The most common injuries gerbils suffer are cuts and scratches. These can be caused by fights which are not uncommon. The best way to treat these injuries is to dab them with an antiseptic, which can be purchased from your vet. It is quite rare for gerbils to break bones. If a gerbil has broken a bone, it is unlikely to be detected by the owner.
Most breaks seem to heal without bandages or any other supports.
However, on rare occasions, some breakages can be fatal. Pinning gerbil bones together can be virtually impossible due to the thickness of the bone. Applying a cast would also be impractical as a gerbil would be able to gnaw though it very quickly. Considering the gerbil's quality of life if other injuries, including infection, occur. It may be a wiser and kinder choice to have the animal put to sleep.