Knock knee is fairly common in healthy children under six or seven years of age. It occurs because a child’s weight falls to the outside of their knee joint, which is a normal part of their growth and development.
In most cases, knock knee corrects itself without the need for treatment. A child's body undergoes many changes as they grow, including their legs, which gradually change shape and become straighter.
If knock knee does not correct itself and the distance between your child’s ankles is greater than 10cm (about 4 inches) or if their knees are not symmetrical (even), they may have an underlying health condition or growth problem.
In most cases the cause is unknown, although childhood conditions that can be responsible for knock knee include:
- rickets - a rare condition that affects a child's bone development and is usually caused by a vitamin D deficiency (sunlight is a source of vitamin D and it is also found in oily fish, eggs and fortified spreads and breakfast cereals)
- nutritional conditions - such as scurvy (a vitamin C deficiency) which can adversely affect the development of bones and joints - however, this is rare
- rare genetic conditions - such as Cohen syndrome, which causes a number of problems including moderate to severe learning difficulties, progressive visual problems and over bendy joints
A family history of skeletal abnormality can also be an underlying cause of knock knee in children.
Adults
In adults, knock knee can occur following an injury, such as an uncorrected fracture of the shin bone (tibia) or as a result of joint conditions, such as osteoarthritis and rheumatoid arthritis.
Arthritis in the knee joint can sometimes cause knock knee to develop. Having knock knees can also place the knee joint under extra pressure which can lead to arthritis in later life.
