What is the primary purpose of a cast in medical treatment?

The primary purpose of a cast in medical treatment is to help heal a fracture. When a bone is broken, it must be properly immobilized to ensure that it heals correctly and maintains the appropriate alignment. A cast serves as a solid shell around the injured area, keeping the fractured bones together and restricting movement, which is essential for the healing process.

Using a cast helps provide stability, prevents further injury, and enables the body to repair itself. The immobilization allows the bones to connect and form new bone tissue as they heal over time. The other options, while they may relate to aspects of medical treatment, do not capture the primary role of a cast. For example, while casts provide some protection from external injury and may incidentally help manage swelling, their primary function specifically addresses the healing of broken bones.