Fallout 1 and Fallout 2
In Fallout 1 and Fallout 2, crippled limbs are a serious problem. Having arms crippled lowers your unarmed and melee weapons damage and accuracy with all weapons; with both arms crippled, you will not be able to use weapons at all. Crippled legs lower mobility, increasing the amount of action points required to move during battle. If either or both of your eyes are damaged, your accuracy with every weapon drops substantially. In order to heal crippled limbs you need a decent Doctor skill and a first aid box or doctor's bag, or you have to find a doctor that can heal crippled limbs. In Fallout 1, the doctor in Vault 13 can do this. The Ripper is a very effective weapon to use when attempting to cripple an enemy's limbs.
In Fallout 3 your head and torso can be crippled as well as your arms and legs, though they tossed the Crippled Eye idea, there is a similar effect with a crippled head. When your head is crippled, you receive a concussion, constantly blurring your vision and making sounds like ringing in your ears so it is difficult to see or hear what you are shooting at; you also receive a -4 reduction to your Perception. Having your torso crippled affects your Endurance, making you react more violently to being hit and potentially disrupting your actions. Having crippled arms has the same effect as in Fallout 1 and Fallout 2, lower damage with melee and lower accuracy, and crippled legs lower your overall speed. If you had any crippled limbs in Fallout 3, you can either use a stimpak, find a doctor, or even sleep for as much as an hour. Eating food or drinking water does not regenerate limbs. After completing the optional method of completing "Contract Radiation Sickness" in Chapter 1 of "The Wasteland Survival Guide" Quest, Moira will heal your 600 rads of radiation and you will mutate, giving you a new perk; "Rad Regeneration", which allows you to regenerate crippled limbs while experiencing advanced radiation poisoning.
Fallout New Vegas
In normal play, a doctor's bag or sleeping will heal all crippling. Stimpaks can be used to heal individual limbs. In hardcore mode, stimpaks will not heal limbs and doctor's bags will only work on one limb at a time. Sleep will only heal crippling if it is in an "owned" bed.