Prof. Okechukwu Nwankwo is an orthopaedic surgeon at the University of Nigeria Teaching Hospital, Enugu. He talks about knock knees, otherwise known as K-leg or bow legs, with DOLAPO AKITOYE
How would you define knock knees?
Knock knees is a layman’s language for what is called genu valgum in orthopaedics which is an angular deformity in which the leg bends outwards from the midline at the knee making the knees knock to each other especially when the person is walking particularly when both limbs are involved. This is the origin of the name, knock knees.
What causes knock knees?
There are two major types. There is the physiological one and the pathological one. The physiological one is a kind of normal growth pattern in children. If you watch children, you find out that when they start walking, they tend to develop bow legs up to about the age of two years. Then from two years to about five to seven years, they develop knock knees or genu valgum. This is physiological and then, at about five to seven years, the knock knee starts to correct as the child is growing. It is a physiological phenomenon and not pathological and it doesn’t need any treatment. One thing that one must note is that this type is usually bilateral – which means that it occurs in both limbs. If it is not bilateral, then, it is not the physiological type.
Then, the pathological type has many causes, ranging from bone disorders like bone dysplasia, bone weakening from rickets, injury to the growing part of the bone at the knee level – either at the lower end of the femur or the upper end of the tibia. There is a growing end for each bone and if an injury happens there, such that it damages the lateral side, then only the medial side will be growing and that results in the angular deformity – knock knees. These pathological ones may be either bilateral or unilateral. In adults, arthritis of the knee may result in that deformity.
Most times, especially in adolescence, there is no cause and this type is known as idiopathic knock knees because the cause is unknown. This idiopathic type is the commonest cause of the deformity among adolescents.
Females have wider pelvis than men and nature tends to balance this by a mild degree of knock knees or genu valgum. So, mild knock knees are common in women. There are other causes but these are the common ones.
Can obesity cause it in adults?
Obesity per se will not cause knock knee but when there are other predisposing conditions like bone weakening, as in dysplasias and rickets, it can worsen it.
How can it be diagnosed?
Well, it is obvious to the eye because it is an angular deformity but we still measure the angle between the femur and the tibia which is known as the tibiofemoral angle to assess the degree of the deformity. The degree should not be more than five to seven degrees. If it is more than that, then, that is one way of knowing that the deformity is significant. Another method is by calculating the intermalleolar distance.
It is the distance between the medial malleoli of both feet when the person is standing with both limbs touching. This distance should be zero in a normal person.
What are the symptoms of knock knees?
The obvious one is the knock knee deformity itself. They may have knee pain – anterior and medial knee pain – because of the stress of that angle. They have circumduction gait i.e. they sweep their leg and foot while walking to avoid their knees knocking together. Sometimes, they might even start falling depending on the degree of the deformity. This is due to instability due to loss of balance of the limb because of severe angulation and weakness of the ligaments supporting the knee. Also, they tend to have flat-foot because of flattening of the inner arch of the foot due to the way they stand.
How can it be treated?
Well, the physiological type does not need treatment. However, for the pathological type, the cause of the knock knees needs to be treated. For example, if the child has rickets, you treat rickets first. If you are able to see the child early when the deformity is not so much, a brace can be used to support the limb while the medicine is being administered for rickets. The most important thing is to treat the cause and after treating the cause, if for instance, the deformity persists and it is significant, it needs an operation to correct the deformity.
This operation also depends on the age of the patient as well. In a growing child, you can still fix medial side of the growing end of the bone which makes it stop growing and as the lateral side keeps growing, the deformity will be corrected. In all age groups, the deformity can be corrected by wedge osteotomy which is cutting through the bone and using some degree of wedging of the cut ends of the bone to realign the limb correctly.
Can certain habits of mothers while pregnant cause it?
No. It is not possible. However, some hereditary conditions can cause it. For example, sometimes bone dysplasia can be hereditary; so sometimes, it runs in the family.
What are the common misconceptions about knock knees?
I’m not aware of any. The only one that I know is that some people say that those that have bow legs are good footballers. But it is untrue.
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