Lower Limb Anatomy Set 2

The sciatic nerve is the largest nerve in the
body. It is so large that it receives its own blood
supply from the inferior gluteal artery. It runs
inferolaterally under cover of the gluteus maximus, midway between the greater trochanter
and the ischial tuberosity. The sciatic nerve is
really two nerves, the tibial and common fibular

The superior cluneal nerves are dorsal
rami of L1–L3 and the middle cluneal nerves
are dorsal rami of S1–S3. The sciatic, pudendal, posterior cutaneous nerve of the thigh,
and the gluteal nerves are all ventral primary
rami

The adductor canal (Hunter’s canal) is
approximately 15 cm long and is a narrow fascial tunnel in the thigh running from the apex
of the femoral triangle to the adductor hiatus in
the tendon of the adductor magnus. Located
deep or posterior to the middle third of the sartorius, the adductor canal provides an intermuscular passage through which the femoral
vessels pass to reach the popliteal fossa. The
contents of the adductor canal include the
femoral vessels, saphenous nerve, and nerve to
the vastus medialis

The medial compartment of the femoral
sheath is the femoral canal. It extends distally to
the level of the proximal edge of the saphenous
opening. It allows the femoral vein to expand
when venous return from the lower limb is increased. It contains loose connective tissue, fat,
a few lymphatic vessels, and sometimes a deep
inguinal lymph node (Cloquet’s node)

The femoral ring is closed at the proximal end by extraperitoneal fatty tissue, which
forms the femoral septum. The boundaries of
the femoral ring include the partition between
the femoral canal and the femoral vein laterally.
Posteriorly, the superior ramus of the pubis is
covered by the pectineus muscle. Its medial
boundary is the lacunar ligament; anteriorly,
the boundary is the medial part of the inguinal
ligament

The long head of the biceps femoris is
innervated by the tibial division of the sciatic
nerve and the short head of the biceps is innervated by the fibular division of the sciatic nerve

The internal pudendal artery leaves the
gluteal region immediately by crossing the ischial spine and re-entering the pelvis through
the lesser sciatic foramen. The artery passes to
the perineum with the pudendal nerve and
supplies the external genitalia and muscles in
the pelvic region. It does not supply any structures in the gluteal region

The medial circumflex femoral artery is
especially important because it supplies most
of the blood to the head and neck of the femur

The obturator internus and the superior
and inferior gemelli form a tricipital (threeheaded) muscle that is sometimes called the
triceps coxae

The floor of the popliteal fossa is formed by
the popliteal surface of the femur, the oblique
popliteal ligament, and the popliteal fascia over
the popliteus

The greater sciatic foramen is the passageway for structures entering or leaving the pelvis, whereas the lesser sciatic foramen is the
passageway for structures entering or leaving
the perineum. The greater sciatic foramen is the
opening for all lower limb arteries and nerves
leaving the pelvis and entering the gluteal
region

The gluteus maximus is used when rising
from the sitting position or straightening from
the bending position. It is used in climbing
steps and running. It also assists in making the
knee stable. It is used very little during casual
walking and when one is standing motionless

The greater sciatic foramen is the passageway for the sciatic nerve, piriformis muscle,
and gluteal vessels. The pudendal nerve
enters the perineum through the lesser sciatic
foramen

The deep artery of the thigh is the largest
branch of the femoral artery and the chief artery
of the thigh. It arises in the femoral triangle from
the lateral side of the femoral artery

A line drawn from the anterior superior
iliac spine to the ischial tuberosity (Nélaton’s
line), passing over the lateral aspect of the hip
region, normally passes over or near the top of
the greater trochanter

The femoral artery is the chief artery of the
lower limb and is the continuation of the external iliac artery. It bisects the femoral triangle at
its apex and enters the adductor canal deep to
the sartorius muscle

The three muscles in the posterior aspect
of the thigh are the hamstrings, which include
the semitendinosus, semimembranosus, and
biceps femoris

) The biceps femoris forms the superolateral border and the semimembranosus muscle
forms the superomedial border. The medial and
lateral heads of the gastrocnemius form the
inferolateral and inferomedial borders. The
contents of the fossa include the small saphenous vein, popliteal arteries and veins, and tibial and common fibular nerves

The inferior clunial nerves are gluteal
branches of the posterior cutaneous nerve of
the thigh, a derivative of the sacral plexus (ventral rami S1 through S3). These nerves curl
around the inferior border of the gluteus maximus and supply the inferior half of the buttock

The hamstring muscles arise from the ischial tuberosity and are innervated by the tibial division of the sciatic nerve. The short
head of the biceps does not meet these criteria. The hamstrings are extensors of the thigh
and flexors of the leg. A person with paralyzed
hamstrings tends to fall forward because the
gluteus maximus muscles cannot maintain the
necessary muscle tone to stand straight

The ischial bursa separates the inferior
part of the gluteus maximus from the ischial
tuberosity, which is often absent

A pain in the buttock may result from compression of the sciatic nerve by the piriformis
muscle (piriformis syndrome)

The gluteus maximus, piriformis, obturator internus and externus, and superior and
inferior gemelli are all lateral rotators of the
thigh. Both the gluteus medius and the gluteus minimus are medial rotators of the thigh

The gluteus medius and minimus have the
same actions and nerve supply and are supplied by the superior gluteal arteries. Both muscles abduct the thigh and rotate it medially.
They play an essential role during locomotion
and are largely responsible for preventing sagging of the unsupported side of the pelvis during walking

When the weight is on both feet, the pelvis
is evenly supported and does not sag. When the
weight is borne by one foot, the muscles on the
same side hold the pelvis so the pelvis will not
sag on the side of the raised foot. When the gluteus medius and minimus (abductors of the
thigh) are inactive owing to injury of the superior gluteal nerve, the supporting and steadying action of these muscles is lost and the pelvis falls on the side of the raised limb. This is
referred to as a positive Trendelenburg sign