MSK Pt 1 Flashcards
The skeleton is composed of? (2 tissues, 3 cell types)
bone/cartilage
osteoblasts/osteoclasts/chrondrocytes
Skeletal tissue is derived from three embryonic cell lineages. What are they?
cranial neural crest cells (head)
paracial mesoderm cells/somites (axial skel)
lateral plate mesoderm (limbs)
Limb buds begin to develop during the _____ week.
4th
What are the 4 steps of skeletogenesis?
patterning
organogenesis
growth
homeostasis
When can we see limb buds?
7th week (I’m pretty sure in OB we learned wk 9 buuuuuut what else is new)
What can we see during the 9-11th week?
clavicle + mandible
When do we see hands and feet?
12-14wks
When do we see the distal femoral epiphysis? The proximal tibial epiphysis?
29-34wks
35wks
How is the femur length measured?
b/w the distal and proximal ossification centres of the femoral diaphysis
The cardio-thoracic circumference ratio increases through gestation, but should not measure more than ______. What can it indicate if the ratio is increased?
0.5
cardiac- fetal cardiomegaly
thoracic- pulmonary hypoplasia
Thoracic/abdominal circumference should measure _____ after 20 weeks.
> 0.8
Skeletal dysplasia aka
dwarfism
umbrella term for conditions affecting bone and cartilage growth
The most common severe skeletal dysplasias manifest with:
severe micromelia (shortening of all limbs) and thoracic dysplasia
Most common types of skeletal dysplasias can be detected by what?
FL
if it’s 1-4mm below 2 SD points, more measurements are required.
If it’s 5mm below 2 SD points, there’s a high likelihood of SD
What helps distinguish skeletal dysplasia from severe IUGR?
femur length to foot length ratio
*foot length is not affected with most SD so the ratio is decreases
What are the 4 patterns of shortening of the long bones?
rhizomelia: proximal segment (femur, hum)
mesomelia: middle segment (radius, ulna, tib/fib)
acromelia: distal segment (hands + feet)
micromelia: entire limb (mild, bowed, severe)
What type of skeletal dysplasia is lethal?
severe micromelia
earlier the diagnosis, the worse the prognosis
Thoracic dysplasia is associated with:
pulmonary hypoplasia
heart may appear abnormally enlarged–pseudocardiomegaly
What are the signs of pulomary hypoplasia:
narrow AP diameter of chest (<0.8)
dec thoracic circum (measure @ level of 4CH)
short ribs (normally encircle 70-80% of thorax)
abnormal contour thorax in coronal (bell shaped)
dec thoracic length (apex–>diaphragm)
Frontal bossing:
development of an unusually pronounced forehead bc of enlargement of frontal bone
What is the first bone in the fetal limb to develop?
humerus
What step of skeletogenesis determines the final size of bone?
patterning
How do fetal biometric ratios help in the diagnosis of skeletal dysplasia?
FL/HC ratio < 3 SD below the mean suggests SD
