Lower Extremity Anatomy II > Lecture 2 > Flashcards

Lecture 2 Flashcards

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1
Q

Limb bud

A
  • Appear in the 4th week as small elevations on the ventrolateral body wall
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2
Q

Limb bud are derived from

A
  • Somatic body wall (lateral plate mesoderm)
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3
Q

Ectoderm covers

A
  • Mesenchyme (embryonic tissue)
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4
Q

Upper limb buds

A
  • Visible in the cervical region ~ 24
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5
Q

Lower limb buds

A
  • Visible in the lumbar region ~ day 28
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6
Q

Limb axis formation

A
  • Directional axes of limb
  • Proximal/Distal
  • Dorsal/Ventral
  • Cranial/Caudal
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7
Q

Proximal/Distal limb axis formation applies to

A
  • Thigh
  • Leg
  • Foot
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8
Q

Dorsal/Ventral limb axis formation applies to

A
  • Anterior vs. posterior thigh/leg

- Dorsum vs. plantar foot

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9
Q

Cranial/Caudal limb axis formation applies to

A
  • Big toe (cranial, preaxial) to little toe (caudal, postaxial)
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10
Q

Limb bud contains mesenchyme that will form

A
  • Cartilage/bone

- Dermis of the lower extremity

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11
Q

Muscles are derived from

A
  • Somites

- Myoblast migrate into developing limb

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12
Q

Motor neurons are derived from

A
  • Spinal cord
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13
Q

Structures derived from neural crest cells

A
  • Schwann cells
  • Melanocytes
  • Sensory neurons
  • Sympathetics
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14
Q

Limb elongation

A
  • Progresses from proximal to distal

- Thigh (stylopod), leg (zeugopod), foot (autopod)

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15
Q

Early stage of limb elongation

A
  • Limbs appear as flippers on the ventrolateral wall
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16
Q

Ectoderm over distal tip of limb

A
  • Condenses, forming apical ectodermal ridge (AER)

- Represents the dorsal/ventral boundary

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17
Q

Underlying mesenchyme

A
  • Induces the formation of the AER
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18
Q

Apical ectodermal ridge (AER) induces

A

P-roliferation of underlying mesenchyme

- Elongation of the limb (progress zone)

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19
Q

Mesenchyme obtains

A
  • Positional information about future proximal/distal location
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20
Q

Studies that removed the AER showed

A
  • Formation of a truncated limb
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21
Q

Mesenchyme will differentiate into

A
  • Cartilage (cartilage model precursor to bone)
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22
Q

Pre-axial and post-axial borders

A
  • Location where flexor and extensor compartments of the limb meet in fetal development
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23
Q

Pre-axial (cranial) border

A
  • Medial side (tibial side) of the limb

- Demarcated by the great saphenous vein

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24
Q

Post-axial (caudal) border

A
  • Lateral side (fibular side) of the limb

- Demarcated by the small saphenous vein

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25
Bone formation
- Mesenchyme --> cartilage - Ossification from cartilage template (most bones) or connective tissue - Once ossifying, visible on radiograph
26
Ossification from cartilage template/connective tissue
- Tips of distal phalanges (ungal tuberosity, tufts) | - Develops from intramembranous ossification
27
Joint formation
- Forms from mesenchyme between cartilage templates of future bone
28
Mesenchyme between cartilage templates of future bone can differentiate into
- Collagen (fibrous) - Hyaline cartilage (synchondrosis) - Joint cavity (synovial)
29
Synovial joint
- Development of an interzone between cartilage templates (trilaminar) - Cavitation develops within interzone
30
Limb muscles
- Derived from hypaxial myogenic precursors - Migrate ventrally along dorsolateral body wall - Migration starts week 4/5 - Muscle mass increases by mitosis until mid-fetal period
31
2 condensations formed by myoblast
- Dorsal mass (extensors) | - Ventral mass (flexors)
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Dorsal mass (extensors) initially located
- Posteriorly (dorsally) before limb roation
33
After limb rotation, dorsal mass (extensors) located
- Posterior in upper limb - Anterior in lower limb - Not lower limb girdle (pelvic girdle)
34
Ventral mass (flexors) initially located
- Anteriorly (ventrally) before limb rotation
35
After limb rotation, ventral mass (flexors) located
- Anterior in upper limb - Posterior in lower limb - Not lower limb girdle
36
Innervation of developing limb
- Ventral rami from spinal cord segments migrate into developing limb - Axons innervate muscle masses before they split into individual muscle
37
Dorsal branches (divisions) of ventral rami innervate
- Dorsal muscle mass
38
Ventral branches (divisions) ventral rami innervate
- Ventral muscle mass
39
Subcostal nerve
- Ventral rami T12 | - Cutaneous supply to superior anterolateral thigh
40
Lumbar plexus branches
- Iliohypogastric (ventral division of L1) - Ilioinguinal (ventral division of L1) - Genitofemoral (ventral divisions of L1,2) - Lateral femoral cutaneous (dorsal divisions of L2,3) - Nerves to psoas major muscle (dorsal divisions of L2-4) - Femoral (dorsal divisions of L2-4) - Nerve to iliacus muscle Obturator (ventral divisions of L2-4) - Accessory obturator (ventral divisions of L3,4)
41
Part of L4 joins with L5 ventral rami to form
- Lumbosacral trunk
42
Sacral plexus branches
- Superior gluteal (dorsal divisions of L4-S1) - Inferior gluteal (dorsal divisions of L5-S2) - Nerve to piriformis (dorsal divisions of S1,2) - Perforating cutaneous nerve (dorsal divisions of S2,3) - Sciatic (dorsal divisions of L4-S2 and ventral divisions of L4-S3) - Posterior cutaneous nerve of thigh (dorsal divisions of S1,2 and ventral divisions of S2,3) - Nerve to quadratus femoris (ventral divisions of L4-S1) - Nerve to obturator internus (ventral divisions of L5-S2) - Pudendal (ventral divisions of S2-4)
43
Digit formation
- Zone of polarizing activity (ZPA) - Signaling center that forms in the dorsal mesenchyme just below AER - Controls pattern formation on an anterior/posterior axis - Hallux vs. little toe
44
Axis artery (axial)
- Primary vessel that supplies the developing limb
45
Axis artery arises from
- Dorsal root of umbilical artery
46
Axis artery pathway
- Passes along posterior aspect of developing limb to plantar foot
47
External iliac forms from
- Dorsal root of umbilical artery - Femoral artery then forms from external iliac artery - Travels to posterior thigh and communicates with axial artery
48
Once femoral artery forms and communicated with axial artery
- Axis artery proximal to this disappears | - Inferior gluteal and ischiadic artery persist
49
Axial artery eventually becomes
- Major supplier to lower extremity through its communication with popliteal artery
50
Dorsal root of umbilical artery becomes
- Common iliac
51
Remnants of axis artery
- Inferior gluteal - Popliteal - Ischiadic artery (sciatic artery) - Fibular
52
5th week
- Hand and foot plates develop (hands develop earlier) | - Flat and paddle shaped
53
6th week
- Joints become more observable - Digital rays of hand plate develop - Limbs move to a more ventral position
54
7th week
- Digital rays of the foot develop | - Limb rotation
55
Limb rotation
- Knee/elbows initially face laterally | - Upper/lower limbs rotate in opposite directions
56
8th week
- Fetal position is attained by the end of the week | - Mesenchyme between digits degenerates (apoptosis)
57
Upper limb rotation (7th week)
- Rotate laterally/externally to face caudally
58
Lower limb rotation (7th week)
- Rotate medially/internally so the knees face cephalically
59
Tarsal coalition
- Complete or partial union between 2 or more tarsal bones | - Developmental fusion that results from incomplete or faulty mesenchymal segmentation
60
Tarsal coalition development
- Genetically programed to develop | - Calcaneonavicular and talocalcaneal are most common
61
Tarsal coalition classification
- Classified by the type of tissue that bridges the bones - Fibrous (syndesmosis) - Cartilaginous (synchondrosis) - Bony (synostosis)
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Syndactyly
- Congenital malformation caused by the the failure of differentiation of digits - Mesenchyme doesn’t separate
63
Syndactyly effects
- Fusion of toes (or fingers) - May be single or multiple - Can affect skin and soft tissue, or soft tissue and bone
64
Cutaneous syndactyly
- Failure of mesenchyme degeneration between digits - Causes webbing between digits - Can be complete or partial More of a functional problem in the hand
65
Osseous syndactyly
- Failure of mesenchyme to segment in the foot
66
Amelia
- Absence of an entire limb (failure of formation) | - Can be 1 or multiple
67
Amelia is caused by
- Interruption of the limb formation process (prevented or interrupted early on)
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Tetra-amelia
- Absence of all limbs
69
Meromelia
- Partial absence of limb | - Can occur at any level of the limb
70
Phocomelia (“seal limb”)
- Type of meromelia where rudimentary hands or feet are attached to trunk
71
The various types of missing limb or limb malformations can result from
- Vascular interruption - Genetic - Teratogens
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Teratogens
- Agents that can cause malformation of embryo | - Thalidomide, chemicals, radiation
73
Congenital absence of bone
- Fibula (fibular hemimelia) | - Can be partial or complete
74
Cleft foot/hand (ectrodactylyl
- “Lobster Claw Foot (hand)” - Rare anomaly - Central conical defect from periphery to tarsals - Presentation varies - Affects central rays - Surgically addressed early on to prevent pathological adaptation
75
Polydactyly (“many digits”)
- Formation of extra digits - Can be due to genetic defect or part of a syndrome - Different appearances
76
Polydactyly in lower limb
- Pre-axial - Post-axial - Centra
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Pre-axial polydactyly
- Extra digit towards the hallux
78
Post-axial polydactyly
- Extra digit towards little toe - More common - Surgically corrected
79
Central polydactyly
- Extra digit involves digits 2, 3, or 4
80
Macrodactyly (“large digits”)
- Enlargment of digits | - Overgrowth of bone/tissue
Lower Extremity Anatomy II
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