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 (letters on right correspond to histology)
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 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