Effects of horizontal versus vertical bolster alignment on anatomical orientation of kidney as applied to prone percutaneous nephrolithotomy

Purpose: To evaluate the anatomical changes in kidney orientation in prone position with use of horizontal or vertical bolster alignment. Methods: Patients having renal stone(s) on ultrasonogram or X-ray underwent split bolus computed-tomo-urography (CTU) in prone position with horizontal and vertical bolster positions. CTUs were read by a single radiologist to quantify the cranio-caudal, antero-posterior, side to side and rotational movements of kidneys as relevant to prone percutaneous nephrolithotomy. Results: 19 adult patients with 38 renal units and mean basal metabolic index of 25.6 kg/m² underwent CTU. Greater inferior displacement of both kidneys was seen with horizontal bolsters as compared to vertical bolsters. The right upper calyceal-diaphragm distance was 2.1 ± 1.5 cm and the lower calyceal-diaphragm distance was 2.0 ± 1.6 cm greater with the horizontal bolsters (p < 0.01). Similarly, the displacement on the left side was 1.5 ± 0.8 cm and 1.4 ± 0.8 cm, respectively (p < 0.01). Horizontal bolsters also result in significantly longer calyceal-skin distance at both poles of both kidneys [right upper: 0.4 ± 0.5 cm (p < 0.01), right lower: 0.8 ± 0.7 cm (p < 0.01), left upper: 0.4 ± 0.6 cm (p = 0.02), left lower: 0.8 ± 1.1 cm (p < 0.01)] and wider erector spinae-mid posterior calyceal-colon angle (124.8 v/s 110.0 on the right and 96.2 v/s 85.7 on the left) (p < 0.01). Conclusion: Horizontal bolsters provide significantly more caudal displacement of the kidneys; the right kidney being displaced more as compared to the left. However, there is also an increase in the skin-calyceal distance with horizontal as compared to the vertical bolsters. These assessments may help the surgeons decide optimal bolster position individualized to the patient.