MSK Pt 1

Question 1

The skeleton is composed of? (2 tissues, 3 cell types)

Answer 1

bone/cartilage

osteoblasts/osteoclasts/chrondrocytes

Question 2

Skeletal tissue is derived from three embryonic cell lineages. What are they?

Answer 2

cranial neural crest cells (head)
paracial mesoderm cells/somites (axial skel)
lateral plate mesoderm (limbs)

Question 3

Limb buds begin to develop during the _____ week.

Answer 3

4th

Question 4

What are the 4 steps of skeletogenesis?

Answer 4

patterning
organogenesis
growth
homeostasis

Question 5

When can we see limb buds?

Answer 5

7th week (I’m pretty sure in OB we learned wk 9 buuuuuut what else is new)

Question 6

What can we see during the 9-11th week?

Answer 6

clavicle + mandible

Question 7

When do we see hands and feet?

Answer 7

12-14wks

Question 8

When do we see the distal femoral epiphysis? The proximal tibial epiphysis?

Answer 8

29-34wks

35wks

Question 9

How is the femur length measured?

Answer 9

b/w the distal and proximal ossification centres of the femoral diaphysis

Question 10

The cardio-thoracic circumference ratio increases through gestation, but should not measure more than ______. What can it indicate if the ratio is increased?

Answer 10

0.5

cardiac- fetal cardiomegaly
thoracic- pulmonary hypoplasia

Question 11

Thoracic/abdominal circumference should measure _____ after 20 weeks.

Answer 11

> 0.8

Question 12

Skeletal dysplasia aka

Answer 12

dwarfism

umbrella term for conditions affecting bone and cartilage growth

Question 13

The most common severe skeletal dysplasias manifest with:

Answer 13

severe micromelia (shortening of all limbs)
and thoracic dysplasia

Question 14

Most common types of skeletal dysplasias can be detected by what?

Answer 14

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

Question 15

What helps distinguish skeletal dysplasia from severe IUGR?

Answer 15

femur length to foot length ratio

*foot length is not affected with most SD so the ratio is decreases

Question 16

What are the 4 patterns of shortening of the long bones?

Answer 16

rhizomelia: proximal segment (femur, hum)
mesomelia: middle segment (radius, ulna, tib/fib)
acromelia: distal segment (hands + feet)
micromelia: entire limb (mild, bowed, severe)

Question 17

What type of skeletal dysplasia is lethal?

Answer 17

severe micromelia

earlier the diagnosis, the worse the prognosis

Question 18

Thoracic dysplasia is associated with:

Answer 18

pulmonary hypoplasia

heart may appear abnormally enlarged–pseudocardiomegaly

Question 19

What are the signs of pulomary hypoplasia:

Answer 19

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)

Question 20

Frontal bossing:

Answer 20

development of an unusually pronounced forehead bc of enlargement of frontal bone

Question 21

What is the first bone in the fetal limb to develop?

Answer 21

humerus

Question 22

What step of skeletogenesis determines the final size of bone?

Answer 22

patterning

Question 23

How do fetal biometric ratios help in the diagnosis of skeletal dysplasia?

Answer 23

FL/HC ratio < 3 SD below the mean suggests SD