Quantitative anatomy of the ulna's shaft primary ossification center in the human fetus

PURPOSE

There has been little information in the medical literature regarding the growing ulna in the human fetus, though such knowledge appears to be potentially useful in diagnosing skeletal dysplasias, characterized by a disrupted or completely halted growth of the fetus. Therefore, longitudinal measurements of long bones are extremely conducive in assessing both pregnancy and fetal anatomy.

MATERIALS AND METHODS

Using methods of CT, digital-image analysis and statistics, the size of the ulna's shaft primary ossification center in 48 (26 males and 22 females) spontaneously aborted human fetuses aged 17-30 weeks was studied.

RESULTS

With no sex differences, the best fit growth dynamics for the ulna's shaft primary ossification center was modeled by the following functions: y = - 8.476 + 1.561 × age ± 0.019 for its length, y = - 2.961 + 0.278 × age ± 0.016 for its proximal transverse diameter, y = - 0.587 + 0.107 × age ± 0.027 for its middle transverse diameter, y = - 2.865 + 0.226 × age ± 0.295 for its distal transverse diameter, y = - 50.758 + 0.251 × (age)2 ± 0.016 for its projection surface area, and y = - 821.707 + 52.578 × age ± 0.018 ± 102.944 for its volume.

CONCLUSIONS

The morphometric characteristics of the ulna's shaft primary ossification center show neither sex nor bilateral differences. The ulna's shaft primary ossification center grows linearly with respect to its length, transverse dimensions and volume, and follows a quadratic function with respect to its projection surface area. The obtained morphometric data of the ulna's shaft primary ossification center is considered normative for respective prenatal weeks and may be of relevance in both the estimation of fetal ages and the diagnostic process of congenital defects.

Mouse TBX3 mutants suggest novel molecular mechanisms for Ulnar-mammary syndrome

The transcription factor TBX3 plays critical roles in development and TBX3 mutations in humans cause Ulnar-mammary syndrome. Efforts to understand how altered TBX3 dosage and function disrupt the development of numerous structures have been hampered by embryonic lethality of mice bearing presumed null alleles. We generated a novel conditional null allele of Tbx3: after Cre-mediated recombination, no mRNA or protein is detectable. In contrast, a putative null allele in which exons 1-3 are deleted produces a truncated protein that is abnormally located in the cytoplasm. Heterozygotes and homozygotes for this allele have different phenotypes than their counterparts bearing a true null allele. Our observations with these alleles in mice, and the different types of TBX3 mutations observed in human ulnar-mammary syndrome, suggest that not all mutations observed in humans generate functionally null alleles. The possibility that mechanisms in addition to TBX3 haploinsufficiency may cause UMS or other malformations merits investigation in the human UMS population.

Orofaciodigital syndrome type IV (Mohr-Majewski syndrome): report of a family with two affected siblings

We report on sibling fetuses with orofaciodigital syndrome (OFDS) type IV (Mohr-Majewski syndrome). The 1st was a 13-week-old fetus with hypertelorism; a median cleft defect of the upper lip, soft palate, and uvula; a polypoid lower lip and multiple frenula of the tongue adherent to the mandible; a congenital heart defect; pre- and postaxial polydactyly of the upper and preaxial polydactyly of the lower limbs; and an intersex genitalia. However, the shortening of both arms and forearms was particularly striking, with shortening of the ulna and ulnar deviation of both hands. The 2nd fetus was of the same parents, was 11 weeks old, and presented with a similar spectrum of malformations. The features of both fetuses showed a transitional phenotype between the OFDS type II (Mohr syndrome) and the short rib-polydactyly syndrome type II (Majewski syndrome), thus extending the known spectrum of the OFDS type IV.

Possible roles of Runx1 and Sox9 in incipient intramembranous ossification

We evaluated the detailed expression patterns of Runx1 and Sox9 in various types of bone formation, and determined whether Runx1 expression was affected by Runx2 deficiency and Runx2 expression by Runx1 deficiency. Our results indicate that both Runx1 and Sox9 are intensely expressed in the future osteogenic cell compartment and in cartilage. The pattern of Runx1 and Sox9 expression suggests that both genes could potentially be involved in incipient intramembranous bone formation during craniofacial development.

INTRODUCTION

Runx1, a gene essential for hematopoiesis, contains RUNX binding sites in its promoter region, suggesting possible cross-regulation with Runx2 and potential regulatory roles in bone development. On the other hand, Sox9 is essential for chondrogenesis, and haploinsufficiency of Sox9 leads to premature ossification of the skeletal system. In this study, we studied the possible roles of Runx1 and Sox9 in bone development.

MATERIALS AND METHODS

Runx1, Runx2/Osf2, and Sox9 expression was evaluated by in situ hybridization in the growing craniofacial bones of embryonic day (E)12-16 mice and in the endochondral bone-forming regions of embryonic and postnatal long bones. In addition, we evaluated Runx2/Osf2 expression in the growing face of Runx1 knockout mice at E12.5 and Runx1 expression in Runx2 knockout mice at E14.5.

RESULTS

Runx1 and Sox9 were expressed in cartilage, and the regions of expression expanded to the neighboring Runx2-expressing osteogenic regions. Expression of both Runx1 and Sox9 was markedly downregulated on ossification. Runx1 and Sox9 expression was absent in the regions of endochondral bone formation and in actively modeling or remodeling bone tissues in the long bones as well as in ossified craniofacial bones. Runx2 expression was not affected by gene disruption of Runx1, whereas the expression domains of Runx1 were extended in Runx2(-/-) mice compared with wildtype mice.

CONCLUSIONS

Runx1 and Sox9 are specifically expressed in the osteogenic cell compartments in the craniofacial bones and the bone collar of long bones, and this expression is downregulated on terminal differentiation of osteoblasts. Our results suggest that Runx1 may play a role in incipient intramembranous bone formation.

Protection from ethanol‐induced limb malformations by the superoxide dismutase/catalase mimetic, EUK‐134

Based on previous in vitro studies that have illustrated prevention of ethanol-induced cell death by antioxidants, using an in vivo model, we have tested the anti-teratogenic potential of a potent synthetic superoxide dismutase plus catalase mimetic, EUK-134. The developing limb of C57BL/6J mice, which is sensitive to ethanol-induced reduction defects, served as the model system. On their ninth day of pregnancy, C57BL/6J mice were administered ethanol (two intraperitoneal doses of 2.9 g/kg given 4 h apart) alone or in combination with EUK-134 (two doses of 10 mg/kg). Pregnant control mice were similarly treated with either vehicle or EUK-134, alone. Within 15 h of the initial ethanol exposure, excessive apoptotic cell death was observed in the apical ectodermal ridge (AER) of the newly forming forelimb buds. Forelimb defects, including postaxial ectrodactyly, metacarpal, and ulnar deficiencies, occurred in 67.3% of the ethanol-exposed fetuses that were examined at 18 days of gestation. The right forelimbs were preferentially affected. No limb malformations were observed in control fetuses. Cell death in the AER of embryos concurrently exposed to ethanol and EUK-134 was notably reduced compared with that in embryos from ethanol-treated dams. Additionally, the antioxidant treatment reduced the incidence of forelimb malformations to 35.9%. This work illustrates that antioxidants can significantly improve the adverse developmental outcome that results from ethanol exposure in utero, diminishing the incidence and severity of major malformations that result from exposure to this important human teratogen.

The cyclin-dependent kinase inhibitor p57(Kip2) mediates proliferative actions of PTHrP in chondrocytes

Parathyroid hormone-related peptide (PTHrP) is a positive regulator of chondrocyte proliferation during bone development. In embryonic mice lacking PTHrP, chondrocytes stop proliferating prematurely, with accelerated differentiation. Because the bone phenotype of mice lacking the cyclin-dependent kinase inhibitor p57(Kip2) is the opposite of the PTHrP-null phenotype, we hypothesized that PTHrP's proliferative actions in chondrocytes might be mediated by opposing p57. We generated p57/PTHrP-null embryos, which showed partial rescue of the PTHrP-null phenotype. There was reversal of the loss of proliferative chondrocytes in most bones, with reversal of the accelerated differentiation that occurs in the PTHrP-null phenotype. p57 mRNA and protein were upregulated in proliferative chondrocytes in the absence of PTHrP. Metatarsal culture studies confirmed the action of PTHrP to decrease p57 mRNA and protein levels in a model in which parathyroid hormone (PTH), used as an analog of PTHrP, increased chondrocyte proliferation rate and the length of the proliferative domain. PTH treatment of p57-null metatarsals had no effect on proliferation rate in round proliferative chondrocytes but still stimulated proliferation in columnar chondrocytes. These studies suggest that the effects of PTHrP on both the rate and extent of chondrocyte proliferation are mediated, at least in part, through suppression of p57 expression.

Teratogenic Mechanisms of Longitudinal Deficiency and Cleft Hand

In order to better understand the teratogenic mechanisms of congenital defects of the digits, we analyzed clinical cases and induced similar types of congenital hand anomalies in rat fetuses by oral administration of busulfan. In clinical cases, radial and ulnar deficiencies had common characteristic features. We induced radial and ulnar deficiencies in rat fetuses with the same drug. Radial and ulnar deficiencies induced in rats have similar clinical manifestations and these anomalies might be caused by the same teratogenic mechanism. Then, the formation of the digital rays was examined histologically. The results of histological examination suggested that these deficiencies were not caused by localized damage of the limb bud. They also suggested that the cause of missing digits in longitudinal deficiency is closely related to a deficit of mesenchymal cells in the limb bud. Cleft hand is considered to be one of the types of longitudinal deficiency. However, several investigators have suggested that the abnormal induction of finger rays in the process of formation of fingers induced central polydactyly, osseous syndactyly and also cleft hand. X-rays of the clinical cases and skeletal changes of the anomalies induced in rats appear to demonstrate that cleft hand formation proceeds from osseous syndactyly and central polydactyly. The results of our experimental study show that the critical periods of central polydactyly, osseous syndactyly and cleft hand are the same. They also suggest that central polydactyly, syndactyly and cleft hand might be induced when the same teratogenic factor acts on embryos at the same developmental stage in the human being. Because they have a similar causation, cleft hand, syndactyly and central polydactyly should be classified into the same entity, that is, abnormal induction of digital rays. Based on these clinical and experimental studies, we modified the Swanson classification. In our modified classification, typical cleft hand, syndactyly and polydactyly are included in the same category of abnormal induction of digital rays as the fourth new category.

Multiple roles of Hoxa11 and Hoxd11 in the formation of the mammalian forelimb zeugopod

Mutations in the 5' or posterior murine Hox genes (paralogous groups 9-13) markedly affect the formation of the stylopod, zeugopod and autopod of both forelimbs and hindlimbs. Targeted disruption of Hoxa11 and Hoxd11 or Hoxa10, Hoxc10 and Hoxd10 result in gross mispatterning of the radius and ulna or the femur, respectively. Similarly, in mice with disruptions of both Hoxa13 and Hoxd13, development of the forelimb and hindlimb autopod is severely curtailed. Although these examples clearly illustrate the major roles played by the posterior Hox genes, little is known regarding the stage or stages at which Hox transcription factors intersect with the limb development program to ensure proper patterning of the principle elements of the limb. Moreover, the cellular and/or molecular bases for the developmental defects observed in these mutant mice have not been described. In this study, we show that malformation of the forelimb zeugopod in Hoxa11/Hoxd11 double mutants is a consequence of interruption at multiple steps during the formation of the radius and ulna. In particular, reductions in the levels of Fgf8 and Fgf10 expression may be related to the observed delay in forelimb bud outgrowth that, in turn, leads to the formation of smaller mesenchymal condensations. However, the most significant defect appears to be the failure to form normal growth plates at the proximal and distal ends of the zeugopod bones. As a consequence, growth and maturation of these bones is highly disorganized, resulting in the creation of amorphous bony elements, rather than a normal radius and ulna.

IL-1- and TNF-induced bone resorption is mediated by p38 mitogen activated protein kinase

We have previously shown that p38 mitogen-activated protein kinase (MAPK) inhibitors, which block the production and action of inflammatory cytokines such as tumor necrosis factor (TNF) and interleukin-1 (IL-1), are effective in models of bone and cartilage degradation. To further investigate the role of p38 MAPK, we have studied its activation in osteoblasts and chondrocytes, following treatment with a panel of proinflammatory and osteotropic agents. In osteoblasts, significant activation of p38 MAPK was observed following treatment with IL-1 and TNF, but not parathyroid hormone, transforming growth factor-beta (TGF-beta), 1,25(OH)(2)D(3), insulin-like growth factor-1 (IGF-1), or IGF-II. Similar results were obtained using primary bovine chondrocytes and an SV40-immortalized human chondrocyte cell line, T/C28A4. SB 203580, a selective inhibitor of p38 MAPK, inhibited IL-1 and TNF-induced p38 MAPK activity and IL-6 production (IC(50)s 0.3--0.5 microM) in osteoblasts and chondrocytes. In addition, IL-1 and TNF also activated p38 MAPK in fetal rat long bones and p38 MAPK inhibitors inhibited IL-1- and TNF-stimulated bone resorption in vitro in a dose-dependent manner (IC(50)s 0.3--1 microM). These data support the contention that p38 MAPK plays a central role in regulating the production of, and responsiveness to, proinflammatory cytokines in bone and cartilage. Furthermore, the strong correlation between inhibition of kinase activity and IL-1 and TNF-stimulated biological responses indicates that selective inhibition of the p38 MAPK pathway may have therapeutic utility in joint diseases such as rheumatoid arthritis (RA).

Which morphologies of synovial folds result from degeneration and/or aging of the radiohumeral joint: an anatomic study with cadavers and embryos

The synovial folds of the radiohumeral joints in cadaveric elbows from 179 elderly subjects and 40 embryos were investigated macroscopically and histologically to determine any morphologic changes caused by aging or degeneration. The anterior and posterior folds found in the elderly population shared characteristics of folds seen in embryos, with some modifications, and were thought to originate from the primitive septum. Proportionally, the length, width, and thickness of these folds were consistent between adults and embryos. However, the embryonic folds showed a homogenous morphology. In contrast, in the adult the anterior fold was characterized by a shorter and narrower villous pattern, and the posterior fold tended to be wider. Lateral extension of the anterior or posterior folds was also observed. Moreover, the lateral fold, never seen in embryos, was present and characterized by a hard plicate pattern in the adult. These derived or specific morphologies in adults probably result from alterations in the movement of the radial head caused by aging.

Developmental morphological and histological studies on structures of the human fetal elbow joint

In the present work, morphological changes in the developing human elbow joint were studied at different prenatal ages (8, 12, 16, 20, 29 and 40 weeks) and were compared with the same structures in the adult joint. The elbow joint had gone through its most important developmental changes during the 20th week of prenatal life, probably due to the direct dynamic effect of the newly developed fetal movement. During later prenatal development, the articular surfaces of the lower end of humerus and the upper ends of radius and ulna developed their characteristic congruencies, so that the highly curved convexities always articulate with the highly curved concavities. That process progressed postnatally and even till adult age. In full-term infants it was found that the lower end of humerus had acquired its adult shape, while the shape of the upper ends of radius and ulna were still not fully developed. They continued development in postnatal life even till adult age. In the present work, histological prenatal studies were done on longitudinal sections from the back of the capsule and synovial tissue, early (8 weeks) and late in full term, and the results were also compared with the same structures in adults. It was found that at all ages, the capsules were formed of cellular and fibrous elements, but at early prenatal age (8 weeks), this cellular condensation was more massive and prominent while in full-term infants, it became generally more fibrous, but was still different compared to adults. Basic cellular structures of the synovial tissue changed very little during the late prenatal developmental stage, as it did not become more fibrous than cellular during these periods, but differences in vascularity became more obvious. The cartilaginous content of the articular surface at 8 weeks was highly cellular with very little intercellular matrix. In contrast to that of full term, this cartilage became fully chondrogenous with a notable decrease in cellular density and massive increase in matrix content.

Development of the human elbow joint

Many studies have been published on the development of the human elbow joint, but authors disagree on its morphogenetic timetable. Most discrepancies center on the cavitation of the elbow joint (including the humeroradial, humeroulnar, and superior radioulnar joints), and the organization of the tunnel of the ulnar nerve. We summarize our observations on the development of the elbow joint in 49 serially sectioned human embryonic (n = 28) and fetal (n = 21) upper limbs. During week 12, ossification begins in the epiphyses of the elements comprising the elbow joint. At the end of the embryonic period, the shallow groove between the posterior aspect of the medial epicondyle and the olecranon process, begins to be visible. The elbow joint cavity appears in O'Rahilly stage 21 (51 days) at the level of the humeroulnar and humeroradial interzones. Formation of the cavity begins at the medialmost portion of the humeroradial interzone and the lateralmost portion of the humeroulnar interzone. The annular ligament begins to develop in O'Rahilly stage 21 (51 days), and the superior radioulnar joint cavity appears between this ligament and the lateral aspect of the head of the radius during O'Rahilly stage 23 (56 days). We established the morphogenetic timetable of the human elbow joint.

Prenatal ultrasound diagnosis of a femur-fibula-ulna complex during the first half of pregnancy

A case of fetal femur-fibula-ulna (FFU) complex diagnosed by ultrasound is presented. Ultrasonographic features of a fetus displaying bilateral femoral hypoplasia, aplasia of the right forearm and the right hand, ray defects of the left hand are described. The importance of an early diagnosis of this malformation is emphasized with respect to parental counselling concerning prognosis and further prenatal management.

1,25-dihydroxyvitamin D3 inhibits parathyroid hormone-related peptide mRNA expression in fetal rat long bones in culture

When fetal rat long bones are incubated in the presence of 10(-8) M 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], steady-state parathyroid hormone-related peptide (PTHrP) mRNA levels are decreased. This decrease is temporary: it is observed as soon as after 3 h of exposure and reaches a nadir after 6 h. At that time, PTHrP mRNA levels are significantly lower in the experimental than in the control bones. However the inhibitory effect vanishes after 24 h, despite continuous exposure to 1,25(OH)2D3 for even 48 h. This is the first report showing that PTHrP mRNA expression can be regulated in rat fetal long bones in vitro by 1,25(OH)2D3.

Retinoid signaling is required for chondrocyte maturation and endochondral bone formation during limb skeletogenesis

Retinoids have long been known to influence skeletogenesis but the specific roles played by these effectors and their nuclear receptors remain unclear. Thus, it is not known whether endogenous retinoids are present in developing skeletal elements, whether expression of the retinoic acid receptor (RAR) genes alpha, beta, and gamma changes during chondrocyte maturation, or how interference with retinoid signaling affects skeletogenesis. We found that immature chondrocytes present in stage 27 (Day 5.5) chick embryo humerus exhibited low and diffuse expression of RARalpha and gamma, while RARbeta expression was strong in perichondrium. Emergence of hypertrophic chondrocytes in Day 8-10 embryo limbs was accompanied by a marked and selective up-regulation of RARgamma gene expression. The RARgamma-rich type X collagen-expressing hypertrophic chondrocytes lay below metaphyseal prehypertrophic chondrocytes expressing Indian hedgehog (Ihh) and were followed by mineralizing chondrocytes undergoing endochondral ossification. Bioassays revealed that cartilaginous elements in Day 5.5, 8.5, and 10 chick embryo limbs all contained endogenous retinoids; strikingly, the perichondrial tissues surrounding the cartilages contained very large amounts of retinoids. Implantation of beads filled with retinoid antagonist Ro 41-5253 or AGN 193109 near the humeral anlagens in stage 21 (Day 3.5) or stage 27 chick embryos severely affected humerus development. In comparison to their normal counterparts, antagonist-treated humeri in Day 8.5-10 chick embryos were significantly shorter and abnormally bent; their diaphyseal chondrocytes had remained prehypertrophic Ihh-expressing cells, did not express RARgamma, and were not undergoing endochondral ossification. Interestingly, formation of an intramembranous bony collar around the diaphysis was not affected by antagonist treatment. Using chondrocyte cultures, we found that the antagonists effectively interfered with the ability of all-trans-retinoic acid to induce terminal cell maturation. The results provide clear evidence that retinoid-dependent and RAR-mediated mechanisms are required for completion of the chondrocyte maturation process and endochondral ossification in the developing limb. These mechanisms may be positively influenced by cooperative interactions between the chondrocytes and their retinoid-rich perichondrial tissues.

Regulation of chondrocyte differentiation by Cbfa1

Cbfa1, a developmentally expressed transcription factor of the runt family, was recently shown to be essential for osteoblast differentiation. We have investigated the role of Cbfa1 in endochondral bone formation using Cbfa1-deficient mice. Histology and in situ hybridization with probes for indian hedgehog (Ihh), collagen type X and osteopontin performed at E13.5, E14.5 and E17.5 demonstrated a lack of hypertrophic chondrocytes in the anlagen of the humerus and the phalanges and a delayed onset of hypertrophy in radius/ulna in Cbfa1-/- mice. Detailed analysis of Cbfa1 expression using whole mount in situ hybridization and a lacZ reporter gene reveled strong expression not only in osteoblasts but also in pre-hypertrophic and hypertrophic chondrocytes. Our studies identify Cbfa1 as a major positive regulator of chondrocyte differentiation.

The evolution of the distal radio-ulnar joint

The pectoral girdle and the distal radio-ulnar joint have evolved over a period of 400 million years. Clinical circumstances exist that may represent atavistic development in modern man. Current understanding of this complex area does not explain all clinical situations.

Ossification and growth rates of the limb long bones during the prehatching period in the quail (Coturnix coturnix japonica)

The timing of ossification and the growth of six long bones of the prehatching period in the quail was studied. Ninety-nine quail eggs were incubated and in total nine fetuses were selected daily from the sixth to the sixteenth day of incubation. The fetuses were stained with alizarine and alcian blue double colouration. The fetuses were studied under the stereoscopic microscope and linear measurements were obtained from the humerus, ulna, radius, femur, tibia and fibula. The first appearance of the primary ossification centres in the diaphysis of the studied bones was found to occur between the sixth and the seventh day of incubation. Different growth patterns between the bones of the leg and of the wing were observed. Humerus and tibia showed the greatest growth rate while the radius and fibula showed the lowest.

The mouse Ulnaless mutation deregulates posterior HoxD gene expression and alters appendicular patterning

The semi-dominant mouse mutation Ulnaless alters patterning of the appendicular but not the axial skeleton. Ulnaless forelimbs and hindlimbs have severe reductions of the proximal limb and less severe reductions of the distal limb. Genetic and physical mapping has failed to separate the Ulnaless locus from the HoxD gene cluster (Peichel, C. L., Abbott, C. M. and Vogt, T. F. (1996) Genetics 144, 1757–1767). The Ulnaless limb phenotypes are not recapitulated by targeted mutations in any single HoxD gene, suggesting that Ulnaless may be a gain-of-function mutation in a coding sequence or a regulatory mutation. Deregulation of 5′ HoxD gene expression is observed in Ulnaless limb buds. There is ectopic expression of Hoxd-13 and Hoxd-12 in the proximal limb and reduction of Hoxd-13, Hoxd-12 and Hoxd-11 expression in the distal limb. Skeletal reductions in the proximal limb may be a consequence of posterior prevalence, whereby proximal misexpression of Hoxd-13 and Hoxd-12 results in the transcriptional and/or functional inactivation of Hox group 11 genes. The Ulnaless digit phenotypes are attributed to a reduction in the distal expression of Hoxd-13, Hoxd-12, Hoxd-11 and Hoxa-13. In addition, Hoxd-13 expression is reduced in the genital bud, consistent with the observed alterations of the Ulnaless penian bone. No alterations of HoxD expression or skeletal phenotypes were observed in the Ulnaless primary axis. We propose that the Ulnaless mutation alters a cis-acting element that regulates HoxD expression specifically in the appendicular axes of the embryo.

Ulnaless (Ul), a regulatory mutation inducing both loss-of-function and gain-of-function of posterior Hoxd genes

Ulnaless (Ul), an X-ray-induced dominant mutation in mice, severely disrupts development of forearms and forelegs. The mutation maps on chromosome 2, tightly linked to the HoxD complex, a cluster of regulatory genes required for proper morphogenesis. In particular, 5′-located (posterior) Hoxd genes are involved in limb development and combined mutations within these genes result in severe alterations in appendicular skeleton. We have used several engineered alleles of the HoxD complex to genetically assess the potential linkage between these two loci. We present evidence indicating that Ulnaless is allelic to Hoxd genes. Important modifications in the expression patterns of the posterior Hoxd-12 and Hoxd-13 genes at the Ul locus suggest that Ul is a regulatory mutation that interferes with a control mechanism shared by multiple genes to coordinate Hoxd function during limb morphogenesis.

Control of the limb bud outgrowth in quail-chick chimera

It is well known that the apical ectodermal ridge (AER) and the zone of polarizing activity (ZPA) play a major role in growth and patterning of the limb. But a mechanism underlying species-specific growth of the limb has not yet been fully elucidated. To investigate the role of AER and ZPA in limb size control, we constructed quail-chick limb chimeras. When we grafted a whole forelimb bud from one species to another, the size of the developed grafted limb was comparable to the limb of the donor species. Moreover, we demonstrated that neither the interspecific substitution of the posterior half region of the limb bud containing the ZPA nor the exchange of the ectodermal component of the limb involving the AER could alter the species-specific size of the limb. These results indicate that the factors affecting the size of the limb are already involved in the mesodermal component of the limb bud at stage 20 of chick embryo. Thus, the mesoderm dictates limb specificity including size.

Skeleton pattern and joint formation in chorioallantoic grafts lacking the anterior or posterior necrotic zones

Skeletal pattern and joints formation were examined in chick limb bud grafts using the chorioallantoic grafting method which enabled the separation of the limb bud from the body wall and also restricted the influence of some of the morphogenetic zones of the limb. The embryonic chick limb buds from the experimental group were transplanted without the prospective anterior necrotic zone (ANZ) or the posterior necrotic zone (PNZ). Transplants with intact limb bud material served as the control group. Elimination of the ANZ or PNZ mainly affected the skeleton of the zeugopod and elbow joint. Most grafts lacking the ANZ or PNZ showed fusion of the ulna and radius and complete regression of the elbow joint. The most common abnormality was fusion of the humerus, ulna and radius into a single cartilaginous block which was rarely observed in control grafts. As the separation of the ulna and radius depends on cell death in the "opaque patch', it is likely that mechanical elimination of the ANZ or PNZ suppressed cell death in this zone and caused a typical fusion in the zeugopod skeleton and elbow joint and growth retardation in grafts lacking the ANZ or PNZ.

On the assessment of the growth patterns in human fetal limbs: longitudinal measurements and allometric analysis

The total length (TL) and length of the ossified part (OL) of some long bones of the upper (humerus, ulna, radius) and lower limb (femur, tibia, fibula) were evaluated in 58 aborted human fetuses (crown-rump length, CRL, between 38 and 116 mm, developmental age from 8 to 14 weeks). The specimens, without any detectable malformation, were cleared and double-stained with alcian blue and alizarin red S to obtain a differential detection of the ossified part within the comprehensive outline between the cartilaginous epiphyses. The correlation between the values of TL and OL and those of CRL emphasized that the systematic OL measurement in limb long bones correlated better than TL with development age, since OL increased faster than TL. TL and OL also correlated with the CRL by bivariate allometry (ln y = ln a + b ln x) and the data obtained showed that they grew with positive allometry. The comparison between the cumulative values of the bones examined in each limb showed that both TL and OL grew relatively faster in the lower limb than the upper; the greatest growth rate was found for OL in the lower limb. These results many provide a tool for a comprehensive assessment of long bone growth patterns and may be useful in determining fetal growth even in incomplete specimens, in which one or some long bones can still be measured.

Citral, an inhibitor of retinoic acid synthesis, modifies chick limb development

Exogenously applied retinoic acid (RA) is known to affect cartilage pattern in developing and regenerating limbs. There are, however, few reports which analyze the participation of endogenous RA in limb pattern formation. Using an organ culture system, we attempted to reduce the concentration of endogenous RA in the developing chick wing buds by the treatment with citral (3,7-dimethyl-2,6-octadienal), an inhibitor of retinoic acid formation. After this treatment, the cultured wing buds were grafted to the stumps of host embryos. These citral-treated limb buds frequently formed truncated cartilage elements and the defects were rescued by simultaneous treatment with an appropriate concentration of RA. These results suggest that endogenous RA plays a role in chick limb bud development.

Histologic analysis of fetal ulnar variance

Twenty-eight fetal wrists aged 5 to 21 weeks gestation were examined histologically to assess ulnar variance. There was a trend from ulna negative to ulna neutral among this population. Of 10 wrists in group I (5-8 weeks gestation), 8 were ulna negative and 2 were ulna neutral. Of nine wrists in group II (11-13 weeks gestation), three were ulna negative and six were ulna neutral. Of nine wrists in group III (18-21 weeks gestation), two were ulna negative and seven were ulna neutral. Overall, 13 embryos demonstrated an ulna negative variance; the remainder had ulna neutral variance. These results are significantly different than the incidence of ulnar variance in adults. With growth, factors must occur that change this fetal relationship of radius to ulna.

Effects of experimental conditions on the release of 45calcium from prelabeled fetal mouse long bones

Embryonic/neonatal bones in culture are commonly used for the study of osteoclastic resorption in vitro. For this purpose, the release of 45calcium (45Ca) from prelabeled bones is measured as an index of resorption. We studied 45Ca release from two types of long bone explants after different preparation methods: 17-day-old fetal mouse radii/ulnae with and without cartilage ends (intact radii/ulnae and shafts, respectively), and intact 18-day old metacarpals/metatarsals. In addition, we examined the effect of different culture conditions, such as cultures performed under the surface of the medium or at the interphase of medium and air, on 45Ca release and histology. When intact radii/ulnae were cultured under the surface of the medium, there was always a significant amount (10%) of net basal 45Ca release (corrected for physicochemical exchange) that was not due to osteoclastic resorption, as it could not be suppressed by inhibitors of resorption even at high concentrations. Moreover, histologically TRAcP-positive cells were almost absent after culture and the bone marrow/stromal cells in the center of the bone appeared necrotic, possibly due to a lack of oxygen. Under these culture conditions, osteoclasts could survive in shafts as well as in PTH-stimulated intact radii/ulnae, but a constant amount of 10% 45Ca, not due to resorption, was still released in the medium. When these explants were cultured at the interphase of medium and air, basal and stimulated 45Ca release originated from osteoclastic resorption. In contrast, in 18-day-old fetal mouse metacarpals/metatarsals, the experimental conditions applied did not affect 45Ca release, which was always due to resorption of the explants by osteoclasts.(ABSTRACT TRUNCATED AT 250 WORDS)

Multivariate analysis of limb long bone growth during the human prenatal period

Prenatal development of the human limb bones (humerus, ulna, radius, femur, tibia, fibula) was studied. Cross-sectional data, consisting of 21 anthropometric measures of these bones were collected from 122 Japanese fetuses between the gestational ages of 18 and 40 weeks. Principal component analysis was applied to the data to provide multivariate assessments of morphological patterning among the variables. Three orthogonal components that accounted for 94.2% of the overall sample variation were extracted. The first component accounted for 88.2% of the variation and represented an axis of overall body size that was dependent on gestational age. The second and third components both reflected a trend in shape involving the cartilaginous parts of the humerus and femur. The findings indicated that different growth factors existed between the ossified and cartilaginous parts of fetal long bones. Multivariate allometric coefficients were extracted from the first principal component. The variables that were related to the construction of the articulate showed positive allometry, and the central widths of the diaphysis showed negative allometry compared with total size. In prenatal skeleton, certain shape changes are functionally linked to and required by changes in body size. A comparison among the coefficients of long bone length revealed that lower limb bones grew faster than upper limb bones during the period under study here. Allometric coefficients were equivalent among bones within a limb, whereas homologous bones in the upper and lower limb grew at different rates.

Heparin fails to potentiate the effects of IL-1 beta-mediated bone resorption of fetal rat long bones in vitro

Heparin has been identified as a potent modulator of bone resorption. Heparin induces osteoporosis during long-term administration and has been shown in vitro to enhance the effects of other bone resorbing factors, including parathyroid hormone. In this study, we examined the effects of heparin on the bone-resorbing activity of the inflammatory cytokine IL-1 beta. Resorption was determined by measuring release of previously incorporated 45Ca from fetal rat long bones cultured in medium supplemented with either 0.1% bovine serum albumin or 10% heat-inactivated fetal calf serum. Heparin, in the absence of serum, decreased basal resorption at 4 and 10 units/ml, and slightly increased resorption at 30 units/ml. Heparin had no effect on IL-1 beta-stimulated resorption. In the presence of serum, heparin induced a two-fold increase in resorption alone, however, when cocultured with IL-1 beta, heparin failed to further enhance IL-1 beta-stimulated resorption.

Structural requirements for bisphosphonate actions in vitro

We investigated the structural requirements for the binding of bisphosphonates to bone mineral and the relation between their affinity for bone and their effects on bone resorption in vitro. For this we used fetal mouse long bones in culture and bisphosphonates with variable R1 and R2 structures. In addition, we studied the effect of structural differences in the incorporation of calcium into bone. We found that bisphosphonates containing a hydroxyl group in the R1 position have the highest affinity for bone mineral. This was related to their capacity to inhibit the incorporation of calcium into long bones but not to their antiresorptive potency. The latter was primarily determined by R2. Furthermore, the effect of bisphosphonates on calcification, but not on resorption of bone explants, was mainly determined by the mode of addition. The continuous presence of bisphosphonate during culture inhibited calcification even at very low concentrations, but short incubation of the bones with relatively high concentrations had no effect. This is probably a result of differences in the availability of the compound to the process of calcification. Because, in vivo, the more potent bisphosphonates inhibit resorption without adversely affecting mineralization of the skeleton and they disappear rapidly from the circulation after administration, we suggest that cultures of bone explants incubated with bisphosphonates for short times rather than cultures in which the drugs are continuously present provide more accurate information about the in vivo effect of these compounds on both resorption and calcification.

The growth of long bones in human embryological and fetal upper limbs and its relationship to other developmental patterns

Measurements were made of the long bones of the upper limbs (humerus, ulna, radius) of 58 aborted embryos and fetuses, developmental age from 8 to 14 weeks, crown-rump length (CRL) between 38 and 116 mm. The specimens were cleared and double-stained, using alcian blue and alizarin red S for a differential detection of cartilage and bone. The values of both the total length (TL) and the ossified part (OL) of each long bone were related to the fetal developmental age previously estimated by freshly measured CRL. The relationship to another developmental pattern, i.e. the number of ossified centres in the vertebral column, suggested that the OL values could be much more significant than TL for the assessment of fetal growth.

Expression of mRNA of parathyroid hormone-related peptide in fetal bones of the rat

Previous studies have indicated that 19-day-old fetal long bones of the rat contain an adenylyl cyclase-stimulating activity antigenically related to parathyroid hormone-related peptide. To ascertain its origin, Northern blotting and in situ hybridization histochemistry were performed. Results demonstrate that mRNA of parathyroid hormone-related peptide is present in RNA extracted from fetal long bones of the rat and that cells responsible for its production are localized in the periosteum. These cells are not mature osteoblasts because they do not synthesize mRNA of osteocalcin. Thus the present study shows that parathyroid hormone-related peptide could be produced locally, at least in part, in the skeleton of fetal rats.

Comparative skeletogenesis of the forearm of the little brown bat (Myotis lucifugus) and the Norway rat (Rattus norvegicus)

This study describes, quantifies, and compares the growth and development of the volant forelimb morphology of Myotis lucifugus with that of the terrestrial forelimb morphology of Rattus norvegicus. In M. lucifugus there is 1) accelerated growth in forearm length after parturition, 2) cessation in growth of the midshaft diameter of the ulna just after the onset of osteogenesis, 3) proximal fusion of the radius and ulna, which results in the radius occupying 97% of the articular surface of the elbow joint in adults, 4) fusion between the cartilaginous distal epiphyses of the radius and ulna which results in formation of a radioulnar bridge that becomes fully ossified in adults, and 5) incomplete ossification of the ulna with a section of the diaphysis becoming ligamentous. None of these events occurs during development in R.norvegicus.

Does lateral bending lead to bowing fracture in an infantile lower arm?

In a postmortem study on 50 lower arms of fetuses of the 25th week of gestation and newborn we performed three-point bending experiments to find out the stability of the lower arm after bending to the resulting fracture. Lower arms with intact soft tissue show an elastic behavior when bent from the side until fracture occurs. Applying the loading deflection diagrams we could classify the fractures into three types which differ significantly by means of bending moment, maximal deflection per unit length, and force required.

Direct and sex-specific enhancement of bone formation and calcification by sex steroids in fetal mice long bone in vitro (biochemical and morphometric study

The study was carried out to examine the direct effect of the sex hormones 17 beta-estradiol (E2) and testosterone on the modeling of cultured fetal mouse long bones separated according to their sex. The culture system used allowed for the simultaneous assessment of bone growth, mineralization, and resorption on each bone. Bones from 16-day-old male and female mouse fetuses were cultured in BGJ medium, supplemented with either 10% fetal calf serum or 4 mg/ml BSA (serum-free medium) for 48 h. The bones were harvested, and their length; the length of their diaphyses; their hydroxyproline, calcium, and phosphorus contents; and their 45Ca release were measured. Histomorphometric analyses on midlongitudinal sections of bones from parallel experiments were also performed. The results indicate that in medium supplemented with 10% fetal calf serum, E2 had a dose-dependent stimulatory effect on bone formation and mineralization at 10(-7) and 10(-9) M, with no effect on bone resorption. This effect was specific to bones from female mice and to E2, since 17-alpha-estradiol had no effect. Testosterone had similar effects specific to bones from male mice, resulting in the stimulation of bone formation and mineralization at 10(-7)- and 10(-9)-M concentrations. These effects were absent when serum-free medium was used. E2 and testosterone had an anabolic effect on endochondral and periosteal bone formation and mineralization, but no effect on bone resorption. This effect is dependent on the presence of a serum factor(s).

Adenylate cyclase stimulating activity immunologically similar to parathyroid hormone-related peptide can be extracted from fetal rat long bones

We observed that culture medium conditioned with fetal rat long bones contained peptides immunologically related to the parathyroid hormone-related peptide of malignancy (PTHrP) and stimulated cyclic AMP production in canine renal cortical membranes. Because the adenylate cyclase stimulating activity (CSA) of the medium increased when bone resorption was stimulated, it was suspected that these peptides were stored in the matrix and released during the resorption process. In this work, we extracted the noncollagenous proteins of fetal rat long bones and found that the extract contained significant amounts of CSA. The biologic activity of the extract was abolished after trypsin digestion and eluted at 24 and 37 kD on filtration HPLC. The CSA of bone extract and of both HPLC peaks could be inhibited by 3-34 and 7-34 parathyroid hormone analogs. It was not blocked by an antiserum directed against the N-terminal region of parathyroid hormone, but it was significantly inhibited after an overnight preincubation with an antiserum directed against the 1-11 fragment of PTHrP. One band migrating at 18 kD could be visualized after SDS-PAGE electrophoresis of bone extract and immunoblotting with the anti-PTHrP antiserum. We conclude that an adenylate cyclase stimulator immunologically similar to PTHrP is present in the matrix of fetal rat long bones. Adenylate cyclase stimulating peptides of lower molecular weight found in bone-conditioned medium could be active fragments formed by proteolysis during the resorption process.

[Experimental study on radial ray deficiency in rat]

Radial ray deficiency were induced in WKAH/Hkm rat fetuses by maternal administration of myleran on either day 10.0, 10.5, or 11.0 of pregnancy. In radial ray deficiency, the severity of absence of the fingers was classified into three types and the degree of radial arrest was classified into four types. The degree of radial arrest was closely related to the severity of absence of the fingers. The greater the dose of myleran was given, the more severe was the radial arrest. As for the soft tissue, the more radial the muscular, nervous and vascular systems were located, the more they were severely affected. The degree of dysplasia of muscular, nervous, and arterial systems depended on the status of dysplasia of the radius. The skeletal and soft tissue anomalies in rats were the same as those in human beings, suggesting that exposure to some environmental factors at a sensitive period of embryogenesis may cause radial deficiency in humans. The critical period for radial ray deficiency is one day later than that for ulnar deficiency in rats, which may contribute to the greater frequency of radial deficiency than ulnar deficiency in humans. It was suggested that the difference of the susceptibility to the environmental factors may determine the phenotype of longitudinal ray deficiencies in embryogenesis.

Congenital proximal radio-ulnar synostosis: clinical and anatomical features

A new radiographic classification is proposed based on a study of 31 cases of congenital proximal radio-ulnar synostosis in which close correlation was observed between the clinical and radiographic pictures. The authors attempt to clarify some aspects of the pathogenesis of this rare disease.

Tubular hand bone growth during the latter half of the prenatal period: an allometric analysis

The growth of the 19 tubular hand bones from fetal months 5 to 9 was studied by the allometric method. The hand bones were carefully dissected under a low power stereoscopic microscope. The length and breadth of all bones was found to be monophasic in relation to crown-rump length. In general, maximum bone and ossified shaft lengths in the same row group demonstrate similar allometric coefficients. The specific growth rate of ossified shaft length for all fetal hand bones is greater than the growth rate of maximum length. The highest allometric coefficients for both maximum length and ossified shaft length were obtained from the middle phalanges. The shape of the metacarpals and distal phalanges becomes thinner, while the other bones become thicker or maintain their length-breadth ratio. The relative growth pattern of the first proximal phalanx differed from the middle phalangeal group of the other digits. This suggests that current nomenclatures for the three bones of the pollex is appropriate.

The effect of ipriflavone (TC-80) on bone resorption in tissue culture

The fetal long bone culture system developed by Raisz for the assessment of bone resorption was modified to improve the sensitivity, by using radii and ulnae separately, based on the observation of the consistently higher release of 45Ca from the radii than ulnae. Effects of ipriflavone (TC-80), an isoflavonoid derivative currently under clinical trial for its effect on osteoporosis, on bone resorption were examined in this new system. Ipriflavone and its metabolites (5 out of 6) at 10 micrograms/ml or more inhibited basal 45Ca release from bones. The inhibitory effects were still demonstrated in the presence of submaximal concentration of parathyroid hormone (12.5 ng/ml). The effect of ipriflavone on bone resorption was apparently not due to its toxicity on bone cells, since the inhibition was reversible.

Parathyroid hormone and calcitonin modify inositol phospholipid metabolism in fetal rat limb bones

Inositol-containing phospholipids are believed to be intimately involved in the first steps of cellular signalling by certain hormones and neurotransmitters. We examined whether parathyroid hormone (PTH) and calcitonin (CT), two hormones that affect bone physiology, would elicit changes in inositol-phospholipid metabolism in cultured bone. [3H]inositol readily entered into the tissue phospholipid pool in fetal rat limb bones, and incorporated into phosphatidylinositol (92.9%), phosphatidylinositol-4-P (4.5%), and phosphatidylinositol-4,5-P2 (2.6%). PTH enhanced the incorporation of inositol into PtdIns in limb bones following 2- or 24-h hormone treatments. The effect of PTH was dose dependent (EC50 of 0.3-0.4 nM) and occurred in a concentration range similar to that for hormone-stimulated bone resorption. In contrast, 24-h treatment with CT-inhibited inositol incorporation, also in a dose-dependent manner. Two-hour CT treatment had variable effects on labeling. CT inhibited the stimulatory effect of PTH at both 2 and 24 h. The effects induced by PTH and CT were specific for PtdIns and were independent of the [3H]inositol pool size. These results indicate that inositol-phospholipid turnover can be modified during the action of these hormones on bone tissue. Although the time course of hormone-stimulated inositol incorporation observed here is slower than that found in other tissues, the change in phosphatidylinositol metabolism could mediate delayed effects of PTH or CT. Alternatively, alterations induced by PTH and CT in bone cell membranes, cell populations, or in the mineralized matrix could conceivably result in secondary changes in phosphatidylinositol metabolism.

Ulnar ray a/hypoplasia: evidence for a developmental field defect on the basis of genetic heterogeneity. Report of three Brazilian families

We report on five Brazilian patients from three unrelated families with congenital anomalies of the upper limbs. Ulnar aplasia/hypoplasia was the main reason for examining these patients. Evidence for existence of an ulnar developmental field is based on genetic heterogeneity. Clinical and genetic aspects of the ulnar ray defects are discussed.

The development of fetal mice long bones in vitro: an assay of bone modeling

This study was carried out to develop an in vitro system for the analysis of bone modeling (coincidentally occurring bone growth, formation, mineralization, and resorption) as is seen during bone development. The fetuses of pregnant mice previously labeled with 45Ca were removed on Days 15, 16, and 17 of gestation. The radii and ulnae were dissected free and cultured for up to 6 days in a chemically defined medium (BGJ) supplemented with fetal calf serum or human serum albumin and 150 micrograms/ml vitamin C. The change in bone length over the culture period was measured as were the changes in calcium and phosphorus content, the hydroxyproline: protein ratio, and the percent 45Ca released into the medium. The effect of insulin and parathyroid extract on the system was also examined. The results indicate that cultures of 16-day-old fetal bones provided the most suitable model. During culture there was a continuous increase in bone length as well as calcium and phosphorus content in the ratio of 2:1, a significant increase in the hydroxyproline content, and a continuous release of 45Ca into the medium. Parathyroid extract caused a dose-dependent inhibition of both growth in diaphyseal length and calcium and phosphorus uptake with an increase in 45Ca release into the medium. Insulin at 10(-9) M and 10(-10) M resulted in a significant increase in diaphyseal length and calcium and phosphorus uptake without affecting 45Ca release. These results indicate that the assay described is suitable for the study of bone modeling, providing a means to measure bone growth, formation, calcification, and resorption. The direct effect of various factors on bone modeling can also be measured.

Ultrasonic measurement of the growth of fetal limb bones in normal pregnancy

From sonographic measurements, normal curves for the fetal growth of extremity bones (humerus, ulna, radius, femur, tibia) were established. They are based on 40 measurements for each bone weekly between the 17th and 41st gestational week. Tabs. II and III summarize the data. Figs. 4-8 furnish the smoothened normal curves for 10th, 50th and 90th percentile. Values for the 14-16 and the 42nd week were extrapolated from the results and the course of the curves. A comparison of sonographic measurements with findings from dissected stillborn fetuses (Tab. I) demonstrated an accuracy of the sonographic measurements of +/- 2 mm. We established that the radius is significantly shorter than the ulna (Figs. 1 and 2) whereas tibia and fibula are of identical length (Fig. 3). The growth rate of the femur throughout pregnancy is greater than that of the other bones. The mathematical correlation between pregnancy duration and length of bones is best described by polynomial formulas (Tabs. IV and V), because the growth rate declines from 4 mm per week in early mid-trimester to 1 mm per week toward the end of the third trimester. A comparison with other published data shows the values in the current study to be within the range of variability of these publications. Sonographic measurements of extremity bones are suitable for determining gestational age.

High-resolution sonographic assessment of the fetal extremities

Recent advances in ultrasound technology, especially phased-array sonography, now permit striking visualization of fetal morphology. Although several reports document the sonographic appearance of the fetal appendicular skeleton, no reports describe the nonosseous structures of the fetal limbs. Prior to the middle of the second trimester of pregnancy, adequate size and intrinsic subject contrast enable distinction among numerous limb structures. The sonographic features of the fetal limbs are described, with emphasis upon the visible nonosseous structures. All images were obtained between August 1983 and January 1984 using a 128-channel phased-array real-time scanner (Acuson) with a 3.5-MHz transducer.

[Biometry of the large bones of fetal extremities in the 3d trimester]

Ultrasound measurement of head, thorax and the limb bones femur, tibia, humerus and radius was made of 285 fetuses with known gestational age. In addition measurements of the fibula were obtained in 120 fetuses and of the ulna in 125 fetuses. With the use of these data a normal growth curve for each limb bone was established, which can be helpful in detecting late fetal limb malformations as heterozygous achondroplasia. All limb bones show a nearly linear growth rate so that the length of the bones can alternatively be used to determine gestational age. The linear relationship between growth of the limb bones and the fetal head can be used to diagnose fetal head malformations as microcephaly.

Development of the lizard limb as shown by the distribution of [35S]sulphate incorporation

In the forelimb of the lizard, Chalcides ocellatus (Forskal), the chondrogenic pattern is laid down in a proximodistal direction commencing with the proximal regions. The chondrogenic skeletal pattern along the antero-posterior axis gives humerus, radius, ulna and the distal region. The radius and ulna differ in their length and level of sulphation. The end result is a periodic pattern resembling that in other amniotes. The peripheral areas and distal region show an almost uniform uptake of [35S]sulphate, the basement membrane taking up [35S]sulphate at a higher rate between embryonic stages with limb lengths 0.2 mm and 0.75 mm.

Estimation of gestational age from measurements of fetal long bones

The general practice of using fetal long bone growth charts to derive gestational age does not yield mathematically valid results. The authors tried to calculate gestational age from the lengths of long bones (femur, humerus, tibia, ulna) from 12 to 40 weeks of gestation. The combined use of the four bones allows a good estimation of gestational age that may be useful should the biparietal diameter measurement be unreliable, unobtainable, or abnormal.

A longitudinal study of fetal limb growth

This article is based on the same population that was previously reported. In this paper, we report the results concerning the fetal limb bones. Growth charts and velocity charts were produced for the humerus, ulna, femur, and tibia. The results are compared with those of the cross-sectional literature.

Ultrasonic evaluation of fetal limb growth: part II

The length of the ulna, radius, tibia, and fibula was measured in 220 normal fetuses. Computerized curve fitting provided normal values of bone length for age and biparietal diameter. Ratios of the length of the different bones are presented. Possible applications of these measurements include: in utero diagnosis of fetal dwarfism, limb malformations, microcephaly, determination of gestational age, archeological dating of fetuses, and forensic applications.