Musculoskeletal System - Shoulder Development
Introduction
The skeletal shoulder consists of: the clavicle (collarbone), the scapula (shoulder blade), and the humerus. Development of his region occurs through both forms of ossification processes.
The mesoderm forms nearly all the connective tissues of the musculoskeletal system. Each tissue (cartilage, bone, and muscle) goes through many different mechanisms of differentiation.
The musculoskeletal system consists of skeletal muscle, bone, and cartilage and is mainly mesoderm in origin with some neural crest contribution.
The intraembryonic mesoderm can be broken into paraxial, intermediate and lateral mesoderm relative to its midline position. During the 3rd week the paraxial mesoderm forms into "balls" of mesoderm paired either side of the neural groove, called somites.
Somites appear bilaterally as pairs at the same time and form earliest at the cranial (rostral,brain) end of the neural groove and add sequentially at the caudal end. This addition occurs so regularly that embryos are staged according to the number of somites that are present. Different regions of the somite differentiate into dermomyotome (dermal and muscle component) and sclerotome (forms vertebral column). An example of a specialized musculoskeletal structure can be seen in the development of the limbs.
Skeletal muscle forms by fusion of mononucleated myoblasts to form mutinucleated myotubes. Bone is formed through a lengthy process involving ossification of a cartilage formed from mesenchyme. Two main forms of ossification occur in different bones, intramembranous (eg skull) and endochondrial (eg limb long bones) ossification. Ossification continues postnatally, through puberty until mid 20s. Early ossification occurs at the ends of long bones.
Musculoskeletal and limb abnormalities are one of the largest groups of congenital abnormalities.
Some Recent Findings
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Textbooks
- The Developing Human: Clinically Oriented Embryology (8th Edition) by Keith L. Moore and T.V.N Persaud - Moore & Persaud Chapter 15 the skeletal system
- Larsen’s Human Embryology by GC. Schoenwolf, SB. Bleyl, PR. Brauer and PH. Francis-West - Chapter 11 Limb Dev (bone not well covered in this textbook)
- Before we Are Born (5th ed.) Moore and Persaud Chapter 16,17: p379-397, 399-405
- Essentials of Human Embryology Larson Chapter 11 p207-228
Myogenesis
- Early myogenic progenitor cells in the dermomyotome can be initially identified by the transcription factor Pax3.
- Subsequent myogenic program development then depends on the myogenic determination factors (Myf5, MyoD, and MRF4), both Myf5 and MyoD are expressed in the limbs.
- Final differentiation of these cells into post-mitotic muscle fibers in the limb bud is regulated by another myogenic determination factor, Myogenin.
Some text modified from[3]
Links: Muscle Development
Limb Bone
Bone formation within the limb occurs by endochondral ossification of a pre-existing cartilage template. Ossification then replaces the existing cartilage except in the regions of articulation, where cartilage remains on the surface of the bone within the joint. Therefore bone development in the limb is initially about cartilage development or chondrogenesis.
In addition, there are two quite separate aspects to this development.
- Pattern - where the specific regions will commence to form cartilage, which will be different for each cartilage element.
- Chondrogenesis - the differentiation of mesoderm to form cartilage, which will be essentially the same program for all cartilage templates.
A recent study has identified that the overlying limb surface ectoderm potentially inhibits limb early chondrogenesis through Wnt6 signaling.[4]
Links: Cartilage Development | Bone Development
Clavicle Development
(collarbone)
Postnatal Growth
A recent paper has characterised the postnatal growth of male and female clavicles (data shown below).[5]
- 18 years of age the mean clavicle length +/-SD for females was 149+/-12 mm and for males it was 161+/-11 mm.
- 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).
- Females achieve 80% of their clavicle length by 9 years of age and boys by 12 years of age.
Scapula Development
(shoulder blade)
Humerus Development
Pelvis
The skeletal pelvis consists of: the sacrum and coccyx (axial skeleton), and pelvic girdle formed by a pair of hip bones (appendicular skeleton). Before puberty, he pelvic girdle also consists of three unfused bones: the ilium, ischium, and pubis. In chicken, the entire pelvic girdle originates from the somatopleure mesoderm (somite levels 26 to 35) and the ilium, but not of the pubis and ischium, depends on somitic and ectodermal signals.[6]
- Links: Pelvis Development
Molecular
Fibroblast Growth Factors
- Fgf8 - morphogen gradient forms by a source-sink mechanism with freely diffusing molecules.[7]
T-box Transcription Factors
References
Reviews
<pubmed>17006658</pubmed> <pubmed>11170011</pubmed> <pubmed>3324657</pubmed>
Articles
<pubmed>19763557</pubmed> <pubmed>9272998</pubmed> <pubmed>531584</pubmed>
Search PubMed
Search Pubmed: Shoulder Development | Clavicle Development | Scapula Development
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Cite this page: Hill, M.A. (2024, April 19) Embryology Musculoskeletal System - Shoulder Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Musculoskeletal_System_-_Shoulder_Development
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G