Two-thirds of the way along a line from the umbilicus to the right anterior superior iliac spine
Mnemonic
“Two thirds of the way from the umbilicus to the right anterior superior iliac spine”, about one third of the way along from the spine.
Tenderness here is the classic sign of appendicitis, and the point marks the base of the appendix, which is constant even though the tip is not.
The related eponyms:
- Rovsing’s sign - pressing the left iliac fossa hurts in the right
- Psoas sign - pain on extending the right hip, suggesting a retrocaecal appendix
- Obturator sign - pain on internal rotation of the flexed hip, suggesting a pelvic appendix
- Blumberg’s sign - rebound tenderness
The appendix base is fixed but the tip is not, lying retrocaecal in about 65 per cent and pelvic in about 30 per cent, which is why the presentation varies so widely and why a normal examination does not exclude it.
Expansion
McBurney’s point lies at the junction of the lateral third and medial two-thirds of a line drawn from the umbilicus to the right anterior superior iliac spine, that is, about 2 to 3 cm from the spine.
It marks the base of the appendix, where the three taeniae coli converge on the caecum. That base is anatomically constant, even though the tip may lie retrocaecal, pelvic, subcaecal or preileal.
The classical sequence of appendicitis follows the innervation: early periumbilical pain from visceral afferents of the midgut (T10), then localised right iliac fossa pain once the inflamed appendix irritates the parietal peritoneum, which is somatically innervated.
A gridiron (McBurney) incision is made at right angles to that line, splitting each muscle layer along its own fibre direction.