[Diagnosis of conductive deafness by static compliance]

The diagnosis of the ossicular condition, fixation or interruption, is often not achieved by the tympanometry, because the overlap of the distribution of the static compliance (SC) is so great with the normal group in these two groups. Therefore, it has been said that SC, by itself, has little diagnostic value for differentiating the ossicular lesion. The overlap of the distribution of SC, however, was much smaller between the group with ossicular fixation and the one with ossicular discontinuity. So, apart from deviation from the normal range of SC, the limiting value of SC for discriminating the two groups was determined in ears with conductive hearing loss. The subjects were fifty-one ears with ossicular fixation and seventeen ears with ossicular discontinuity, in which ossicular lesions were surgically confirmed. All ears showed intact tympanic membrane. The limiting value of SC was 0.9 cc. The internal check using this discriminant value showed high ratio of discrimination, i.e. 94.1% in the fixation group and 64.7% in the discontinuity one were diagnosed correctly. Therefore the author proposed this value as the new criteria to differentiate type As ("s" mean sclerosis) tympanogram from type Ad ("d" means discontinuity) one. In addition, the comparison of SC with the normal side in twenty-five unilaterally affected ears showed smaller SC in 75% of the fixation group and larger SC in 92.3% of the discontinuity one than the normal side. Thus, it can be said that SC have useful value in separating ossicular fixation from ossicular discontinuity, if one compares ears with both the intact tympanic membrane and conductive hearing loss.