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Basic Science > Skeletal embryology and limb growth > Flashcards

Skeletal embryology and limb growth Flashcards

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1
Q

When do the upper limb bub appear?

A
  • 4 weeks of age
  • the lower limb buds appear a few days later
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2
Q

What does a limb consist of?

A
  • Mesoderm covered by a thin surface of ectoderm
  • the mesoderm** forms somite and lateral mesodermal plate**
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3
Q

What does the lateral mesoderm form?

A
  • Bone and connective tissue
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4
Q

What does the somite form?

A
  • Muscle
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5
Q

What gene controls mass and local growth in a distal direction?

A
  • Homeobox (HOX) gene
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6
Q

What mediates the activity of the zone of proliferating activity in the ectoderm?

A
  • The sonic the hedgehog gene
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7
Q

What directs the development of the limb in a anterior to posterior direction?

A
  • The sonic the hedgehog gene
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8
Q

What does the zone of proliferating activity produce?

A
  • Apical ectodermal ridge from which the digits form
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9
Q

How does embyrological limb development continue?

A
  • The mesenchyme condenses
  • chondrocytes then differentitiate within mesenchyme = chondrifcation
  • first occurs in diaphsysis of humerus and femur
  • new chondrocytes produce a matrix of glycosaminogylcans
  • the cartilagninous mesenchyme ( the cartilage anlage) then undergoes resorption and cavitation between future segements= segmentation -> primitve joint
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10
Q

How is the joint formed?

A
  • The primary ossification centre develops with hypertrophy of the middiaphyseal chondrocytes and invasion of blood vessels which form the primitive nutrient artery system.
  • Initally intramembranous ossification occurs circumferentially from the periosteum around the primary ossification centre
  • However in the epiphyseal regions, the cartilage cells become hypertrophic and after vascular invasion the process of enchondral ossification commences
  • by 12th week ossification centres are present in all bones
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11
Q

What happens to the limb at 9 wks?

A
  • The limb rotates thru 90 degrees laterally and medially
  • results in lateral thumb and medial hallux
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12
Q

When do the secondary ossification centres develop?

A
  • At the end of fetal development in the distal femur- after 36 weeks
  • a separate blood system has grown into epiphysis
  • these vascualrised chondrocytes hypertrophy to form a central mass
  • the central mass forms a spherical physis over its entire surface, which later reshapes in to a hemispherical outer surface and a discoid non-physeal surface towards the metaphysis
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13
Q

When does the capital femoral epiphysis secondary ossification centre appear?

A
  • After 3 months before 1 year
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14
Q

What effect did thalidomide have on the developing limbs?

A
  • Antiangiogenic effecft that interupted the development of the vascularization of the ossification centres -> phocomelia
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15
Q

What is the classiifcation for congential limb deformities?

A
  • Swanson 1976
  • International society of hand surgeons
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16
Q

Can you describe Swanson’s classification for congential limb deformities?

A
  • Failure of formation = ​fibular hemimelia
  • Failure of separation = ​Tarsal coalition
  • Hypoplasia = hypoplastic digit
  • **Overgrowth = **​macrodactyly
  • Duplication = ​polydactyly
  • **Constriction ring syndrome = **​Aminotic bands
  • Dysplasias or syndromes = achondroplasia
17
Q

In longitudinal deformities what is in seen?

A
  • Abnormality is produced along one side of the whole limb
  • Preaxial ( radial ) or postaxial ( ulna)
18
Q

In transverse deformities in the limbs what is in seen?

A
  • Proximal to the level of insult there is normal growth
  • Distal to the insult growth and development are affected variably
19
Q

In the lower limb a defect in the cartilage anlage ( primary ossification centre) may lead to what?

A
  • Proximal focal femoral deficiency
  • Autosomal dominant
  • assoc with Sonic the hedhehog gene
  • 50% bilateral
  • spectrum of disease
    • ​absent hip
    • cervical pseudoarthrosis
    • absent /shortened femur
  • Aitken classified
  • Class A femoral head present, acetabulum normal
  • Class B femoral head present, acetbulum mildy dysplasic
  • Class C femoral head absent, severly acetabular dysplasia
  • Class D femoral head absent, acetbular absent
  • assoc with ACL deficiency, fibular hemimelia, coxa vara, knee contractures
20
Q

Name a post -axial lower limb deficiency?

A
  • Fibular hemimelia
    • complete absent or fibular short
    • most common congential Long bone abnormality
    • sonic hedgehog gene involved
    • anteromedial bowing
    • absent lateral rays
    • tarsal coalition 50% -> ball and socket ankle joint and ankle instability
    • femoral abnormalities - PFFD/coxa vara
    • Genu valgum due to hypoplasic lateral femoral condyle
    • absent cructiate ligaments
21
Q

Name a preaxial lower limb abnormality?

A
  • Tibial hemimelia
  • less common
  • Autosomal dominant inheritance = Genetic counselling
  • medial ray toe deformities
  • anterolateral bowing
  • prominent fibular
  • assoc polydactyly/ ulnar aplasia/ cleft hand ( ectrodactyly)
  • Jones classification
    • complete absence of tibia
    • partial absence divided into
      • proximal
      • distal
      • ankle diastasis
  • Tx based on knee stability
  • no active knee extension/ absence = amputation
  • prox tib and extensor mechanism intact= tibiofibular synpstosis with syme amputation
  • ankle diastasis = syme amputation
22
Q

Is there any association with a preaxial ( radial ) upper limb abnormality?

A
  • relatively common abnormality
  • other congential abnormalities = VACTERL
  • vertebral
  • anal atresia
  • cardiac anomlies
  • tracheo-oesphageal fistula
  • renal disorders
  • limb abnormalities
23
Q

What is radio-ulnar synostosis a type in swanson’s classification?

A
  • failure of separation
  • synostosis in proximal half as the radius and ulna separates from distal to proximal
  • Bilateral in 60%
  • pts frequently have duplication in sex chromosome
  • no pronationor supination
  • pronation limited ( 50% pts have >50o of pronation)
  • Tx observe if unilateral but if fuse 10-20o pronation
  • if bilateral dominant hand fuse in 30-40o then non dominant supination 20-30o
24
Q

What are packaging disorders?

A
  • disorders in which the limb that have been formed normally are moulded into abnormal position in the third trimester
  • include
  • plagiocephaly
  • torticollis
  • infantile skeletal skew and calcaneovalgus feet
  • normally self correcting and
25
Q

How does the bone grow longitudinally?

A
  • By enchondral ossification at the physis
26
Q

How does the bone grow circumferentially?

A
  • Zone of Ranvier at the level of the physis
  • Appositional ossification in the osteogenic layer of the periosteum along the diaphysis
27
Q

What does the zone of Ranvier contain?

A
  • Osteoblasts
  • fibroblasts
  • chondrocytes
28
Q

What is the perichondial ring of LaCroix?

A
  • Is a sting fibrous structure that secures the epiphysis to the metaphysis
29
Q

Describe the layers of the physis?

A
  • **Resting zone= **low O2 tension. Small chondrocytes
  • Proliferative = chondrocytes increase, High O2 tension
  • Hypertrophic zone= chondrocytes enlarge 5-10x
    • zone of maturation
    • zone of degeneration
    • Zone of calcification
30
Q

Name the physis and appearance in the developing elbow?

A
  • Capitellum 2 yrs
  • Radial head 4yrs
  • Internal ( medial ) epicondyle 6yrs
  • Trochlear 8yrs
  • Olecranon 10 yrs
  • Lateral epicondyle 12 yrs
31
Q

Where does 2/3rds of lower limb growth come from?

A
  • the knee with 70% around distal femur
  • estimate distal femur 9mm/year of growth and prox tibia 6mm/year
  • proximal femur and distal tibia account for only a few mm (3-4mm) each per year
32
Q

Where do fractures around the physis occur?

A
  • Thru the hypertrophic zone
    • zone of calcification
33
Q

Describe the salter harris classification?

A
  • Type 1 - thru physis
  • type 2 away from physis with Thurtson-holland metaphsyeal fx
  • type 3 towards physis/ intra-articular
  • type 4- thru both sides of physis
  • type 5 - crush
  • type 6 - added by Mercer Rang = injury to perichondral ring
34
Q

How can growth disturbance can occur?

A
  • From a bride of bone forming across the physeal cartilage
  • Can be Peripheral, Central or linear
  • may lead to LLD or angular deformity
  • if the bony bridge is >40% of growth plate then non resectible
35
Q

Why will remodelling occur at the physis?

A
  • Due to forces acting in the plane of motion of the joint according to Wolfe’s law which states that
  • bone remodels according to the applied stresses
36
Q

Who classified skeletal dysplasia?

A
  • Ruben
  • divided in location of the defect adn whether there is an increased or decreased activity
37
Q

Can you describe Ruben’s classification of skeletal dysplasia’s?

A
  • Epiphysis
    • Hyperplasia - Trevor’s disease
    • Hypoplasis - SED, MED, pseudoachondroplasia
  • Physis
    • Hyperplasia - Enchondromatosis- ollier’s
    • Hypoplasia - Achondroplasia
  • Metaphysis
    • Hyperplasia - Hereditary multiple exostoses
    • Hypoplasia- Osteopetrosis
  • Diaphysis
    • Hyperplasia- Diaphyseal dysplasia
    • Hypoplasia- osteogenesis imperfecta
38
Q

How does rickets affect the growth plate?

A
  • Failure of calcification of the chondrocytes in the provisional zone of calcification in the physis
  • there is normal matrix but it fails to calcify
  • this in the followed by disordered invasion by blood vessels
  • radiographically this results in widening, thickened physis and hazy appearance of metaphysis with flaring and cupping due to persistence of cartilage in the metaphysis

Basic Science (31 decks)

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