If you suspect a limb fracture, you should immobilise the casualty’s:

In accordance with the basic principle of first aid for bone injuries (known as Pott's rule), it is necessary to immobilise not only the site of the fracture itself, but also the two adjacent joints. This action effectively prevents the displacement of bone fragments, which minimises the risk of additional damage to blood vessels, nerves and soft tissues, and also significantly reduces pain for the casualty.