Anatomy of Incudostapedial Joint, Stapes and Facial Nerve in Stapes Surgery

Purpose To provide anatomic date for the stapes operation of otosclerosis by means of measuring the common anatomic data and analysizing the relationship between the adjacent structures in the stapes surgery. Methods The angle of incudostapedial joint, the vertical distance of the long process of incus to the stapes footplate and the thickness of the stapes were measured. The relation of the fallopian aqueduct and the oval windows were observed. Results The angle of incudostapedial joint is 86.5± 8.6°, tlie distance of the long process of incus to the stapes footplate is 3.58± 0.35 mm, and the thickness of the stapes is 0.31 ±0.03 mm. 90% of oval windows were totally exposed, and 10% were half covered with facial nerve. Conclusion The normal angle of incudostapedial joint is not absolutely 90°. The length of stapes prosthesis equals to distance of the long process of incus to the stapes footplate plus the thickness of the stapes plus 0.5 mm. The low positioned facial nerve may impede the placement of the pison.