Axonemal positioning and orientation in three-dimensional space for primary cilia: what is known, what is assumed, and what needs clarification.

Two positional characteristics of the ciliary axoneme--its location on the plasma membrane as it emerges from the cell, and its orientation in three-dimensional (3D) space--are known to be critical for optimal function of actively motile cilia (including nodal cilia), as well as for modified cilia associated with special senses. However, these positional characteristics have not been analyzed to any significant extent for primary cilia. This review briefly summarizes the history of knowledge of these two positional characteristics across a wide spectrum of cilia, emphasizing their importance for proper function.

Orientation of primary cilia of articular chondrocytes in three-dimensional space.

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.

The effect of fluoroquinolone antibiotics on growing cartilage in the lamb model.

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.

Histomorphometric analysis of an adolescent distal tibial physis prior to growth plate closure.

Purpose: Our current understanding of the rate and pattern of physeal closure is based on roentgenographic, magnetic resonance imaging, and qualitative histological studies. The purpose of this report is to provide a detailed histomorphometric/stereological analysis of a distal tibial human growth plate in the process of physiological epiphysiodesis.

Methods: A human distal tibial growth plate was sampled in three regions (anterior, central, and posterior), with each region further separated medially, in the middle, and laterally.

The effect of periosteal resection on tibial growth velocity measured by microtransducer technology in lambs.

Background: Disruption of the periosteum, whether traumatic or elective, has long been known to accelerate growth in the developing skeleton. However, the extent, timing, and mechanism of the resultant increase in growth velocity (if any) remain undefined. The primary research questions were: Does periosteal resection result in a change (increase) in growth velocity of a long bone at the growth plate? When does the effect start after the resection and for how long? Finally, which of several cellular mechanisms is most likely responsible for the change in growth velocity?

Methods: Five lambs underwent proximal tibial growth plate periosteal resection with subsequent measurement of growth velocity by implantable microtransducers or fluorochrome labeling.

Age and pattern of the onset of differential growth among growth plates in rats.

Differential growth is the phenomenon whereby growth plates in the same individual at the same time all have uniquely different axial growth velocities. Differential growth is clearly present in the adolescent skeleton. In this study we ask two questions.

Mechanical behavior of the lamb growth plate in response to asymmetrical loading: a model for Blount disease.

Blount disease is a deformity of the knee as a result of abnormal mechanical forces known to influence the growth of the physis. Despite existing studies on mechanical forces on chondrocyte cultures or limited growth plate specimens, very little information characterizes the whole growth plate to asymmetrical loading. In this study, we evaluate the response of 5 ovine proximal tibial growth plates to asymmetrical mechanical loading.

Growing pains: are they due to increased growth during recumbency as documented in a lamb model?

The rate and patterns of longitudinal bone growth are affected by many different local and systemic factors; however, uncompromised growth is usually considered to be smoothly continuous, with predictable accelerations and decelerations over periods of months to years. The authors used implanted microtransducers to document bone growth in immature lambs. Bone length measurements were sampled every 167 seconds for 21 to 25 days.

Bone elongation in rats with renal failure and mild or advanced secondary hyperparathyroidism.

Background: Impairment of growth in children with chronic renal failure may be due, in part to the insensitivity to the actions of growth hormone by insulin-like growth factor-I (IGF-I) because of accumulations of IGF binding proteins. There are a few studies describing the changes that occur in the growth plate in renal failure. None of these studies has simultaneously compared the modifications in the expression of selected markers of endochondral bone formation in renal failure with mild or advanced secondary hyperparathyroidism.

Effect of short-term fasting on bone elongation rates: an analysis of catch-up growth in young male rats.

Bone elongation in the postnatal animal is a result of cellular activity during endochondral ossification. Growth plate chondrocytes undergo a differentiation cascade involving stem cell clonal expansion and cellular enlargement during hypertrophy. Nutritional status has a significant effect on rates of bone growth, and a period of accelerated growth will occur if nutritional stunting of growth in early childhood can be corrected.