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 (R² = 0.74) for transverse diameter, y = −7.945 + 3.225 × ln(age) ± 0.262 (R² = 0.78), y = −4.503 + 2.007 × ln(age) ± 0.218 (R² = 0.68), and y = −4.860 + 2.117 × ln(age) ± 0.200 (R² = 0.73) for sagittal diameters of the lateral, middle and medial ends respectively, y = −31.390 + 2.432 × age ± 4.599 (R² = 0.78) for cross-sectional area, and y = 28.161 + 0.00017 × (age)⁴ ± 15.357 (R² = 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.

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.

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.

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.

Solitary osteochondroma of the clavicle

There are no clinicopathologic reports of solitary osteochondroma of the clavicle other than listings in tumor registries. Two boys had solitary asymptomatic osteochondroma, in one at the medial and in the other at the lateral aspect of the clavicle. One underwent excision to correct cosmetic deformity. Several histologic and experimental studies have shown that osteochondromas originate from cells of the growth plate. During development of the clavicle, cartilage appears on both the medial and lateral aspects. Histologic studies have suggested that this cartilage is similar to a physeal growth plate. Experimental studies, however, have shown it to be a randomly organized secondary cartilage that develops in membranous bones once ossification has begun. The occurrence of an osteochondroma at the ends of the clavicle lends support to the theory that the cartilage at the ends of the developing clavicle functions as a growth plate.

Growth of the clavicle and development of clavicular secondary cartilage in the embryonic mouse

Whether secondary cartilage develops in the mammalian clavicle has been a matter of controversy. This study documents, in the embryonic mouse: (a) the onset of clavicular osteogenesis at 14 days of gestation (Theiler stage 22); (b) the appearance of secondary cartilage at 16 days of gestation (Theiler stage 24) and its persistence as a prominent cartilage until 18 days of gestation; (c) that the relative growth rate of the clavicle is much higher (0.097 mg/g body weight/day) between 16 and 17 days of gestation than at later ages (mean of 0.005 mg/g/day between 17 days of gestation and 4 days postnatally), and (d) that secondary cartilage failed to form in clavicles from 15-day-old embryos maintained in vitro. We conclude that secondary cartilage is a feature of the developing mouse clavicle, that it arises when the relative growth rate of the clavicle is highest, and that the most likely stimulus for differentiation of this cartilage is mechanical, muscle-based and associated with rapid relative clavicular growth.

The role of movement and tissue interactions in the development and growth of bone and secondary cartilage in the clavicle of the embryonic chick

There has been debate in the literature concerning whether the clavicle arises by intramembranous ossification, i.e. is a membrane bone, and whether secondary cartilage develops from its periosteal cells. A histological study of carefully staged embryos revealed that pre-clavicular mesenchyme undergoes condensation at H.H. stage 31-32, bone forms by H.H. stage 33 and that a transitory secondary cartilage appears late in H.H. stage 35, only to disappear by H.H. stage 36. Except for the transitory nature of the secondary cartilage, this histogenetic sequence is as seen in craniofacial membrane bones. Enzymic removal of the epithelium overlying clavicular mesenchyme from embryos of H.H. stages 26-34 and chorioallantoic grafting of the isolated mesenchyme, revealed an epithelial requirement for initiation of intramembranous ossification during H.H. stages 26-29, again similar to initiation of craniofacial osteogenesis. Secondary chondrogenesis was initiated neither in embryos paralysed with decamethonium iodide nor when clavicular mesenchyme (H.H. stages 29-33.5) was grafted to the chorioallantoic membranes of paralysed embryos, but did form in a small percentage (16-23%) of clavicles grafted to the membranes of mobile embryos. Failure of chondrogenesis in the former was attributed to a requirement for movement as a proximate chondrogenic stimulus and the low incidence of chondrogenesis in the latter to the stimulus provided by amniotic movements which persist in paralysed embryos. Secondary cartilage did form when clavicles were organ cultured, either submerged, or at the air-medium interface. This stands in contrast to craniofacial membrane bone such as the quadratojugal, which only forms secondary cartilage in vitro when cultured submerged. Growth of the clavicle was shown to increase 53-fold between 10 and 11 days of incubation, an increase which was diminished but not eliminated in paralysed embryos, and which correlated closely with the dramatic increase in embryonic movement which occurs between 10 and 11 days of incubation. Thus, the clavicle of the embryonic chick shares all of the features and epigenetic requirements of the craniofacial the embryonic chick shares all of the features and epigenetic requirements of of the craniofacial membrane bones, but is more dependent upon biomechanical factors for its growth.

Pseudarthrosis of the clavicle. A case report

Congenital pseudarthrosis of the clavicle is a rare condition usually affecting the right side. The causation is unknown, but it is probably due to an environmental factor such as fetal position and excessive pressure from the subclavian artery. The embryology of the clavicle is discussed, and the differential diagnosis and treatment are described. A case occurring in a 12-year-old girl is reported.