**Question:** Regarding Sudeck's osteodystrophy, all of the following statements are true except:

A. Sudeck's osteodystrophy is a rare condition.
B. It is a complication of paralysis or neurological disorders.
C. It is characterized by osteopenia and increased bone resorption.
D. It is seen in patients with cancer.

**Correct Answer:** **A. Sudeck's osteodystrophy is a rare condition.**

**Core Concept:** Sudeck's osteodystrophy, also known as post-traumatic osteolysis or algodystrophy, is a disorder affecting bone quality and quantity following trauma, surgery, or immobilization. It is characterized by pathological alterations in bone remodeling leading to osteopenia and increased bone resorption.

**Why the Correct Answer is Right:** Sudeck's osteodystrophy is not a rare condition, but rather a common post-traumatic complication affecting approximately 5-20% of patients after fractures or joint immobilization. It is often caused by disruption in the normal balance between bone formation and resorption resulting from trauma or immobilization.

**Why Each Wrong Option is Incorrect:**

A. This statement is incorrect as Sudeck's osteodystrophy is not rare.
B. Although it can occur after paralysis or neurological disorders, the condition is not limited to these causes. It can be seen after various types of trauma or immobilization.
C. While osteopenia is a feature of Sudeck's osteodystrophy, the statement that "it is characterized by osteopenia and increased bone resorption" is correct, as it highlights the key pathological changes in the disease.
D. Sudeck's osteodystrophy is not specifically associated with cancer; it can occur after trauma or immobilization irrespective of a cancer diagnosis.

**Clinical Pearl:** Sudeck's osteodystrophy is a clinical entity that must be considered in patients who develop bone pain, swelling, and deformity following trauma, surgery, or immobilization. Early recognition and intervention can help prevent progression and complications such as non-union or malunion of fractures.