Quantitative anatomy of the growing clavicle in the human fetus: CT, digital image analysis, and statistical study.

PURPOSES: Knowledge of dimensions of fetal long bones is useful in both the assessment of fetal growth and early detection of inherited defects. Measurements of the fetal clavicle may facilitate detection of numerous defects, e.g., cleidocranial dysplasia, Holt-Oram syndrome, Goltz syndrome, and Melnick-Needles syndrome. METHODS: Using the methods of CT, digital image analysis, and statistics, the size of the growing clavicle in 42 spontaneously aborted human fetuses (21 males and 21 females) at ages of 18-30 weeks was studied. RESULTS: Without any male-female and right-left significant differences, the best fit growth models for the growing clavicle with relation to age in weeks were as follows: y = -54.439 + 24.673 × ln(age) ± 0.237 (R 2 = 0.86) for length, y = -12.042 + 4.906 × ln(age) ± 0.362 (R 2 = 0.82) for width of acromial end, y = -4.210 + 2.028 × ln(age) ± 0.177 (R 2 = 0.77) for width of central part, y = -4.687 + 2.364 × ln(age) ± 0.242 (R 2 = 0.70) for width of sternal end, y = -51.078 + 4.174 × ln(age) ± 6.943 (R 2 = 0.82) for cross-sectional area, and y = -766.948 + 281.774 × ln(age) ± 19.610 (R 2 = 0.84) for volume. CONCLUSIONS: With no sex and laterality differences, the clavicle grows logarithmically with respect to its length, width, and volume, and linearly with respect to its projection surface area. The obtained morphometric data of the growing clavicle are considered normative for their respective weeks of gestation and may be of relevance in the diagnosis of congenital defects.

Developmental origin of the clavicle, and its implications for the evolution of the neck and the paired appendages in vertebrates.

In fish, the pectoral appendage is adjacent to the head, but during vertebrate evolution a long neck region emerged via caudal relocation of the pectoral appendage. The pectoral appendage is comprised of endochondral portions, such as the humerus and the scapula, and a dermal portion, such as the clavicle, that contributes to the shoulder girdle. In the search for clues to the mechanism of the caudal relocation of the pectoral appendage, the cell lineage of the rostral lateral plate mesoderm was analyzed in chickens. It was found that, despite the long neck region in chickens, the origin of the clavicle attached to the head mesoderm ranged between 1 and 14 somite levels. Because the pectoral limb bud and the endochondral pectoral appendage developed on 15-20 and 15-24 somite levels, respectively, the clavicle-forming region corresponds to the embryonic neck, which suggests that the relocation would have been executed by the expansion of the source of the clavicle. The rostral portion of the clavicle-forming region overlaps the source of the cucullaris muscle, embraces the pharyngeal arches caudally, and can be experimentally replaced with the head mesoderm to form the cucullaris muscle, which implies that the mesodermal portion could have been the head mesoderm and that the clavicle would have developed at the head/trunk boundary. The link between the head mesoderm and the presumptive clavicle appears to have been the developmental constraint needed to create the evolutionarily conserved musculoskeletal connectivities characterizing the gnathostome neck. In this sense, the dermal girdle of the ganathostomes would represent the wall of the branchial chamber into which the endochondral pectoral appendage appears to have attached since its appearance in evolution.

Morphometric study of the two fused primary ossification centers of the clavicle in the human fetus.

PURPOSES: A satisfactory understanding of the clavicle development may be contributing to both the diagnosis of its congenital defects and prevention of perinatal damage to the shoulder girdle. This study was carried out to examine the transverse and sagittal diameters, cross-sectional area and volume of the two fused primary ossification centers of the clavicle. METHODS: Using the methods of CT, digital-image analysis and statistics, the size for two fused primary ossification centers of the clavicle in 42 spontaneously aborted human fetuses at ages of 18-30 weeks was studied. RESULTS: Without any male-female and right-left significant differences, the best fit growth models for two fused primary ossification centers of the clavicle were as follows: y = -31.373 + 15.243 × ln(age) ± 1.424 (R (2) = 0.74) for transverse diameter, y = -7.945 + 3.225 × ln(age) ± 0.262 (R (2) = 0.78), y = -4.503 + 2.007 × ln(age) ± 0.218 (R (2) = 0.68), and y = -4.860 + 2.117 × ln(age) ± 0.200 (R (2) = 0.73) for sagittal diameters of the lateral, middle and medial ends respectively, y = -31.390 + 2.432 × age ± 4.599 (R (2) = 0.78) for cross-sectional area, and y = 28.161 + 0.00017 × (age)(4) ± 15.357 (R (2) = 0.83) for volume. CONCLUSIONS: With no sex and laterality differences, the fused primary ossification centers of the clavicle grow logarithmically in both transverse and sagittal diameters, linearly in cross-sectional area, and fourth-degree polynomially in volume. Our normative quantitative findings may be conducive in monitoring normal fetal growth and screening for inherited faults and anomalies of the clavicle in European human fetuses.

Tunnels and grooves for supraclavicular nerves within the clavicle: review of the literature and clinical impact.

Perforation of the clavicle by supraclavicular nerves is a common anatomical variation. This variation has been reported in several studies based on post-mortem, surgical and radiologic findings, with an overall frequency between 1 and 6.6 %. The penetrating branch passes either through a bony tunnel or a groove on the superior surface of the bone. Entrapment neuropathy of the perforating branch is a documented clinical entity reported in the literature. The intraosseous course of the supraclavicular nerves makes them vulnerable to injury in case of clavicular fractures or during surgical manipulations of these fractures. Furthermore, this variation should be taken into account during the interpretation of chest and shoulder radiographs. The purpose of the current study is to perform an extended review of the relevant literature, highlighting the clinical impact of this variation, as well as to incorporate our own findings into them.

The clavicular part of the pectoralis major: a true entity of the upper limb on anatomical, phylogenetic, ontogenetic, functional and clinical bases. Case report and review of the literature.

The pectoralis major consists of three parts: clavicular, sternocostal and abdominal. The first is usually separated from the deltoid by a deltopectoral triangular space, and often from the sternocostal part by another triangular space. The clavicular part is a new acquisition in Anthropoids, to optimize stabilization of the upper limb to the thorax thus permitting an increased limb mobility in Primates. It is synergetic with the deltoid in arm flexion and even more in adduction. This action is important in Humans, as the coracobrachialis becomes smaller in Mammals. Among non human Primates, those having cranially displaced shoulder joint show a significant clavicular origin of the pectoralis major. The clavicular origin might be necessary in flexion of the forelimb, when the humeral insertion of the muscle is on the same transverse plane as, or cranial to, the sternal manubrium. As to the blood and nerve supply, occurrence in Humans of a neuro-vascular pedicle for the clavicular part, shared with the deltoid, indicates a relatively morpho-functional independence of this part from the rest of the muscle. Under this regard, the width of the lateral pectoral nerve, which supplies the clavicular part of the muscle, may be related to a greater functional ability. Many manoeuvres for plastic and reconstructive surgery are performed by isolating the clavicular part of the pectoralis major. Indeed, this part may be considered as a true, self-standing anatomical entity. In fact, it has morphological individuality, peculiar bony attachments and functional autonomy, so that it is simply adjacent to the sternocostal part. Moreover, according to phylogenesis, this topographic relation develops secondarily, in parallel with the development of the clavicle. Therefore, it may be regarded not only as a simple part of an extrinsic muscle of the thorax, but also as an intrinsic muscle of the upper limb.

A computational model of clavicle bone formation: a mechano-biochemical hypothesis.

Clavicle development arises from mesenchymal cells condensed as a cord extending from the acromion towards the sternal primordium. First two primary ossification centers form, extending to develop the body of the clavicle through intramembranous ossification. However, at its ends this same bone also displays endochondral ossification. So how can the clavicle be formed by both types of ossification? Developmental events associated with clavicle formation have mainly used histological studies as supporting evidence. Nonetheless, mechanisms of biological events such as molecular and mechanical effects remain to be determined. The objective of this work was to provide a mathematical explanation of embryological events based on two serial phases: first formation of an ossified matrix by intramembranous ossification based on three factors: systemic, local biochemical, and mechanical factors. After this initial phase expansion of the ossified matrix follows with mesenchymal cell differentiation into chondrocytes for posterior endochondral ossification. Our model provides strong evidence for clavicle formation integrating molecules and mechanical stimuli through partial differentiation equations using finite element analysis.

Shoulder dystocia.

The frequency of shoulder dystocia in different reports has varied, ranging 0.2-3% of all vaginal deliveries. Once a shoulder dystocia occurs, even if all actions are appropriately taken, there is an increased frequency of complications, including third- or fourth-degree perineal lacerations, postpartum hemorrhage, and neonatal brachial plexus palsies. Health care providers have a poor ability to predict shoulder dystocia for most patients and there remains no commonly accepted model to accurately predict this obstetric emergency. Consequently, optimal management of shoulder dystocia requires appropriate management at the time it occurs. Multiple investigators have attempted to enhance care of shoulder dystocia by utilizing protocols and simulation training.

Morphogenesis of the manubrium of sternum in human embryos: a new concept.

To revisit many theories on fetal development of the manubrium of the sternum, we examined 25 mid-term fetuses at 6-9 weeks of gestation. The initial developmental stage of the manubrium was characterized by a distinct interclavicular mesenchyme that was continuous with the developing clavicles. Because parts of the clavicle in which endochondral ossification occurs originate from the neural crest, the interclavicular mesenchyme seems to be of the same origin. The sternal bands, possibly of the lateral plate origin, were restricted at the anterior ends of the ribs in the paired thoracic walls. The interclavicular mesenchyme extended caudally and laterally to reach the anterior ends of the first ribs, and thus the interclavicular mesenchyme expanded into the intercostoclavicular mesenchyme. Then, the primitive manubrium was delimited by the sternoclavicular joint and its related ligaments, all of which developed from the interclavicular and intercostoclavicular mesenchymes. Although the first ribs were attached to the intercostoclavicular mesenchyme, the former was vimentin-negative in contrast to the latter, positive mesenchyme. Soon afterwards, the small upper end of the sternal bands was integrated into the intercostoclavicular mesenchyme to form the primitive manubrium. The infrahyoid muscles and their supplying nerves maintained a close topographical relation to the interclavicular or intercostoclavicular mesenchyme, whereas the pectoralis major muscle kept attachments to the sternal bands. Consequently, the manubrium of sternum appeared to develop in a complex way at a junction area between derivatives of the neural crest, lateral plate, and somite.

A Runx2 threshold for the cleidocranial dysplasia phenotype.

Cleidocranial dysplasia (CCD) in humans is an autosomal-dominant skeletal disease that results from mutations in the bone-specific transcription factor RUNX2 (CBFA1/AML3). However, distinct RUNX2 mutations in CCD do not correlate with the severity of the disease. Here we generated a new mouse model with a hypomorphic Runx2 mutant allele (Runx2(neo7)), in which only part of the transcript is processed to full-length (wild-type) Runx2 mRNA. Homozygous Runx2(neo7/neo7) mice express a reduced level of wild-type Runx2 mRNA (55-70%) and protein. This mouse model allowed us to establish the minimal requirement of functional Runx2 for normal bone development. Runx2(neo7/neo7) mice have grossly normal skeletons with no abnormalities observed in the growth plate, but do exhibit developmental defects in calvaria and clavicles that persist through post-natal growth. Clavicle defects are caused by disrupted endochondral bone formation during embryogenesis. These hypomorphic mice have altered calvarial bone volume, as observed by histology and microCT imaging, and decreased expression of osteoblast marker genes. The bone phenotype of the heterozygous mice, which have 79-84% of wild-type Runx2 mRNA, is normal. These results show there is a critical gene dosage requirement of functional Runx2 for the formation of intramembranous bone tissues during embryogenesis. A decrease to 70% of wild-type Runx2 levels results in the CCD syndrome, whereas levels >79% produce a normal skeleton. Our findings suggest that the range of bone phenotypes in CCD patients is attributable to quantitative reduction in the functional activity of RUNX2.

Congenital pseudarthrosis of the clavicle: a case report.

Congenital pseudarthrosis of the clavicle is a rare entity of unknown aetiology. Its pathogenesis is related to the embryology of the clavicle. We present a 6-year-old girl with congenital pseudarthrosis of the right clavicle. A prominence was noticed at birth between the middle and distal ends of the clavicle that increased in size when the right shoulder was actively mobilised. Radiographic examination revealed a hypertrophic pseudarthrosis of the clavicle. The pseudarthrosis was resected and the clavicular segments were fixed with an external fixator for 2 months until union. Clinical results were excellent at the 7-year follow-up: the right shoulder was pain-free and the appearance satisfactory. Surgical treatment of congenital pseudarthrosis of the clavicle in children using an external fixator provides a better cosmetic outcome with smaller postoperative scars and avoids a second surgical procedure to remove the implants.

Development of the mouse mandibles and clavicles in the absence of skeletal myogenesis.

In this report we employed double-knock-out mouse embryos and fetuses (designated as Myf5-/-: MyoD-/- that completely lacked striated musculature to study bone development in the absence of mechanical stimuli from the musculature and to distinguish between the effects that static loading and weight-bearing exhibit on embryonic development of skeletal system. We concentrated on development of the mandibles (= dentary) and clavicles because their formation is characterized by intramembranous and endochondral ossification via formation of secondary cartilage that is dependent on mechanical stimuli from the adjacent musculature. We employed morphometry and morphology at different embryonic stages and compared bone development in double-mutant and control embryos and fetuses. Our findings can be summarized as follows: a) the examined mutant bones had significantly altered shape and size that we described morphometrically, b) the effects of muscle absence varied depending on the bone (clavicles being more dependent than mandibles) and even within the same bone (e.g., the mandible), and c) we further supported the notion that, from the evolutionary point of view, mammalian clavicles arise under different influences from those that initiate the furcula (wishbone) in birds. Together, our data show that the development of secondary cartilage, and in turn the development of the final shape and size of the bones, is strongly influenced by mechanical cues from the skeletal musculature.

Fetal clavicle length throughout gestation: a nomogram.

OBJECTIVE: To create a nomogram of fetal clavicle length (CL) throughout gestation. METHODS: Cross-sectional study of patients between 14 and 42 weeks' gestation. Inclusion criteria consisted of well-established dates (consistent with early ultrasound), singleton, non-anomalous fetuses, and intact amniotic membranes. Sonographic measurements included biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), femur length (FL), humerus length (HL) and sonographically estimated fetal weight (SEFW). For every case, the average of three separate measurements of the CL was used. The 5th, 50th and 95th centiles were obtained by least squares regression. Pearson's correlation coefficient and associated P-values for the relationships between CL and other biometric measurements were calculated. The data were compared to a nomogram of the CL generated in 1985 from the measurement of 85 fetuses. RESULTS: A total of 623 consecutive patients were studied. In all but three cases, CL was successfully measured. Mean maternal age was 27.7 +/- 6.2 years, median gravidity 3 (range, 1-14) and median parity 1 (range, 0-9). Mean CL (mm) = -75.30 + 32.70*ln(GA) and SD = -0.41 + 0.08328*GA, where ln represents the natural logarithm and GA the gestational age in weeks. Fetal CL correlated significantly and strongly with BPD, HC, AC, HL, FL and the logarithm of SEFW, with Pearson correlation values of 0.973, 0.977, 0.976, 0.979, 0.977 and 0.979, respectively (all P < 0.001). Measurements according to comparable 1985 data were consistently substantially below the present data (smaller CL for any given GA except below 17 weeks' gestation). CONCLUSIONS: We propose a new nomogram of CL, which differs significantly from the previously published nomogram. We suggest that the present data reflect the use of high-resolution ultrasound technology and propose that these data, based on a large number of fetuses, replace the previous nomogram. We also suggest that the '1 mm = 1 week' rule of thumb should no longer be used, since it can be erroneous by as much as 6 weeks.

On the development of the shoulder girdle in Crocidura russula (Soricidae) and other placental mammals: evolutionary and functional aspects.

The development of the shoulder girdle was studied in embryonic stages and a neonate of Crocidura russula using histological sections and 3-D reconstructions. Neonatal stages of Suncus etruscus and Mesocricetus auratus, both altricial placentals, were also studied. The earliest stage of C russula, in which the scapula is still partially blastematous, has already a supraspinous fossa. The dorsal portion of the scapular spine does not develop from the anterior margin of the scapula. Its mode of development varies among the placentals studied to date. In some it is completely appositional bone, in others it consists of bone formed mostly by endochondral ossification of a dorsal cartilaginous process stemming from the acromium. During development the supraspinatus muscle increases in size in proportion to the infraspinatus muscle and the humeral head increases in size in relation to the glenoid fossa. Placentals have secondary cartilage in the sternal and acromial ends of the clavicle, a derived feature absent in Marsupialia. Even the most altricial placentals have a more developed shoulder girdle at birth than any newborn marsupial studied to date.

A population of caudally migrating cranial neural crest cells: functional and evolutionary implications.

The deployment of the cranial neural crest is central to the patterning of the skeletomuscular elements of the vertebrate head, with cranial muscles invariably attaching to skeletal elements formed by crest from the same axial level. Here we demonstrate, through gene expression analysis, ablation studies and fate-mapping, the existence of a population of caudally migrating cranial crest that arise from the postotic neural tube. As with the rest of the postotic crest, these cells express the transcription factor Mafb, and this marker can be used to highlight their posterior migration. They pass out between the anterior somite and the otic vesicle, before turning caudally and running along the base of the somites. With long-term fate mapping, we show that these cells migrate to the clavicle and settle at the site of formation of the attachment point for the cleidohyoid muscle. As such, the influence of the cranial neural crest in organising skeletomuscular connectivity seems to extend beyond the head into the trunk. These results are of further importance as they help explain how, even though the pectoral girdle and the skull became physically dissociated during tetrapod evolution, skeletomuscular connectivity has been maintained.

Development of the clavicles in birds and mammals.

Clavicles (collar bones) are variably present in mammals. Furculae (wishbones)--which may or may not be homologous with clavicles--are variably present and/or fused in birds and present in theropod dinosaurs. In this overview the development of clavicles and furculae is discussed with special attention to modes of skeletogenesis (whether intramembranous or endochondral), numbers of centres of ossification (one in chick furculae; two in murine clavicles), presence of cartilage (primary in clavicles, secondary in furculae), evidence from experimental analysis and from mutations for dependence of both clavicular and furcular growth on mechanical stimulation, and syndromes and mutations affecting clavicular development leading to both under and over development. J. Exp. Zool. 289:153-161, 2001.

Increased expression of TGF-beta 2 in osteoblasts results in an osteoporosis-like phenotype.

The development of the skeleton requires the coordinated activities of bone-forming osteoblasts and bone-resorbing osteoclasts. The activities of these two cell types are likely to be regulated by TGF-beta, which is abundant in bone matrix. We have used transgenic mice to evaluate the role of TGF-beta 2 in bone development and turnover. Osteoblast-specific overexpression of TGF-beta 2 from the osteocalcin promoter resulted in progressive bone loss associated with increases in osteoblastic matrix deposition and osteoclastic bone resorption. This phenotype closely resembles the bone abnormalities seen in human hyperparathyroidism and osteoporosis. Furthermore, a high level of TGF-beta 2 overexpression resulted in defective bone mineralization and severe hypoplasia of the clavicles, a hallmark of the developmental disease cleidocranial dysplasia. Our results suggest that TGF-beta 2 functions as a local positive regulator of bone remodeling and that alterations in TGF-beta 2 synthesis by bone cells, or in their responsiveness to TGF-beta 2, may contribute to the pathogenesis of metabolic bone disease.

An anatomical and embryological study of the clavicle in cats (Felis domestus) and sheep (Ovis aries) during the prenatal period.

The prenatal development of the clavicular area was studied in two species: the domesticated sheep, which lacks a clavicle, and the cat, with a nonfunctional, rudimentary clavicle. A morphological and computerized morphometric study of the clavicle was performed in 18 cat embryos between 25 and 48 days of gestation, and in 12 sheep embryos of 37-45 days. One group of embryos was processed with double staining in toto according to Hanken and Wassersug in 1981. The other group was examined by histological techniques: hematoxylineosin-Alcian blue and picrosirius. In both species, clavicular ossification is delayed (27% of gestation time elapsed in sheep and 53% in cats) compared to 16% in humans. Histological and morphological differences in shape and length of the clavicle were observed in both species. The clavicle is transient in sheep, whereas in the cat it persists with little change. In neither species does secondary cartilage develop. In cats, the periosteum is well developed with active osteoblasts, whereas in sheep the clavicle is surrounded by a single layer of epitheloid cells and the periosteum is less developed and contains osteoclasts. These results suggest that the morphogenetic pattern for the clavicle is altered at about day 34 in cats and day 40 in sheep, and is subsequently partly inhibited in the former and blocked in the latter.

Expression and function of Pax 1 during development of the pectoral girdle.

Pax 1 is a member of the paired-box containing gene family. Expression has previously been observed in the developing sclerotomes and later in the anlagen of the intervertebral discs. Analysis of Pax 1-deficient undulated mice revealed an important role for this gene in the development of the axial skeleton, in which Pax 1 apparently functions as a mediator of notochordal signals during sclerotome differentiation. Here we demonstrate that Pax 1 is also transiently expressed in the developing limb buds. A comparative phenotypic analysis of different undulated alleles shows that this expression is of functional significance. In mice that are mutant for the Pax 1 gene severe developmental abnormalities are found in the pectoral girdle. These include fusions of skeletal elements which would normally remain separate, and failures in the differentiation of blastemas into cartilaginous structures. Although Pax 1 is also expressed in the developing hindlimb buds and Wolffian ridge, no malformations could be detected in the corresponding regions of Pax 1 mutant mice. These findings show that, in addition to its role in the developing vertebral column, Pax 1 has an important function in the development of parts of the appendicular skeleton.

Embriogénesis del área clavicular en oveja (ovis aries) y gato (felis catus) / Embryogenesis of clavicle area in sheep (ovis aries) and cat (felis catus)

La forma y complejidad de la clavícula varía en las distintas especies animales: es máxima en aquellas que vuelan o mantienen una posición bípeda y reducida o no existe en las que se apoyan y desplazan sobre sus cuatro miembros. Se estudió la evolución prenatal del área clavicular en felinos: animales con clavícula afuncional y ovinos que no presentan este carácter. Se realizó un estudio morfológico y morfométrico computacional de la clavícula en 12 embriones y fetos felinos entre 25 y 48 días de gestación y 6 embriones y fetos ovinos de 37 a 45 días. En ambas especies se detectó un desplazamiento en el inicio de la osificación clavicular (27 por ciento de gestación transcurrida en ovino y 53 por ciento en felinos) lo cual es tardío en comparación con el 16 por ciento de la especie humana. La forma y longitud de la clavícula es diferente en las dos especies, su presencia es efímera en ovinos, en cambio, en el gato se mantiene con pocos cambios. Ninguna de las dos desarrolla cartílagos secundarios. Si bien especies tendrían información genética para desarrollar este caracter, su aparición heterocrónica en relación a las especies claviculados, sumado a la falta de formación de cartílagos secunadarios serían responsables de la involución que la lleva a mantener una presencia vestigial o su regresión definitiva