Which symptom is most critical for diagnosing peritonitis or bowel perforation?

Rigidity is a critical symptom when diagnosing peritonitis or bowel perforation because it indicates significant inflammation in the abdominal cavity. In peritonitis, the irritation of the peritoneum (the lining of the abdominal cavity) often results in muscle guarding and rigidity as a protective response. This involuntary contraction of the abdominal muscles is a sign that the body is reacting to the underlying pathology, which may include infection, perforation, or other serious conditions.

While guarding is also an important symptom, it can be a voluntary reaction to pain rather than the involuntary spasm that rigidity represents. Distention may occur in various abdominal conditions but is less specific for peritonitis or perforation. Rebound tenderness may suggest peritoneal irritation, but rigidity is generally considered a more definitive physical exam finding indicative of an acute abdomen requiring immediate attention.