M J Simmons1, C W Parkins. 1. Louisiana State University Medical Center, Department of Otolaryngology and Biocommunication, Kresge Hearing Research Laboratory, New Orleans, USA.
Abstract
OBJECTIVE: It has been stated in the clinical literature that stapedial fractures could produce a significant conductive hearing loss while leaving the contralateral stapedial reflex intact. The objective of this study is to test this hypothesis in an animal model. DESIGN: Nine hooded rats underwent acoustic-stapedial reflex (ASR) and cochlear microphonic (CM) threshold determinations before and after middle ear surgery. An argon laser was used to divide the tensor tympani tendon, the anterior stapedial curs, and the posterior stapedial crus, sequentially. The initial functional measures were repeated after each laser procedure to document its effect. RESULTS: Dividing the tensor tympani tendon and the anterior stapedial crus had variable and small effects on ASR and CM thresholds. Division of the second (posterior) crus eliminated stapedial reflexes and produced a significant hearing loss. CONCLUSIONS: This study refutes the hypothesis that fracture of one (anterior) stapedial crus will significantly alter ossicular sound transmission, but it supports the hypothesis that measured stapedial reflexes would not be significantly altered by a single crus fracture. Therefore, the surgeon exploring an ear for a conductive hearing loss with an intact contralateral stapedial reflex should look carefully for another source of the hearing loss if finding only a single stapedial arch fracture.
OBJECTIVE: It has been stated in the clinical literature that stapedial fractures could produce a significant conductive hearing loss while leaving the contralateral stapedial reflex intact. The objective of this study is to test this hypothesis in an animal model. DESIGN: Nine hooded rats underwent acoustic-stapedial reflex (ASR) and cochlear microphonic (CM) threshold determinations before and after middle ear surgery. An argon laser was used to divide the tensor tympani tendon, the anterior stapedial curs, and the posterior stapedial crus, sequentially. The initial functional measures were repeated after each laser procedure to document its effect. RESULTS: Dividing the tensor tympani tendon and the anterior stapedial crus had variable and small effects on ASR and CM thresholds. Division of the second (posterior) crus eliminated stapedial reflexes and produced a significant hearing loss. CONCLUSIONS: This study refutes the hypothesis that fracture of one (anterior) stapedial crus will significantly alter ossicular sound transmission, but it supports the hypothesis that measured stapedial reflexes would not be significantly altered by a single crus fracture. Therefore, the surgeon exploring an ear for a conductive hearing loss with an intact contralateral stapedial reflex should look carefully for another source of the hearing loss if finding only a single stapedial arch fracture.