**Core Concept**
Intravenous regional anaesthesia (IVRA), also known as Bier block, is a technique that involves administering local anaesthetics into a limb, isolated from the systemic circulation, to provide regional anaesthesia. This procedure relies on the principles of vasodilation and the diffusion of anaesthetics through the bloodstream to achieve analgesia.

**Why the Correct Answer is Right**
The correct answer is **B. Distal radius fractures**. IVRA is particularly useful in the management of distal radius fractures, where the patient is often anxious, and the procedure allows for precise anaesthesia of the affected limb. The mechanism involves the administration of local anaesthetics, such as lignocaine or prilocaine, into a vein of the isolated limb, which then diffuses through the bloodstream to the nerves, providing analgesia. This technique is ideal for procedures like closed reduction and immobilization of the fracture.

**Why Each Wrong Option is Incorrect**
**Option A:** IVRA is not suitable for **obstetric procedures** as it does not provide adequate anaesthesia for the upper body and is contraindicated in pregnant women due to the potential for fetal toxicity.
**Option C:** IVRA is not typically used for **orthopaedic surgeries** that require more extensive anaesthesia, such as hip or knee replacement surgery, where general anaesthesia or spinal anaesthesia may be more appropriate.

**Clinical Pearl / High-Yield Fact**
IVRA is contraindicated in patients with certain medical conditions, such as vascular disease, infection, or previous trauma to the affected limb, which may compromise the integrity of the vascular system and increase the risk of complications.

**Correct Answer: B. Distal radius fractures**