Renal Displacement with Supine to Prone Positional Change: Effect of Sex and Body Mass Index

Objective: To determine patterns of kidney and retroperitoneal organ movement during positional change between the supine and prone positions as seen on CT scans. Methods: Axial CT scans of 75 subjects who underwent supine and prone positions were retrospectively analyzed. A total of 1650 measurements were taken for anterior/posterior, medial/lateral, cranial/caudal, skin-to-calix distance, kidney-to-liver distance, and kidney-to-colon distance in both positions. Results: Pronation shortens the distance from the skin to renal calix for both the right (99.62 mm vs 85.14 mm; p < 0.00001) and left (96.67 mm vs 90.80 mm; p < 0.00001) sides. The reduction in left-side tract length for obese patients is significantly greater than that of normal weight patients (11.88 mm vs −5.02 mm; p = 0.001). The left kidney displaces ventrally (11.12 mm vs 18.59 mm; p < 0.00001), while the right kidney does not (14.26 mm vs 15.30 mm; p = 0.30). The right kidney displaces cranially (62.76 mm vs 79.51 mm; p < 0.00001), while the left kidney does not (64.35 mm vs 66.52 mm; p = 0.14). The left kidney in females moves medially, while no change is seen in males (4.22 mm vs −0.48 mm; p = 0.0004). The left kidney in females displaces toward the descending colon, while it moves farther away in males (2.73 mm vs −2.01 mm; p = 0.011). Conclusions: Both sex and body mass index had effects on the movement of the kidneys upon pronation. The differences can be clinically useful to help pre- and intraoperative planning.