What is the aim of using a retrograde urethrogram in trauma assessment?

The use of a retrograde urethrogram (RUG) in trauma assessment primarily serves to diagnose urethral injury. During trauma assessments, especially in cases involving pelvic fractures or penetrating injuries, urethral injuries are a common concern. A retrograde urethrogram employs a contrast agent injected into the urethra while imaging is performed, allowing for clear visualization of the urethra's structure and any potential abnormalities or injuries. Observing extravasation of contrast material indicates urethral disruption or injury, which is critical information for surgical planning and management of the patient.

In contrast, the other options address different clinical issues that do not directly pertain to the specific diagnostic purpose of a RUG. For instance, kidney function evaluation involves different imaging techniques such as ultrasound or CT scans, bladder capacity is assessed through different means such as cystometry, and bladder stones are typically diagnosed through imaging like ultrasound or a CT scan rather than a retrograde urethrogram. Thus, using a RUG is specifically tailored to revealing the integrity of the urethra in trauma scenarios, emphasizing its role in diagnosing urethral injuries.