Conjoint Tendon (Inguinal Falx / Falx Inguinalis)

Formation

• Internal oblique (IO) muscle
• Transversus abdominis (TA) muscle

Important note: According to Sabiston Textbook of Surgery, a true fused conjoint tendon is actually present in only about 5% of patients. In most people, the IO and TA aponeuroses remain separate or are only loosely approximated. The term is used loosely in clinical and surgical contexts.

Insertion

• Pubic crest and pectineal line of the pubis

Location / Relations

• Lies medially in the groin
• Sits posterior to the superficial (external) inguinal ring, reinforcing it from behind
• The arching fibers of the IO and TA form the roof of the inguinal canal, converging medially as they descend to become the conjoint tendon

Role in Inguinal Canal Walls

Clinical Significance

1. Direct inguinal hernia: Occurs through Hesselbach's triangle, medial to the inferior epigastric vessels. Weakness or thinning of the posterior wall (where the conjoint tendon should reinforce) predisposes to this hernia type.
2. Hernia repair: In open inguinal hernia repair (e.g., Bassini, Shouldice), the conjoint tendon (or the IO-TA aponeurotic arch) is sutured to the inguinal or Cooper's ligament to reconstruct the posterior inguinal wall.
3. Shoulder surgery: The term "conjoint tendon" is also used in the shoulder for the combined tendon of coracobrachialis and the short head of biceps brachii, which arise together from the coracoid process - this is a completely different structure relevant in deltopectoral approaches.

Also Called

• Inguinal falx
• Falx inguinalis
• (In surgery texts) - the "triple layer" of IO + TA + cremasteric fascia

• Gray's Anatomy for Students, p. 354
• Sabiston Textbook of Surgery, p. 1680

Transversalis Fascia (Endoabdominal Fascia)

Definition

According to Mulholland & Greenfield's Surgery, it is "perhaps the most commonly misunderstood structure in the literature devoted to groin hernia," because different surgeons may be referring to very different structures when they use the term.

Layers - Is it One or Two?

• Most authors: a single layer
• Others: two laminae (the bilaminar view)
  • Anterior lamina: more uniform; adherent to the deep surface of the transversus abdominis and rectus abdominis
  • Posterior lamina: variable in density; interspersed with adipose tissue; lies within the preperitoneal space (between peritoneum and the anterior lamina); the inferior epigastric vessels run within this layer

Role in the Inguinal Region

Derivatives / Analogs

1. Iliopubic tract - the thickened band of transversalis fascia at the zone of transition between iliacus and transversus abdominis; runs parallel to (but posterior to) the inguinal ligament; extends from the iliac crest to the pubic tubercle. Critical landmark in laparoscopic hernia repair - nerves of the lumbar plexus run below it, so tacks/staples must not be placed inferior to it.
2. Iliopectineal arch - condenses where it overlies the iliopsoas; separates the vascular compartment (femoral vessels) from the neuromuscular compartment (iliopsoas, femoral nerve, lateral femoral cutaneous nerve). Contributes to the femoral sheath.
3. Crura of the deep inguinal ring - the superior and inferior crura form a transversalis fascia sling shaped like a "monk's hood" around the deep inguinal ring. When the transversus abdominis contracts, the crura are pulled upward and laterally, producing a valvular action that actively prevents indirect herniation.

Clinical Significance

• Hernia formation: All groin hernias ultimately represent failure of the transversalis fascia. Direct hernias arise through a weakened posterior wall; indirect hernias pass through the deep inguinal ring.
• Bassini / Shouldice repair: Both operations rely on tightening the internal ring and suturing the transversalis fascia (together with the transversus abdominis aponeurosis) to the inguinal ligament as the primary repair step.
• Laparoscopic hernia repair (TEP/TAPP): The surgeon works in the preperitoneal space, posterior to the transversalis fascia, making a thorough understanding of its layers and derivatives essential for safe dissection.
• Robustness: It tends to be thicker and stronger in the lower abdomen (inguinal region) compared to elsewhere.

• Mulholland & Greenfield's Surgery, p. 3647-3650
• Sabiston Textbook of Surgery, p. 1680
• Gray's Anatomy for Students, p. 352

Diagram 1 - Bassini's Original Inguinal Canal Anatomy (Bailey & Love's Surgery)

• A - Subcutaneous fat (skin edges)
• B - External oblique aponeurosis (opened and retracted)
• C - Inferior epigastric vessels
• D - Poupart's (inguinal) ligament
• E - Spermatic cord (retracted)
• F - Conjoint tendon (the red/salmon-coloured muscle layer = triple layer of internal oblique + transversus abdominis + cremasteric fascia)
• G - Transversalis fascia (the white shiny layer forming the posterior wall, visible below the conjoint tendon)

Diagram 2 - Sabiston's 3D Inguinal Region

• Yellow arrow - Transversus abdominis muscle / posterior wall (transversalis fascia)
• Blue arrow - Conjoint tendon inserting medially at the pubic crest

How they relate in these images:

• Bailey & Love's Short Practice of Surgery, Fig. 64.14, p. 1089
• Sabiston Textbook of Surgery, Fig. 82.9, p. 1683