Ossification processes and perichondral ossification groove of Ranvier: a morphological study in developing human calcaneus and talus

The developing juvenile talus: Radiographic identification of distinct ontogenetic phases and structural trajectories

Trabecular bone architecture in the developing skeleton is a widely researched area of bone biomechanics; however, despite its significance in weight-bearing locomotion, the developing talus has received limited examination. This study investigates the talus with the purpose of identifying ontogenetic phases and developmental patterns that contribute to the growing understanding of the developing juvenile skeleton. Colour gradient mapping and radiographic absorptiometry were utilised to investigate 62 human tali from 38 individuals, ranging in age-at-death from 28 weeks intrauterine to 20 years of age. The perinatal talus exhibited a rudimentary pattern comparable to the structural organisation observed within the late adolescent talus. This early internal organisation is hypothesised to be related to the vascular pattern of the talus. After 2 years of age, the talus demonstrated refinement, where radiographic trajectories progressively developed into patterns consistent with adult trabecular organisation, which are linked to the forces associated with the bipedal gait, suggesting a strong influence of biomechanical forces on the development of the talus.

Are we crying Wolff? 3D printed replicas of trabecular bone structure demonstrate higher stiffness and strength during off-axis loading

Roux's principle of bone functional adaptation postulates that bone tissue, and particularly trabecular bone tissue, responds to mechanical stimuli by adjusting (modeling) its architecture accordingly. Hence, it predicts that the new modeled trabecular structure is mechanically improved (stiffer and stronger) in line with the habitual in vivo loading direction. While previous studies found indirect evidence to support this theory, direct support was so far unattainable. This is attributed to the fact that each trabecular bone is unique, and that trabecular bone tissue tends to be damaged during mechanical testing. Consequently, a unique modeled trabecular structure can be mechanically tested only along one direction and a comparison to other directions for that specific structure is impossible. To address this issue, we have 3D printed 10 replicas of a trabecular structure from a sheep talus cropped along the 3 principal axes of the bone and in line with the principal direction of loading (denoted on-axis model). Next, we have rotated the same cropped trabecular structure in increments of 10° up to 90° to the bone principal direction of loading (denoted off-axis models) and printed 10 replicas of each off-axis model. Finally, all on-axis and off-axis 3D printed replicas were loaded in compression until failure and trabecular structure stiffness and strength were calculated. Contrary to our prediction, and conflicting with Roux's principle of bone functional adaptation, we found that a trabecular structure loaded off-axis tended to have higher stiffness and strength values when compared to the same trabecular structure loaded on-axis. These unexpected results may not disprove Roux's principle of bone functional adaptation, but they do imply that trabecular bone adaptation may serve additional purposes than simply optimizing bone structure to one principal loading scenario and this suggests that we still don't fully understand bone modeling in its entirety.

Meta analysis identifies a novel susceptibility locus associated with heel bone strength in the Korean population

INTRODUCTION

Calcaneal quantitative ultrasound has been recognized as a non-invasive method for evaluation of bone strength and prediction of osteoporotic fracture.

METHODS

To extend a thorough genetic catalog for osteoporotic bone properties, we performed a genome-wide association study (rural cohort I, n=1895) of speed of sound (SOS) using the 1000 genome-based imputation in the discovery stage and then carried out in silico lookups (rural cohort II and III, n=2,967) and de novo genotyping (rural cohort IV, n=4,296) in the replication stage.

RESULTS

In the combined meta-analysis (n=9,158), we identified a novel variant associated with SOS (rs2445771 in the GLDN gene, P=2.27×10(-9)) reaching genome-wide significance in the Korean population. We further demonstrated that allele-specific regulatory modifications found to be associated with functional enrichments by ENCODE annotations.

CONCLUSION

Our findings could provide additional insights into understanding of genetic and epigenetic regulations on bone metabolism.

Mechanical properties of human fetal talus

Mechanical characterization of human cartilage anlagen is required to effectively model congenital musculoskeletal deformities. Such modeling can effectively explore the effect of treatment procedures and potentially suggest enhanced treatment methods. Using serial MRI, we have noted shape changes of the cartilaginous hindfoot anlagen in patients with clubfoot, suggesting they are soft and deformable. We therefore determined the stress relaxation behavior of cartilage plugs obtained from third-trimester stillborn fetuses in unconfined and confined compression geometries. The material parameters determined were the aggregate modulus H(A) = 0.15 +/- 0.07 MPa, Poisson's ratio nu = 0.4 +/- 0.06, Young's modulus E(s) = 0.06 +/- 0.03 MPa, and permeability coefficients k(0) = 2.01 +/- 0.8 x 10(-14) m(4) N(-1) s(-1) and M = 4.6 +/- 1.0. As compared with adult articular cartilage, stiffness was an order of magnitude lower than the values reported in the literature, suggesting the relative softness of the tissue, and the permeability was an order of magnitude higher, indicating relative ease of flow in the tissue. Poisson's ratio also was close to the higher end of the range reported in previous studies. Such material is expected to deform and relax to larger extents. These findings are consistent with the deformability of the cartilage anlagen during manipulation and casting for treatment of clubfoot.

Ossification in the human calcaneus: a model for spatial bone development and ossification

Perichondral bone, the circumferential grooves of Ranvier and cartilage canals are features of endochondral bone development. Cartilage canals containing connective tissue and blood vessels are found in the epiphysis of long bones and in cartilaginous anlagen of small and irregular bones. The pattern of cartilage canals seems to be integral to bone development and ossification. The canals may be concerned with the nourishment of large masses of cartilage, but neither their role in the formation of ossification centres nor their interaction with the circumferential grooves of Ranvier has been established. The relationships between cartilage canals, perichondral bone and the ossification centre were studied in the calcaneus of 9 to 38-wk-old human fetuses, by use of epoxy resin embedding, three-dimensional computer reconstructions and immunhistochemistry on paraffin sections. We found that cartilage canals are regularly arranged in shells surrounding the ossification centre. Whereas most of the shell canals might be involved in the nourishment of the cartilage, the inner shell is directly connected with the perichondral ossification groove of Ranvier and with large vessels from outside. In this way the inner shell canal imports extracellular matrix, cells and vessels into the cartilage. With the so-called communicating canals it is also connected to the endochondral ossification centre to which it delivers extracellular matrix, cells and vessels. The communicating canals can be considered as inverted 'internal' ossification grooves. They seem to be responsible for both build up intramembranous osteoid and for the direction of growth and thereby for orientation of the ossication centre.

Intrachondral microvasculature in the human fetal talus

The intrachondral microvasculature of the growing talus of human was studied in 16 fetuses aged from 15 to 44 weeks of gestation, using interrupted serial sections and vascular injection of ink. The cartilage model of the talus was shown to be well vascularized throughout by cartilage canals. The cartilage canal contained blood vessels and connective tissue, with vessels originating from the perichondrial vessels. They were covered by a thick connective tissue wall that was continuous with the perichondrium. The functions of the cartilage canals were mainly to nourish the large masses of cartilage and to supply osteogenic tissue, which initiates the primary ossification center. As in the adult, the fetal talus was supplied with four to five main branches originating from the sinus tarsi and the tarsal canal; there were no anastomoses between the vessels of the adjacent cartilage canals and between the branches within the cartilage canal. This type of microvasculature is vulnerable to injury and, if impaired, may cause serious complications.

The ossification centre of the talus

The ossification of the talus was studied in plastinated and histological preparations of normal feet of eight newborn children. Quantitative data on the newborn talus were obtained with the IBAS image analysis system and by point counting methods. In the newborn talus up to 24 percent of the talar anlage already consists of bony tissue. The ossification centre is situated in the neck, which includes the non-articulating surfaces of the talus. Periosteal bone joins the endochondral centre below and, in well-differentiated specimens also above. The basal periosteal collar forms the surfaces of the sinus and canalis tarsi, whereas the cranial bony collar is included in the tibiotalar joint. The histological architecture of these periosteal collars differs. Four arteries contribute to the blood supply of the talar ossification centre.