Anatomy: Gateways to the Lower Limb and Muscles of the Pelvic Girdle

Gateways to the Lower Limb

• There are four major routes by which structures pass from the abdomen and pelvis into and out of the lower limb.
• The greater sciatic foramen is a posterior gate for the passage of the sciatic nerve.
• The inguinal gate is an anterior gate for the passage of the femoral vein, artery, and nerve.

Muscles of the Pelvic Girdle

• The gluteus maximus muscle originates from the ilium and sacrum, and inserts into the gluteal tuberosity of the femur.
• It is innervated by the gluteal nerve and acts to externally rotate the lower limb.

Muscles of the Thigh

• The quadriceps femoris muscle has four separate heads: rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis.
• It originates mainly from the femur and inserts into the tibial tuberosity.
• It is innervated by the femoral nerve and acts to extend the knee.

Muscles of the Posterior Compartment of the Thigh

• The hamstring muscles consist of three muscles: biceps femoris, semitendinosus, and semimembranosus.
• They have a common origin from the ischial tuberosity and insert into the upper end of the fibula and tibia.
• They are innervated by the sciatic nerve and act to flex the knee.

Muscles of the Anterior Compartment of the Leg

• The tibialis anterior muscle originates from the tibia and inserts into the first metatarsal bones of the foot.
• It is innervated by a branch of the sciatic nerve and acts to dorsiflex the foot.

Muscles of the Posterior Compartment of the Leg

• The gastrocnemius muscle originates from the femur and inserts into the calcaneus via the tendo calcaneus (Achilles tendon).
• It is innervated by a branch of the sciatic nerve and acts to plantar flex the foot.
• The soleus muscle originates from the fibula and tibia and inserts into the calcaneus via the tendo calcaneus (Achilles tendon).
• It is innervated by a branch of the sciatic nerve and acts to plantar flex the foot.

Muscles of the Anterior Abdominal Wall

• The muscles of the anterior abdominal wall consist of four muscles on each side: external oblique, internal oblique, transverse abdominal, and rectus abdominis.
• They originate from the side of the abdomen and insert into the linea alba in the midline.
• The rectus abdominis muscle is surrounded by the rectus sheath formed by the aponeurosis of the other three muscles.

Inguinal Ligament

• The inguinal ligament is formed by the lower boundary of the external abdominal oblique aponeurosis.

Nerve Plexuses

• The brachial plexus originates from C5-8 and T1, and mainly supplies the upper limb.
• The lumbosacral plexus originates from L1-5, S1-5, and Coc.1, and mainly supplies the lower limb.

Carpal Tunnel Syndrome

• Carpal tunnel syndrome results from increased pressure inside the tunnel compressing structures affecting the median nerve.

Joints of the Upper Limb

• The shoulder joint is an articulation of the humerus head with the glenoid cavity of the scapula.
• The elbow joint is an articulation of the humerus with the ulna and radius.
• The wrist joint is an articulation of the radius and triangular articular disc with the carpal bones.

Pelvic Girdle

• The pelvic girdle consists of one bone on each side, called the hip bone.
• It forms the pelvic cavity with the sacrum posteriorly.
• The acetabulum is a socket for articulation with the head of the femur, forming the hip joint.

Iliac Crest and Ischial Spine

• The iliac crest has a large amount of red bone marrow, and is used in bone marrow transplantation.
• The top of the iliac crests marks the level of the fourth lumbar vertebral body (L4).
• The ischial spine is a landmark for the plane of the obstetric outlet (plane of least pelvic dimensions).