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.
If it is desired to expose the kidney, a straight incision 10 cm. (4 in.) long may be made between the last rib and middle of the crest of the ilium along the outer edge of the quadratus lumborum. This may sometimes necessitate cutting the last thoracic nerve near the rib and the iliohypogastric and ilioinguinal nerves near the crest. They should if possible be pulled aside, but if cut are to be stitched together again. This gives only sufficient room to bring a normal-sized kidney out of the wound; if the kidney is enlarged, Edebohls recommends prolonging the incision along the crest of the ilium. This longitudinal incision lies just back of the external oblique, traverses in its upper part the latissi-mus dorsi (the fibres of which may be parted by blunt dissection) then the lumbar fascia or anterior edge of the quadratus lumborum muscle, and lastly the transversa-lis fascia behind the peritoneum (Fig. 411).
When an incision for enlarged kidneys, tumors, or abscesses is desired, it can be made obliquely downward and forward from the twelfth rib - anterior to its middle - toward the anterior portion of the crest of the ilium. This parts the fibres of the external oblique and divides the fibres of the transversalis muscle obliquely, and those of the internal oblique almost transversely, but the nerves (twelfth thoracic and iliohypogastric) are more readily drawn aside than if the longitudinal incision is used. Care is to be taken not to go farther back than the middle of the twelfth rib, because the pleura usually crosses at that point to reach the lower edge of the rib, or even a little below it at its posterior extremity. As it is sometimes difficult to identify the twelfth rib, because it may be so short as to be hidden beneath the muscles, the most certain way is to count downward from the angle of the sternum opposite the second costal cartilage. There may be some bleeding at the lower portion of the wound from the ascending branch of the deep circumflex iliac artery near the anterior portion of the crest of the ilium.
Fig. 411. - Lumbar incisions for operations on the kidney, showing the direction of the muscular fibres.