Knock Knees

What is knock knee?

A person with knock knees (genu valgum) has a large gap between their feet when they're standing with their knees together.

Many young children have knock knees, which tend to be most obvious at around the age of 4.

It's almost always just a normal part of their development, and their legs will normally straighten by the age of 6 or 7.

Slight knock knees can continue into adulthood, but this also isn't usually anything to worry about unless it causes other problems.

However, knock knees can very occasionally be a sign of an underlying condition that needs treatment, especially if the condition develops in older children or adults, or doesn't improve with age.

Are knock knees normal?

Temporarily knocked knees are part of a standard developmental growth stage for most children. This usually corrects itself as the child grows. Knock knees that persist beyond six years of age, are severe or affect one leg significantly more than the other may be a sign of knock-knee syndrome.

Most children experience normal angular changes in their legs as they grow. Children are typically bowlegged until they begin walking at around 12 to 18 months. By about 2 to 3 years of age, their legs have usually begun to angle inward, making them knock-kneed. During normal growth phases, the child's legs will straighten out by age 7 to 8.

Knock knees that remain outside of these normal developmental growth patterns may be caused by disease, infection or other conditions. If the angle of the legs from hip to foot falls outside normal patterns, worsens over time, or is present on only one side of the body, this suggests a person has a more serious form of knock knees, and further evaluation by an orthopedic specialist may be necessary. Surgery may be needed to treat the condition.

What causes knock knee?

Knock knee can be caused by an underlying congenital or developmental disease or arise after an infection or a traumatic knee injury. Common causes of knock knees include:

  • metabolic disease

  • renal (kidney) failure

  • physical trauma (injury)

  • arthritis, particularly in the knee

  • bone infection (osteomyelitis)

  • rickets (a bone disease caused by lack of vitamin D)

  • congenital (inborn) conditions

  • growth plate injury

  • benign bone tumors

  • fractures that heal with a deformity (malunion)

Being overweight or obese can also put extra pressure on the knees and contribute to knock knee.

What are the symptoms of knock knee?

The most prominent symptom of knock knee is a separation of a person’s ankles when their knees are positioned together. Other symptoms, including pain, are often a result of the gait (manner of walking) adopted by people with knock knees.

These symptoms may include:

  • knee or hip pain

  • foot or ankle pain

  • feet not touching while standing with knees together

  • stiff or sore joints

  • a limp while walking

  • reduced range of motion in hips

  • difficulty walking or running

  • knee instability

  • progressive knee arthritis in adults

  • patients or parents may be unhappy with aesthetics

A person may also have other symptoms from an underlying condition that is causing the knock-knee syndrome. In people of all age groups who have knock knees, one or both knees is abnormally overloaded. This excessive force can lead to pain, further bone deformity, knee instability and progressive degeneration of the knee joint. In particular, adult patients who have been knock-kneed for many years often overload the outside (lateral compartment) of the knee, and stretch the inside (medial collateral ligament – MCL). These forces can cause pain, knee instability and arthritis.

How is knock knee diagnosed?

An orthopedic specialist will review the patient’s medical and family history, any pre-existing conditions and current health. They will also do a physical examination of the legs and gait. Standing-alignment X-ray or EOS images will help confirm the diagnosis. These are radiological images of the leg from hip down to the ankle, which help the doctor locate the exact location and mechanical axis of the deformity.

How is knock knee treated?

  • In most cases, knock knees don't need to be treated because the problem tends to correct itself as a child grows.

  • Your child doesn't need to avoid physical activity, wear supportive leg braces or shoes, or do any special exercises.

  • Mild knock knees that persist into adulthood don't need to be treated unless they're causing problems, such as knee pain.

Treating the underlying cause

If knock knees are caused by an underlying condition, treatment for this may be necessary. For example, rickets can be treated with vitamin D and calcium supplements.


Surgery for knock knees is rarely necessary, although it may be recommended if the condition is severe or persistent.

There are 2 main types of operation that may be carried out:

  • guided growth – where small metal plates are placed on the inside of the knees, which helps correct their growth over a period of around 12 months; the plates will be removed once the treatment is complete

  • an osteotomy – where a thin wedge of bone is removed from the leg bones so they're realigned into the correct position; plates and screws are used to fix the bones in their new position

Children with persistent knock knees who are still rapidly growing are more likely to be offered the guided growth operation. Osteotomies are mainly used for adults with severe knock knees.

Both procedures are carried out under general anaesthetic, which means you or your child will be unconscious while having the operation.

A child can usually start walking again within a few days of having a guided growth procedure and return to sports within a few weeks. It can take a few months to return to all your normal activities after having an osteotomy.