The twisted structure of the fetal calcaneal tendon is already visible in the second trimester.

INTRODUCTION: The progress in morphological science results from the greater possibilities of intra-pubic diagnosis and treatment of congenital disabilities, including the motor system. However, the structure and macroscopic development of the calcaneal tendon have not been investigated in detail. Studies on the adult calcaneal tendon showed that the calcaneal tendon is composed of twisted subtendons. This study aimed to investigate the internal structure of the fetal calcaneal tendon in the second trimester. MATERIALS AND METHODS: Thirty-six fetuses fixed in 10% formaldehyde were dissected using the layer-by-layer method and a surgical microscope. RESULTS: The twisted structure of the calcaneal tendon was revealed in all specimens. The posterior layer of the calcaneal tendon is formed by the subtendon from the medial head of the gastrocnemius muscle. In contrast, the anterior layer is formed by the subtendon from the lateral head of the gastrocnemius muscle. The subtendon from the soleus muscle constitutes the anteromedial outline of the calcaneal tendon. The lateral outline of the calcaneal tendon is formed by the subtendon originating from the medial head of the gastrocnemius muscle. In contrast, the medial outline is formed by the subtendon from the soleus muscle. In most of the examined limbs, the plantaris tendon attached to the tuber calcanei was not directly connected to the calcaneal tendon. CONCLUSIONS: The twisted structure of the subtendons of the fetal calcaneal tendon is already visible in the second trimester and is similar to that seen in adults.

The Role of Hox in Pisiform and Calcaneus Growth Plate Formation and the Nature of the Zeugopod/Autopod Boundary.

The mesopodium forms at the boundary between the zeugopod and autopod and is composed of short nodular bones that typically lack growth plates. Hoxa11 and Hoxa13 are expressed in mutually exclusive proximal-distal domains that demarcate the zeugopod/autopod boundary. Similarly, Hoxd genes are deployed in two distinct phases during limb development. The early phase corresponds to proximal segments including the zeugopod, and a late phase occurs in the digits. This arrangement produces a gap of low Hoxd expression that is traditionally viewed to correspond to the mesopodium. In contrast to the other mesopodials, the mammalian pisiform and calcaneus form true growth plates. We show that these bones, along with other proximal mesopodials, develop within the Hoxa11 and Hoxd11 expression domains. We also observe that the pisiform growth plate becomes disorganized with Hoxa11 or Hoxd11 loss of function, indicating a direct role for Hox11 in its development. Hoxa13 loss of function has minimal effect on the pisiform and proximal calcaneus as these bones still form secondary centers and undergo longitudinal growth. Consideration of the phenotypes resulting from hypodactyly (Hd) and synpolydactyly homolog (spdh) mutations, which result from altered HOXA13 and HOXD13 proteins, respectively, confirms that Hox13 plays a limited role in the development of the pisiform and calcaneus and suggests that they lie within the early phase of Hox expression. Therefore, with respect to patterns of ossification and gene expression, these bones share much more in common with the zeugopod than the autopod. Such an interpretation fits with the timing of autopod origins during tetrapod evolution.

Development of the human Achilles tendon enthesis organ.

The attachment of the Achilles tendon is part of an 'enthesis organ' that reduces stress concentration at the hard-soft tissue interface. The organ also includes opposing sesamoid and periosteal fibrocartilages, a bursa and Kager's fat pad. In addition, the deep crural and plantar fasciae contribute to Achilles stress dissipation and could also be regarded as components. Here we describe the sequence in which these various tissues differentiate. Serial sections of feet from spontaneously aborted foetuses (crown rump lengths 22-322 mm) were examined. All slides formed part of an existing collection of histologically sectioned embryological material, obtained under Spanish law and housed in the Universidad Complutense, Madrid. From the earliest stages, it was evident that the Achilles tendon and plantar fascia had a mutual attachment to the calcaneal perichondrium. The first components of the enthesis organ to appear (in the 45-mm foetus) were the retrocalcaneal bursa and the crural fascia. The former developed by cavitation within the mesenchyme that later gave rise to Kager's fat pad. The tip of the putative fat pad protruded into the developing bursa in the 110-mm foetus and fully differentiated adipocytes were apparent in the 17-mm foetus. All three fibrocartilages were first recognisable in the 332-mm foetus--at which time adipogenesis had commenced in the heel fat pad. The sequence in which the various elements became apparent suggests that bursal formation and the appearance of the crural fascia may be necessary to facilitate the foot movements that subsequently lead to fibrocartilage differentiation. The later commencement of adipogenesis in the heel than in Kager's pad probably reflects the non-weight environment in utero. The direct continuity between plantar fascia and Achilles tendon that is characteristic of the adult reflects the initial attachment of both structures to the calcaneal perichondrium rather than to the skeletal anlagen itself.

Are distributions of secondary osteon variants useful for interpreting load history in mammalian bones?

BACKGROUND/AIMS: In cortical bone, basic multicellular units (BMUs) produce secondary osteons that mediate adaptations, including variations in their population densities and cross-sectional areas. Additional important BMU-related adaptations might include atypical secondary osteon morphologies (zoned, connected, drifting, elongated, multiple canal). These variants often reflect osteonal branching that enhances toughness by increasing interfacial (cement line) complexity. If these characteristics correlate with strain mode/magnitude-related parameters of habitual loading, then BMUs might produce adaptive differences in unexpected ways. METHODS: We carried out examinations in bones loaded in habitual torsion (horse metacarpals) or bending: sheep, deer, elk, and horse calcanei, and horse radii. Atypical osteons were quantified in backscattered images from anterior, posterior, medial, and lateral cortices. Correlations were determined between atypical osteon densities, densities of all secondary osteons, and associations with habitual strain mode/magnitude or transcortical location. RESULTS: Osteon variants were not consistently associated with 'tension', 'compression', or neutral axis ('shear') regions, even when considering densities or all secondary osteons, or only osteon variants associated with relatively increased interfacial complexity. Similarly, marrow- and strain-magnitude-related associations were not consistent. CONCLUSION: These data do not support the hypothesis that spatial variations in these osteon variants are useful for inferring a habitual bending or torsional load strain history.

Ontogenetic structural and material variations in ovine calcanei: a model for interpreting bone adaptation.

Experimental models are needed for resolving relative influences of genetic, epigenetic, and nonheritable functionally induced (extragenetic) factors in the emergence of developmental adaptations in limb bones of larger mammals. We examined regional/ontogenetic morphologic variations in sheep calcanei, which exhibit marked heterogeneity in structural and material organization by skeletal maturity. Cross-sections and lateral radiographs of an ontogenetic series of domesticated sheep calcanei (fetal to adult) were examined for variations in biomechanically important structural (cortical thickness and trabecular architecture) and material (percent ash and predominant collagen fiber orientation) characteristics. Results showed delayed development of variations in cortical thickness and collagen fiber orientation, which correlate with extragenetic factors, including compression/tension strains of habitual bending in respective dorsal/plantar cortices and load-related thresholds for modeling/remodeling activities. In contrast, the appearance of trabecular arches in utero suggests strong genetic/epigenetic influences. These stark spatial/temporal variations in sheep calcanei provide a compelling model for investigating causal mechanisms that mediate this construction. In view of these findings, it is also suggested that the conventional distinction between genetic and epigenetic factors in limb bone development be expanded into three categories: genetic, epigenetic, and extragenetic factors.

Relationships of loading history and structural and material characteristics of bone: development of the mule deer calcaneus.

If a bone's morphologic organization exhibits the accumulated effects of its strain history, then the relative contributions of a given strain stimulus to a bone's development may be inferred from a bone's hierarchical organization. The artiodactyl calcaneus is a short cantilever, loaded habitually in bending, with prevalent compression in the cranial (Cr) cortex, tension in the caudal (Cd) cortex, and shear in the medial and lateral cortices (i.e., neutral axis). Artiodactyl calcanei demonstrate unusually heterogeneous structural and material organization between these cortices. This study examines potential relationships between developmental morphologic variations and the functional strain distribution of the deer calcaneus. One calcaneus was obtained from each of 36 (fetus to adult) wild deer. Predominant collagen fiber orientation (CFO), microstructural characteristics, mineral content (% ash), and geometric parameters were determined from transversely cut segments. Radiographs were examined for arched trabeculae, which may reflect tension/compression stress trajectories. Results showed that cross-sectional shape changes with age from quasi-circular to quasi-elliptical, with the long axis in the cranial-caudal direction of habitual bending. Cranial ("compression") cortical thickness increased at a greater rate than the Cd ("tension") cortex. Fetal bones exhibited arched trabeculae. Percent ash was not uniform (Cr > Cd), and this disparity increased with age (absolute differences: 2.5% fetuses, 4.3% adults). Subadult bones showed progressively more secondary osteons and osteocyte lacunae in the Cr cortex, but the Cd cortex tended to have more active remodeling in the subadult and adult bones. Nonuniform Cr:Cd CFO patterns first consistently appear in the subadults, and are correlated with secondary bone formation and habitual strain mode. Medial and lateral cortices in these groups exhibited elongated secondary osteons. These variations may represent "strain-mode-specific" (i.e., tension, compression, shear) adaptations. The heterogeneous organization may also be influenced by variations in longitudinal strain magnitude (highest in the Cr cortex) and principal strain direction-oblique in medial-lateral cortices (where shear strains also predominate). Other factors such as local reductions in longitudinal strain may influence the increased remodeling activity of the Cd cortex. Some structural variations, such as arched trabeculae, that are established early in ontogeny may be strongly influenced by genetic- or epigenetic-derived processes. Material variations, such as secondary osteon population densities and CFO, which appear later, may be products of extragenetic factors, including microdamage.

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.

Ossification of the calcaneus in the normal fetal foot and in clubfoot.

The ossification of the fetal calcaneus was studied in a series of plastinated sections of 44 normal feet and three clubfeet. The results documented a precise sequence of perichondral and endochondral ossification in the normal calcaneus characterized by ossification grooves and associated cartilage canals. Within the clubfoot calcaneus, the coordination of perichondral and endochondral ossification is disturbed, ossification grooves and associated cartilage canals are not found in regular positions, and the process of endochondral ossification obviously is disturbed. The findings in the clubfoot specimens point to grave irregularities of the extracellular matrix within or outside the calcaneus.

Anatomy of the Achilles tendon and plantar fascia in relation to the calcaneus in various age groups.

Ten adult cadaver feet, three neonatal feet, and the feet of two fetuses were dissected to investigate whether an anatomical continuity exists between the fibers of the Achilles tendon and the plantar fascia. Histologic sections of the feet were done in three age groups: neonate, persons in their mid-20s, and the elderly. As the foot ages, there appears to be continued diminution of the number of fibers connecting the Achilles tendon and plantar fascia. The neonate has a thick continuation of fibers, while the middle-aged foot has only superficial periosteal fibers that continue from tendon to fascia. The elderly feet show simply an insertion of fibers of both structures into the calcaneus with periosteum in between.

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.

Bilateral hypoplastic calcanei.

A previously undescribed anomaly of the calcaneus occurred in an otherwise healthy 2-month-old girl. There was marked bilateral hypoplasia of the calcanei, involving approximately the posterior half of each. The child stood at 15 months and walked at 22 months. At age 5 years, the child had a slight in-toed gait that corrected with dorsiflexion. Her only problem has been some difficulty with shoeware. The etiology of this anomaly remains conjectural.

The participation of cartilage canals in the ossification of the human fetal calcaneum.

The relationship of cartilage canals to the developing ossification centres in the human calcaneum was investigated. The cartilage canals were always present in the calcaneum by 78 mm CR length. The calcaneum has two primary ossification centres. The main centre was identified in the deep part of the calcaneum as a spherical zone of cartilage cells in the proliferative phase between 82 and 120 mm CR length and in the hypertrophic phase between 130-156 mm. Numerous cartilage canals entered the calcaneum from its dorsal and ventral surfaces and, between 106 and 156 mm CR length, they formed vascular arcades around this centre. Between 165 and 175 mm, calcification and marrow space formation were noted involving branches from the adjoining cartilage canals within these areas, which provided vascular osteogenic tissue to the early spaces. The inconstant parachondral centre, when present, may appear first during the fourth month as a periosteal reaction on the inferolateral side in the anterior wall of a deep groove in front of the posterior tuberosity of the calcaneum. By 120 mm CR length, a thin layer of subperiosteal bone was present along with a zone of early hypertrophic cartilage cells deep to it. Calcification and marrow space formation occurred by 165 mm and these marrow spaces were supplied by periosteal buds. Osteoid tissue was formed in them between 186 and 206 mm CR length. The main centre was oval in shape due to its posterolateral extension irrespective of the presence or absence of the parachondral centre.(ABSTRACT TRUNCATED AT 250 WORDS)

[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.

Fetal ossification centers as predictors of gestational age in normal and abnormal pregnancies.

The main fetal ossification centers appear ultrasonically as egg-shaped echo-rich areas. The calcaneal and talar ossification centers are seen at the level of the tarsus osseus, and the distal femoral epiphyseal and proximal tibial epiphyseal ossification centers are found at the level of the knee. Examination of 312 normal pregnancies between 20 and 40 weeks of gestation showed that the calcaneal ossification center was detectable for 24 weeks of gestation, the talar ossification center from 26 weeks, and the distal femoral epiphyseal and proximal tibial epiphyseal ossification centers, from 32 and 36 weeks, respectively. Corresponding figures found for 36 pregnancies showing intrauterine growth retardation (IUGR), examined between 34 and 40 weeks of gestation, were similar for the calcaneal and talar ossification centers but showed delays in the development of the epiphyseal ossification centers, which were particularly striking in cases of symmetrical IUGR. The amniotic fluid lecithin/sphingomyelin ratio was also evaluated in 51 normal pregnancies between 31 and 38 weeks of gestation and was found to be greater than or equal to 2 in every case where the distal femoral epiphyseal ossification center was greater than or equal to 6 mm in diameter. Evaluation of fetal ossification centers may be another useful means to evaluate gestational age in late pregnancy

[Excessively long calcaneal spur. A rudimentary form of calcaneo-navicular synostosis]. / Un bec calcanéen trop long. Une forme rudimentaire de synostose calcanéo-scaphoïdienne.

The authors have seen 5 children aged between 12 and 16 years suffering from a painful foot described as a recurrent sprain. Movements of the subtalar joint were limited and radiographs showed a hypertrophic calcaneal spur projecting towards the navicular but without fusion between the calcaneus and navicular. The calcaneal spurs were resected with good results and with an immediate symptomatic improvement.

The onset of ossification in the human calcaneus.

A (silver) radiographic and microscopic study of the onset of ossification in the calcaneus of 177 human fetuses between 49 and 150 mm C.-R. length has revealed the presence of two independent and developmentally different ossific sites. A lateral locus, intramembranous (parachondral) in origin and precocious in appearance, was observed in slightly over 16% of the fetuses examined between 93 mm (the first appearance of this bone) and 150 mm C.-R. It occupied the vascular connective tissue within the anterior portion of a distinct groove on the inferolateral wall of the cartilaginous calcaneus between the retrotrochlear eminence anterosuperiorly, and the lateral process of the tuber posteroinferiorly. A centrally situated, primary ossific centre, endochondral in origin, was detected in only 11% of the fetuses between 118 mm (the initial appearance of this centre) and 150 mm C.-R. It was situated in the centre of the anterior third of the cartilaginous calcaneus in relation to the sustenaculum tali medially and to a distinct cartilaginous prominence on its lateral surface. Only four fetuses possessed both ossific sites (lateral and central): at 122, 143, 145, and 150 mm C.-R., and in only one of these was continuity established between them. One fetus (122 mm) possessed two independent endochondral centres (superior and inferior).