Middle ear mechanics of Type III tympanoplasty (stapes columella): II. Clinical studies.

Abstract

To determine the structural features that are responsible for the large variation in postoperative hearing results after Type III stapes columella tympanoplasty, to compare the clinical results after Type III tympanoplasty with predictions based on experimental investigations using a temporal bone model, and to investigate the effectiveness of a modification in surgical technique for Type III reconstruction. Retrospective case review. Tertiary referral center. The ear was healed with an intact tympanic membrane graft; the status of the stapes was known, whether mobile or fixed; and the postoperative status of aeration of the middle ear was known, whether aerated or not. Air-bone gap at frequencies 250, 500, 1,000, 2,000 and 4,000 Hz. In ears with temporalis fascia graft onto stapes head: mobile stapes and aerated middle ear (n = 34), mean air-bone gaps at audiometric frequencies were 15 to 30 dB, consistent with predictions of the experimental model; mobile stapes and nonaerated middle ear (n = 16), large air-bone gaps of 35 to 55 dB; fixed stapes and aerated middle ear (n = 4), large air-bone gaps of 30 to 50 dB; fixed stapes and nonaerated middle ear (n = 2), large air-bone gaps of 30 to 70 dB. In ears with a fascia-cartilage graft onto stapes head, where a thin disc of meatal cartilage, 0.3 to 0.5 mm thick and 4 to 6 mm in diameter was interposed between the fascia graft and the stapes head: mobile stapes and aerated middle ear (n = 9), mean air-bone gaps at audiometric frequencies were 10 to 25 dB, about 5 dB better at 250, 500, and 2,000 Hz than in ears with only a fascia graft ( <0.05), improvement consistent with that observed experimentally when a thin cartilage disc was used in the temporal bone model, hypothesis that the cartilage increased the effective vibrating area of the graft; mobile stapes and nonaerated middle ear (n = 2), air-bone gaps were 40 to 50 dB. Large air-bone gaps of 30 to 70 dB occurred as a result of stapes fixation, nonaeration of the middle ear, or both. When the stapes was mobile and the middle ear was aerated, a fascia graft resulted in air-bone gaps of 15 to 30 dB. Interposing a thin disc of cartilage between the fascia graft and stapes head to improve the effective vibrating graft area gave better hearing, with air-bone gaps of 10 to 25 dB. The clinical Type III results were consistent with predictions based on experimental investigations of mechanics of the Type III procedure in a temporal bone model.