Removing ritual impurity (hadath) on injured body parts
If one has an injury/wound with a bandage/splint and it would be harmful to remove it, then one first washes all one is able to wash without harm, then wipes what one is able to (i.e. without harm) of the body part and wipes most of the bandage/splint.
If the bandage falls off while the wound has not yet healed, then one does not need to wipe its replacement, but it is better to do so. If the bandage falls off and reveals a healed wound, then the wiping has been invalidated, and one must wash what has not been washed.
General rule in ablution (wuduu’) or the Complete Body Wash (ghusl)
If one is able to wash an injury/wound without harm one must do so (if washing the body part is an obligation). If not, then one must wipe it if this can be done without harm. If there is ointment or the like on the wound and it would be harmful to remove it, then one wipes the ointment if it is not harmful to do so.
Becoming partially excused from taking ablution
Having an excuse requires that something is breaking the ablution continuously. A person who, within the entire time period of any prayer which is obligatory to perform, could not keep his ablution for the amount of time it takes to perform the obligatory prayer and its ablution, becomes an excused person.
For example, if one of the causes breaking an ablution exists continuously, such as irregular vaginal blood (lasts less than 3 days or more than 10 days, or it falls within 15 days of an ended menstruation), urine leaks, nose bleed etc. so that from the beginning till the end of any prescribed prayer time one could not stop it long enough to take ablution and perform only the obligatory prayer, one becomes a person with an excuse.
One remains in this state until an entire prayer time passes without the occurrence of the reason for ones excuse, such as urine leakage.
A person with an excuse does not take ablution if his excuse occurs, but his ablution is invalidated by the exit of any obligatory prayer time. It is also invalidated if his ablution is broken for any other reason than the one that he is excused for. As long as his ablution is not invalidated, he can pray as much as he wants, but he cannot lead the prayer of those who are not excused.