Physeal Considerations - Pediatrics

Introduction
- Always look to see if physis is open
- Unique principals in pediatric bone
  - elasticity
    
    more elastic which leads to unique fracture patterns
    
    buckle fractures
    
    greenstick fractures
  - remodeling potential
    
    open physes (growth plates) can allow extensive bone deformity remodeling potential
    
    occurs more rapidly in plane of joint motion
    
    sagittal plane in wrist, due to primarily extension/flexion
    
    occurs more at the most active physes, due to most growth and potential for remodeling
    
    most active physes in upper extremity
    
    proximal humerus
    
    distal radius
    
    most active physes in lower extremity
    
    distal femur
    
    proximal tibia
    
    distal tibia
    
    lateral ligament sprains are more common than Salter-Harris 1 fractures in pediatric ankle inversion injuries
- Same principles as adult bone
  - intra-articular fractures must be reduced

                        Physeal Anatomy
                    
                                            Physeal Growth Plate

                                            Reserve zone (B) 

                                            • Cells store lipids, glycogen, and proteoglycan aggregates for later growth and matrix production
• Low oxygen tension
                                        
                                            • Gaucher's
• Diastrophic dysplasia
• Kneist
• Pseudoachondroplasia
                                        
                                            Proliferative zone (C)

                                            • Proliferation of chondrocytes with longitudinal growth and stacking of chondrocytes.
• Highest rate of extracellular matrix production
• Increased oxygen tension in surroundings inhibits calcification
                                        
                                            • Achondroplasia
• Gigantism
• MHE
                                        
                                            Hypertrophic zone (D)

                                            • 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

                                            • SCFE (not renal)
• Rickets (provisional calcification zone)
• Enchondromas
• Mucopolysacharide disease
• Schmids
• Fractures most commonly occur through zone of provisional calcification

                                            Primary spongiosa (E)
(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
                                        
                                            Secondary spongiosa
(metaphysis) 

                                            • Internal remodeling (removal of cartilage bars, replacement of fiber bone with lamellar bone)
• External remodeling (funnelization)
                                        
                                            • Renal SCFE
                                        
                                            Physis Periphery
                                        
                                            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 the periphery 

                                            • Osteochondroma
                                        
                                            Perichondrial fibrous ring of La Croix
                                        
                                            • Dense fibrous tissue that is the primary limiting membrane that anchors and supports the physis through peripheral stability
                                        
                                            Perichondrial artery

                                            • Major source of nutrition to physis

Injury Classification
- Salter-Harris classification
  - Type 1: physeal separation
  - Type 2: fracture traverses physis and exits metaphysis
    
    most common type
    
    Thurston Holland fragment
  - Type 3: fracture traverses physis and exits epiphysis
  - Type 4: fracture passes through epiphysis, physis, metaphysis
    
    Thurston Holland fragment
  - Type 5: crush injury to physis

Treatment
- Closed reduction vs. CRPP vs. ORIF
  - depends on injury pattern
  - intra-articular fractures must be reduced

Complications
- Growth arrests
  - overview
    
    complete arrest leads to shortening
    
    see Leg Length Discrepancy
    
    partial arrest leads to angulation
  - treatment
    
    bar resection with interposition
    
    indications
    
    < 50% physeal involvement
    
    > 2 years or 2cm growth remaining
    
    ipsilateral completion of arrest
    
    indications
    
    > 50% physeal involvement
    
    can combine with contralateral epiphysiodesis and/or ipsilateral lengthening

Physeal Growth Plate
Reserve zone (B)	• Cells store lipids, glycogen, and proteoglycan aggregates for later growth and matrix production • Low oxygen tension	• Gaucher's • Diastrophic dysplasia • Kneist • Pseudoachondroplasia
Proliferative zone (C)	• Proliferation of chondrocytes with longitudinal growth and stacking of chondrocytes. • Highest rate of extracellular matrix production • Increased oxygen tension in surroundings inhibits calcification	• Achondroplasia • Gigantism • MHE
Hypertrophic zone (D)	• 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	• SCFE (not renal) • Rickets (provisional calcification zone) • Enchondromas • Mucopolysacharide disease • Schmids • Fractures most commonly occur through zone of provisional calcification
Primary spongiosa (E) (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
Secondary spongiosa (metaphysis)	• Internal remodeling (removal of cartilage bars, replacement of fiber bone with lamellar bone) • External remodeling (funnelization)	• Renal SCFE

Physis Periphery
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 the periphery	• Osteochondroma
Perichondrial fibrous ring of La Croix	• Dense fibrous tissue that is the primary limiting membrane that anchors and supports the physis through peripheral stability
Perichondrial artery	• Major source of nutrition to physis