This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
Access to the kidney is demanded for fixing it in place when movable, for the removal of calculus, for the treatment of cystic conditions, abscesses, growths, and even for the entire removal of the organ, which sometimes is greatly enlarged.
Lumbar incisions have already been discussed (see page 395). There are three things to be borne in mind, viz.: the direction of the muscular fibres and position of the muscles, the position of the nerves, and, last, the pleura. A longitudinal incision along the outer edge of the erector spinas muscle is large enough to remove a normal-sized kidney, but large kidneys or growths require an oblique incision. This latter begins 2 cm. (3/4 in.) below the last rib, at the edge of the erector spinae muscle and passes downward and forward almost or quite parallel to the twelfth rib, toward the anterior extremity of the crest of the ilium. Mayo Robson (Lancet, May 14, 1898) made an incision from the inner edge of the anterior superior spine of the ilium to the tip of the last rib. The fibres of the external oblique were then split and retracted. Then the fibres of the internal oblique and transversalis were split, and retracted in the opposite direction. For this method it is claimed that no muscles, nerves, or vessels are divided, and the patient can be operated on while lying on the back. (Consult the Lumbar Muscles, page 392; Fascia, page 393; and Incisions, page 395).
The nerves to be avoided in making lumbar incisions are the last thoracic, the iliohypogastric, and the ilio-inguinal. The last thoracic nerve, accompanied by the first lumbar artery, runs parallel to the last rib a short distance below - 1.25 cm. (1/2 in.) - and thence pursues a direct course toward a midpoint between the umbilicus and top of the pubes. It emerges from beneath the external arcuate ligament about the middle of the kidney, crossing the quadratus lumborum, pierces the tendon of the transversalis muscle and runs between it and the internal oblique to pierce the sheath of the rectus and be distributed to the skin midway between the umbilicus and top of pubes and supply the pyramidalis muscle. This portion of the nerve will be injured only if the incision is carried up to the twelfth rib. When it is about opposite the tip of the eleventh rib it gives off a lateral (or iliac) branch which goes downward and slightly forward to pierce the internal and external oblique muscles above the crest of the ilium, about 5 cm. (2 in.) posterior to the anterior superior spine. This branch will be cut in making the incision, - but it is only a sensory nerve, not a motor.
The iliohypogastric and ilio-inguinal nerves, from the first lumbar, come out together from beneath the psoas muscle opposite the lower third of the kidney, cross the quadratus lumborum, and pass downward and forward toward the crest of the ilium a little in front of its middle. The iliohypogastric is above the ilio-inguinal, and, piercing the transversalis muscle, divides into the hypogastric and iliac branches. The former pierces the external oblique 2.5 cm. (1 in.) above and a little to the outer side of the external inguinal ring. The latter goes over the crest of the ilium to the gluteal region. The ilio-inguinal pierces the transversalis and enters the inguinal canal to go to the genitals and anterior inner portion of the thigh.
These nerves will probably be seen in making the longitudinal incision, toward its upper portion, - they should be pulled aside. In the oblique incision they will be posterior and not visible.