Importance of Diameter of Long Process of Incus in Stapedotomy-New Findings From In Vivo Study.

Stapes surgery for otosclerosis is a precise surgical procedure. To achieve excellent hearing results, a firm and stable attachment of the prosthesis to the long process of incus (LPI) is necessary. The present study provides details on the attachment site in two dimensions to choose an appropriate prosthesis and to ensure firm attachment for better surgical outcomes.  To study the diameter of the LPI and its relevance in determining the piston, used in stapes surgery by an in vivo method.  This study was conducted in 41 patients who underwent stapedotomy, where both Anteroposterior (AP) and Mediolateral (ML) diameters of the LPI were measured at the site of attachment of the piston using specially designed instruments, intraoperatively. Radiological data were obtained to measure the LPI diameter from the normal ears of 46 patients. It was measured from both the right and left side, hence 92 LPI diameters were obtained.  The most commonly used site for prosthesis attachment is between 1-1.5 mm away from the tip of the LPI. We found great variability in the diameters of LPI in the attachment site, with the AP diameter ranging between 0.6 -1.5mm and the ML diameter ranging between 0.5mm-1.2 mm.  Pistons by design have characteristics of gripping incus that will vary between types. Based on LPI dimensions, ideal piston types with appropriate inner loop diameters are suggested in this study. HRCT before surgery should include measurements of the LPI as a guide to the choice of the prosthesis during surgery.