The incudostapedial articulation in Down's syndrome (trisomy 21): a temporal bone study.

HYPOTHESIS: Anomaly in the incudostapedial articulation (IS) may be responsible for persistent conductive hearing loss (HL) in Down's syndrome (DS) patients. Our goal was to perform a detailed histopathologic assessment of the role of the IS joint in the conductive HL. BACKGROUND: In addition to other disabilities, 38% to 78% of patients with Down's syndrome (Trisomy 21) have CHL, some of which are persistent despite maximum treatment. The cause of the persistent conductive HL remains unclear. METHODS: Retrospective analysis of temporal bone histopathology. Analyses of the midsection through the IS joint of 21 temporal bones (13 subjects) patients with DS and 31 temporal bones (18 subjects) from healthy subjects, performed by 2 blinded authors. The length of 7 different parameters of the width of the IS joint was measured and compared between the 2 groups. RESULTS: The IS joint of patients with DS was significantly wider than the normal control. As opposed to the control, it did not decrease because of age. CONCLUSION: The persistent conductive HL in some patients with DS might be caused by anomaly of the IS joint. In severe cases, corrective surgery should be considered.

The incudostapedial articulation: new concepts.

HYPOTHESIS: To study the detailed anatomy of the incudostapedial joint (ISJ). BACKGROUND: Detailed study of the anatomy of the ISJ has been surprisingly neglected and continues to be controversial. METHODS: 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. RESULTS: 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. CONCLUSION: 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.