This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Vermiform Appendix, Subject name: Surgery
Which muscle is irritated by inflamed retrocaecal appendix - 
Select and explain. 
A. Psoas major, B. Gluteus maximus, C. Quadratus femoris, D. Obturator internus
A: Psoas major
Answer: A: Psoas major 
Explanation: Ans. is 'a' i.e., Psoas major Abdominal pain in appendicitis:* In children with abdominal pain, who hold their right hip in a flexed position to obtain relief from the pain, one should suspect retrocaecal appendicitis causing irritation of the psoas muscle.