Developmental anatomy of the mouse stapediovestibular and temporomandibular joints

The genesis, development and growth of the mouse stapediovestibular joint (SVJ), which contains the annular ligament, and the temporomandibular joint (TMJ) were examined in an attempt to study the stress-bearing articular tissue that is thought to be derived from embryonic mesenchyme; the findings were also compared with those in the ossicular joints. The following conclusions were obtained: 1) The articular cartilage of the mandibular condylar process, stapedial foot plate and otic capsule is derived from fetal fibrous articular tissue. 2) The fetal TMJ developed into a typical double diarthroses containing an articular disc. 3) The fetal syndesmodial SVJ differentiated into the annular ligament containing characteristic palisade-like fibroblasts and hammock-like fibers; no interzone formation or synovial cavities were observed in the completed and mature syndesmodial SVJ. 4) Like the TMJ, the major elastic system fibers in the annular ligament were also mechanical-resistant elaunin. 5) Elastogenesis was closely related to functional and mechanical factors in the auditory ossicular chain, TMJ and annular ligament; the mature incudomalleal and incudostapedial joints contained mainly mature elastic fibers, but the mature SVJ and immature TMJ contained mainly pre-elastic elaunin fibers. 6) Stress elastosis, turnover of the fibrillar component and age changes in cellular and fibrous components were not evident in either the mature SVJ or the young functional TMJ.