Developmental biomechanics Flashcards
What is developmental biomechanics the study of?
Study of how forces affect the MSK system over the life span
Main forces impacting developmental biomechanics
Body weight/gravity (external)
Alignment + pull/force of muscles (internal)
Why is developmental biomechanics important
Development of MSK system is part of tx and dx
When does formation of MSK system occur
2nd - 8th week of post conception (embryonic period)
When do limb buds appear?
4th week (upper limb slightly before lower limb)
Up to what week do major congenital abnormalities occur?
8 weeks (start of the fetal period)
Categories of congenital abnormalities and what phase they occur in
Malformations (embryonic)
Deformations (fetal)
Disruptions (fetal)
Dysplasias (fetal)
During what period do malformations arise?
Period of organogenesis (weeks 2-8)
Of what origin are malformations?
Teratogenic
Genetic
Idiopathic
Examples of malformations
Phocomelia
Limb hypoplasis
Terotogenic origin
Something external (meds, radiation, illness/fever)
Genetic origin
Mutation
Is lower or upper limb more susceptible to congenital limb loss
Lower
What is a key difference between infant + children bones and adult bones
Bones are softer in infants/children because they haven’t been ossified
When do deformations occur in development?
Occur at the end of gestation (fetal stage)
Cause of deformations
Intrauterine crowding
Position
Examples of deformation
Torticollis
Club foot
t/f deformations are more common in multiples
true
When do disruptions occur
Later in gestation (fetal stage)
Cause of disruptions
Teratogenic, traumatic, or other physical insults to the fetus interfere with growth
Examples of disruptions
Congenital/amniotic constriction bands
Why do dysplasias occur
Result from altered growth that occurs before and/or after birth
Examples of dysplasias
Achondroplasia
Developmental hip dysplasia
Are dysplasias isolated?
They can be, but can also be more widespread
2 distinct processes of bone formation
Endochondral ossification
Intramembranous ossification
Role of ossification
Form bone by replacing cartilage, but differing in method
What type of ossification is more common and what bones do not follow this method
Endochondral ossification is more common
Clavicle, mandible and skull are formed by intramembranous
Primary ossification center
Midportion of long bones
Ossify outward until entire shaft are ossified at birth
Secondary ossification centers
Develop during infancy and early childhood at the end of bones
Growth plate
Cartilage between 1st and 2nd ossification centers
Directions bones grow
Length: long bones grow in length at epiphyseal plate
Girth: bones increase in size through addition and accumulation of new bone on the bone surface
When is the most rapid period of growth in long bone girth
Prenatally
What is necessary for bones to growth
WB + muscle forces
2 ways that muscle fibers increase
Hyperplasia: Prenatally increase in # of muscle cells
Hypertrophy: after birth increase in size of muscle cells
How to stimulate growth of muscle fibers
Resistance training
Directions of muscle growth
Diameter: related to intensity of activity during growth
Length: addition of sarcomeres and lengthening of sarcomeres
Clinical implications of the MSK system development
-immature MSK system is vulnerable to abnormal mechanical forces + pressures
-Compliance of MSK system procides for successful response to tx intervention (plasticity)
Wolff Law of bone transformation
Mechanical stresses modulate bone shape + internal architecture
Proportional: High strength = high stress
Skeletal molding mechanism
Strain
Components of strain
Compression
Tension
Torsion
Tension modeling effects
Tendon + ligament attachments are loaded in tension, resulting in trochanters, tubercles, prominences and ridges
Compression modeling effects
WB results in increase in growth rate at the compression sites of epiphyseal plate and increase in cross sectional diameter
Torsion modeling effects
Twisting thru the shaft or longitudinal axis of a bone (tibial torsion)
Clinical significance of adaptations of muscles and bone
Mechanical forces affect the shape of the maturing skeleton which in turn affect the biomechanical function of the MSK system
Norma developmental progression of the knees
Genu varum earlier on
straight limbs due to WB
Genu valgum; development of more mature gait pattern
Clinical implications of tension
Spasticity provides asymmetric pull risk of subluxation/dislocation
Ilizarov disease
Clinical implications of compression
Ankle and genu varum/valgum
Flattening of femoral head resulting in slipped capital femoral epiphysis + osteopenia
Clinical implication of torsion
Femoral anteversion results in in toeing
