Joint Development (HIP)

Question 1

Joint Development

Answer 1

• žBasic structure of joints formed during wks 6-7 of gestation
• žFinal shape develops throughout early childhood under influences of the forces of movement and compression

Question 2

Hip Joint- 12 weeks of GA

Answer 2

• žvery deep acetabulum
• very round femoral head
• …femoral head very well covered

Question 3

Hip joint- Birth

Answer 3

• žvery shallow acetabulum
• hemispheric femoral head
• so…<1/2 of femoral head covered

Question 4

Hip Joint- Birth considerations

Answer 4

• žThis is an unstable hip but necessary for the infant to pass through birth canal
• Risk of dislocation is greatest if in single breech position (hips flexed/knees extended)
  
  • b/c hamstrings could pull head of femur downward
• After birth-risk of dislocation is with extending the hips
  
  • b/c iliopsoas could pull femur upward
• Birth-10 years: forces of compression and movement contribute to an increase in depth of acetabulum
  
  • adult level of femoral head coverage reached by 10
  • femoral head also rounds again but never to the level of early fetal period

Question 5

Prenatal Deformities

Answer 5

• žFetal position is related to various deformities
  
  • Like hip dysplasia
• especially true toward end of pregnancy when skeletal growth continues but space can be limited.
• žOther space limiting factors:
  
  • Decreased amniotic fluid
  • Multiple births
  • Excessive force from tightly stretched uterine and abdominal walls

Question 6

Bone Growth

Answer 6

• žCompression or tension: loading a bone longitudinally
  
  • wt bearing or ms pullÜgrowth
• Shear forces Ütorsional or twisting change

***normal pull of muscles around joint contributes to shear forces resulting in normal torsional changes in long bones

Question 7

What about Tibia?

Answer 7

• žAt birth-0-5°medial tibial torsionÜ 25° lateral torsion as adult
• žAt birth—infant knee in genu varum → netrual alignment by 2yo →peak of genu valgum between 2-4yo →adulthood
  
  • (differs between genders and races)

***Note: if find genu varus in child aged 2-6yo ►Send for orthopedic consult!!!!

Question 8

TORSION/Hip

Answer 8

• žAt birth: hip is at maximal antetorsion (30-40°)
• Rapid decrease in first year then slow until 8yo then rapid again into adoloscence to an average of 16° by 16
  
  • the femur “untwists” through growth, muscle action, reduction of coxa valga angle, and reduction of hip flexion contracture
  • active external hip rotation and external forces created during walking impact the changes in femoral anteversion

Question 9

VERSION

Answer 9

• žFemoral version = position of head of femur in acetabulum
• Anteversion positions head anteriorly leading to hip external rotation
• Retroversion positions head posteriorly leading to hip internal rotation
• At birth: neonate with 40-60° of anteversion which resolves (“de-rotates) to 15-20° by 8-10 years old à 12° in adulthood

Question 10

Who wins?

Answer 10

• žAt birth; 30-40° of antetorsion, 40-60° of anteversion
• Anteversion wins out and you have thighs in external rotation at typical term birth

***If you have persistent antetorsion or too much, you will see in-toeing as the hip “de-rotates”