Objective: To assess whether horizontal vs vertical bolster orientation affects kidney position during prone percutaneous nephrolithotomy as this could impact the need for supracostal access and therefore the likelihood of pleural injury.

Materials and methods: In a prospective trial, 10 subjects with 20 renal units underwent magnetic resonance imaging in prone position with standard cylindrical bolsters oriented vertically and then horizontally. Vertical bolsters were placed along the lateral aspect of the chest. Horizontal bolsters were placed at the xiphoid and symphysis pubis. The position of the kidney relative to the pleura was assessed by measuring distances from the kidney upper pole to diaphragm, to the top of the first lumbar vertebra, and inferior-most rib. Nephrostomy tract length and tract proximity to adjacent organs were also measured.

Results: Right and left kidney-to-diaphragm distance significantly increased with horizontal vs vertical bolsters by 3.44 cm and 1.86 cm, respectively (P = .02, P = .01). Right kidney-to-rib distance significantly increased by 2.4 cm (P = .025); left kidney-to-rib distance increased by 0.5 cm (P = .123). Right kidney-to-vertebral distance significantly increased by 2.16 cm (P = .007); left kidney-to-vertebral distance increased by 0.9 cm (P = .059). There was no significant difference in maximum access angle, overall tract length, or colon position between horizontal and vertical bolsters.

Conclusion: Orienting bolsters horizontally results in caudal kidney displacement without affecting access angle, overall tract length, or colon position. In comparison with vertical orientation, this may improve safety of percutaneous nephrolithotomy by decreasing the need for supracostal access and increasing the safety of supracostal access when required.