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Primary cilia have functions as sensory organelles integral to signal transduction and establishment of cell polarity. In articular cartilage the primary cilium has been hypothesized to function as an antenna to sense the biomechanical environment, regulate the secretion of extracellular matrix components, and maintain cellular positional information, leading to high tissue anisotropy. We used analysis of electron microscopy serial sections to demonstrate positional attributes of the primary cilium of adult equine articular chondrocytes in situ. Data for ~500 axonemes, comparing superficial to radiate chondrocytes from both load-bearing and non-load-bearing regions, were graphed using spherical co-ordinates θ, φ. The data demonstrate the axoneme has a definable orientation in 3D space differing in superficial and radiate zone chondrocytes, cells that differ by 90° in the orientation of their major axes to the articular surface. Axonemal orientation is more definable in load-bearing than in non-load-bearing areas. The position of emergence of the axoneme from the cell also is variable. In load-bearing regions of the superficial zone, extension of the axoneme is from the cellular side facing the subchondral bone. In radiate zone cells, axonemes extend from either face of the chondrocyte, that is, both toward the articular surface or toward the subchondral bone. In non-load-bearing regions this consistency is lost. These observations relate to current hypotheses concerning establishment of tissue anisotropy in articular cartilage during development, involving both migration of cells from the joint periphery and a restricted zone of division within the tissue resulting in the columnar arrangement of radiate zone cells., (Copyright © 2011 Wiley-Liss, Inc.)

Background: The fluoroquinolones are a relatively new class of antimicrobials with an appealing spectrum of activity. Their use in pediatric medicine is limited because of the concern over possible growth inhibition, as published reports have documented articular cartilage damage in animal models after their administration. These data, extrapolated to include the epiphyseal cartilage, suggest that these agents may reduce growth rates, but limited human data are at the least equivocal, if not strictly contradictory to such claims. Specific investigations into the effects of fluoroquinolones on epiphyseal plate cartilage and growth velocity have not been performed., Methods: Gatifloxacin and ciprofloxacin were used as representative agents of the fluoroquinolone class. Each drug was administered to experimental lambs over a 14-day interval at a dose designed to reflect those used in pediatric medicine. Recumbent versus standing intervals were used to monitor for arthropathy. Upon completion of fluoroquinolone administration, lambs underwent double fluorochrome labeling for determination of growth velocity. Gross and microscopic analysis of articular cartilage was performed to assess for pathologic changes. Age- and sex-matched lambs served as controls., Results: Neither gatifloxacin nor ciprofloxacin negatively affected growth velocity of the proximal tibial growth plate as measured by double fluorochrome labeling. In addition, no difference between experimental and control lambs in regard to recumbent versus standing intervals was noted. Examination of the articular cartilage failed to suggest chondrotoxicity., Conclusion: Fluoroquinolone antimicrobials do not affect growth velocity in the ovine model when administered along a dosing regimen that closely models that seen in pediatric medicine., Clinical Relevance: Fluoroquinolones may be acceptable for use in the pediatric population, as concerns over chondrotoxicity and growth inhibition may not be valid. These data suggest that expanded studies in lambs and other species, including humans, with differences in dosing and duration are justified to ultimately demonstrate clinical safety.

A stereological expression relating the mean number of organelle profiles per cell profile, Np, to the mean number of organelles per cell, Nc, is first derived and then tested for cilia in tangenital articular chondrocytes where Nc is known to be 1.0. Nc derived stereologically for this organelle-cell model is 1.19. This close approximation of the estimate to a known value provides empirical evidence of the usefulness of the derived stereological expression.

The incidence and structure of equine and murine chondrocytic cilia were studied using serial sections and transmission electron microscopy. Overall, 96% of all equine chondrocytes and 100% of all murine chondrocytes had one cilium. The structure of these cilia included rootlets, basal feet, alar sheets, and an axoneme of nine peripheral doublets which progressively bent and terminated as they coursed towards the tip of the ciliary shaft. Together with the previous studies on neonatal and adult canine chondrocytic cilia, we conclude that the structure and incidence of chondrocytic cilia does not vary among species, regions within a joint, cell types, or age groups.