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AN44.1-7 | Anterior abdominal wall — Part 2

Part 4: The Inguinal Canal and Hernia (AN44.4, AN44.5)

The inguinal canal is an oblique passage (~4 cm long) through the lower anterior abdominal wall, running from the deep (internal) inguinal ring to the superficial (external) inguinal ring. It runs parallel to and just above the inguinal ligament.

Figure: Part 4: The Inguinal Canal and Hernia (AN44.4, AN44.5)

The inguinal canal has four walls, a roof, and a floor:

Component	Structure
Anterior wall	External oblique aponeurosis (whole length); internal oblique muscle (lateral third)
Posterior wall	Transversalis fascia (whole length); conjoint tendon (medial third)
Roof	Arching fibres of internal oblique + transversus abdominis
Floor	Upper surface of inguinal ligament; lacunar ligament (medially)

Rings:
- Deep (internal) inguinal ring: An oval defect in the transversalis fascia. Location: 1.25 cm above the midpoint of the inguinal ligament (midinguinal point). The inferior epigastric vessels lie medial to this ring — this is the key landmark distinguishing direct from indirect hernia.
- Superficial (external) inguinal ring: A triangular gap in the external oblique aponeurosis, just above and medial to the pubic tubercle.

Figure: The inguinal canal has four walls, a roof, and a floor:

Contents in the male:
1. Spermatic cord (vas deferens + testicular artery + pampiniform plexus + genital branch of genitofemoral nerve + ilioinguinal nerve + lymphatics)
2. Ilioinguinal nerve (L1) — lies outside the spermatic cord proper but passes through the canal

Contents in the female: Round ligament of the uterus (homologue of the gubernaculum)

Hesselbach's triangle (inguinal triangle):
Boundaries: Medially — lateral border of rectus abdominis; Laterally — inferior epigastric vessels; Inferiorly — medial half of inguinal ligament.
Direct hernias emerge within this triangle.

Inguinal hernias — Direct vs Indirect:

Feature	Indirect inguinal hernia	Direct inguinal hernia
Mechanism	Passes through the deep inguinal ring, through the full length of the canal, and out through the superficial ring	Pushes directly through Hesselbach's triangle (no canal traversal)
Relation to inferior epigastric vessels	Lateral (outside Hesselbach's triangle)	Medial (inside Hesselbach's triangle)
Covering	Has all three layers of spermatic cord covering (derived from transversalis fascia, internal oblique, external oblique)	Covered only by transversalis fascia and skin
Age/risk	Young men, persistent processus vaginalis, high intra-abdominal pressure	Older men, weakness of transversalis fascia/conjoint tendon
Risk of strangulation	Higher (tight ring can compress contents)	Lower (broad-based defect)
Reduction with digital pressure	Deep inguinal ring compression stops hernia reappearing	Does NOT stop it reappearing

Mnemonic: MALL — Medial = direct, Lateral = indirect (relative to inferior epigastric vessels)

Figure: Inguinal hernias — Direct vs Indirect:

Part 5: Common Abdominal Incisions (AN44.7)

Surgical incisions are designed around the muscular anatomy of the abdominal wall — their choice balances access, wound strength, nerve preservation, and healing.

Figure: Part 5: Common Abdominal Incisions (AN44.7)

1. Midline incision (laparotomy)
- Through the linea alba, from xiphisternum to pubic symphysis (or any portion)
- Advantages: avascular (linea alba), extensible, rapid, no major nerve damage
- Disadvantage: weaker wound → higher incisional hernia rate
- Uses: emergency laparotomy, exploratory surgery

2. Paramedian incision
- Vertical, 2–3 cm lateral to midline, opening the anterior rectus sheath, displacing rectus laterally, and opening the posterior sheath
- Better wound strength than midline (intact sheath reapposed over the muscle)
- Less common now (replaced by midline + adequate closure)

3. Kocher's (right subcostal) incision
- Oblique, parallel to right costal margin (~2.5 cm below it)
- Divides external oblique, internal oblique, transversus abdominis; preserves nerve supply (nerves enter from below)
- Uses: cholecystectomy (right), splenectomy (left), bilateral subcostal = "rooftop" for liver transplantation
- Note: cuts across dermatomes T7–T9 (no paralysis; dermatomal overlap preserves sensation)

4. Gridiron (McBurney's) incision
- 2.5 cm perpendicular to the line from ASIS to umbilicus at McBurney's point (1/3 of the way from ASIS)
- Split (not cut) muscles — external oblique split in line of fibres; internal oblique and transversus split perpendicular to each → no muscle is actually cut
- Uses: appendicectomy
- Self-sealing wound (muscle layers close as wall tension is restored)

5. Lanz incision
- Transverse version of the gridiron at the same point; cosmetically superior
- Uses: appendicectomy, better cosmesis (Langer's lines)

6. Pfannenstiel incision
- Low transverse, ~3 cm above pubic symphysis, within the pubic hair line
- Transverse skin + anterior rectus sheath; rectus muscles are split vertically and retracted laterally
- Virtually cosmetically invisible → standard for caesarean section, hysterectomy, bladder surgery
- Disadvantage: limited access superiorly

7. Rutherford Morison (oblique right iliac fossa) incision
- Extends from near the ASIS laterally and curves medially and downward
- Uses: renal transplant surgery

Laparoscopic port placement anatomy:
- 10 mm umbilical port: through the umbilicus (avascular, thin)
- Working ports at 5 mm: lateral to the inferior epigastric vessels (marked by transillumination or Doppler)
- Injury to the inferior epigastric artery during port insertion → port-site haematoma or catastrophic haemorrhage