Muscles of the gluteal region consist predominantly of extensors, rotators, and abductors of the hip joint (Fig. 6.11). In addition to moving the thigh on a fixed pelvis, these muscles also control the movement of the pelvis relative to the limb bearing the body’s weight (weight-bearing or stance limb) while the other limb swings forward (swing limb) during walking.
Major flexor muscles of the hip (iliopsoas—psoas major and iliacus) do not originate in the gluteal region or the thigh. Instead, they are attached to the posterior abdominal wall and descend through the gap between the inguinal ligament and pelvic bone to attach to the proximal end of the femur (Fig. 6.12).
Muscles in the thigh and leg are separated into three compartments by layers of fascia, bones, and ligaments (Fig. 6.13).
In the thigh, there are medial (adductor), anterior (extensor), and posterior (flexor) compartments:
Most muscles in the medial compartment act mainly on the hip joint.
The large muscles (hamstrings) in the posterior compartment act on the hip (extension) and knee (flexion) because they attach to both the pelvis and bones of the leg.
Muscles in the anterior compartment (quadriceps femoris) predominantly extend the knee.
Muscles in the leg are divided into lateral (fibular), anterior, and posterior compartments:
Muscles in the lateral compartment predominantly evert the foot.
Muscles in the anterior compartment dorsiflex the foot and extend the digits.
Muscles in the posterior compartment plantarflex the foot and flex the digits; one of the muscles can also flex the knee because it attaches superiorly to the femur.
Specific muscles in each of the three compartments in the leg also provide dynamic support for the arches of the foot.
Muscles found entirely in the foot (intrinsic muscles) modify the forces produced by tendons entering the toes from the leg and provide dynamic support for the longitudinal arches of the foot when walking, particularly when levering the body forward on the stance limb just before toe-off.
Unlike in the upper limb where most structures pass between the neck and limb through a single axillary inlet, in the lower limb, there are four major entry and exit points between the lower limb and the abdomen, pelvis, and perineum (Fig. 6.14). These are: the gap between the inguinal ligament and pelvic bone, the greater sciatic foramen, the obturator canal (at the top of the obturator foramen), and the lesser sciatic foramen.
The lower limb communicates directly with the abdomen through a gap between the pelvic bone and the inguinal ligament (Fig. 6.14). Structures passing though this gap include: muscles—psoas major, iliacus, and pectineus; nerves—femoral and femoral branch of the genitofemoral nerves, and the lateral cutaneous nerve of the thigh; vessels—femoral artery and vein; and lymphatics.
This gap between the pelvic bone and the inguinal ligament is a weak area in the abdominal wall and often associated with abnormal protrusion of the abdominal cavity and contents into the thigh (femoral hernia). This type of hernia usually occurs where the lymphatic vessels pass through the gap (the femoral canal).
Structures within the pelvis communicate with the lower limb through two major apertures (Fig. 6.14).
Posteriorly, structures communicate with the gluteal region through the greater sciatic foramen and include: a muscle—piriformis; nerves—sciatic, superior and inferior gluteal, and pudendal nerves; and vessels—superior and inferior gluteal arteries and veins, and the internal pudendal artery.
The sciatic nerve is the largest peripheral nerve of the body and is the major nerve of the lower limb.