Vitamin D Regulation, Classification of Rickets and Management of Severe Genu Valgum
DNB Orthopaedics • October 2023 • Paper I • Question 4 • 10 Marks [3+3+4]
Introduction
1,25-dihydroxy vitamin D [1,25-(OH)₂D; calcitriol] is the active hormonal form of vitamin D and is a major regulator of calcium and phosphate homeostasis. Deficiency of mineral availability at the growing physis results in rickets, characterized by defective mineralization of growth plate cartilage and newly formed osteoid.
Severe rickets may produce progressive angular deformity such as bilateral genu valgum. Management requires correction of the underlying metabolic disorder before definitive deformity correction.
Key orthopaedic principle: Do not correct a rachitic deformity surgically until the metabolic disease has been treated and the child is biochemically healing.
A. Regulation of Mineral Metabolism by 1,25-(OH)₂ Vitamin D [3 Marks]
Vitamin D Metabolism
Skin / Diet ↓ Vitamin D3 / D2 ↓ LIVER 25-hydroxylase ↓ 25-hydroxy vitamin D [25(OH)D] ↓ KIDNEY 1α-hydroxylase ↓ 1,25-(OH)₂ vitamin D CALCITRIOL
25(OH)D is the major circulating storage form and is the preferred test for assessing vitamin D status. The kidney converts it to the active hormone 1,25-(OH)₂D.
Regulation of Renal 1α-Hydroxylase
| Stimulates Calcitriol Formation | Inhibits Calcitriol Formation |
|---|---|
| Parathyroid hormone |