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.
If someone with knock knees stands with their knees together, their lower legs will be spread out so their feet and ankles are further apart than normal.
A small distance between the ankles is normal, but in people with knock knees this gap can be up to 8cm (just over 3 inches) or more.
Knock knees that don't improve on their own can also place your knees under extra pressure, which may increase your risk of developing arthritis.
Knock knees in children aren't usually a cause for concern and should improve as your child gets older.
However, visit your GP if:
Your GP will examine your or your child's legs, ask about any pain or walking difficulties, and may take some measurements.
Knock knees are fairly common in healthy children under the ages of 6 or 7, and are just a normal part of growth and development.
The legs will usually gradually straighten as the child grows, although mild knock knees can last into adulthood.
Knock knees that develop later in childhood or don't improve with age can sometimes be associated with an underlying problem, such as:
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.
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.
Read more about treating rickets.
Adults with arthritis may benefit from wearing leg braces or special insoles to reduce the strain on their knees.
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:
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.