Knock Knees Symptoms & Causes

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Right now, you probably have lots of questions: How serious are knock knees? Does my child need treatment? What do we do next? We’ve provided some answers to your questions on this site, and our experts at Boston Children’s Hospital can explain your child’s condition fully when you meet with us.

What are knock knees, and when do they become obvious?

Knock knees are angular deformities at the knee, in which the head of the deformity points inward. A standing child whose knees touch, but whose ankles do not, is usually said to have knock knees. During early childhood, knock knees are a part of normal growth and development.

Knock Knees at Boston Children's HospitalThe condition usually becomes apparent when a child is 2 to 3 years old, and it may increase in severity until about age 4. It usually self-corrects by the time a child is about 7 or 8 years old. But if the condition doesn’t appear until a child is 6 or older, it could be a sign that she has an underlying bone disease.

During early childhood, knock-knees actually help a child to maintain balance, particularly when she begins to walk, or if her foot rolls inward or turns outward. When a child has knock knees, both knees usually lean inward symmetrically. One knee, however, may "knock" less than the other, or may even remain straight.

Knock knees usually correct themselves by the time a child is 7 or 8 years old. Occasionally, they persist into adolescence. The condition is slightly more common in girls, although boys can develop it, too.

What causes knock knees?

•   Knock knees are usually part of the normal growth and development of the lower extremities.
•   Some cases, especially in a child who’s 6 or older, may be a sign of an underlying bone disease, such as
    osteomalacia or rickets.
•   Obesity can contribute to knock knees—or can cause gait (walking) problems that resemble, but aren’t actually,
    knock knees.
•   The condition can occasionally result from an injury to the growth area of the shin bone (tibia), which may result
    in just one knocked knee.

What are the signs and symptoms of knock knees?

A standing child of average weight whose knees touch, but whose ankles do not, is usually considered to have knock knees. An abnormal walking gait can also be a sign of the condition.

How common are knock knees?

In the course of developing normal alignment of their lower extremities, all young children have knock knees to some degree for a period of time. At the age of 3, more than 20 percent of children have at least a 5-centimeter gap between their ankles. By the age of 7, only 1 percent of children have this gap.

Is my child in pain?

Usually, only severe cases of knock knees cause a child pain. If there’s pain in a severe case, it’s usually in the front (anterior) of the knee.

How serious are knock knees?

For the vast majority of children with knock knees (experts estimate as high as 99 percent), the condition self-corrects and normalizes by the time a child is 7 or 8. Very few cases are severe enough to need surgery.

FAQ for Parents

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If my child has knock knees, what should I ask my Children’s doctor?

Some of the questions you may want to ask include:

   •   Could you describe what’s wrong with my child’s knee(s)?
   •   Are other tests needed to confirm this diagnosis?
   •   Is there, or could there be, damage to her tissues or blood vessels?
   •   Does my child need treatment? Does she need surgery?
   •   Will knock knees affect her growth plate or the normal growth of her leg?
   •   Could there be long-term effects? Pain? Arthritis?
   •   Could this condition affect my child’s ability to walk, run or play sports?
   •   How long should my child be followed by her care team?

If my child has only one knocked knee, can she develop it in the other knee, too?

Knock knees usually develop symmetrically in both knees. But the condition can develop on just one side, particularly if there’s been an injury to the growth area of one shin bone (tibia).

If my child has knock knees, is she at risk for arthritis or other conditions later in life?

For most children with natural (physiologic) knock knees, there’s no added risk of developing arthritis as a result of the condition. For children with surgically repaired knock knees caused by an underlying condition (pathologic), adulthood can bring can risks for arthritis, meniscal tears, pain or dislocation.

When to seek medical advice for knock knees

Contact your child’s doctor if:

•   she walks with an abnormal gait
•   her ankles can’t touch when her knees do
•   she runs with her legs swinging out 
•   her knees knock together when she’s walking
•   she’s having trouble with walking or running in sports or everyday activities

Questions to ask your doctor

If your child is diagnosed with knock knees, you may feel a bit worried. It can be easy to lose track of the questions that occur to you. Lots of parents find it helpful to jot down questions as they arise—that way, when you talk to your child’s doctors, you can be sure that all your concerns get addressed.

Some of the questions you may want to ask include:

•   Could you describe what’s wrong with my child’s knee(s)?
•   Are other tests needed to confirm this diagnosis?
•   Is there, or could there be, damage to her tissues or blood vessels?
•   Does my child need treatment? Does she need surgery?
•   Will knock knees affect her growth plate or the normal growth of her leg?
•   Could there be long-term effects? Pain? Arthritis?
•   Could this condition affect my child’s ability to walk, run or play sports?
•   How long should my child be followed by her care team?

Who’s at risk for knock knees?

•   Most cases of knock knees occur sporadically (by chance), with no clear reason.
•   Knock knees do tend to run in families, suggesting a genetic connection.
•   Knock knees are slightly more common in girls than boys.
•   Obesity can contribute to a child developing knock knees.

For parents

At Boston Children’s, we make it a point to emphasize to parents that most children with knock knees have normal development. There’s a virtually 99 percent chance that your child’s knees will straighten out on their own by the time she’s 7 or 8 years old. Your child’s doctors are thoroughly experienced in diagnosing, observing and treating this condition, regardless of how severe your child’s case may be. So you can have confidence that your child is receiving the best care that our Orthopedic Center has to offer.

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Knock knees glossary

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   •  anterior: front

   •   arthritis: joint inflammation and damage, resulting in pain, swelling, stiffness and limited movement. Arthritis
       can occur when a joint’s cushioning cartilage wears away. Knock knees that have straightened on their own
       naturally don’t usually lead to arthritis; but children with surgically repaired knock knees caused by an underlying
       condition can be at risk for arthritis

   •   The Hale Family Center for Families: dedicated to helping families find the information, services and
       resources they need to understand their child’s medical condition and take part in their care

   •   guided-growth procedure: a surgical procedure for severe cases of knock knees, in which the surgeon
       manipulates areas of the growth plates to bring about straightening

   •   diagnosis, diagnostics: identifying disease or injury through examination, testing and observation

   •   femoral or tibial osteotomy:a surgical procedure for severe cases of knock knees, in which the surgeon cuts
       and straightens the femur or tibia, then reattaches the bone.

   •   femur: the thigh bone, the longest and strongest of your child’s bones; one of the bones that forms the knee
       joint

   •   gait: manner of walking

   •   knock knees: angular deformities at the knee, in which the head of the deformity points inward

   •   lower extremities: parts of the body from the hip to the foot, including hip, thigh, ankle, leg and foot

   •   onset (of signs or symptoms): the first appearance of signs or symptoms

   •   orthopedic surgeon, orthopedist: a doctor who specializes in surgical and non-surgical treatment of the
       skeletal system, spine and associated muscles, joints and ligaments

   •   orthopedics: the medical specialty concerned with diagnosing, treating, rehabilitating and preventing disorders
       and injuries to the spine, skeletal system and associated muscles, joints and ligaments

   •   pathologic valgus: knock knees caused by some underlying systemic or metabolic condition, such as rickets
       or osteomyelitis

   •   physiologic valgus: a temporary condition of knock knees; a stage in the normal development of a child’s
       leg alignment

   •   prognosis: outlook for the future

   •   sporadic: by chance

   •   tibia: with the femur, one of the large, weight-bearing bones in the lower leg (below the knee)

   •   valgus: an alignment deformity in which the angle formed by the bones on both sides of a joint points toward
       the body; in knock knees, the tibiofemoral angle

   •   x-rays: a diagnostic test that uses invisible electromagnetic energy beams to produce images of internal tissues,
       bones, and organs onto film

See our extensive Glossary of Orthopedic Terms.

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