Abstract
Objective: 1) Determine whether tuning fork material (aluminum vs stainless steel) affects Rinne testing in the clinical assessment of conductive hearing loss (CHL). 2) Determine the acoustic and mechanical impedance properties of 512 Hz tuning forks made of aluminum and stainless steel.
Method: Prospective, randomized observational study of 38 subjects presenting to outpatient clinic May 2011 through February 2012 with negative or equivocal Rinne and same-day audiogram. Laboratory tuning fork impedance measurements were obtained using sound-level meter and artificial mastoid (simulating air and bone conduction). Outcome: Sensitivity of negative Rinne in predicting air-bone gap at 500 Hz.
Results: Patients with CHL were more likely to produce a negative Rinne test with a steel fork than with an aluminum fork. Logistic regression revealed that the probability of a negative Rinne reached 50% at 20.3 (±2.5) dB air-bone gap for stainless steel versus 27.5 (±2.6) dB with aluminum. In a supporting laboratory study, steel forks exhibited comparable air and bone conduction efficiencies while aluminum forks favored air conduction. This results in a larger CHL being required to overcome aluminum forks’ increased air conduction efficiency before producing a negative Rinne.
Conclusion: We have found steel tuning forks are more sensitive in detecting the presence of an air-bone gap. This is substantiated by significant differences in the relative acoustic versus mechanical impedances of steel and aluminum forks. These findings have clinical implications for using tuning forks to determine candidacy for stapes surgery.
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