This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: ENT
Unilateral conductive hearing loss in a patient with history of head injury. On examination, tympanic membrane is normal and mobile. The cause for deafness could be 
Select and explain. 
A. Collection of fluid in the middle ear, B. Otosclerosis, C. Dislocation of the incudostapedial joint, D. ASOM
C: Dislocation of the incudostapedial joint
Answer: C: Dislocation of the incudostapedial joint 
Explanation: Acquired causes of conductive hearing loss include: Perforation of tympanic membrane Fluid in the middle ear-acute otitis media, serous otitis media, hemotympanum Mass in the middle ear (benign/malignant) Disruption of ossicles-trauma to ossicular chain, CSOM, cholesteatoma Fixation of ossicles-otosclerosis, tympanosclerosis Eustachian tube blockage