UROGENITAL TRAUMA

Three-dimensional analysis of pelvic volume in an unstable pelvic fracture
Stover MD, Summers HD, Ghanayem AJ, Wilber JH
Department of Orthopaedic Surgery, Loyola University Medical Center, Maywood, Illinois, USA
J Trauma. 2006; 61: 905-8

• Background: A model was developed to predict changes in pelvic volume associated with increasing pubic diastasis in unstable pelvic fractures.
• Methods: Intact and postfracture pelvic volumes were calculated in 10 cadavers using computerized axial tomography (CT). The true pelvis was assumed to be either a sphere, a cylinder, or a hemi-elliptical sphere. Using the appropriate equations for calculating the volume of each of these shapes, pelvic volume was predicted and then compared with the measured values.
• Results: The observed volume changes associated with increasing pubic diastasis were much smaller than previously reported. The mean difference between the measured and predicted volume was 20.0 +/- 9.9% for the sphere, 10.7 +/- 6.5% for the cylinder, and 4.5 +/- 5.9% for the hemi-elliptical sphere. The differences between these means were statistically significant (p < 0.001).
• Conclusions: This data suggests that the hemi-elliptical sphere best describes the geometric shape of the true pelvis and better predicts quantitative changes in pelvic volume relative to an increasing pubic diastasis as the radius has little effect on the change in volume. Due to the small changes in volume observed with increasing diastasis, factors other than the absolute change in volume must account for the clinically observed effects of emergent pelvic stabilization.
  
  
• Editorial Comment
  This article is a complement to the above article on pelvic fracture. Reducing the absolute pelvic volume by pelvic reduction and stabilization is critical to helping venous bleeders to tamponade. Traditionally, the true pelvis is thought to be a sphere in shape, where an increase in pubis diastasis results in a marked volume increase, proportional to the radius cubed. They contend from their cadaveric experiments that the true pelvis is actually a hemi-elliptical sphere. Therefore, pelvic rind disruptions only increase the volume by the radius squared. This study suggests that reduction and stabilization of the pelvic ring disruption is more important then the reduction in volume.

Dr. Steven B. Brandes
Associate Professor, Division of Urologic Surgery
Washington University in St. Louis
St. Louis, Missouri, USA
E-mail: brandess@wustl.edu