Analysis of McRoberts' maneuver by x-ray pelvimetry.

Abstract

To document radiographically the changes in pelvic dimensions created by McRoberts' maneuver. Women at least 37 weeks' pregnant who presented to labor and delivery were eligible for study entry. Anterior-posterior and lateral x-rays were taken with women in the dorsal lithotomy position and after application of McRoberts' maneuver, in which the maternal legs were hyperflexed 45 degrees onto the maternal abdomen. A two-tailed paired t test was used to assess the changes in the pelvic diameters, with P < .05 considered statistically significant. Thirty-six subjects were enrolled in the study and 34 x-rays were suitable for analysis. McRoberts' maneuver was associated with an increase in the mean angle of inclination between the symphysis pubis and the sacral promontory (51.53 +/- 2.03 versus 38.07 +/- 1.96 degrees, P < .001). There was a 24% decrease in the angle created by drawing a line bisecting the symphysis pubis relative to the horizontal (P < .001). With McRoberts' maneuver the angle created by a line bisecting the longitudinal axis of the fifth lumbar vertebra and the longitudinal axis of the upper sacrum also increased (133.75 +/- 2.25 to 140.14 +/- 2.12 degrees, P = .04). Ours are the first systematic observations of pelvic changes associated with McRoberts' maneuver, confirming the traditional thinking that the maneuver causes a significant cephalad rotation of the symphysis pubis and subsequent flattening of the sacrum.