Skeletal embryology and limb growth Flashcards
When do the upper limb bub appear?
- 4 weeks of age
- the lower limb buds appear a few days later
What does a limb consist of?
- Mesoderm covered by a thin surface of ectoderm
- the mesoderm** forms somite and lateral mesodermal plate**
What does the lateral mesoderm form?
- Bone and connective tissue
What does the somite form?
- Muscle
What gene controls mass and local growth in a distal direction?
- Homeobox (HOX) gene
What mediates the activity of the zone of proliferating activity in the ectoderm?
- The sonic the hedgehog gene
What directs the development of the limb in a anterior to posterior direction?
- The sonic the hedgehog gene
What does the zone of proliferating activity produce?
- Apical ectodermal ridge from which the digits form
How does embyrological limb development continue?
- 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
How is the joint formed?
- 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
What happens to the limb at 9 wks?
- The limb rotates thru 90 degrees laterally and medially
- results in lateral thumb and medial hallux
When do the secondary ossification centres develop?
- 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
When does the capital femoral epiphysis secondary ossification centre appear?
- After 3 months before 1 year
What effect did thalidomide have on the developing limbs?
- Antiangiogenic effecft that interupted the development of the vascularization of the ossification centres -> phocomelia
What is the classiifcation for congential limb deformities?
- Swanson 1976
- International society of hand surgeons
Can you describe Swanson’s classification for congential limb deformities?
- 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
In longitudinal deformities what is in seen?
- Abnormality is produced along one side of the whole limb
- Preaxial ( radial ) or postaxial ( ulna)
In transverse deformities in the limbs what is in seen?
- Proximal to the level of insult there is normal growth
- Distal to the insult growth and development are affected variably
In the lower limb a defect in the cartilage anlage ( primary ossification centre) may lead to what?
- 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
Name a post -axial lower limb deficiency?
- 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
Name a preaxial lower limb abnormality?
- 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
Is there any association with a preaxial ( radial ) upper limb abnormality?
- relatively common abnormality
- other congential abnormalities = VACTERL
- vertebral
- anal atresia
- cardiac anomlies
- tracheo-oesphageal fistula
- renal disorders
- limb abnormalities
What is radio-ulnar synostosis a type in swanson’s classification?
- 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
What are packaging disorders?
- 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
How does the bone grow longitudinally?
- By enchondral ossification at the physis
How does the bone grow circumferentially?
- Zone of Ranvier at the level of the physis
- Appositional ossification in the osteogenic layer of the periosteum along the diaphysis
What does the zone of Ranvier contain?
- Osteoblasts
- fibroblasts
- chondrocytes
What is the perichondial ring of LaCroix?
- Is a sting fibrous structure that secures the epiphysis to the metaphysis
Describe the layers of the physis?
- **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
Name the physis and appearance in the developing elbow?
- Capitellum 2 yrs
- Radial head 4yrs
- Internal ( medial ) epicondyle 6yrs
- Trochlear 8yrs
- Olecranon 10 yrs
- Lateral epicondyle 12 yrs
Where does 2/3rds of lower limb growth come from?
- 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
Where do fractures around the physis occur?
- Thru the hypertrophic zone
- zone of calcification
Describe the salter harris classification?
- 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
How can growth disturbance can occur?
- 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
Why will remodelling occur at the physis?
- 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
Who classified skeletal dysplasia?
- Ruben
- divided in location of the defect adn whether there is an increased or decreased activity
Can you describe Ruben’s classification of skeletal dysplasia’s?
-
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
How does rickets affect the growth plate?
- 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
