The WT embryo shows normal neural tube (NT) and a well-defined emerging sclerotome
Tessier-Lavigne, "Patterning of mammalian somites by surface ectoderm and notochord: evidence for sclerotome
induction by a hedgehog homolog," Cell, vol.
The vertebral column is formed from the sclerotome
of the somites.
DISCUSSION: The vertebral column develops from paired somites, each composed of a dermatome, myotome and sclerotome
. They arise initially in cervical region (4thweek), increasing in number cranio-caudally.
It results due to failure of segmentation and separation of the most caudal occipital sclerotome
and the first cervical sclerotome
during the first few weeks of fetal life.
DISCUSSION: Block vertebrae mostly are attributed to developmental defects during differentiation of vertebral column, caused by non-segmentation of the primitive sclerotome
. It has also been hypothesised that decreased local blood supply during 3rd to 8th week of development results in inappropriate segmentation.
The "classic theory" claims the presence of an early embryonic infection of a sensory nerve inducing changes in the respective sclerotome
. The second is the concept of "Mosaicism" which better explains the sporadic occurrence, the asymmetric "segmental" pattern with variable extent of involvement and equal gender ratio of the disease.
At the early stage of embryo, paravertebral sclerotome
(mesoderm) differentiates into two parts
Several patterns of melorheostosis have been described including the monostotic (involving one bone), polyostotic (involving multiple bones) and the most common monomelic (involving one limb).Within a limb, melorheostosis is usually confined to a single sclerotome
and even within a particular sclerotome
, the lesions may cross the joint space to involve bones on either side but the intervening joint is usually not involved (5).
Anomalies and malformations of the occipital sclerotomes
result in irregular geometry of the FM and related structures.
(6) Furthermore, in the study conducted by Imamura et al., (5) PPT values of myotomes, sclerotomes
and dermatomes between L1 and S3 segments were evaluated and lower PPT values were reported in CLBP patients.
(18) This type of pain should be differentiated from the less well-defined deep aching pain that is confined to the sclerotomes
of the spine, commonly known as referred pain.