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How does chronic kidney disease lead to renal osteodystrophy?

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bone disease Defect of tibia, caused by septic osteomyelitis in childhood, with compensatory thickening of the fibula (right). Normal bones are shown at left.

Renal osteodystrophy is a complex bone disorder that develops as a complication of chronic kidney disease (CKD). The progression of this condition is primarily driven by the kidneys' declining ability to maintain mineral homeostasis.1

In healthy individuals, the kidneys help regulate calcium and phosphate levels. In CKD, the kidneys lose the capacity to effectively excrete phosphate and activate vitamin D. This leads to two critical imbalances:
* Hyperphosphatemia: High levels of phosphate accumulate in the blood.
* Hypocalcemia: Low levels of calcium occur because of reduced vitamin D activation, which impairs intestinal calcium absorption.1

These imbalances trigger secondary hyperparathyroidism, where the parathyroid glands overproduce parathyroid hormone (PTH) in an attempt to restore normal calcium levels. While PTH works to increase calcium, it does so by stimulating excessive bone resorption. Over time, this process leads to the breakdown of bone structure and the replacement of healthy tissue with fibrous tissue, resulting in weakened bones, skeletal deformities, and an increased risk of fractures.1