Rickets

• Bone is a dynamic organ capable of rapid turnover, weight bearing, and withstanding various physical stresses.
• It is constantly being formed (modeling) & re-formed (remodeling).
• It is the body’s main reservoir for Ca, PO4, & Mg.
• Bone consists of a protein matrix, 90% of which is a collagen-containing protein (osteoid) & also osteocalcin.
• The matrix is deposited with Ca & PO4 crystals including hydroxyapatite [C10(PO4). 6H2O] & octacalcium PO4 [Ca8(H2PO4).5H2O] & less organized CaPO4, CaHCO3, Na, Mg, & citrate.

• This occurs by calcification of the chondrocytes at the ends of the bones (the growth plate).
• Vitamin D & PTH maintain ECF Ca & PO4 levels to enable mineralization.

Important Hormones

• Vitamin D:
• ↑ Ca & P absorption from GIT
• ↑ Ca & P re-absorption from the kidneys
• PTH:
• ↑ serum Ca by increasing bone resorption
• ↑ activation of Vit D.

Bone Cells

• Osteoblasts – responsible for bone formation; matrix deposition & mineralization.
• Osteoclasts – cause bone resorption by secreting enzymes which dissolve bone.
• Osteocytes – bone resorb and re-deposit bone.

Other Hormones

• GH, IGF, thyroid hormones, insulin, androgens, and estrogen all regulate bone growth.
• Glucocorticoids impair bone growth and ↑ bone resorption.

Vitamin D is a fat-soluble vitamin that is naturally present in very few foods. It is also produced endogenously when ultraviolet rays from sunlight strike the skin and trigger vitamin D synthesis.

Process of Vitamin D Metabolism

1. Synthesis: Vitamin D is synthesized in the skin in response to exposure to UVB radiation. This form of Vitamin D, known as Vitamin D3 or cholecalciferol, is inactive and needs to undergo further metabolism to become active.
2. Hydroxylation in the Liver: The inactive Vitamin D3 is transported to the liver, where it is converted into 25-hydroxyvitamin D, also known as calcidiol, through a process called hydroxylation.
3. Activation in the Kidney: The calcidiol is then transported to the kidney, where it is further hydroxylated to form 1,25-dihydroxyvitamin D, also known as calcitriol. This is the active form of Vitamin D.

The active form of Vitamin D, calcitriol, plays a crucial role in maintaining the body’s calcium and phosphate levels, promoting bone mineralization, and regulating immune function.

Both diet and sunlight exposure can contribute to maintaining adequate levels of Vitamin D in the body.

• Occurs all over the world.
• Commonest cause used to be Vitamin D deficiency due to inadequate exposure to sunlight, now less common in industrialized nations except in dark-skinned people (due to Vitamin D fortification).

• Hypocalcemic Rickets (Common):
• Vitamin D deficiency (lack of sunlight, pigmentation, dressing, 'breastfeeding')
• Malabsorption of Vitamin D
• Calcium deficiency (poor intake, high phytates in diet, high palmitic acid - common in Nigeria & SA)
• Hepatic diseases
• Renal osteodystrophy
• Vitamin D dependent (deficiency of 1α-hydroxylase)
• Hypophosphatemic Rickets (Rare):
• Genetic (x-linked, autosomal dominant)
• Fanconi’s syndrome
• Renal Tubular Acidosis - Phosphate deficiency
• Vitamin D Resistant Rickets

• In rickets, there is defective mineralization from either deficiency of calcium or phosphorus, resulting in a frayed, irregular epiphyseal line.
• Over time, more osteoid is deposited with mineralization, so the end of the bone is wider.
• Bone resorption continues, and the shaft loses its rigidity.

• Craniotabes
• Rachitic rosary
• Harrison’s groove
• Delayed closure of anterior fontanelle
• Cranial bossing
• Box-like head
• Bow-legs (varum)
• Knock-knees (valgum)
• Deformed pelvis
• Delay in standing & walking
• Delayed eruption of teeth
• Protuberant abdomen
• Risk of respiratory infections

• Biochemical:
• Calcium - Normal or decreased
• Phosphate - Decreased
• Alkaline phosphatase - Markedly increased
• Vitamin D - Decreased
• Radiological: Plain x-rays of the wrist showing cupping, fraying, splaying.

• Single dose of intramuscular Vitamin D 600,000 IU
• Daily oral dose of 5,000 – 10,000 IU of Vitamin D for 1-3 months
• In Nigeria, add calcium supplements: 1,000 mg of calcium daily for 3-6 months
• Surgical correction may be necessary for:
• Varus or valgum >15°
• Limb asymmetry
• Inter-malleolar distance >7.5 cm

• Rickets is not a fatal disease, but complications & infections, particularly pneumonia, can cause death.
• It can lead to permanent disability if not treated promptly.