Sound energy absorbance characteristics of cartilage grafts used in type 1 tympanoplasty.

OBJECTIVE: The purpose of this prospective case-control study is to evaluate the sound energy absorbance characteristics of cartilage grafts in patients, who have undergone type 1 cartilage tympanoplasty. METHODS: Thirty-four operated ears of 32 patients and 70 ears of 35 control subjects were included. Differences of pure-tone audiometry thresholds and wideband ambient-pressure absorbance ratios with respect to the graft material, graft thickness, cartilage surface area ratio and elapsed time after surgery were analyzed. Receiver operating characteristics curve was generated to detect the absorbance level at which the reconstructed tympanic membrane behaves as 'near-normal tympanic membrane'. RESULTS: In the surgical group, wideband energy absorbance ratios at all 1/2-octave band frequencies were significantly worse than normal ears. Energy absorbance ratios at 2000 and 2828Hz frequencies were higher in patients with tragal cartilage grafts. Higher absorbance ratios at 250-750Hz range were obtained in patients with 400µm cartilage graft thickness, <50% cartilage surface area ratio and ≥5 years since surgery. A multivariate generalized linear model revealed common effects of the independent variables at 8000Hz. The receiver operating characteristics analysis generated a cut-off level of 63.20% of sound energy absorbance at 1400Hz with 83% sensitivity and 88% specificity. CONCLUSION: Even though no differences in hearing thresholds were observed; graft material, graft thickness, cartilage surface area ratio and elapsed time after surgery affected the course of sound energy absorbance after type 1 cartilage tympanoplasty as evidenced by wideband tympanometry.