Explanation:

Osteitis fibrosa cystica is a skeletal disorder that occurs due to overproduction of parathyroid hormone (PTH) by the parathyroid glands. This condition is also known as von Recklinghausen's disease of bone or osteitis fibrosa.

Causes:
The major cause of osteitis fibrosa cystica is hyperparathyroidism, which is a condition in which the parathyroid glands produce too much PTH. This hormone regulates calcium and phosphate levels in the body. When the parathyroid glands produce too much PTH, it causes calcium to be leached from the bones, resulting in bone loss, weakness, and deformity. This condition is commonly seen in individuals with chronic kidney disease, where the kidneys are unable to filter out excess calcium.

Symptoms:
The symptoms of osteitis fibrosa cystica include:
- Bone pain
- Weakness
- Deformities
- Increased risk of fractures
- Kidney stones
- Abdominal pain
- Nausea and vomiting

Treatment:
The treatment of osteitis fibrosa cystica involves managing the underlying cause of hyperparathyroidism. This may involve surgery to remove the parathyroid gland or medication to reduce the levels of PTH. Calcium and vitamin D supplements may also be given to help improve bone density.

Conclusion:
In conclusion, osteitis fibrosa cystica is a skeletal disorder that develops due to hyperparathyroidism. It is a serious condition that can lead to bone loss, weakness, and deformity. Early diagnosis and treatment are important in preventing complications.

Osteitis fibrosa cystica (OFC) is a skeletal disorder caused by a surplus of parathyroid hormone (PTH) from overactive parathyroid gland(s), i.e, hyperparathyroidism. This surplus stimulates the activity of osteoclasts, cells that breakdown bone. So, option a is correct.