Rickets

What it is

Rickets and osteomalacia are disorders of bone mineralization. In osteomalacia, remodeling of preexisting bone is defective; it can affect any age and usually presents with bone pain and tenderness. In rickets, new bone formation is defective, so it can only occur in children with open growth plates, and it presents as bone deformities and impaired growth - failure of growing bone mineralization. Vitamin D deficiency in children is rickets; in adults it is osteomalacia. The defect is insufficient calcium, phosphate depletion, and/or direct inhibition of bone mineralization, and the most common cause of both is vitamin D deficiency. Over time both may lead to bowing of the long bones and/or pathological fractures.

Behind all of it is calcium homeostasis. Blood calcium is held at 9-11 mg/100 ml. When blood Ca2+ rises, the thyroid gland releases calcitonin, which stimulates calcium salt deposit in bone. When blood Ca2+ falls, the parathyroid glands release parathyroid hormone, and under PTH the osteoclasts degrade bone matrix and release Ca2+ into the blood.