Middle ear mechanics of type IV and type V tympanoplasty: II. Clinical analysis and surgical implications.

Type IV and type V tympanoplasty operations are simple, robust, and well-established techniques to reconstruct middle ears that have been severely altered by chronic otitis media. In a previous paper, the authors developed a simple four-block physiologic model to describe hearing results after these procedures. This paper presents a comparison of model predictions to hearing results obtained from a detailed retrospective clinical review of 30 type IV and type V procedures. Audiograms predicted by the model and those observed clinically show good agreement over a wide frequency range (500-4000 Hz) and for many different clinical conditions. Thus, this model reliably predicts postsurgical hearing results. The application of quantitative analyses provided by this model permits the formation of a few simple surgical rules that may improve postoperative hearing results. (1) The footplate should be left as mobile as possible (e.g., by covering it with a very thin split-thickness skin graft, as opposed to a fascia graft, which will tend to stiffen it). If the footplate is ankylosed, it should be removed and replaced with a compliant tissue graft, such as fat. (2) The round window acoustic graft shield should be made as stiff as possible. If the shield material used is temporalis fascia, then one should consider using more than one layer, or reinforcing it with cartilage. (3) An attempt should be made to create an aerated cavum minor containing at least 0.03 cc of air.