Knock knees

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 Children’s Hospital Boston 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.

The 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.

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.

Do splints, braces or special shoes help correct knock knees (valgus)?

Splints and other devices aren’t usually needed for a child at a natural stage of valgus up to age 7. These devices can be useful if the child’s natural valgus doesn’t straighten out on its own by about the time she’s 7 or 8 years old—or if the valgus has an underlying systemic or metabolic condition causing it.                                                                              

Who’s at risk for developing knock knees?

• Overweight children can be at risk for developing knock knees, because their growing bones and joints have trouble supporting their weight, and as a result they tend to lean inward.
• The condition is slightly more common in girls than boys.

How does a doctor diagnose knock knees?
Knock knees are obvious when a child stands with her legs straight and her toes pointed forward. Your child’s doctor can determine the severity of knock knees by observing the position of her legs, knees and ankles, and by measuring the distance between her inner ankle bones—the greater the distance between the ankles, the more severe the condition.

If your child is within the normal age for knock knees and has no functional problems, Children’s doctors don’t usually take x-rays, in order to avoid unnecessary radiation. But if a child is older than the expected age range—or if her legs aren’t symmetrical—our doctors usually order standing x-rays.

How does Children’s treat knock knees?
Doctors treat most children who have knock knees with close observation during the years when a natural (physiologic) valgus is expected, since the condition usually corrects itself. As a child grows, normal or near-normal walking patterns typically resume by 7 to 8 years old, or occasionally by the time the child becomes a teen.

In a very few cases, the valgus may be severe and may not self-correct. For children with severe, unresolved knock knees, doctors may recommend:

• a night brace, particularly if a family history of knock knees exists; the brace attaches to a shoe and pulls the knee up into a straight position
• orthopedic shoes, which usually have a heel wedge and sometimes an arch pad

In the rare event that natural growth, braces or shoes don’t correct your child’s knock knees, her doctor may recommend surgery.

Are there consequences for severe cases that go untreated?

Severe knock knees may restrict a child's physical activities. She may not be able to run easily, putting some sports or other physical activities out of reach. If her knock knees persist into adolescence, she may become self-conscious about her appearance.

Will my child be OK?

This condition has a very good prognosis. Unless there’s an underlying systemic or metabolic condition associated with your child’s knock knees, her condition should correct itself as she grows, reaching normalcy or near-normalcy by the time she’s 7 or 8 years old.

Does Children’s do research on lower-extremity developmental conditions?

The clinical and basic science researchers in Children’s Orthopedic Centerare recognized throughout the world for their achievements in the field, including groundbreaking studies of the lower extremities. Our breakthroughs mean that we can provide your child with the most innovative care available.

For more on Children’s extensive orthopedic research, see Research & Innovation.

FAQ

Q: What are knock knees?
A: 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 don’t, usually has knock knees. During early childhood, knock knees are a part of normal growth and development. The condition tends to become apparent when a child is 2 to 3 years old, and become more severe until about age 4. It usually self-corrects by the time a child is about 7 or 8 years old.

Q: If my child has knock knees, will she be OK?
A: Knock knees has a very good prognosis. Unless there’s an underlying systemic or metabolic condition associated with a child’s knock knees, her knees typically correct themselves as she grows, becoming normal or near-normal by the time she’s 7 or 8 years old.

Q: What are the signs and symptoms of knock knees?

A: A child whose ankles can’t touch when she stands with her knees touching probably has knock knees. An abnormal walking gait can also be a sign of the condition.

Q: How are knock knees usually diagnosed?
A: Knock knees are obvious when a child stands with her legs straight and her toes pointed forward. Your child’s doctor can determine the severity of your child’s knock knees by observing the position of her legs, knees and ankles, and by measuring the distance between her inner ankle bones—the greater the distance between the ankles, the more severe the condition.

If your child is within the normal age for knock knees, has a normal exam and no functional problems, Children’s doctors don’t usually take x-rays, preferring to avoid unnecessary radiation. But if a child is older than the expected age range, or if her legs aren’t symmetrical, our doctors usually opt for standing x-rays.

Q: How does Children’s treat knock knees?
A:

• close observation for most cases
• rarely, braces and special shoes
• surgery for severe cases that don’t resolve on their own or

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

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.

Q: If my child has only one knocked knee, can she develop it in the other knee, too?
A: 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).

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

Q: What are the causes and risk factors for knock knees?
A: Knock knees are usually part of the normal childhood growth and development of the legs. But some cases, especially in a child 6 or older, may signal an underlying bone disease, such as osteomalacia or rickets.

Obesity can contribute to knock knees—or can cause gait problems that mimic knock knees. While knock knees usually occur symmetrically, a single knocked knee can sometimes result from an injury to the growth area of the shin bone.

Q: What’s the long-term outlook for a child who has knock knees?
A: The long-term outlook for knock knees is very positive. The condition usually corrects itself during a child’s growth years, and the child’s bone alignment is usually normal by the time she’s 7 or 8 years old.
 

Q: What is Children’s experience treating developmental bone problems in children and teens?
A: At Children’s, we’re known for our clinical innovations, breakthrough research and leadership in treatment for bone problems in the lower extremities. Children’s Orthopedic Center offers the most advanced diagnostics and treatments—several of which were pioneered and developed by Children’s researchers and clinicians.

Causes

Knock knees are usually part of normal childhood growth and development. But some cases, especially in a child 6 or older, may signal an underlying bone disease, such as rickets or osteomalacia.

Obesity can contribute to knock knees—or can cause gait (walking) problems that look like knock knees. While the knees usually knock symmetrically, a single knocked knee can sometimes result from an injury to the growth area of the tibia.

Signs and symptoms

A standing child whose knees touch, but whose ankles can’t also touch at the same time, is usually said to have knock knees. An abnormal walking gait can also be a sign of knock knees.

When to seek medical advice

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

• 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.

Complications

Surgery for knock knees is uncommon, because most of the time the condition goes away on its own. But if your child’s case is unusually severe and needs surgery, the vast majority of such procedures at Children’s are successful, and occur without major complications. After surgery, patients are at a very small risk for infection, bleeding or poor bone healing (malunion).

For parents

At 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.

Long-term outlook

The long-term outlook for this condition is very positive. Most cases of knock knees correct themselves during a child’s growth years, becoming normal or near-normal by age 7 or 8.

Knock knees glossary

• anterior: front
   
• arthritis: jointinflammation 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 Center for Families at Children’s: 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.