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Physeal Growth Plate
(letters on left correspond to histology in top right)
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| B. Reserve zone |
- Cells store lipids, glycogen, and proteoglycan aggregates for later growth and matrix production
- Low oxygen tension
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- Gaucher’s
- diastrophic dysplasia
- Kneist*
- pseudoachondroplasia*
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| C. Proliferative zone |
- Proliferation of chondrocytes with longitudinal growth and stacking of chondrocytes.
- Highest rate of extracellular matrix production
- Increased oxygen tension in surroundings inhibits calcification
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- Achondroplasia
- Gigantism
- MHE
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| D. Hypertrophic zone |
- Zone of chondrocyte maturation, chondrocyte hypertrophy, and chondrocyte calcification.
- Three phases occur in the hypertrophic zone
- Maturation zone: preparation of matrix for calcification, chondrocyte growth
- Degenerative zone: further preparation of matrix for calcification, further chondrocyte growth in size (5x)
- Provisional calcification zone: chondrocyte death allows calcium release, allowing calcification of matrix
- Chondrocyte maturation regulated by local growth factors (parathyroid related peptides, expression regulated by Indian hedgehog gene)
- Type X collagen produced by hypertrophic chondrocytes important for mineralization
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- SCFE (not renal)
- Rickets (provisional calcification zone)
- Enchondromas
- Mucopolysacharide disease
- SED
- MED
- Schmids
- Kneist*
- Pseudoachondroplasia*
- Fractures most commonly occur through the zone of provisional calcification, specifically Salter-Harris I fractures
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E. Primary spongiosa
(metaphysis) |
- Vascular invasion and resorption of transverse septa.
- Osteoblasts align on cartilage bars produced by physeal expansion.
- Primary spongiosa mineralized to form woven bone and then remodels to become secondary spongiosa (below)
|
- Metaphyseal “corner fracture” in child abuse
- Scurvy
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Secondary spongiosa
(metaphysis) |
- Internal remodeling (removal of cartilage bars, replacement of fiber bone with lamellar bone)
- External remodeling (funnelization)
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Physis Periphery
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| Groove of Ranvier |
- During the first year of life, the zone spreads over the adjacent metaphysis to form a fibrous circumferential ring bridging from the epiphysis to the diaphysis.
- This ring increases the mechanical strength of the physis and is responsible for appositional bone growths
- supplies chondrocytes to periphery
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| Perichondrial fibrous ring of La Croix |
- Dense fibrous tissue that is the primary limiting membrane that anchors and supports the physis through peripheral stability
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