Inguinal ligament

The inguinal ligament (a.k.a. the Poupart's ligament) is a thickened fibrous band formed by the rolled inferior border of the external oblique aponeurosis. It extends from the anterior superior iliac spine (ASIS) to the pubic tubercle and represents an important anatomical landmark at the junction between the anterior abdominal wall and the thigh.

The external oblique muscle arises from the outer surfaces of the lower eight ribs, and its fibres run inferomedially before becoming aponeurotic anteriorly. Inferiorly, the aponeurotic fibres fold inward upon themselves to form the inguinal ligament. The ligament is continuous Inferiorly with the fascia lata of the thigh, contributing to its characteristic inferior convexity.

Inguinal canal - anterior wall and floor

Due to its inward folding, the superior surface of the inguinal ligament is grooved and forms the floor of the inguinal canal. The anterior wall of the canal is formed primarily by the external oblique aponeurosis. The inguinal canal transmits the spermatic cord in males and the round ligament of the uterus in females, together with the ilioinguinal nerve.

Structures passing deep to the inguinal ligament

The inguinal ligament forms an important boundary between the abdomen and lower limb and bridges major neurovascular and muscular structures passing from the pelvis into the thigh. From lateral to medial, the principal structures passing deep to the inguinal ligament are: lateral femoral cutaneous nerve, femoral nerve, femoral artery, femoral vein, femoral canal containing deep inguinal lymphatics, and the iliopsoas and pectineus muscles.

Mid-inguinal point and midpoint of the inguinal ligament

The mid-inguinal point is located midway between the ASIS and the pubic symphysis. This landmark is clinically important because the external iliac artery becomes the femoral artery deep to this point, and the femoral pulse can be palpated immediately inferior to it.

The midpoint of the inguinal ligament, sometimes referred to as the middle inguinal point, lies midway between the ASIS and the pubic tubercle and is therefore slightly lateral to the midinguinal point. The deep inguinal ring lies superior to this midpoint.

Inguinal canal - roof and posterior wall

Superiorly, the inguinal ligament gives attachment to the internal oblique muscle along its lateral two-thirds and to the transversus abdominis muscle along its lateral third. Fibres of these muscles arch superior to the inguinal canal to form its roof and contribute to the medial part of the posterior wall, reinforcing the canal against increases in intra-abdominal pressure.

Medial extensions of the inguinal ligament

Medially, the inguinal ligament gives rise to several important fibrous extensions:

• Lacunar ligament: A posteriorly reflected extension of the medial end of the inguinal ligament that attaches to the pectin pubis.

• Pectineal ligament (Cooper's ligament): A strong fibrous band formed by the lateral continuation of the lacunal ligament along the pectineal line of the pubis.

• Reflected inguinal ligament (Colles ligament): Fibres arising from the inguinal ligament and the inferior crus of the superficial inguinal ring that pass superomedially behind the spermatic cord (or round ligament of the uterus) to interlace with fibres from the opposite side near the linea alba.

Clinical correlates

The inguinal ligament is an important diagnostic and surgical landmark in the assessment of groin hernias. It forms the inferior boundary of the Hesselbach triangle and helps distinguish inguinal from femoral hernias. Inguinal hernias occur superior to the ligament, whereas femoral hernias protrude inferior to it through the femoral ring.

Direct inguinal hernias protrude through the Hesselbach triangle medial to the inferior epigastric vessels, while indirect inguinal hernias enter the deep inguinal ring lateral to the inferior epigastric vessels and may traverse the entire inguinal canal before emerging through the superficial inguinal ring.

The inguinal and lacunar ligaments also contribute to the boundaries of the femoral ring, and weakness in this region predisposes to femoral hernias.