Limb development defects

Question 1

Skeletal system develops from?

Answer 1

• Sclerotome: vertebrae & ribs
• Somatopleure: appendicular skeleton
• Neural crest cells: bones face & cranium

Question 2

Appendicular Skeleton & Long Bones Growth

Answer 2

• most formed by Endochondral Ossification except for clavicle (Intramembranous)
• Diaphysis appears by 7 to 8th wk of intrauterine life
• Epiphyses appear during 1st & 5th except Distal Femur & Proximal Tibia (9th month intrauterine)

Question 3

Achondroplasia

Answer 3

• premature closure of epiphyseal plates
• AD

Question 4

Skeletal muscle development

Answer 4

• Develop from 4 sources:
  
  1. Preotic somites: extrinsic eye muscles
  2. Pharyngeal arch mesoderm: muscles of head & neck
  3. Occipital somites: Intrinsic & Extrinsic tongue muscles
  4. Body somites (myotomes)
  • Hypaxial musculature: ventrolateral body; wall muscles & limb)
  • Epaxial: Instrinsic back & neck muscles

Question 5

Limb buds: 4th wk

Answer 5

• Upper limb buds appear oppoiste C5-T1 segments by 26th to 27th day
• Lower limb buds appear opposite L2-S3 segments 1-2 days after upper limb buds uppear
• Critical period: 4th to 5th wk
• 5 dermatomes
• 5 sclerotomes
• Apical Ectodermal ridge
  
  • Thickening at apex (tip) of each limb bud
  • induces & controls differentiation of bones & muscles

Question 6

Syndactyly

Answer 6

• fusion of digits: more common in lower limb
• failure of digital rays to separate
• may be cutaneous (most common limb anomaly) or bony

Question 7

Polydactyly

Answer 7

• apical ectodermal ridge divides into extra digital rays
• extra digit has incomplete musculature

Question 8

Ectrodactyly

Answer 8

• “lobster claw” deformity or cleft hand/foot
• absence of central digit(s) from failure of digital ray development
• usually there is syndactyly of remaining digits

Question 9

Amelia

Answer 9

• absence of limb(s)
• caused by:
  
  • ischaemia of developing limb
  • genetic factors
  • exposure to causitive agent early in critical period (4th wk)

Question 10

Meromelia

Answer 10

• Absence of PART of limb(s)
• caused by:
  
  • ischaemia of developing limb
  • genetic factors
  • exposure to a causitive agent in critical period (5th wk)

Question 11

Poland syndrome

Answer 11

• absence of pec major
• syndactyly
• shortened upper limb(s) & digits
• nipple aplasia or hypoplasia

Question 12

Talipes (Club foot)

Answer 12

• foot inverted & turned medially
• 1 in 1000 births; twice as frequent in males
• 50% of cases are bilateral