Regional differences in zygapophysial joint cavities: A histological study of human fetuses

Abstract

Human zygapophysial joints (ZJ) have regional differences in shape and orien-tation during prenatal growth. However, there is limited knowledge of thesynovial recess during fetal development. We examined sagittal and horizontalhistological sections of the vertebral columns of 30 human fetuses at gesta-tional ages of 8–37 weeks. Fetuses of all gestational ages had subaxial cervicalarticular processes that were thicker than in the thoracolumbar regions, and aslarge as the corresponding vertebral bodies. A small or large synovial recessextending beyond the articular cartilage was evident at most regions. The cer-vical ZJ had large or deep recesses that extended inferiorly in midterm fetusesand posteromedially along the vertebral pedicle and lamina in near-termfetuses. Likewise, the thoracic ZJ had small recesses that extended superiorlyin midterm fetuses and medially in near-term fetuses. The lumbar recessesextended laterally beyond the medially shifted articular cartilage of the upperadjacent vertebrae in near-term fetuses and the lumbar articular surface wassmallest in the three regions at all stages. At any region, a deep recess appearedbefore an area expansion of the ZJ cartilage. A drastic change in direction andsize of the prenatal recess seemed to occur depending on a possible minute dis-location of the ZJ. In particular, a deep posteromedial recess of the cervical ZJ,which extended far beyond the articular cartilage, might be necessary to main-tain high flexibility suitable for the strong flexion posture in utero.