Development of synovial joints

Abstract

Synovial joints arise through two main processes. In long bone elements, cartilaginous differentiation occurs across the locations of the prospective joints that then segment secondarily. This process occurs through the development of a noncartilaginous region known as the interzone. The interzone becomes an important signaling center to the opposing elements, which can regulate growth through such factors as GDF-5. The interzone also expresses bone morphogenetic proteins (BMPs) and their antagonists, such as noggin. Overexpression of BMPs, or the loss of noggin leads to joint fusions. The interzone also expresses Wnt-14, which appears to be specific for this region in the developing anlagen, and regulates its nonchondrogenic nature. Cavitation of the joint follows, driven by selective high-level synthesis of hyaluronan by interzone cells and presumptive synovial cells. In addition, as the interzone disperses during cavity enlargement, data are now accruing that suggest that both the synovium and articular cartilage develop from this population. Finally, the development of articular cartilage progresses through appositional growth driven by a progenitor/stem cell subpopulation that resides in the articular surface. The individual elements of the skeleton are connected together at regions termed joints or articulations. Classically, there are three broad categories of joints: immovable joints (syntharthroses); mixed articulations, in which the range of movement is limited (amphiarthroses); and the movable, or synovial, joints (diarthroses). This review concentrates on the development of the synovial joints.

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“…In lieu of examining only the morphology of incompletely ossified and burr-shaped carpal elements in dissections, this study focused on the position of fibrous, uncavitated joints that surround individual carpal cartilages which usually encased a carpal ossification center (Flower, 1885;Eschricht and Reinhardt, 1866). Each fibrous joint indicates where joint cavitation and articular cartilage would form if a complete synovial joint were to develop (Archer et al, 2003). Carpal ossification begins at the center of these Kunze (1912) I Disagreed with Kü kenthal's (1893) hypothesis No evidence indicating which digit was lost Howell (1930) I Reduced number of phalanges in digit I of pentadactylous baleen whales cartilages and radiates toward the fibrous joints lining the perimeter of each carpal cartilage (Archer et al, 2003).…”

“…Each fibrous joint indicates where joint cavitation and articular cartilage would form if a complete synovial joint were to develop (Archer et al, 2003). Carpal ossification begins at the center of these Kunze (1912) I Disagreed with Kü kenthal's (1893) hypothesis No evidence indicating which digit was lost Howell (1930) I Reduced number of phalanges in digit I of pentadactylous baleen whales cartilages and radiates toward the fibrous joints lining the perimeter of each carpal cartilage (Archer et al, 2003). By examining the position of these fibrous joints, the number of carpal elements could be determined, and the carpal-carpal and carpometacarpal articulations could be identified.…”