Bow Legs and Knock Knees in Children – Information for Referrers


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What are Bow Legs and Knock Knees?

Bow-legs (genu varum) and knock-knees (genu valgum) are common reasons for referrals to paediatric orthopaedic clinics and are what we term “normal variants”. Bow-legs mean that there is a gap between the knees when the ankles are pressed together. Knock-knees are present when there is a gap between the malleoli when the knees are pressed together.

Bow Legs and Knock Knees

Are Bow-Legs or Knock-Knees Abnormal?

Usually no. There is a very famous study from Scandinavia in 1975 which demonstrated the changing alignment of children’s leg as they age. This is often remembered and shown in the Salenius Curve.

Salenius Curve

The Salenius curve shows that all children are born with bow legs and that these are usually present until about the age of 2. After this they become knock kneed. The degree of knock-knee is most obvious between ages of 3-4. The legs then gradually straighten reaching an adult shape by the age of 10-12. This is often a very small degree of valgus. Heavy children and children with loose ligaments stretch their knee joints and will appear to have greater deformity. Many babies have big calf muscles, which can make the leg seem quite bent even the bones are only slightly curved.

Symmetrical bow-legs before the age of two, and symmetrical knock-knees seen between the ages of 2 and 12 are termed “physiological” because these appearance are part of the normal growth and development.  It should be remembered that we are all slightly different in appearance and this goes for leg shape too.

Reasons for Referral

  • Asymmetry
  • Pain
  • Progressive deformity out with that expected
  • Concern regarding metabolic bone disease
  • Bow legs > age 3
  • Knock-knees worsening > age 10

Is Treatment Necessary?

For physiological symmetrical bow-legs and knock-knees, no. It is helpful to explain the normal to the parents and it can be helpful to ask them to take photos 3 or 4 months apart which usually demonstrates to them that things are moving the way we would expect There is no place for physiotherapy, special shoes or braces as this is the normal development of lower limb alignment. Occasionally if there is an underlying cause this may require treatment. This is indicated with the presence of asymmetric, pain, progressive deformity out with the normal curve.

Last reviewed: 29 November 2021

Next review: 29 November 2024

Author(s): Kim Ferguson

Version: V1

Approved By: Orthopaedic Clinical Director

Reviewer Name(s): Kim Ferguson

Document Id: June 2022