Which of the following surgical procedures is considered emergent?

A ruptured spleen is classified as an emergent surgical procedure due to the critical nature of the condition it presents. When the spleen is ruptured, there is a significant risk of internal bleeding, which can result in severe blood loss and rapid deterioration of the patient's condition. As such, it requires immediate medical intervention to stabilize the patient and address the life-threatening hemorrhage.

In contrast, a planned knee replacement is a scheduled procedure that can be postponed without immediate risk to the patient. An appendectomy, while often performed on an emergency basis if the appendix is ruptured, may also be planned in cases of non-perforated appendicitis. Gallbladder removal, like the appendectomy, can be urgent but is typically not as immediately life-threatening as a ruptured spleen. Therefore, the urgency and potential complications associated with a ruptured spleen distinctly categorize it as an emergent surgical procedure.