Cast

A cast is a rigid support made of plaster or fiberglass that wraps around a broken bone to hold it still while it heals. By keeping the fracture ends from moving, it allows new bone tissue to bridge the gap and gradually knit back together, similar to how a splint provides temporary support before or instead of a full cast.

While casts are essential for healing, the immobility they cause has a downside for bone itself. Bone responds to the forces placed on it, and when a limb goes weeks without normal weight-bearing or muscle pulling on it, the body treats that bone as less necessary and begins removing some of it. This is why an arm or leg that comes out of a cast often looks visibly thinner on an X-ray than before the injury.

This bone loss is usually temporary and tends to rebuild once normal activity, weight-bearing, and muscle use resume — though recovery of strength and density takes time and often benefits from guided rehabilitation. Your doctor or physical therapist can advise on safe ways to reload the limb gradually after cast removal.