Changes in mechanics and composition of human talar cartilage anlagen during fetal development.

OBJECTIVE: Fetal cartilage anlage provides a framework for endochondral ossification and organization into articular cartilage. We previously reported differences between mechanical properties of talar cartilage anlagen and adult articular cartilage. However, the underlying development-associated changes remain to be established. Delineation of the normal evolvement of mechanical properties and its associated compositional basis provides insight into the natural mechanisms of cartilage maturation. Our goal was to address this issue. MATERIALS AND METHODS: Human fetal cartilage anlagen were harvested from the tali of normal stillborn fetuses from 20 to 36 weeks of gestational age. Data obtained from stress relaxation experiments conducted under confined and unconfined compression configurations were processed to derive the compressive mechanical properties. The compressive mechanical properties were extracted from a linear fit to the equilibrium response in unconfined compression, and by using the nonlinear biphasic theory to fit to the experimental data from the confined compression experiment, both in stress-relaxation. The molecular composition was obtained using Fourier transform infrared (FTIR), and spatial maps of tissue contents per dry weight were created using FTIR imaging. Correlative and regression analyses were performed to identify relationships between the mechanical properties and age, compositional properties and age, and mechanical vs compositional parameters. RESULTS: All of the compositional quantities and the mechanical properties excluding the Poisson's ratio changed with maturation. Stiffness increased by a factor of ∼2.5 and permeability decreased by 20% over the period studied. Collagen content and degree of collagen integrity increased with age by ∼3-fold, while the proteoglycan content decreased by 18%. Significant relations were found between the mechanical and compositional properties. CONCLUSION: The mechanics of fetal talar cartilage is related to its composition, where the collagen and proteoglycan network play a prominent role. An understanding of the mechanisms of early cartilage maturation could provide a framework to guide tissue-engineering strategies.

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.

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.

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

In this histologic-radiologic investigation of 32 feet of 16 fetuses and newborns ranging in age from 15 to 44 weeks, two types of ossification, i.e., endochondral ossification through primary ossification center and intramembraneous ossification through periosteal bone formation (PBF), were found to coexist in both calcaneus and talus. In addition, Ranvier's grooves (RG), or perichondral ossification groove, also was observed as a shallow, saucer-like or semicircular structure. As with PBFs, there are three and two RGs in the calcaneus and talus, respectively. RG and PBF appeared in time order and were located regularly in the concave areas of the adult calcaneus and talus. The findings support the hypothesis that one function of PBF and RG is to limit the growth of the calcaneus and talus. Thus, they are responsible for the irregular contour of the calcaneus and talus.

[Congenital round talus]. / Der angeborene runde Talus.

The collective consists of 11 patients with a "ball and socket"-anomaly of the talus with a mean age of 13.7 years. All patients demonstrated typical symptoms of the FFU-syndrome with a leg length discrepancy of 4.3 cm (2-20). In 6 patients a close follow-up was done in the early development of the talus form. In the metacarpal region also synostosis of some bones were seen at a mean age of 4.8 years (3.2-5.9). No clinical complaints but a slight reduction of hind foot mobility could been registered. Ball and socket deformity can not been seen as congenital, but as a subsequent deformity after congenital fusions in the metatarsal bones.

[Sonographic detection of fetal epiphyseal centers--an additional parameter for determining delivery date]. / Der sonographische Nachweis fetaler Epiphysenkerne--ein zusätzlicher Parameter zur Bestimmung des Geburtstermins.

A new ultrasonic method based on X-ray concepts for depicting prenatally developed centers in the tarsal bones, calcaneus and talus, as well as and especially in the epiphysis centers of the fetal knee joint is described. Investigations of average collectives show that the center in the calcaneus becomes visible during the 24th week of pregnancy, on the average, whereas the center in the talus becomes visible during the 26th week after begin of amenorrhea. The growth charts of both these tarsal centers demonstrate almost linear growth until parturition, the very slight increase per week, however, limits the possibilities for their use in determining the period of gestation. The epiphysis center in the distal femur becomes visible by ultrasonic methods during the 32nd week of pregnancy, on the average, the center in the proximal tibia appears later, during the 37th week after amenorrhea begins. Both epiphysis centers show an almost linear increase in size from the time they first appear; the center in the femur, however, has a growth chart that shows levelling off after the 38th week of pregnancy. The differences between X-ray and ultrasonic representation, which become evident upon comparing growth charts as well as in a separate and direct comparison are shown to be due, through the results of a parallel histological study, to an increase in density of the cartilage matrix prior to ossification. Of the fetal factors which were investigated only the weight and length of the child show a slight, and for practical purposes negligable influence on the size of the epiphysis centers, whereby only the results showing that the femur centers tend to be larger when the child is heavier and longer appear significant. Neither sex nor maternal factors influence the size of the visible epiphysis centers in any way. A slight modification in the case of diabetics and pregnancy induced hypertension patients seems to most likely be due to the macrosomal and retarded children occurring in these groups. None of the factors investigated effect a significant difference in the ultrasonic development or time of appearance of the epiphysis centers. In view of the fact that growth charts show levelling off and of the wider biological scattering range of all parameters currently used to determine the duration of gestation during the last trimenon, making use of this new ultrasonic method with its double advantage - the first appearance of the centers during the last quarter of pregnancy as well as the following near-linear increase in size - seems to suggest itself.(ABSTRACT TRUNCATED AT 400 WORDS)

The subtalar joint: embryology and morphology.

Several different aspects of the subtalar joint are studied. Embryology indicates that it is a recently acquired structure. The anterior subtalar joint does not have a uniform morphology, and it has been subdivided into three anatomical descriptions (ovoid, bean, and two part). To correct the confusion found in other papers, we intend to clearly describe the anatomy of the ligaments. The form and function of the retinacula, cervical ligament, and ligament of the canal are studied. The microscopic anatomy of ligaments is studied, dealing specifically with their innervation and the structure of their fibers.

The role of cartilage canals in the ossification of the talus.

Interrupted serial sections of the foot region from 14 human fetuses, crown-rump (CR) lengths between 32 and 240 mm, were studied, using HE, PAS, Alcian blue, Gomori's trichrome and von Kossa stains. Cartilage canals carrying vascular connective tissue from the perichondrium entered the talus by 68-mm. The centre of ossification developed in the neck region of the talus cartilage by 240 mm CR length, but early stages of chondrocyte proliferation and hypertrophy were noted by 108-mm CR length. The latter is marked by 170 mm CR length. A number of cartilage canals were observed around the developing centre. Branches from these cartilage canals appeared to supply vascular osteogenic tissue to its marrow spaces.