We use the term knock knees or genu valgum to refer to the posture in which, when the knees touch, the ankles are separated from each other. The legs thus acquire a symmetrical X-shaped appearance, a posture typical of children between 3 and 5 years of age and often accompanied by a flat-footed appearance. But during development the valgus posture will decrease to a discrete valgus situation that will be definitive from 7 years of age. This is what we call the normal angular pattern of the child. If the valgus does not decrease and is accompanied by an outward disposition of the foot we will call it: rotational pattern in “outoeing”.
When do we know if the position is normal or not?
First of all by age, X-legs is a typical situation in children between 3 and 5 years of age. Also look at the angle of the knees. In general, with the knees together, the distance between the ankles should not exceed 8 centimeters.
It is also important if the load axis between hip and ankle is contained within the knee (normal) and not external to it. It should be noted that overweight children often have a false appearance of greater knee impingement.
Another question to assess is whether the disorder is symmetrical, as asymmetrical disorders are not normal and usually have a pathologic cause. Whether the knee knock produces an altered gait, especially during running, is another factor to recognize. And sometimes the child presents pain on the inner side of the knees or on the soles of the feet, although it is important to assess the intensity of the pain. Finally, if the situation persists in the older child or if the appearance is marked, it is advisable to consult a specialist in pediatric orthopedics.
In short, a careful physical examination of the limbs and the child’s walking ability is important. Sometimes, it is even necessary to perform a radiological analysis to confirm normality and rule out pathology.
It is important to rule out the following diseases:
1. Metabolic diseases with ossification disorders. Of note are those of renal origin such as hypophosphatemic rickets.
2. Sequelae of tibia fractures, especially near the knee.
3. Skeletal dysplasias, which are congenital disorders of bone development, and usually occur in children of very short stature with multiple bone involvement.
Treatment
Once other diseases have been ruled out, the specialist should perform periodic clinical observation. It should be remembered that the angular pattern of the lower extremities of children varies during growth and the normal evolution is towards a decrease in knee impingement. Thus, when the valgus knee is asymmetric, it may be effective to place a long knee brace (image). The placement of other types of orthopedic devices in extremities (often indicated for sleeping) have not been shown to be effective in the physiological valgus knee.
Corrective surgery is already indicated when genu valgum exceeds normal values, especially if there is any bone disease such as those mentioned above.