We have several kids who have varying degrees of knee hyper-extension when they stand. Knee hyper-extension is when their knee bends backwards past zero degrees of extension. This can happen for many reasons and many children and young adults do this without having any predisposing factors. In fact it can be common in gymnasts and adolescent girls. For kids with neuromuscular disorders such as cerebral palsy, knee hyper-extension in standing can be common in one or both legs. One of the ways to correct for this is to use a brace called an AFO (ankle foot orthosis). If it is set so that the child can’t point their toe, it can prevent them from going into knee hyper-extension. Many families go back and forth on the debate of whether their child should wear AFO’s or be allowed to wear a less restrictive brace. I myself go back and forth as well and try to help the families see the pros and cons of both choices. As I have been observing some of our kids recently I have noticed some of the side effects of increased knee hyper-extension.
First, there is always the potential damage that is being done to the child’s joints and ligaments due to the repetitive stress of going into hyper-extension with every step.
Second, when a child’s knees are hyper-extending they need to make other postural compensations to keep their body balanced over their base of support. To do this the tend to arch their low back more (increase their lumbar lordosis) causing their hips to flex more. This over time (not even a very long time) can cause their hip flexors to get tight. Specifically their ilopsoas which causes hips to flex and low backs to extend (arch).
Third, with the flexed hips and increase arch in the low back it causes their stomach and behinds to stick out further making it a challenge for them to activate their gluteal (butt) muscles or their abdominal (stomach) muscles. These are two important sets of muscles for maintaining balance and posture.
In addition to this there are down sides to wearing the AFO’s. If the child has decreased strength, they have trouble lifting their foot up when they are walking so they tend to turn their feet in (internally rotate their hips) more.
Also, with decreased strength they may not be able to overcome the tension on the AFO to achieve more ankle bending (dorsiflexion) so they can lose more strength in their calves.
I think the whole process is a balance that needs to take into consideration the goals of the family and child as well as the pros and cons. I’m sure there are plenty that I have not mentioned but I wanted to start to point out some postural challenges created by knee hyper-extension. As always, I think working towards a balance with the family and child can be effective.