Chapter 35. Gluteal Region and Hip

Big Picture

The bony component of the gluteal (buttocks) region consists of two pelvic bones (os coxae) joined anteriorly by the symphy-sis pubis and posteriorly by the sacrum. Each os coxa is composed of three fused bones: ilium, ischium, and pubis. The bones of the gluteal region contain foramina (notches), which serve as conduits for nerves and blood vessels that travel between the pelvis, gluteal region, perineum, and lower limb. Muscles of the gluteal region primarily act on the hip joint.

Actions of the Hip Joint

The hip joint is a synovial, ball-and-socket joint. The “ball” is the head of the femur, and the “socket” is the acetabulum of the pelvic bone. The motions of the hip joint are as follows (Figure 35-1A):

• Flexion. Movement anterior in the sagittal plane.
• Extension. Movement posterior in the sagittal plane.
• Abduction. Movement away from the midline in the frontal plane.
• Adduction. Movement toward the midline in the frontal plane.
• Medial rotation. Movement toward the midline in the transverse or axial plane.
• Lateral rotation. Movement away from the midline in the transverse or axial plane.
• Circumduction. A combination of hip joint motions that produces a circular motion.

Big Picture

The muscles of the gluteal region primarily act on the hip joint, producing extension, medial rotation, lateral rotation, and abduction. In addition to producing motion, the muscles of the gluteal region are important for stability of the hip joint as well as for locomotion.

Gluteal Muscles (Figure 35-1B)

• Gluteus maximus muscle. Attaches proximally on the ilium behind the posterior gluteal line, the sacrum, the coccyx, and the sacrotuberous ligament; distally, the muscle attaches at the iliotibial tract and the gluteal tuberosity of the femur. The gluteus maximus muscle is a powerful extensor of a flexed femur at the hip joint and a lateral stabilizer of the hip joint. The inferior gluteal nerve (L5, S1, S2) innervates this muscle.
• Gluteus medius muscle. Attaches proximally on the ilium between the anterior and posterior gluteal lines; distally, the muscle attaches on the greater trochanter of the femur. The gluteus medius muscle abducts and medially rotates the femur at the hip joint. In addition, the gluteus medius holds the pelvis secure over the stance leg, preventing pelvic drop on the opposite swing side during gait. The superior gluteal nerve (L4, L5, S1) innervates this muscle.
• Gluteus minimus muscle. Attaches proximally on the ilium between the anterior and posterior gluteal lines; distally, the muscle attaches on the greater trochanter of the femur. The action of the gluteus minimus muscle is the same as that of the gluteus medius—it abducts the femur at the hip joint, holding the pelvis secure over the stance leg and preventing pelvic drop on the opposite swing side during gait and hip medial rotation. The inferior gluteal nerve (L5, S1, S2) innervates this muscle.
• Tensor fascia lata muscle. Attaches more anteriorly than the other muscles of the gluteal region. The tensor fascia lata muscle attaches proximally at the lateral aspect of the iliac crest between the anterior superior iliac spine and the tubercle of the crest. Distally, the muscle attaches to the iliotibial tract of the fascia lata, which extends to the tibia. Because of its distal insertion, the tensor fascia lata muscle is unique when compared to the other gluteal muscles. The main action of this muscle is to stabilize the knee in extension and in hip flexion. The superior gluteal nerve (L4, L5, S1) innervates this muscle.

Deep Hip Rotator Muscles

The deep hip rotator muscles all have several common characteristics—they are deep to the gluteal muscles, they arise from the pelvis, they share common attachments around the greater trochanter of the femur, and they laterally rotate the hip. The deep hip rotator muscles are as follows (Figure 35-1C):

• Piriformis muscle. Attaches proximally on the anterior surface of the sacrum; distally, the muscle attaches at the greater trochanter of the femur. The piriformis muscle laterally rotates the femur at the hip joint. The nerve to the piriformis muscle (S1, S2) innervates this muscle.
• Superior gemellus muscle. Attaches proximally at the ischial spine; distally, the muscle attaches on the greater trochanter of the femur. The superior gemellus muscle laterally rotates the femur at the hip joint. The nerve to the obturator internus and superior gemellus muscles (L5, S1, S2) innervates this muscle.
• Obturator internus muscle. Attaches proximally on the deep surface of the obturator membrane and surrounding bone; distally, the muscle attaches at the greater trochanter of the femur. The obturator internus muscle laterally rotates the femur at the hip joint. The nerve to the obturator internus and superior gemellus muscles (L5, S1, S2) innervates this muscle.
• Inferior gemellus muscle. Attaches proximally on the ischial spine; distally, the muscle attaches at the greater trochanter of the femur. The inferior gemellus muscle laterally rotates the femur at the hip joint. The nerve to the inferior gemellus and quadratus femoris muscles (L4, L5, S1) innervates this muscle.
• Quadratus femoris muscle. Attaches proximally at the lateral aspect of the ischium just anterior to the ischial tuberosity; distally, the muscle attaches on the intertrochanteric crest. The quadratus femoris muscle laterally rotates the femur at the hip joint. The nerve to the inferior gemellus and quadratus femoris muscles (L4, L5, S1) innervates this muscle.

Big Picture

The lower limb is innervated by the ventral rami from nerve roots L1–S4, which form two separate networks of nerves and are referred to as the lumbar plexus (L1–L4) and the sacral plexus (L4–S4). The lumbar plexus communicates with the sacral plexus via the lumbosacral trunk (L4, L5), which descends into the pelvic cavity to contribute to the sacral plexus. Most of the sacral plexus is divided into anterior and posterior divisions. The anterior division provides the primary motor innervation to the posterior compartment of the thigh and leg. The posterior division provides the primary motor innervation to the anterior and lateral compartments of the leg.

Anterior Division of the Sacral Plexus

The anterior division of the sacral plexus consists of ventral rami from L4 to S4, which form a network and give rise to the following five nerves (Figure 35-2A):

• Pudendal nerve (S2–S4). Exits the pelvis via the greater sciatic foramen, enters the gluteal region, and courses to the perineum through the lesser sciatic foramen. The pudendal nerve provides motor innervation to the muscles of the pelvic floor and sensory innervation to the skin of the perineum, penis, and clitoris.
• Posterior femoral cutaneous nerve (S1–S3). Exits the pelvis via the greater sciatic foramen, inferior to the piriformis muscle. The posterior femoral cutaneous nerve receives half of its innervation levels (S1 and S2) from the posterior division of the sacral plexus and the other half (S2 and S3) from the anterior division. The nerve remains deep to the gluteal maximus muscle and emerges at the inferior border, providing sensory innervation to the posterior region of the thigh.
• Nerve to the superior gemellus and obturator internus muscles (L5–S2). Exits the pelvis via the greater sciatic foramen, inferior to the piriformis muscle, and provides motor innervation to the superior gemellus muscle. The nerve then reenters the pelvis, via the lesser sciatic foramen, providing motor innervation to the obturator internus muscle.
• Nerve to the inferior gemellus and quadratus femoris muscles (L4–S1). Exits the pelvis via the greater sciatic foramen, inferior to the piriformis, and travels along the deep surface of the superior gemellus muscle and the obturator internus tendon, providing innervation to the inferior gemellus and quadratus femoris muscles on their deep surface.
• Tibial nerve (L4–S3). The tibial nerve (a division of the sciatic nerve) exits the pelvis via the greater sciatic foramen to enter the gluteal region inferior to the piriformis muscle. The nerve descends along the posterior aspect of the thigh, providing motor innervation to the hamstring muscles (excluding the short head of the biceps femoris muscle) and a hamstring head of the adductor magnus muscle in the medial compartment of the thigh. The tibial nerve descends through the popliteal fossa and enters the posterior compartment of the leg, deep to the gastrocnemius and soleus muscles. It provides motor innervation to the posterior compartment of the leg as well as to the plantar muscles of the foot. Sensory branches provide cutaneous innervation to the posterolateral region of the leg and the lateral region of the foot.

Posterior Division of the Sacral Plexus

The posterior division of the sacral plexus consists of ventral rami from L4–S3, which form a network and give rise to the following six nerves:

• Perforating cutaneous nerve (S2–S3). Pierces the sacrotuberous ligament and travels to the inferior edge of the gluteus maximus muscle, providing sensory innervation to the skin over the inferior aspect of the gluteus maximus (inferior gluteal fold).
• Nerve to piriformis muscle (S1–S2). Travels directly from the plexus to the piriformis muscle, providing motor innervation without leaving the pelvic cavity.
• Posterior femoral cutaneous nerve (S1–S3). Exits the pelvis via the greater sciatic foramen, inferior to the piriformis muscle. The posterior femoral cutaneous nerve receives half of its innervation levels (S1–S2) from the posterior division of the sacral plexus and the other half (S2–S3) from the anterior division.
• Superior gluteal nerve (L4–S1). Exits the pelvis via the greater sciatic foramen and travels superior to the piriformis muscle and between the gluteus medius and minimus muscles, providing innervation to both muscles. The superior gluteal nerve continues anteriorly, providing motor innervation to the tensor fascia latae muscle.
• Inferior gluteal nerve (L5–S2). Exits the pelvis via the greater sciatic foramen and travels inferior to the piriformis, providing motor innervation to the gluteus maximus muscle.
• Common fibular (peroneal) nerve (L4–S3). Is the smallest division of the sciatic nerve (half the size of the tibial nerve). The common fibular nerve exits the pelvis via the greater sciatic foramen to enter the gluteal region inferior to the piriformis muscle. The nerve descends along the posterior aspect of the thigh, providing motor innervation to the short head of the biceps femoris muscle. The common fibular nerve descends to the popliteal fossa and curves laterally around the neck of the fibula to bifurcate into the superficial and deep fibular nerves, providing motor innervation to the lateral and anterior compartments of the leg, respectively. Furthermore, the superficial fibular nerve provides sensory innervation to the anterolateral region of the leg and the dorsum of the foot. The deep fibular nerve provides sensory innervation to a small area between digits 1 and 2. In addition, a branch from the common fibular nerve (lateral sural nerve) provides cutaneous innervation to the superior lateral leg.

Big Picture

The descending aorta bifurcates into the common iliac artery, which provides the blood supply to the lower extremities. The common iliac artery bifurcates into the internal and external iliac arteries. The external iliac artery becomes the femoral artery. The internal artery is the major blood supply to the pelvis and gluteal region.

Arteries of the Gluteal Region

• Internal iliac artery. The superior and inferior gluteal arteries branch from the internal iliac artery and travel with the superior and inferior gluteal nerves.
  • Superior gluteal artery. Travels between the lumbosacral trunk and the first sacral ramus or between the first and second sacral rami to exit the pelvis through the greater sciatic foramen. In the pelvis, the superior gluteal artery supplies blood to the obturator internus and piriformis muscles. In the gluteal region, the superior gluteal artery supplies blood to the muscles and skin in the gluteal region, including the tensor fascia latae muscle.
  • Inferior gluteal artery. The terminal branch of the internal iliac artery; travels between the first and second or the second and third sacral rami. The inferior gluteal artery supplies blood to the muscles of the gluteal region and forms anastomoses with blood vessels surrounding the hip joint.

Veins of the Gluteal Region

The veins of the gluteal region generally follow the arteries; therefore, arteries and veins have the same name, except one is an artery and one is a vein. The veins of the lower extremities generally drain into the internal and external iliac veins. Specifically, the superior and inferior gluteal veins drain into the internal iliac vein, which in turn drains into the common iliac vein and terminates in the inferior vena cava before reaching the heart. Because of its association with the femoral artery, additional vascular supply will be discussed in Chapter 36.

Big Picture

The hip joint is a synovial, ball-and-socket joint that allows for a great deal of freedom, including flexion and extension, abduction and adduction, medial and lateral rotation, and circumduction of the femur. The role of the hip joint is to provide support for the weight of the head, arms, and trunk during static postures (standing) and dynamic movements (walking and running). In addition to the hip joint, the gluteal region also contains the sacroiliac joint and the pubic symphysis, which connect the pelvic bones together as well as connecting the pelvic bones to the spine (i.e., the sacrum).

Structure of the Hip Joint

The articulating surface of the pelvic bone (os coxa) is a concave socket that is composed of three fused bones, the ilium, ischium, and pubis, called the acetabulum (Figure 35-3A). The acetabulum is horseshoe-shaped fossa. The acetabulum articulates with the head of the femur. In addition, the hip joint has a wedge-shaped fibrocartilaginous ring around the periphery of the acetabulum (acetabular labrum), which increases stability by deepening the socket and increasing the concavity of the articulating surface. The wedge shape of the acetabular labrum also assists in maintaining contact of the acetabulum with the femoral head. The medial circumflex femoral artery provides the principal blood supply to the hip.

Ligamentous Support of the Hip Joint

The following structures provide ligamentous support to the hip joint (Figure 35-3B):

• Joint capsule. Is strong and extends like a sleeve from the acetabulum to the base of the neck of the femur. The joint capsule possesses circular fibers, which form a ring around the neck of the femur, called the zona orbicularis. The capsule contains three capsular ligaments: two anterior ligaments and one posterior ligament. The ligaments of the hip primarily become taught with extension of the hip and permit little, if any, distraction between the articulating surfaces.
  • Anterior ligaments
    • Iliofemoral ligament (Y ligament, or ligament of Bigelow). A fan-shaped ligament that resembles an inverted “Y.” The iliofemoral ligament extends from the anterior iliac spine and bifurcates to attach to the intertrochanteric line of the femur.
    • Pubofemoral ligament. Attaches from the anterior aspect of the pubic ramus and extends posteriorly to attach to the anterior surface of the intertrochanteric fossa.
  • Posterior ligament
    • Ischiofemoral ligament. Attaches from the superior acetabular rim and labrum to the inner surface of the greater trochanter.
• Ligament of the head of the femur (ligamentum teres). Attaches to the head of the femur (fovea). The ligament courses deep to the transverse acetabular ligament to attach to the acetabular notch. The ligament of the head of the femur does not appear to play a major role in stability of the hip joint, but rather serves as a conduit for the secondary arterial supply to the head of the femur from the obturator artery.
• Transverse acetabular ligament. Completes the circle of the acetabular labrum by spanning the acetabular notch and forming a foramen for the passage of the ligament of the head of the femur.

Bursae

Bursae are synovial sacs filled with synovial fluid. They are found at areas in the tissue at which friction would otherwise develop. Bursae serve as small cushions because they decrease the friction between two moving structures, such as tendon and bone. The two most important bursae in the gluteal region are as follows:

• Subtendinous iliac bursa. Separates the iliacus and psoas major muscles from the anterior joint capsule.
• Trochanteric bursa. Separates the gluteus maximus muscle from the greater trochanter.

Sacroiliac Joint

The sacroiliac joint is a plane synovial joint that connects the sacrum with the bilateral pelvic bones. This joint transmits forces from the vertebral column to the pelvic bones and lower limbs. The combination of strong ligaments and the irregular shape of the articulating surfaces increases the stability of the sacroiliac joint. In some individuals this joint may be fused, and in others it will allow minimal movement.