Final answer:
The most likely injured structure during an ilioinguinal approach for anterior pelvic ring fixation when brisk bleeding is encountered near the superior pubic ramus is a vessel such as the obturator artery or the corona mortis.
Step-by-step explanation:
During an ilioinguinal approach for fixation of the anterior pelvic ring, brisk bleeding is encountered as the dissection is extended along the superior pubic ramus approximately 5 cm from the midline. The structure that has most likely been injured is a vessel located near the superior pubic ramus, such as a branch of the obturator artery which accompanies the obturator nerve, or less commonly, the corona mortis, which is an anastomotic vessel connecting the obturator and external iliac (or inferior epigastric) vessels.
The superior pubic ramus is a bone extending laterally from the pubic body to join with the ilium, and the area within 5 cm of the midline contains important vascular structures which can be vulnerable during surgical approaches. Given the location of bleeding described, understanding the pelvic anatomy including the relationship between bones, ligaments, and vasculature is essential in managing such surgical complications.