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- A defect in mineralisation of osteoid matrix caused by inadequate calcium and phosphate before physeal closure; normal osteoid.
- Occurs at the zone of provisional calcification of the Hypertrophy zone
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- Aka familial hypophosphatemia due to impaired reabsorption of phosphate in kidney ➔ low phosphate ➔ directly lead to problem with mineralization
- XL-dominant - PHEX gene or Mutations involving FGF-23 gene
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- Type 1 = renal enzyme defect (AR inheritance) - unable to convert
- Type 2 = end organ receptor defect (AR inheritance)
- Nutritional
- GI malabsorption issues
- Lack of sunlight ➔ low vit D ➔ low calcium
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- Hypophosphatemia
- LL deformities - valgum or varum
- Stunted growth rate
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- Type 1 vit D dependant (problem with renal enzyme) - low 1,25 OH Vit D
- Type 2 vit D dependant (problem with end organ) - Raised 1,25 Vit D as cannot be used
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- Affects physis, zone of provisional calcification of the hypertrophic zone
- Difference from osteomalacia = occurs after physeal closure
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- Head to toe -
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- Frontal bossing
- Craniotabes - soft skull bones
- Dental hypoplasia
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- Rachitic Rosary - expansion of anterior rib ends at costochondral junction
- Harrison's sulcus - linear depression at lower ribs at site of attachment to diaphragm
- Pectus Carinatum - chest pused outwards (pigeon chest)
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- Short Stature
- Spine - Kyphosis
- LL - Tibia bowing
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- Hips - looser's zones aka milkman lines (insufficiency # on concave side of bones)
- Limbs - Widened physis, cupped metaphysis/ flaring, bowing of long bones
- Spine - Cod fish vertebrae
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- Low serum phosphate, elevated ALP
- Normal calcium or low normal
- PTH is normal
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- High dose phosphate replacement
- High dose Vit D to counterbalance hypocalcemic effect of Phosphate administration
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- Epiphysis is normal in Rickets
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- 0/2/4/6 yo = 15/0/10/5
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- metaphyseal-diaphyseal angle (MDA) is formed between a line connecting the most distal points of the medial and lateral proximal tibial metaphyseal beak and a line perpendicular to a line parallel to the lateral tibial cortex
- > 16 = blounts
- > 11 in < 2 year = likely progress
- < 9= likely physiological
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- Angle between epiphysis and line from tip of meaphyseal beak to midpoint of tibia plateau
- [normal < 20 °]
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- Look at where mechanical axis passes through the knee
- Divid the Tibia plateau into 4 quarters. Zones 1/2/3 (3 is out of knee)
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- mLDFA (mechanical lateral distal femoral angle) = angle between line from center of femoral head to center of knee // distal femur joint line
- MPTA (Mechanical proximal tibia angle) = angle between tibia axis and tibia plateau
- Both angles normal is 87 °. Measuring the angles can tell us if the valgus is originating from tibia or femur
- In this case, mLDFA is 77 while MPTA is 87, so deformity is in femur ➔will benefit from DFO
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- Similar to protocol for Blounts
- MDT with endocrinologist
- < 3 yo, mild = Brace
- 4-8 = Guided growth +/- proximal tibia or distal femur osteotomy
- > 8
- MAD 2/3 = Guided growth
- MAD 3/4 =
- If adequate bone age = Guided growth (check bone age with Sanders Classifx)
- If fused = Osteotomy