No matter how experienced you are, there's always the risk of slipping and falling when you're in the wilderness. But what if you fall and break your bones? The first thing you need on any outdoor excursion is a first aid kit. This one includes a guide to wilderness and travel medicine, along with some supplies for a broken limb. If you love the wilderness, you should also consider taking a basic first aid class.
Examine the injury to make sure it's a break, not a sprain. You'll need a splint on both sides of a broken leg; if you have a tent, you can use the poles. If not, look for two sturdy long sticks. If you can't find anything, use a bandage wrap from your first aid kit to splint the broken leg to the other leg, and make sure the splint is secure the entire length of the leg. If the fracture is compound (bone breaks through the skin), pull it straight so that the bones align, clean the wound, apply an antibiotic cream, dress and bandage the wound firmly, then splint the leg.
Splint an arm with a rolled up magazine or newspaper, or with shorter poles or sticks. Put the arm in a sling, made from any fabric you have. Whether the break is an arm or leg, give the injured person pain killers from the kit, and make sure you can see fingers or toes so you can tell if the splint is too tight – if the fingers or toes turn red or purple, then it's on too tight. The limb needs circulation.
Step two is to get the injured person to real medical help. If he has a broken arm, he can probably still walk. If it's a leg, and you have two uninjured people, make a litter with the tent fabric or a sleeping bag and two tent poles or two long sticks. If there's only one of you to help, make a travois instead, and keep the leg elevated at the high end of the travois. Keep the injured person warm to avoid shock.
Stay calm, know what to do, and you can survive a fracture in the wilderness.
(Sources: http://www.firstaidweb.com/broken_bone.html , http://life.familyeducation.com/emergency/first-aid/48245.html , http://www.webmd.com/a-to-z-guides/understanding-fractures-basic-information )