tract (Fig. 6.30) to the anterior surface of the lateral tibial
condyle. The nerve supply is from the inferior gluteal nerve (L5, S1 & S2).
Gluteus maximus is a strong extensor of the thigh, especially during
running and climbing, and also produces abduction at the hip joint. As an
antigravity muscle, it extends the trunk on the hip, and through the iliotibial
tract, it extends and stabilizes the knee joint and the supporting limb during
walking and standing.
This small muscle is attached proximally to the ilium between the
anterior superior iliac spine and iliac tubercle (Fig.
6.31) and distally to the anterior border of the iliotibial tract (Fig.
6.30), which it tenses. It is supplied by the superior gluteal nerve.
Structures deep to gluteus maximus
The arrangement of these structures is clarified by noting whether they
enter the buttock above or below the piriformis muscle (Fig. 6.29), which
itself enters via the greater sciatic foramen (Fig. 6.36).
The superior gluteal nerve (L4, L5 & S1) arises within the pelvis
from the lumbosacral plexus and enters the buttock through the greater sciatic
foramen (Fig. 6.36), running laterally between gluteus medius and gluteus
minimus (Fig. 6.32). It supplies both muscles and
terminates in tensor fasciae latae.
The superior gluteal artery arises from the posterior aspect of the
internal iliac artery. It enters the buttock accompanying the corresponding nerve and
divides into a superficial branch, which supplies the overlying gluteus maximus
(Fig. 6.29) and two deep branches, an upper and lower, which supply gluteus
medius and minimus (Fig. 6.32). The deep branches also
contribute to anastomoses around the greater trochanter and anterior superior
iliac spine. The accompanying veins form an extensive plexus between the
muscles and drain into the internal iliac vein.
These fanshaped muscles lie superior to piriformis. Gluteus medius (Fig.
6.29) is attached proximally to the dorsum of the ilium between the posterior
and anterior (middle) gluteal lines and to the gluteal fascia, which separates
it from gluteus maximus. Distally, it is attached to the lateral surface of the
greater trochanter. Gluteus minimus lies immediately deep to gluteus medius and
attaches proximally to the dorsum of the ilium between the anterior and
inferior gluteal lines (Fig. 6.31) and distally to the anterior surface of the
greater trochanter (Fig. 6.32). Both are supplied by
the superior gluteal nerve.
Although both gluteus medius and minimus medially rotate the femur at the
hip joint, their importance is in abduction. During walking, gluteus medius and
minimus of the supporting limb contract, pulling on the pelvis from their
femoral attachments to prevent tilting of the pelvis towards the unsupported
side. Failure of this mechanism is the basis of Trendelenburg’s sign of hip
instability with a dipping gait. It may result from a defective acetabulum (usually
congenital) or loss of function in these muscles.
Structures entering below piriformis
These are: three nerves laterally, the sciatic nerve, nerve to quad
ratus femoris and posterior cutaneous nerve of thigh; medially the internal
pudendal artery, pudendal nerve and nerve to obturator internus; and in
intermediate position, the inferior gluteal nerve and vessels.
The sciatic nerve (Fig. 6.33), the largest nerve in the lower limb,
arises from the spinal nerves L4, L5, S1, S2 and S3 and supplies the entire
limb, except for the gluteal structures and the medial and anterior
compartments of the thigh. It leaves the greater sciatic foramen about halfway
between the posterior superior iliac spine and ischial tuberosity and curves
laterally and downwards, crossing the midpoint between the ischial tuberosity
and greater trochanter. Its location must be remembered to avoid damaging the
nerve when making intramuscular injections into the buttock. The nerve is
separated from the capsule of the hip joint by obtura tor internus and the
gemelli, quadratus femoris and the upper border of adductor magnus (Fig. 6.33).
A branch of the inferior gluteal artery accompanies the nerve.
The nerve to quadratus femoris
(L4, L5 & S1) lies deep to the sciatic nerve, obturator internus and the
gemelli and supplies the inferior gemellus, quadratus femoris and the hip
joint.
Superficial and medial to the sciatic nerve is the posterior cutaneous
nerve of the thigh (Fig. 6.33), which arises from
spinal nerves S1, S2 and S3. Within the buttock, its perineal branch runs
forwards to supply the skin on the posterior part of the scrotum or labium
majus. Other branches curl round the lower border of gluteus maximus to supply
the skin over the buttock.
The inferior gluteal nerve and vessels occupy an intermediate position.
The nerve turns immediately posteriorly to supply gluteus maximus.
The inferior gluteal artery, a branch of the internal iliac artery,
accompanies the nerve and supplies gluteus maximus (Fig. 6.29) and the short
lateral rotators of the hip joint and contributes to the trochanteric and cruciate
anastomoses. Venae comitantes accompany the artery and drain into the internal
iliac system.
The pudendal nerve (S2, S3 & S4), internal pudendal vessels, and nerve to obturator internus (L5,
S1 & S2), also supplying the superior gemellus, enter beneath the medial
part of piriformis (Fig. 6.33). Their course in the
buttock is brief before turning for wards into the lesser sciatic foramen,
crossing the sacrospinous ligament or ischial spine to enter the pudendal canal
(Fig. 6.36 and p. 243).
 |
Fig. 6.32 Reflection of gluteus medius reveals gluteus minimus
and the superior gluteal artery and nerve entering the buttock above
piriformis.
Short muscles of the buttock
The short muscles of the buttock are, from above downwards, piriformis,
obturator internus with the gemelli, and quadratus femoris (Fig.
6.33). Piriformis arises from the ventral surface of the sacrum (p.
235) and runs
laterally through the
greater sciatic foramen to
converge on the medial border of the greater trochanter. It is innervated
within the pelvis by spinal nerves L5, S1 and S2. Obturator internus attaches
to the lateral wall of the pelvic cavity (Fig. 6.72), including the obturator
membrane, and runs backwards towards the lesser sciatic foramen, where its
tendon makes a rightangled turn to run laterally across the buttock to the
medial aspect of the greater trochanter above the trochanteric fossa. The
superior and inferior gemelli are small muscles arising from the upper and
lower margins of the lesser sciatic notch to fuse with the obturator internus
tendon.
Quadratus femoris attaches to the lateral margin of the ischial
tuberosity and to the quadrate tubercle of the femur and the subjacent shaft.
Being behind the hip joint, all the short muscles later ally rotate the hip.
 |
Fig. 6.33 Structures emerging below piriformis
and the course and relations of the sciatic nerve.
Cruciate arterial anastomosis
The cruciate anastomosis lies at the lower border of quadratus femoris
and receives contributions from above, the inferior gluteal artery; below, the
first perforating artery; and on each side, the medial and lateral circumflex
femoral arteries.
