The incudostapedial articulation: new concepts

To study the detailed anatomy of the incudostapedial joint (ISJ).

Detailed study of the anatomy of the ISJ has been surprisingly neglected and continues to be controversial.

We studied the joint in 86 temporal bones from 51 subjects, aged 12 to 104 years, by light microscopy and three-dimensional images of computer-based reconstructions.

In the course of this study, we found that the lenticular process is extremely delicate, consisting of thin trabeculae and spaces filled with areolar tissue. The ISJ is at least partially a bichambered diarthrodial joint divided by a fibrous articular disk into unequal joint spaces. This disk could be identified in all 86 specimens. In addition, we identified for the first time a concavity on the anterior face of the inferior end of the long process of the incus. The asymmetric joint capsule of the ISJ, which completely envelops the lenticular process, extends to this incudal concavity, thereby incorporating part of the long process into the joint complex. We also found that the attachment of the tendon of the stapedius muscle to be more complex than previously described with contributions to the posterior and probably the inferior joint capsule.

On the basis of its finely cohesive anatomic structure, we believe that the incudostapedial articulation should be considered to be a single complex and to be a single entity physiologically.