Children develop the posture of their legs throughout their early years, but it is necessary to know when it is within the normal range and when it is necessary to consult an expert. To do this we must define what we call angular pattern, understood as the appearance of the lower extremities of children when we look at them from the front when we observe them standing with their legs together.
Within that posture we refer to knock knees or genu varum when the ankles touch, the knees are separated from each other and the legs are bowed outward. The term valgus knees or genu valgus is referred to when the knees touch, the ankles are separated from each other and the legs have an X arrangement.
There is great personal variability in the angular pattern that changes as the child develops. The following situations occur naturally (image):
– Birth: there is a normal genu varum (up to 15 degrees on average).
– Up to 2 years of age: loss of genu varum until the legs are completely aligned.
– Up to 3-4 years of age: progressive genu valgum (up to 11 degrees on average).
– Up to 7 years of age: realignment with loss of part of the valgus.
The final anatomical situation is a moderate genu valgum of about 7 degrees on average, with a variation of a scale of 10 degrees, so it is normal to find from a mild varus to a moderate valgus.
The examination
Whether or not the bowing of the legs is normal is an assessment that should be made by a pediatric orthopedic specialist through an appropriate examination of the child’s limbs.
First, the distance between the ankles in genu valgum or the knees in genu varum can be measured. In this exploration, knee separation above 6 cm or ankle separation above 8 cm should be considered outside the normal limit. Secondly, the load axis of the leg should be explored. To do this, a tape is placed from the hip to the second toe and a check is made to see if it is within the knee.
In this case, it is outside the normal limit when the load axis is external or internal to the knee. In the examination it must be taken into account that the clinical aspect usually worsens when the child is standing compared to when he/she is stretched on the stretcher, also it is necessary to know that the knee flexion increases the aspect of genu varum and the knee extension increases the aspect of genu valgum. In addition, the specialist should keep in mind that alterations in the rotational pattern modify the angular aspect.
When examining the legs in profile they should be aligned and should be able to make a full extension of the knee. However, it is possible to perform a forward extension of the knee beyond normal. This is called “recurvatum” of the knee and is common in the young child – and especially in the female sex – due to the great elasticity of their tissues and joints. But it is no longer normal for forward movement to exceed 20 degrees. In the same way, it is also not normal not to be able to fully straighten the knee.
When to see a specialist
So far, the developmental process explained above is normal and may lead the child to be more clumsy and fall during this process of change, so we should not worry. It is necessary to be alerted and to go to a specialist when it exists:
1. A separation of the knees greater than 6 cm when the ankles are together.
2. A separation of the ankles greater than 8 cm when the knees are together.
3. If the knee does not achieve full extension.
4. If the knee extends more than 20 degrees forward.
5. When there is marked asymmetry between one leg and the other.