A broken thighbone (femur) — the strongest bone in your body — usually is obvious because it takes so much force to break. But fractures of your shinbone (tibia) — the major weight-bearing bone in your lower leg — and the bone that runs alongside your tibia below your knee (fibula) may be more subtle.

Signs and symptoms of a broken leg may include:

• Severe pain, which may worsen with movement
• Swelling
• Tenderness
• Bruising
• Obvious deformity or shortening of the affected leg
• Inability to walk

Toddlers or young children who break a leg may simply stop walking, even if they can't explain why. Unexplained crying may be a symptom of a toddler who has a fracture.

There are a number of ways you can break a leg, including:

• Falls. A simple fall can fracture one or both of the lower leg bones. However, the thighbone is unlikely to be broken without more significant trauma.
• Motor vehicle accidents. All three leg bones can break during a motor vehicle accident. Fractures can occur when your knees become jammed against the dashboard during a collision.
• Sports injuries. Hyperextending your leg during contact sports can cause a broken leg. So can a direct blow — such as from a hockey stick or an opponent's body.
• Child abuse. In children, a broken leg may be the result of child abuse, especially when such an injury occurs before the child can walk.
• Overuse. Stress fractures are tiny cracks that develop in the weight-bearing bones of your body, including your shinbone. Stress fractures are usually caused by repetitive force or overuse, such as running long distances. But they can also occur with normal use of a bone that's been weakened by a condition such as osteoporosis.

Stress fractures are often the result of repetitive stress to the leg bones from physical activities, such as:

• Running
• Ballet dancing
• Basketball
• Marching

Contact sports, such as hockey and football, also may pose a risk of direct blows to the leg, which can result in a fracture.

Stress fractures outside of sport situations are more common in people who have:

• Decreased bone density (osteoporosis)
• Diabetes
• Rheumatoid arthritis

Complications of a broken leg may include:

• Knee or ankle pain. A broken bone in your leg may produce pain in your knee or ankle.
• Poor or delayed healing. A severe leg fracture may not heal quickly or completely. This is particularly common in an open fracture of your tibia because of lower blood flow to this bone.
• Bone infection (osteomyelitis). If you have an open fracture, your bone may be exposed to fungi and bacteria that can cause infection.
• Nerve or blood vessel damage. Fracture of the leg can injure adjacent nerves and blood vessels. Seek immediate medical help if you notice any numbness or circulation problems.
• Compartment syndrome. This neuromuscular condition causes pain, swelling and sometimes disability in muscles near the broken bone. This is a rare complication that is more common with high-impact injuries, such as a car or motorcycle accident.
• Arthritis. Fractures that extend into the joint and poor bone alignment can cause osteoarthritis years later. If your leg starts to hurt long after a break, see your doctor for an evaluation.
• Unequal leg length. The long bones of a child grow from the ends of the bones, in softer areas called growth plates. If a fracture goes through a growth plate, that limb might eventually become shorter or longer than the opposite limb.