It seems like a few of you have questions about this.
In all cases breaks should be seen by a vet, however if that is not possible decide whether to try this before euthanasia.
you will need.
a cohesive stretch bandage ( such as co flex, equiwrap, co stretch, vetrap.. etc) This stuff is excellent for any animal, in an emergency it can even be washed and reused.
thin Cotton pads, medical or makeup..
an improvised splint (discussed below)
medical/paper tape (easy to tear and can be removed from feathers.)
if its an open fracture with a wound or bones protruding from skin, all of the above. +
nice clean hands:)
betadine/ antiseptic drops if possible.
Improvised splint: you need to find something sturdy, flattish and about the width of the chickens leg ( I once splint a water hens two broken legs with the cut down handle of a fly swat) the size of the splint is obviously dependent on the size of the chicken, for a small chick it might be possible to use half a paddle pop stick, the flat side of half a peg for a lager chick, perhaps half a ruler for a larger bird.. along those lines. the length of the splint should be at least the length of the bone you are splinting, where ever the break is with the fracture positioned in the middle.eg, If the injury is in the bone between the 'ankle' and the 'knee' at the top of the shaft near the joint, you will need a splint the length of the metatarsus 'shin bone'
prepare the splint. the splint will be in place for two weeks so it is important that is as comfortable as possible and doesn't cause any more damage, file any sharp edges round and pad the side of splint that is going against the skin with cotton pads and then wrap VERY firmly with p.tape.
Treating a break is dependent on the type and placement of the injury.
sometimes the injury is obvious but all times a good inspection is needed, covering your chickens head with a sock or cloth will help keep them calm, particularly when you place them upside down on your lap:)(splinting a break is best done with two ppl, (one to hold bird the other to medic it) particularly if your chicken is feisty). three, if it really really feisty.(like a swamp hen:)
Feel both legs, looking for discrepancies, move the good leg to acquaint yourself with its movement. (this will be of importance when you place the splint).
locate the break/s. the bones need to be aligned as straight as possible and touching so as to heal, (it helps to know the skeletal structure of a chicken ( http://www.google.com.au/imgres?q=chicken+bone+structure&num=10&um=1&hl=en&biw=1280&bih=709&tbm=isch&tbnid=ZaSnL3EQQQbznM:&imgrefurl=http://windward.hawaii.edu/people/brian_richardson/chickens/Skeleton.html&docid=bo-3C-ux4OTT0M&imgurl=http://windward.hawaii.edu/people/brian_richardson/chickens/images/Chicken_Anatomy_Large.jpg&w=1116&h=1614&ei=7Y6fT5r1FK_vmAWvwajsAQ&zoom=1&iact=hc&vpx=190&vpy=125&dur=202&hovh=270&hovw=187&tx=88&ty=140&sig=105421698107902074673&sqi=2&page=1&tbnh=161&tbnw=111&start=0&ndsp=16&ved=1t:429,r:0,s:0,i:67 )
this will sometimes mean pulling the bones back into alignment (if they are through the skin) or maneuvering them back into place (painfull) but necessary. be aware that there are blood vessel, tendons, nerves etc involved here and with more serious breaks this is a very difficult process even for a vet, even with the use of xrays. some bones with multiple fractures will never heal. At all times keep in mind that as blood vessels run through the bone some breaks will compromise circulation and at that point anything below the injury is forfeit.
Is there a wound on top of the break? if there is, clean the wound with warm water with betadine in it, apply a small amount of antiseptic cream and dress with cotton pad and hold in position with paper tape.
Position the bone for splint. with the information above as best you can position the bone, (some fractures will be supported (held in correct position,(very lucky just splint it) and some will be very moveable.
If you have to pull a broken bone back through the skin, pull back through and into position then holding tension cover wound with pad, cover pad with splint then, tape round the leg till you cover splint
with less compounded fractures with no overlapping of the bone, position as best you can, apply splint the same way. tape.
In all cases you are taping the padded splint to leg and being aware of the circulation, it is not the tape that eventually holds the splint and bone in place it is the bandage.
Bandage splint in place. wrap the cohesive bandage from just below the splint all the way round/up the shaft to just above the splint,(and back down if necessary) once again firmly but being aware of circulation. always keep an eye on below the break/ foot for the foot changing colour to Grey and becoming cool. (a very little of this is normal but a lot to blue and cold is bandage too tight no circulation, limb death.
breaks near a joint are tricky but possible even if that means keeping the leg straight (It will be stiff and may need a little physio afterwards) but breaks in a joint inevitably mean the loss of mobility in that joint, chickens are not wild however and many can live with a straight leg, you can try it, see how the bird adapts and if it is terribly unhappy you still have the option of euthanasia, but you have to think about treatment in joint breaks. sometimes in these cases euthanasia is the best option.
if your chickens foot is balled, stretch out toes put a largish cotton ball underneath and tape to foot. this will help retain flexibility in the toes.
other things to keep in mind.
if your chickens bone was through the skin or there was a wound you will need antibiotics to inhibit infection, it is also possible that one day, week, months or years later it will suddenly drop dead from a bone infection.
keep chicken in box to restrict mobility for length of treatment, in most cases this will only be two weeks.
if it is a young animal and still growing the two weeks splinted may inhibit growth, leaving your chicken with one leg a little shorter than the other and thus a permanent limp:)
after the bone is healed and the splint off allow your chicken time for adaptation to its disability (if there is one) like ppl they are very adaptable and do not have to be perfect to be happy.
once again, if you can, take the bird to the vet.:)
p.s a few years ago i received a common pigeon through wildlife rescue, it had been hit by a car and its wing broken in two places, right next to the shoulder joint and a bit lower, the bones had slipped past each other and come through the skin. by any ones assessment it was a bad break and a good case for euthanasia. the kind people who picked it up knew it had a mate and did not want to pit it down, they cleaned the wound (well:) and wrapped it with cloth (not well) they then put in a box for three days before calling me.. for birds whose breaks usually heal in two weeks three days is a long time and by the time i received it the break was healing, it was also obvious that there was no infection (they did clean it well:) and other than his injury he was a very healthy pigeon.
i am too soft sometimes and could not put a healthy healing bird down, so settled down into ownership of a pigeon. Mr pige was a sad bird who did not like me, and as i was very busy at the time he ended up living in a cat crate in the corner of the lounge room. (this is not too my credit, but as a bird who could not climb or fly i had little choice,) I had over fifty birds at the time and soon Mr pige was forgotten.
(he was fed of course but not attended too:) then..
eight months later, i was watching TV when i heard a very unusual sound coming from the corner.. a whooshing sound.. when i went to check, nothing, but in not too long i heard it again.. this time i managed to sneak close enough to observe.
It was Mr Pige and to my complete amazement he was doing flying practice.. good strong beats from a wing i was sure would never fly again!
It took another couple of weeks to bring his wing up to strength but before the end of the month i took him back to the family that had rescued him in the first place, i opened his box and he shot out and up into the air, a little lopsided, (he will always have to flap harder on one side i think:) but he flew well, did a circle of their roof before landing on it a settling down to win a girl that was perched on the gable..:)
Mr pige is a rare story, but the healing of his injury to a point where he regained flight illustrates the adaptation of nature, before he left you could still feel bumps and scar tissue were the skin had grown over badly fused bone..:)
good luck everyone:)