Click here to view next page of this article

 

Bow legs and Knock-knees

Bow legs and Knock-knees. All babies are born bow legged, and then the bowing gradually decreases and between the ages of 2 and 3, kids get knock-kneed and they remain knock-kneed until about the age of seven bowlegs, knock knees, bow leg, bowlegged. Most adults are very slightly knock-kneed and have about 7 degrees of valgus. This is an adaptation of a graph from a very famous paper in which this was delineated by two fins and what their showing is that children are born with about 17 degrees of varus, dip down in that two to three age range to a maximum of 10 to 13 degrees, and then slowly come up.

This is a slide, I am not really sure where I got it, reportedly showing the same child with their physiologic bowing and then straightening out when they get a little older. So genu varum or bow legging is usually physiologic, it is usually part of that progression, but it could be other things, for instance, rickets, Blountís disease, achondroplasia, and the same thing with genu valgum. Itís usually physiologic but it can be other things, rickets can also cause knock-knee as well as bow legging and renal disease.

Again, the idea is try to figure out what the child has then they come to you, and the differential for these things are physiologic, bowing or knock-knee, rickets, skeletal dysplasias, Blountís disease, you always have to think tumor or infection, particularly if itís unilateral or painful, so the things you want to know are pain and symmetry, tumors, infections are often going to be unilateral.

Blountís disease, achondroplasia, rickets, those things should always be pretty symmetrical usually. You want to know the childís growth percentile, kids with Blountís tend to be kind of big, kids with rickets tend t be little, those things will give you an idea. Also, the age at ambulation. Kids with Blountís tend to be early walkers, kids with rickets, achondroplasia, things like that tend to be late walkers. These things will point you in the right direction. In order to keep following them, you want to plot their height and weight, find out where they are in the growth curve, and then to get a sense over time of what the legs are doing, if they have bow legging, you want to lie them down, put their ankles together and measure the distance between their knees, and if you do that at subsequent visits you can get an idea if this is correcting or getting worse. It doesnít matter exactly where between the knees you do it.

For knock knee you are doing the appositive, the knees are going to be together and you are going to be measuring between the ankles. You also want to look at their tibial torsion because tibial torsion will make bow legging look worse than it actually is, so you also want to get a sense of how much tibial torsion they have, if they have a lot, you probably donít have as much bow legging as you think they have. Once you get an x-ray, if the problem is unilateral, if itís painful, or if the child isnít doing what their supposed to be doing in term of their age, so if you have child who is six and very bow legged, you want to get x-rays of that. If you have a child who is one and is very knock-kneed, you probably want to get an x-ray of that too. If their not falling where they ought to be age wise.

This is a child with rickets, they have they set of typical appearance of the widening and sort of cupping and fuzziness of the growth plate here, and you will see this at all the growth plates, not just the knees. This is a child with Blountís disease, and Blountís disease, no one really knows that causes it, itís a condition in which the medial part of the proximal tibial growth plate becomes ill and ceases to function. This lateral portion is still normal and still working, so itís growing here, youíre not growing as fast here, and youíre going to go into varus because of that. Itís more common in African Americans than in other groups, itís most common in girls than in boys, more common in early walkers and kids that are a little heavy, so that gives you an idea.

The classification of Blountís disease is based on two things, how diseased the growth plate is, but also the age of the child. There is increasing degree of this with increasing age, and it really starts because bow legging is normal up until the age of 24 months. We donít start considering anything Blountís until the kids are about 24 months, and I will rarely x-ray a child under 24 months for bow legging. The treatment of Blountís disease is somewhat controversial, bracing probably is not terribly effective and most people go directly to surgery, usually sometime around the age of three to four, so we have a little time to play with this. If I see a child who is two, I usually will follow them for about a year and see whatís happening, make sure their not getting better on their own and then go on to surgery. What we do in the surgery, is we take out a little triangular wedge of bone and that

Club foot as I mentioned before, it has components, metatarsus adductus which you know about, equina which is plantar flexion, you canít dorsiflex their ankle and varus which is supination or inversion, turning in of the foot. This is pretty common, one in a thousand live births, 20% of these children will have development dysplasia of the hip. This is a real association, so you have to be very careful and really examine children with clubfeet very carefully for DDH. If this is unilateral, bilateral half the time, but if itís unilateral the affected foot and calf will always be smaller. Thatís because this is probably not a packaging defect, this is probably either a germ plasm defect, neurovascular insult or intrauterine compartment syndrome. No one is really sure exactly what, but itís not a packaging thing, and these feet and muscles never quite catch up to the other side. It does run in families but it doesnít have an inheritance pattern. Treatment wise, about 25% of these can be corrected with stretch casting alone where you cast the feet every two weeks for several months and gradually correct the deformities out. Itís not an easy thing to do, thereís an art to it and practitioners are different in how much success they have with that, but overall, 75% of these children come to surgery, the surgery is complicated and you basically have to release everything thatís not in the right position or tight, and gradually get the foot into a flat corrected position. After treatment, these children have very good function in their feet.

Cavus foot is a high arched foot, generally speaking, they can usually be managed with bracing, some need surgery, but the important thing here is that particularly unilateral cavus foot or a cavus foot that seems to be progressive is often a marker for a neurologic disorder such as Freidrichís ataxia or a spinal cord tumor or something like that. So you have to do a careful neurologic exam and send the child on to a neurologist if you have any suspicions about this. Calcaneal valgus foot, mentioned it briefly, itís usually a packaging defect that resolves, there is a differential here, it can be congenital vertical talus, or rockerbottom foot where the talus is kind of standing on ití head here.