Talk:Musculoskeletal System - Shoulder Development

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Cite this page: Hill, M.A. (2021, November 30) Embryology Musculoskeletal System - Shoulder Development. Retrieved from


Genetics of scapula and pelvis development: An evolutionary perspective

Curr Top Dev Biol. 2019;132:311-349. doi: 10.1016/bs.ctdb.2018.12.007. Epub 2019 Jan 7.

Young M1, Selleri L2, Capellini TD3.


In tetrapods, the scapular and pelvic girdles perform the important function of anchoring the limbs to the trunk of the body and facilitating the movement of each appendage. This shared function, however, is one of relatively few similarities between the scapula and pelvis, which have significantly different morphologies, evolutionary histories, embryonic origins, and underlying genetic pathways. The scapula evolved in jawless fish prior to the pelvis, and its embryonic development is unique among bones in that it is derived from multiple progenitor cell populations, including the dermomyotome, somatopleure, and neural crest. Conversely, the pelvis evolved several million years later in jawed fish, and it develops from an embryonic somatopleuric cell population. The genetic networks controlling the formation of the pelvis and scapula also share similarities and differences, with a number of genes shaping only one or the other, while other gene products such as PBX transcription factors act as hierarchical developmental regulators of both girdle structures. Here, we provide a detailed review of the cellular processes and genetic networks underlying pelvis and scapula formation in tetrapods, while also highlighting unanswered questions about girdle evolution and development.

© 2019 Elsevier Inc. All rights reserved.

KEYWORDS: Chondrogenesis; Genetic network; Girdle; Human evolution; Patterning; Pbx; Pelvis; Scapula PMID: 30797513 PMCID: PMC6430119 DOI: 10.1016/bs.ctdb.2018.12.007


Congenital Anatomical Variant of the Clavicle

Anat Rec (Hoboken). 2017 Aug;300(8):1401-1408. doi: 10.1002/ar.23596. Epub 2017 Apr 4.

Viciano J1, Urbani V2, D'Anastasio R1,3.


The aim of this study is to present a rare abnormality of the clavicle (Code: SGS01) that was discovered in an ossuary in the Church of San Gaetano (Sulmona, central Italy; XVII-XIX centuries CE). In the middle third, the clavicle had three areas with losses of substance in the form of oval-shaped foramina with maximum diameters of 1-2 cm that were located in the anterior and superior surfaces of the diaphysis. The margins of these foramina were well defined and rounded, and the surfaces of the canal walls were smooth. Additionally, there were no zones of bony activity or reactive changes around the foramina. This new congenital anomaly of the clavicle and blood vessels is consistent with a variant that might have originated during fetal growth in which the subclavian vein or artery remained included during the process of ossification of the clavicle. Anat Rec, 300:1401-1408, 2017.

© 2017 Wiley Periodicals, Inc.

KEYWORDS: anthropology; blood vessels; bone anomaly; circulatory disturbances; paleopathology PMID: 28296289 DOI: 10.1002/ar.23596

The role of embryo movement in the development of the furcula

J Anat. 2017 Mar;230(3):435-443. doi: 10.1111/joa.12571. Epub 2016 Dec 6.

Pollard AS1, Boyd S1, McGonnell IM1, Pitsillides AA1.


The pectoral girdle is a complex structure which varies in its morphology between species. A major component in birds is the furcula, which can be considered equivalent to a fusion of the paired clavicles found in many mammals, and the single interclavicle found in many reptiles. These elements are a remnant of the dermal skeleton and the only intramembranous bones in the trunk. Postnatally, the furcula plays important mechanical roles by stabilising the shoulder joint and acting as a mechanical spring during flight. In line with its mechanical role, previous studies indicate that, unlike many other intramembranous bones, furcula growth during development can be influenced by mechanical stimuli. This study investigated the response of individual aspects of furcula growth to both embryo immobilisation and hypermotility in the embryonic chicken. The impact of altered incubation temperature, which influences embryo motility, on crocodilian interclavicle development was also explored. We employed whole-mount bone and cartilage staining and 3D imaging by microCT to quantify the impact of rigid paralysis, flaccid paralysis and hypermobility on furcula growth in the chicken, and 3D microCT imaging to quantify the impact of reduced temperature (32-28 °C) and motility on interclavicle growth in the crocodile. This revealed that the growth rates of the clavicular and interclavicular components of the furcula differ during normal development. Total furcula area was reduced by total unloading produced by flaccid paralysis, but not by rigid paralysis which maintains static loading of embryonic bones. This suggests that dynamic loading, which is required for postnatal bone adaptation, is not a requirement for prenatal furcula growth. Embryo hypermotility also had no impact on furcula area or arm length. Furcula 3D shape did, however, differ between groups; this was marked in the interclavicular component of the furcula, the hypocleideum. Hypocleideum length was reduced by both methods of immobilisation, and interclavicle area was reduced in crocodile embryos incubated at 28 °C, which are less motile than embryos incubated at 32 °C. These data suggest that the clavicular and interclavicle components of the avian furcula respond differently to alterations in embryo movement, with the interclavicle requiring both the static and dynamic components of movement-related loading for normal growth, while static loading preserved most aspects of clavicle growth. Our data suggest that embryo movement, and the mechanical loading this produces, is important in shaping these structures during development to suit their postnatal mechanical roles.

© 2016 Anatomical Society.

KEYWORDS: chicken embryo; clavicle; crocodile embryo; furcula; intramembranous ossification PMID: 27921302 PMCID: PMC5314390 DOI: 10.1111/joa.12571


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

J Anat. 2016 Oct;229(4):536-48. doi: 10.1111/joa.12502. Epub 2016 Jun 9.

Nagashima H1, Sugahara F2, Watanabe K1, Shibata M3, Chiba A1, Sato N1.

Erratum in Corrigendum. [J Anat. 2018] Abstract 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.

© 2016 Anatomical Society.

KEYWORDS: clavicle; development; evolution; neck; paired appendage PMID: 27279028 PMCID: PMC5013064 DOI: 10.1111/joa.12502 [Indexed for MEDLINE] Free PMC Article

Development of the shoulder girdle musculature

Dev Dyn. 2016 Mar;245(3):342-50. doi: 10.1002/dvdy.24378. Epub 2016 Jan 14.

Pu Q1, Huang R2, Brand-Saberi B1.


The muscles of the shoulder region are important for movements of the upper limbs and for stabilizing the girdle elements by connecting them to the trunk. They have a triple embryonic origin. First, the branchiomeric shoulder girdle muscles (sternocleidomastoideus and trapezius muscles) develop from the occipital lateral plate mesoderm using Tbx1 over the course of this development. The second population of cells constitutes the superficial shoulder girdle muscles (pectoral and latissimus dorsi muscles), which are derived from the wing premuscle mass. This muscle group undergoes a two-step development, referred to as the "in-out" mechanism. Myogenic precursor cells first migrate anterogradely into the wing bud. Subsequently, they migrate in a retrograde manner from the wing premuscle mass to the trunk. SDF-1/CXCR4 signaling is involved in this outward migration. A third group of shoulder muscles are the rhomboidei and serratus anterior muscles, which are referred to as deep shoulder girdle muscles; they are thought to be derived from the myotomes. It is, however, not clear how myotome cells make contact to the scapula to form these two muscles. In this review, we discuss the development of the shoulder girdle muscle in relation to the different muscle groups.

© 2015 Wiley Periodicals, Inc.

KEYWORDS: morphogenesis; myogenesis; shoulder girdle PMID: 26676088 DOI: 10.1002/dvdy.24378


Body structures and physical complaints in upper limb reduction deficiency: a 24-year follow-up study

PLoS One. 2012;7(11):e49727. doi: 10.1371/journal.pone.0049727. Epub 2012 Nov 30.

Postema SG, van der Sluis CK, Waldenlöv K, Norling Hermansson LM. Source Centre for Rehabilitation Research, Örebro County Council, Örebro, Sweden ; Department of Rehabilitation Medicine, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.


OBJECTIVE: To describe upper body structures associated with upper limb reduction deficiency and the development of these structures over time, to examine the presence of physical complaints in this population, and to compare body structures and complaints between groups based on prosthesis use. DESIGN: Prospective cohort study with a follow-up period of 24 years, with matched able-bodied controls. SUBJECTS: Twenty-eight patients with unilateral below-elbow reduction deficiency fitted with myoelectric prostheses, aged 8-18 years at inclusion. METHOD: Measurements of upper arm, trunk and spine were performed and study-specific questionnaires were answered at baseline and follow-up; the Brief Pain Inventory and the Quick Disability of Arm, Shoulder, and Hand questionnaires were answered at follow-up. RESULTS: Both at baseline and follow-up, within-subjects differences in structures of the arm and trunk were shown in patients but not in controls. Spinal deviations, although small, were greater in patients compared to controls. Self-reported disability was higher in patients compared to controls. Differences in back pain and effect of prostheses use could not be shown. CONCLUSIONS: Patients with unilateral below-elbow reduction deficiency have consistent differences in upper body structures. Deviations of the spine, probably of functional origin, do not progress to clinically relevant scoliosis.

PMID 23226218



Commitment of chondrogenic precursors of the avian scapula takes place after epithelial-mesenchymal transition of the dermomyotome

BMC Dev Biol. 2010 Aug 31;10:91.

Wang B, Pu Q, De R, Patel K, Christ B, Wilting J, Huang R.

Department of Anatomy and Cell Biology, University of Goettingen, Kreuzbergring 36, 37075 Goettingen, Germany. Abstract BACKGROUND: Cells of the epithelially organised dermomyotome are traditionally believed to give rise to skeletal muscle and dermis. We have previously shown that the dermomyotome can undergo epithelial-mesenchymal transition (EMT) and give rise to chondrogenic cells, which go on to form the scapula blade in birds. At present we have little understanding regarding the issue of when the chondrogenic fate of dermomyotomal cells is determined. Using quail-chick grafting experiments, we investigated whether scapula precursor cells are committed to a chondrogenic fate while in an epithelial state or whether commitment is established after EMT.

RESULTS: We show that the hypaxial dermomyotome, which normally forms the scapula, does not generate cartilaginous tissue after it is grafted to the epaxial domain. In contrast engraftment of the epaxial dermomyotome to the hypaxial domain gives rise to scapula-like cartilage. However, the hypaxial sub-ectodermal mesenchyme (SEM), which originates from the hypaxial dermomyotome after EMT, generates cartilaginous elements in the epaxial domain, whereas in reciprocal grafting experiments, the epaxial SEM cannot form cartilage in the hypaxial domain.

CONCLUSIONS: We suggest that the epithelial cells of the dermomyotome are not committed to the chondrogenic lineage. Commitment to this lineage occurs after it has undergone EMT to form the sub-ectodermal mesenchyme.

PMID: 20807426

Scapula development is governed by genetic interactions of Pbx1 with its family members and with Emx2 via their cooperative control of Alx1

Development. 2010 Aug 1;137(15):2559-69.

Capellini TD, Vaccari G, Ferretti E, Fantini S, He M, Pellegrini M, Quintana L, Di Giacomo G, Sharpe J, Selleri L, Zappavigna V.

Department of Cell and Developmental Biology, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10021, USA. Abstract The genetic pathways underlying shoulder blade development are largely unknown, as gene networks controlling limb morphogenesis have limited influence on scapula formation. Analysis of mouse mutants for Pbx and Emx2 genes has suggested their potential roles in girdle development. In this study, by generating compound mutant mice, we examined the genetic control of scapula development by Pbx genes and their functional relationship with Emx2. Analyses of Pbx and Pbx1;Emx2 compound mutants revealed that Pbx genes share overlapping functions in shoulder development and that Pbx1 genetically interacts with Emx2 in this process. Here, we provide a biochemical basis for Pbx1;Emx2 genetic interaction by showing that Pbx1 and Emx2 can bind specific DNA sequences as heterodimers. Moreover, the expression of genes crucial for scapula development is altered in these mutants, indicating that Pbx genes act upstream of essential pathways for scapula formation. In particular, expression of Alx1, an effector of scapula blade patterning, is absent in all compound mutants. We demonstrate that Pbx1 and Emx2 bind in vivo to a conserved sequence upstream of Alx1 and cooperatively activate its transcription via this potential regulatory element. Our results establish an essential role for Pbx1 in genetic interactions with its family members and with Emx2 and delineate novel regulatory networks in shoulder girdle development.

PMID: 20627960

A Bayesian approach to age estimation in modern Americans from the clavicle

J Forensic Sci. 2010 May;55(3):571-83. Epub 2010 Apr 8.

Langley-Shirley N, Jantz RL.

Department of Anthropology, University of Tennessee, 250 South Stadium Hall, Knoxville, TN 37996, USA. Abstract Clavicles from 1289 individuals from cohorts spanning the 20th century were scored with two scoring systems. Transition analysis and Bayesian statistics were used to obtain robust age ranges that are less sensitive to the effects of age mimicry and developmental outliers than age ranges obtained using a percentile approach. Observer error tests showed that a simple three-phase scoring system proved the least subjective, while retaining accuracy levels. Additionally, significant sexual dimorphism was detected in the onset of fusion, with women commencing fusion at least a year earlier than men (women transition to fusion at approximately 15 years of age and men at 16 years). Significant secular trends were apparent in the onset of skeletal maturation, with modern Americans transitioning to fusion approximately 4 years earlier than early 20th century Americans and 3.5 years earlier than Korean War era Americans. These results underscore the importance of using modern standards to estimate age in modern individuals.

PMID: 20384935


Postnatal growth of the clavicle: birth to 18 years of age

J Pediatr Orthop. 2009 Dec;29(8):937-43.

McGraw MA, Mehlman CT, Lindsell CJ, Kirby CL.

Ohio University College of Osteopathic Medicine, Division of Pediatric Orthopaedic Surgery, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229-3039, USA. Abstract BACKGROUND: The purpose of our study was to perform a large cross-sectional study aimed at determining the postnatal growth pattern of the clavicle from birth to 18 years of age.

METHODS: We analyzed the digital chest radiographs of a convenience sample of 961 individuals between birth and 18 years of age. Malrotated radiographs were excluded. Right and left clavicle lengths were measured in millimeters from the most lateral ossified border to the most medial ossified border of each clavicle. Study patients were divided into 19 subgroups with the first group being labeled as "birth to 11 months of age" followed by 1-year-olds, 2-year olds, etc. Patients were also grouped by sex. There was a minimum of 25 patients in each group.

RESULTS: At 18 years of age the mean+/-SD clavicle length for females was 149+/-12 mm and for males it was 161+/-11 mm. Although a statistically significant difference (P=0.049) was noted between the length of right and left clavicles it was not clinically significant (0.036 mm). A steady growth rate was noted for both genders from birth to the age of 12 years (8.4 mm/y). Above the age of 12 years there were significant differences in the growth of the clavicles of girls (2.6 mm/y) versus boys (5.4 mm/y) (P<0.001). Our data suggest that females achieve 80% of their clavicle length by 9 years of age and boys by 12 years of age.

CONCLUSION: This cross-sectional study establishes that relatively little clavicle growth (20%) remains for girls beyond age 9 years and for boys beyond 12 years. The length of one clavicle may be properly judged by comparing it with the contralateral clavicle.

CLINICAL RELEVANCE: Remodeling of the clavicle shaft fractures is currently believed to be proportional to remaining growth. Our study questions the capacity of the clavicle to re-establish normal length beyond the age thresholds we have identified.

PMID: 19934713

A Runx2 threshold for the cleidocranial dysplasia phenotype

Hum Mol Genet. 2009 Feb 1;18(3):556-68. Epub 2008 Nov 20.

Lou Y, Javed A, Hussain S, Colby J, Frederick D, Pratap J, Xie R, Gaur T, van Wijnen AJ, Jones SN, Stein GS, Lian JB, Stein JL.

Department of Cell Biology, Cancer Center, University of Massachusetts Medical School, Worcester, MA 01655-0106, USA.

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.

PMID: 19028669


Critical role of the extracellular signal-regulated kinase-MAPK pathway in osteoblast differentiation and skeletal development

J Cell Biol. 2007 Feb 26;176(5):709-18.

Ge C, Xiao G, Jiang D, Franceschi RT.

Department of Periodontics and Oral Medicine, University of Michigan School of Dentistry, Ann Arbor, MI 48109, USA. Abstract The extracellular signal-regulated kinase (ERK)-mitogen-activated protein kinase (MAPK) pathway provides a major link between the cell surface and nucleus to control proliferation and differentiation. However, its in vivo role in skeletal development is unknown. A transgenic approach was used to establish a role for this pathway in bone. MAPK stimulation achieved by selective expression of constitutively active MAPK/ERK1 (MEK-SP) in osteoblasts accelerated in vitro differentiation of calvarial cells, as well as in vivo bone development, whereas dominant-negative MEK1 was inhibitory. The involvement of the RUNX2 transcription factor in this response was established in two ways: (a) RUNX2 phosphorylation and transcriptional activity were elevated in calvarial osteoblasts from TgMek-sp mice and reduced in cells from TgMek-dn mice, and (b) crossing TgMek-sp mice with Runx2+/- animals partially rescued the hypomorphic clavicles and undemineralized calvaria associated with Runx2 haploinsufficiency, whereas TgMek-dn; Runx2+/- mice had a more severe skeletal phenotype. This work establishes an important in vivo function for the ERK-MAPK pathway in bone that involves stimulation of RUNX2 phosphorylation and transcriptional activity.

PMID: 17325210


Mouse clavicular development: analysis of wild-type and cleidocranial dysplasia mutant mice

Dev Dyn. 1997 Sep;210(1):33-40.

Huang LF, Fukai N, Selby PB, Olsen BR, Mundlos S.

Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA. Abstract Cleidocranial dysplasia (CCD) is an autosomal dominant disease characterized by hypoplasia or aplasia of clavicles, open fontanelles, and other skeletal anomalies. A mouse mutant, shown by clinical and radiographic analysis to be strikingly similar to the human disorder and designated Ccd, was used as a model for the human disorder. Since malformation of the clavicle is the hallmark of CCD, we studied clavicular development in wild-type and Ccd mice. Histology and in situ hybridization experiments were performed to compare the temporal and spatial expression of several genes in wild-type and Ccd mutant mouse embryos. Bone and cartilage specific markers--type I, II, and X collagens, Sox9, aggrecan, and osteopontin were used as probes. The analyses covered the development of the clavicle from the initial mesenchymal condensation at embryonic day 13 (E13) to the late mineralization stage at embryonic day 15.5. At day 13.5, cells in the center of the condensation differentiate into characteristic precursor cells that were not observed in other bone anlagen. In the medial part of the anlage these cells express markers of the early cartilage lineage (type II collagen and Sox9), whereas cells of the lateral part express markers of the osteoblast lineage (type I collagen). With further development the medial cells differentiate into chondrocytes and start to express chondrocyte-specific markers such as aggrecan. Cells of the lateral part differentiate into osteoblasts as indicated by the production of bone matrix and the expression of osteopontin. At day 14.5 a regular growth plate has developed between the two parts where type X collagen expression can be demonstrated in hypertrophic chondrocytes. The data indicate that the medial part of the clavicle develops by endochondral bone formation while the lateral part ossifies as a membranous bone. The clavicle of Ccd mice showed a smaller band of mesenchymal cell condensation than in wild-type mice. Cells of the condensation failed to express type I and type II collagen at E13.5. In the lateral part of the clavicle type I collagen expression was not detected until E14.5 and osteopontin expression only appeared at E15.5. At E15.5, a small ossification center appears in the lateral part which is, in contrast to the wild-type clavicular bone, solid and without primary spongiosa as well as bone marrow. In the medial portion, type II collagen expression and endochondral ossification never occurs in Ccd mice; this portion of the clavicle is therefore missing in Ccd.

PMID: 9286593


Conversion of bone marrow in the humerus, sternum, and clavicle: changes with age on MR images

Radiology. 1993 Jul;188(1):159-64. Zawin JK, Jaramillo D.

Department of Radiology, Children's Hospital, Boston, MA 02115. Abstract To study the normal conversion of bone marrow in the humerus, sternum, and clavicle, 101 T1-weighted magnetic resonance (MR) studies obtained in 91 patients aged 2 days to 37 years were retrospectively evaluated. Conversion from hypointense (red) to hyperintense (yellow) bone marrow was assessed by comparison of signal intensity of the bone marrow with that of muscle and fat. Conversion began in the proximal humeral epiphysis (in 16 of 21 adequate studies [76%]), humeral diaphysis (17 of 30 adequate studies [57%]), and distal metaphysis (16 of 25 adequate studies [64%]) before age 1 year and was nearly complete in these regions (20 of 22 adequate studies [91%], 20 of 21 adequate studies [95%], and five of seven adequate studies [71%]) in examinations of children aged 1-5 years. In the proximal humeral metaphysis, conversion was seen in 21 of 22 adequate studies (95%) in children aged 1-5 years and was nearly complete in all by age 20 years. Conversion began in the sternum (six of six studies [100%] in children aged 6-10 years) and clavicle (six of eight studies [75%] in children aged 6-10 years) before age 11 years but was never complete. Bone marrow conversion in the humerus, sternum, and clavicle follows a well-defined pattern and is depicted earlier by MR imaging than one would expect on the basis of histologic data.

PMID: 8511291


The growth pattern of the clavicle in the rat

Rönning O, Kantomaa T.

Institute of Dentistry, University of Oulu, Finland. Abstract The mode of growth of the rat clavicle from 17 to 45 days of age was studied by means of vital staining (alizarin red S), histology and autoradiography (tritiated thymidine). In addition the clavicle on one side was subjected to periostomy at the age of 10 days and its length compared with that of its unoperated counterpart at the ages of 17 and 45 days. The alizarin red staining revealed that the medial end of the clavicle contributes to the length of the bone, while the lateral end appears to have mainly an articulatory function. Histologically, the medial end cartilage closely resembles the condylar cartilage of the mandible, whereas the lateral end appears to be composed of two cartilaginous structures separated by a mesenchymatous layer. Tritiated thymidine was deposited in the mesenchymal cells covering the medial end cartilage, whereas virtually no activity was observed in the mesenchyme of the lateral end cartilage. The periostomised clavicle was more slender in appearance than its control throughout the observation period. The two clavicles were of the same length at 17 days, but by 45 days the periostomised clavicle was significantly longer than the control. It is suggested that the growth of the clavicle is essentially comparable to the growth of the mandible. Length growth occurs in response to the action of the surrounding structures, while analogously to the mandibular condyle, the medial end cartilage actively translates the bone in a direction perpendicular to the articular surface, giving rise to its curved shape.

PMID: 3248965 J Anat. 1988 Aug;159:173-9.