Necrosis of the long process of the incus following stapes surgery: new anatomical observations.

Objectives/hypothesis: The most frequent complication (generally recognized during revision procedures) following seemingly successful stapedotomies and stapedectomies is necrosis of the long process of the incus. This is currently ascribed to a malcrimped stapes prosthesis or to a compromised blood supply of the incus. The two-point fixation can cause a mucosal injury with a resulting toxic reaction, and also osteoclastic activity. An important aspect in the engineering of ideal stapes prostheses is that they should be fixed circularly to the long process of the incus with appropriate strength. The objective of this study was to compare current knowledge relating to the blood supply of the ossicular chain with the present authors' observations on cadaver incudes. Most of the papers dealing with this issue appeared in the mid-20th century.

Methods: The published data were compared with the authors' findings gained from photodocumentation on 100 cadaver incudes. The photos were taken with a Canon EOS 20 digital camera (Canon, Inc., Lake Success, NY) with a 5:1 macro-objective. The long processes of the incudes were examined from four directions under a Leica surface-analyzing microscope (Leica Microsystems GmbH, Wetzlar, Germany).

Results: Analysis of the positions of the entrances of the feeding arteries (nutritive foramina) on the incudes revealed 1-4 nutritive foramina on the long processes of 48% (24) of the left-sided incudes and 56% (28) of the right-sided incudes. The positions of these foramina differed, however, from those previously described in the literature. They were mostly located not on the medial side of the incus body or on the short process or on the cranial third of the long processes, but antero-medially, mostly on the middle or cranial third. In 48% of all the incudes examined, an obvious foramen was not observed either in the body or in the long process of the incus. No relationship was discerned between the chronological age of the incus specimens and the numbers and/or locations of the nutritive foramina. In each case, the opening of the foramen was the beginning of a tunnel running obliquely and medially upward through the corticalis of the long process of the incus. The foramina are thought to be capable of ensuring a richer blood supply between the surface and the inside of the long process, allowing the arteries to run in and out.

Conclusions: These observations indicate that conclusions drawn from classical anatomical works appear to need reconsideration. The present authors consider that the reason for the necrosis of the long process of the incus is not a compromised blood supply, except in some exceptional anatomical situations. They discuss the possible reasons why malcrimping may lead to necrosis of the long process of the incus. To prevent such malcrimping, attention is paid to the new generation of prostheses.