Ch 13 Skeleton Flashcards
Fetal limb buds are seen as early as how many weeks by EV?
8 weeks (lower buds seen before upper buds)
Long bones fully develop during what weeks?
During 7-12 weeks
Bones in hands + feet are developed b/w what weeks?
11-13 weeks
The long bones of the femur, humerus, rad/uln + tib/fib can be accurately measured from what week onward?
12 weeks on
Which femur should we measure?
The most anterior one
(posterior femur looks artifactually bowed + shortens our length inaccurately)
The femur grows how many mm per week?
14-27 weeks: 3mm per week
3rd trimester: 1mm per week
Femur length varies depending on what maternal factors?
Maternal height, weight + ethnicity
Is the tibia or fibula thicker?
Tibia
Location of tib/fib?
Tib: medial
Fib: lateral
Is the radius or ulna longer?
Ulna
Location of rad/uln?
Rad: thumb side (lateral)
Uln: pinky side (medial)
How many independent digits do the hands have?
5 - they vary lengths
How many phalanges does each hand digit have?
3
(thumb only has 2)
Is a constantly fixed hand position abnormal?
Yes - should always be seen in flexion + extension
How many tarsal bones + digits are there in the foot?
5
How many phalanges does each foot digit have?
2
Why can the foot measurement be used to determine gest age?
B/c it has a characteristic pattern of normal growth
What is skeletal dysplasia?
-Abnormal development of cartilaginous + osseous tissues
-Results in bones that appear short, thin, deformed or that fail to forma at all
Is diagnosing skeletal dysplasia hard?
Yes - should document + image each limb at the start of the exam when scanning an at-risk fetus
How do the long bones appear with skeletal dysplasia?
-May be shorter
-Must evaluate for bowing + fractures
What are the 4 categories of short-limbed dysplasias?
Rhizomelia: prox part is shortened
Mesomelia: middle part is shortened
Acromelia: distal part is shortened
Micromelia: entire extremity is shortened
What other abnormalities should be noted when assessing for skeletal dysplasia?
-Abnormal # of digits + fluid volumes
-Facial or cardiac defects
-Skull shape (cloverleaf deformity)
Lethal skeletal dysplasias are often accompanied by what?
Pulmonary hypoplasia
What is the m/c form of lethal skeletal dysplasia?
Thanatophoric dysplasia (TD)
(thanatophoric = death bearing in greek)
Is TD m/c in males or females?
Males
2 types of TD?
Type 1 (m/c):
-extreme rhizomelia (prox) + normal trunk length
-bowed long bones (telephone receiver)
-platyspondyly (widened vertebral bodies)
-frontal bossing (forehead)
Type 2:
-straighter long bones
-taller vertebral bodies
-kleeblattschadel (cloverleaf skull)
What is the āchampagne cork appearanceā associated with?
TD - is a narrow thorax with a protruding abdomen
How is the prognosis for TD?
Poor - m/c stillborn or die after birth due to pulmonary hypoplasia
What is the m/c nonlethal type of dwarfism?
Achondroplasia
(occurs equally in M/F)
Features of achondroplasia?
-Rhizomelic limb bowing (prox part)
-Frontal bossing
-Low nasal bridge
-Trident hand (increased space b/w 3rd/4th digit)
-Macro + hydrocephaly
How is the prognosis with achondroplasia?
Good - orthopaedic problems are only concern
What is achondrogenesis?
Rare + lethal skeletal dysplasia
(lethal b/c of pulmonary hypoplasia)
2 types of achondrogenesis?
Type 1: parenti-fraccaro
-extreme micromelia
-lg head
-short/thin ribs
-poor ossification of skull, spine + pelvic bones
Type 2: langer-saldino
-prominent forehead
-flat face with micrognathia
-absent rib fractures
-less severe mineralization of fetal bones
-less severe micromelia
What is osteogenesis imperfecta (OI)?
Rare inheritable connective tissue disorder, due to defects in type 1 collagen quality/quantity
(type 1 collagen is found in skin, ligaments, tendons + bones)
A defect in type 1 collagen leads to what?
Decreased mineralization of bone + bone fragility found in ptās with OI
Causes:
-long bone + rib fractures
-blue sclera
-hearing impairment
How many types of OI are there?
4
What is type 1 OI?
-Due to abnormal decrease in quantity of collagen produced (milder disease)
-Most fractures donāt appear until after birth
-Normal stature + good prognosis
What is type 3 OI?
-Autosomal dominant or recessive
-Less severe than type 2 in utero
-Limb bowing in utero
-Multiple fractures at birth
List the types of OI from least to most severe?
Type 4 (dominant), type 1 (doesnāt say), type 3 (either) + type 2 (recessive)
What is type 4 OI?
-Mildest form of disease
-Does not present until later in life
-Inherited in autosomal dominant pattern
-Not common to be detected prenatally
-May only see short stature or premature osteoporosis later in life
What is type 2 OI?
-Most severe form + inherited in recessive fashion
-Transparent bone sign (far side of long bone is visualized in addition to near side)
-Poor prognosis, deadly
-Reduced echogenicity + thicker bones
-Concave ribs from fractures
-Bell shaped throax
-Skull lacks ossificaiton (can compress with probe)
What is camptomelic dysplasia?
Rare form of short limbed dwarfism, transmitted in autosomal dominant fashion
(poor prognosis, most die)
Camptomelic dysplasia is characterized by what?
-Short + bowed limbs
-Short trunk
-Large head
-Bell shaped chest
(slide images are pointing to scapula)
What is congenital hypophosophotasia?
-Rare inherited disease of defective bone mineralization
-Low/absent tissue nonspecific alkaline phosphatase activity
2 types of congenital hypophosophotasia?
Type 1: inherited recessive condition, detected prenatally
Type 2: inherited dominant condition, not detected until later in life
Is type 1 or type 2 congenital hypophosophotasia lethal?
Type 1 (recessive)
What is dysostosis?
Any condition characterized by abnormal ossification
List 2 of the m/s sonographically visible types of dysostosis?
Cleidocranial:
-widening of cranial fontanelles with increase in lateral aspect of cranium
Craniofacial:
-associated with craniosynostosis + apert syndrome
Examining the hands is best done in which trimester?
Late 1st or mid 2nd trimester (b/c fetus moves hands more often)
A persistently clenched hand with an overlapping index finger is associated with?
Trisomy 18
A trident hand (3 pronged look) is found in what pathology?
Achondroplasia
What is polydactyly?
Presence of extra digits on hands or feet
What is the m/c hand anomaly?
Polydactyly
Differentiatae preaxial + postaxial polydactyly?
Pre: affects radial (thumb) side
Post (m/c): affects ulnar (pinky) side
(central polydactyly affects the 3 central digits)
What is limb reduction abnormality?
Congenital absence or incomplete development of 1 or more limbs (or segments of limbs)
List the terms associated with limb reduction?
Aplasia: absence of a bone
Hypoplasia: incomplete development of a bone
Amelia: absence of 1 or more limbs
Hemimelia: absence of 1 or more extremities below elbow or knee
Acheiria: absence of 1 or more hands
Apodia: absence of 1 or more feet
Adactyly: absence of 1 or more digits from hands or feet
Phocomelia: absence of prox part of an extremity
Meromelia: absence of part of a limb
What does VACTERL stand for?
Vertebral, anorectal, cardiac, tracheoesophageal, renal, limb abnormalities
(at least 3 anomalies MUST be present to confirm this condition)
What is club foot?
-Common birth defect where foot is excessively medially deviated, the bone of the foot lies in the same plane as the bone of the lower leg
-Check feet again at end of exam to ensure club foot is present
(foot should NOT be in same plane as bones)
Club foot is commonly due to?
Oligohydramnios - or other things that restrict fetal movement
What is amniotic band sequence (ABS)?
Group of fetal abnormalities ranging from constriction rings + edema of digits to multiple complex anomalies
Cause of ABS?
Unknown
SF of ABS?
Linear echogenic band attaching from 1 uterine wall to another (or from uterine wall to fetal part)
(may not be seen at all)
What is known as the mermaid syndrome?
Sirenomelia
What is sirenomelia?
-Rare lethal abnormality associated with maternal diabetes, MZ twinning + maternal cocaine use
-Is the fusion of both or one lower leg with renal agenesis, resulting in severe oligohydramnios
Prognosis of sirenomelia?
Poor - due to renal agenesis
Do we measure all the long bones routinely?
No, just femur + foot length for biometry
When would we measure all the long bones?
If shortening of a long bone we must measure all of them
List 3 steps on how to get paired long bones to image together?
1: Find long bone in SAG, make it parallel to floor + turn into TRV
2: Slide laterally off bone until we can no longer see it
3: Angle back to bone until it is in view again (repeat steps 2 + 3 until we have 2 bones visualized adequately)
What does āVā represent in VACTERL?
Vertebral
How many phalanges does the thumb have?
2
Kleeblattschadel (cloverleaf skull) is seen with which disease?
Thanatophoric dysplasia (TD)
What form of OI is mildest?
Type 4
What does micromelia result in?
Shortening of entire extremity
