A 52-year-old man is being prepared for an elective open cholecystectomy. The surgeon plans a right subcostal (Kocher) incision and wants to preserve the segmental nerve supply to the rectus abdominis as far as possible. During the approach, one small intercostal nerve branch is divided but the larger adjacent nerve in the lateral part of the wound is deliberately spared. Which nerve is typically sacrificed in this incision while the more important one is preserved?

Answer: B. The 8th intercostal branch is sacrificed and the 9th is preserved

Anterior abdominal wall: incisions and innervation

Abdominal incisions are designed to maximise access while minimising damage to the muscles and, critically, their segmental nerve supply. The lateral oblique muscles have a richly anastomosing nerve network, so cutting across them divides one or two nerves with no clinical consequence. The rectus abdominis is different: its segmental nerves (T7-T12) enter laterally and have little cross-communication, so dividing them denervates and atrophies the muscle medial to the cut.

The subcostal (Kocher) incision

• Used on the right for biliary surgery and on the left to expose the spleen.
• Skin incision begins at the midline and runs about 2.5 cm below and parallel to the costal margin.
• The small 8th intercostal branch to the rectus is sacrificed, but the larger, more important 9th nerve in the lateral wound is preserved.
• The divided rectus is held by its tendinous intersections above and below and retracts very little, healing by fibrous tissue.
• Best in patients with a wide subcostal angle; where the angle is narrow a paramedian incision is preferred.

Segmental landmarks worth knowing

• Umbilicus is supplied by T10; the groin and scrotum by L1 (ilioinguinal and iliohypogastric nerves).
• The transrectus incision splits the muscle and denervates the medial part, so it is best avoided.

Other incisions

• Midline - through the bloodless linea alba; fast access top to bottom.
• Gridiron (McBurney) - muscle-splitting for appendicectomy; muscles snap back, leaving the wall virtually undamaged.
• Pfannenstiel - curved suprapubic incision for gynaecological and pelvic surgery.