What Causes a Limp?

2/14/2008

Any problem in a joint, tendon, or muscle of the leg or hip can lead to limping. The cause can be anything from being hit by a baseball to a bacterial infection of the joints to juvenile arthritis. Most limps are transitory, but a limp that persists for more than a few days or causes severe pain calls for a visit to the pediatrician for an evaluation.

I generally start with a good history and exam and a throat culture. If the culture is negative for strep, I do a CBC (complete blood test), checking also for inflammatory markers like ESR (“sed rate”) and C-reactive protein (CRP), as well as antibodies to past streptococcal infections. For a more definitive diagnosis, I may request a parvovirus blood test too. Swelling or a history of trauma would lead me to order an x-ray or refer to an orthopedist.

In toddlers (ages 1-3) the main causes of a limp are (in order of frequency):

1. Trauma. It’s very common for kids this age, who are bouncing everywhere, to twist a hip or knee. If there’s no swelling or bruising of a distinct area, just keep an eye on them. If the limp persists, an x-ray or a visit to a pediatric orthopedist might be in order.

2. Infection. The most serious cause of limp in a toddler is bacterial infection of the fluid around a joint (septic arthritis) or of the bone itself (osteomyelitis). These infections can occur in any bone or joint in the body, but most commonly at the hip and the knee.

Children with a bone or joint infection look sicker, have an intermittent fever, and have very limited, painful movement of the joint involved. They need to see a doctor immediately for referral to an orthopedist and possible hospitalization for intravenous antibiotics. A blood test will usually reveal an elevated white blood cell count and high levels of inflammatory markers.

3. Congenital hip dislocation. Hip dislocations in newborns can be difficult to diagnose. They may not even be discovered until the child begins walking, and a painless limp is noticed. A pediatric orthopedist can assess the need for treatment.

4. Neurological disorder. Occasionally limps are caused by uncommon conditions such as a stroke that occurs before birth, cerebral palsy, or muscular dystrophy. If a limp persists, an MRI of the head or a visit to a pediatric neurologist may be needed.

5. Tumor. A persistent unexplained limp can be a sign of a tumor in the lower extremities, but this is very rare.

If a child over four is suddenly limping around like Dickens’ Tiny Tim, the diagnosis may be different:

1. Synovitis. The most common cause of limp in this age group is  transient or toxic synovitis, a very benign inflammation of the hip joint caused by a viral illness. The virus involved is frequently parvovirus B19, the same one responsible for Fifth Disease. These children don’t look sick, and are generally happy, except for the limp. Unless the problem persists for more than a few days with no sign of improvement, no blood work is needed. However, I usually do a throat culture, because strep throat can also cause a limp and leg or hip pain.

2. Trauma. Bumps, bangs, and wrenches are the second most common cause of limping in school-age children.

3. Infection. Consider bacterial hip or knee infections or osteomyelitis when a child looks very sick, when there is dramatic restriction of the joints involved, or when an unexplained fever persists for more than five days.

4. Rheumatologic disorders. There are two major candidates in this category, and a blood test can help nail down a diagnosis. Reactive arthritis from a past streptococcal infection can cause pain and limping, but responds very well to antibiotic therapy. Juvenile rheumatoid arthritis (JRA) might present as a limp that does not go away,but it will also be accompanied by joint swelling and redness, as well as by symptoms such as long-lasting rashes and unexplained fevers. If suspected, a referral to a pediatric rheumatologist is indicated.

5. Tumor. Tumors or benign cysts of the bones in the leg aren’t common but should be a consideration in any limp that hasn’t resolved within two weeks. The pediatric orthopedist will probably order an x-ray to screen for such problems.