Knock knees in a child aged 2–6 are usually a normal part of development: they are most marked at around 3–4 years of age and usually lessen on their own by about age 7. A problem that should be assessed by an orthopaedist may be knock knees affecting one side only, getting worse, persisting after age 7, with a gap between the ankles of more than about 8 cm, or with pain and limping.
Below we explain how the alignment of a child’s legs changes, how to tell developmental knock knees from a problem, how to measure them at home, when to see a doctor and how a physiotherapist can help.
In brief
- Up to about age 2 the legs are usually slightly bowed (O-shaped), then they move into knock knees (X-shaped).
- Knock knees are most marked at about age 3–4, and by about age 7 the alignment comes close to that of an adult.
- Signs that you should see an orthopaedist: asymmetry, worsening, pain, limping, a gap between the ankles of more than about 8 cm.
- Podoscope foot test in Rydułtowy: 100 PLN; the child comes with a parent or legal guardian.
- The clinic sees private patients only (not covered by NFZ, the Polish public health fund), Mon–Fri 7:00–20:00.
Contents
How does the alignment of a child’s knees change with age?
The alignment of a child’s legs changes in a predictable way. Babies and toddlers who are starting to walk have legs that curve slightly outwards, in an O shape. At around age 2 the legs straighten, and then they move into knock knees, an X shape, which is most marked at around age 3–4. By about age 7 the alignment usually comes close to that of an adult.
This pattern has been described on the basis of measurements of hundreds of healthy children, which is why in a preschool child knees that touch while the ankles are apart are most often no cause for concern. More important than a single photo is whether the alignment improves over time rather than getting worse.
How do developmental knock knees differ from a problem?
Developmental knock knees are symmetrical, painless, do not limit movement and gradually lessen with age. Signs of a problem include: asymmetry between the legs, knock knees appearing or getting worse after age 7, a large gap between the ankles, pain, limping, tiring quickly, and short stature or other general symptoms.
| Criterion | Developmental knock knees (normal) | Knock knees that need a consultation |
|---|---|---|
| Age | about 2–7 years, peak at 3–4 years | persist or appear after age 7 |
| Symmetry | both legs similar | one leg clearly more affected |
| Course | gradually lessen | get worse from month to month |
| Gap between the ankles | usually up to about 8 cm | more than about 8 cm |
| Pain and walking | no pain, walking is normal | knee pain, limping, frequent tripping |
| Other symptoms | none | short stature, deformities of other bones, a previous injury |
| Who assesses | a physiotherapist or a paediatrician at a routine check-up | a paediatric orthopaedist |
Knock knees often come with flat feet and other postural problems in children, which is why it is worth assessing the whole body.
How can you check your child’s knock knees at home?
Ask your child to stand barefoot on the floor with their legs straight and their knees lightly touching on the inside. Use a ruler to measure the gap between the inner ankle bones. Write down the result with the date and repeat the measurement in the same conditions a few months later. A growing gap or a difference between the legs is a reason for a consultation.
You can also take a photo of your child’s legs from the front, at knee height. Comparing photos and measurements over several months tells you more than a single observation.
When should you see a doctor first?
See a paediatrician or paediatric orthopaedist if the knock knees affect one leg, get worse quickly, persist after age 7 or the gap between the ankles is more than about 8 cm. Knee pain, swelling, limping, a deformity after an injury, noticeably short stature and bowing of other bones also need prompt assessment.
The doctor may order an X-ray of the legs or blood tests, for example to check for calcium and phosphate metabolism disorders and vitamin D deficiency. Knock knees that need orthopaedic treatment are assessed and managed by a doctor, and physiotherapy then complements that treatment.
What can a physiotherapist do for knock knees?
The physiotherapist assesses the alignment of the legs, the position of the feet and pelvis, walking and muscle strength, and checks how pressure is distributed across the feet with a podoscope test for 100 PLN. They choose exercises to strengthen the hip and foot muscles and show the parent how to do them at home. Exercises do not straighten the bones, but they support control of knee alignment during movement.
If the examination raises any doubts, the physiotherapist refers the parent to an orthopaedist. A child of any age comes to the visit with a parent or legal guardian, who is present throughout. The rules are described in our Child Protection Standards.
Child foot and posture assessmentassessment of leg and foot alignment on a podoscope, exercise recommendations for the parent100 PLNPrices valid from 08.2026. The physiotherapist decides on the number of visits individually after the examination.
Good to know: record the gap between the ankles every few months and bring your notes to the visit – the change over time is more valuable to the specialist than a single result.
Summary
Symmetrical knock knees in a child aged 2–6, without pain and with a gap between the ankles of up to about 8 cm, are usually a stage of development. Knock knees that affect one side, get worse or persist after age 7, or come with pain or limping, need to be assessed by a paediatric orthopaedist, and a physiotherapist helps with posture assessment and exercises.
Frequently asked questions
Does W-sitting cause knock knees?
There is no strong evidence that W-sitting on its own causes knock knees. Children with loose (hypermobile) joints often choose this position because it feels stable to them. It is still worth encouraging your child to change position, for example to cross-legged sitting or sitting with the legs straight, so that they do not spend a long time in one position.
Do orthotic insoles correct knock knees?
Insoles do not straighten the leg bones, and with developmental knock knees they are usually not needed. They are sometimes recommended when knock knees come with painful flat feet or other indications assessed by an orthopaedist. The decision about insoles is made by a doctor after an examination, not by a parent based only on how the child’s legs look.
Does being overweight affect knock knees in children?
Yes, excess body weight increases the load on the knee joints and is linked with knock knees persisting in older children. That is why, for a child who is overweight and has knock knees, it is worth looking after daily physical activity and healthy eating habits, ideally together with a paediatrician, and arranging a posture assessment.
Can a child with knock knees do sport?
With developmental knock knees and no pain, a child can and should be active: running, cycling, swimming and playing in the playground. Movement strengthens the muscles that stabilise the knees and feet. If knee pain, swelling or limping appear during sport, stop the activity and consult a doctor or physiotherapist.
Sources
- Salenius P., Vankka E., The development of the tibiofemoral angle in children, Journal of Bone and Joint Surgery Am, 1975;57(2):259–261.
- Heath C.H., Staheli L.T., Normal limits of knee angle in white children – genu varum and genu valgum, Journal of Pediatric Orthopaedics, 1993;13(2):259–262.
- Espandar R., Mortazavi S.M.J., Baghdadi T., Angular deformities of the lower limb in children, Asian Journal of Sports Medicine, 2010;1(1):46–53.
About the author: Tatiana Grabowska, MSc – master’s degree in physiotherapy, licence to practise number PWZFz 11646 (Polish licence to practise as a physiotherapist). Since 2013 she has run the “W zdrowym ciele” physiotherapy and rehabilitation clinic in Rydułtowy; she has about 12 years of professional experience.
- Consultation180 PLN
- Referralnot needed
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