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Can you blame grandma if you have bad knees? While not placing moral culpability on anyone, Cincinnati, Ohio researchers publishing in September's British Journal of Sports Medicine looked at one family's propensities for sports injuries to the knees.

Can you blame grandma if you have bad knees?

The Ohio researchers originally recruited two high school-aged twin sisters who were active participants in soccer and basketball to be part of a computer imaging study of knee motion. They were dressed in reflective gear so a computer could track their motion to create an animation sequence for mathematical analysis of knee motion. They jumped off boxes, they flexed their knees forward and back, and their joints were analyzed for shape, size, and flexibility. The girls' performances were included with those of many other volunteers in an attempt to understand the general performance parameters of the knee in healthy teenaged girls.

Within a year of volunteering to participate in the first study, however, both sisters suffered catastrophic injuries to their knees. One suffered a torn ligament in a volleyball game, and the other suffered a torn ligament in a basketball game. (Another older sister also suffered a severe knee injury the same year.) With the permission of the twins and their parents, the researchers then set out to examine whether the sisters had shared, genetically inherited characteristics that would explain their serious knee injuries. To do this, the researchers compared the twins' data to the averages of the other participants in the first study.

The comparison found in a study of knee motion

  • The injured girls' knee joints were "tighter" than average, with about 12 mm (a little more than a quarter of an inch) less gap space in the knee joint than expected.
  • The injured girls' knees tended to "flop" outward, moving outward when the foot went down.
  • The injured girls had much more flexible hamstrings on their injured legs than on their uninjured legs.
There are some strong indications that a tendency to knee injury is probably inherited. White Europeans are 660% more likely to suffer knee injuries during sports than members of other ethnic groups.

Female adolescents, moreover, are at much greater risk of knee injury than male adolescents. Non-contact knee injuries are more common in teenaged girls than in teenaged boys, and these injuries are usually associated with excessively flexible hamstrings, excessive outward "flop" of the knee when the foot impacts the ground or floor, and a narrow gap at the knee joint.

Examination of these girls is consistent with what is believed to be true about the heritability of knee disorders. But what should concerned parents do to prevent knee injuries in their children?
There are also good indications that girls can be trained to avoid knee injuries. Making sure to land feet flat on the playing surface helps prevent torn ligaments. Learning to avoid "sliding" into a goal saves the knee joint. Neuromuscular training can be helpful to all teens who are active in sports, but especially for girls of white European descent.

When one child suffers a knee injury, it's like that her siblings are also at high risk. Prevent serious injury by training how the knee moves, especially during jumping. It is possible to train the muscles that stabilize the knee in ways that compensate for stress and strain that otherwise would cause injury.

  • Hewett TE, Lynch TR, Myer GD, Ford KR, Gwin RC, Heidt RS Jr. Multiple risk factors related to familial predisposition to anterior cruciate ligament injury: fraternal twin sisters with anterior cruciate ligament ruptures. Br J Sports Med. 2010 Sep,44(12):848-55. Epub 2009 Jan 21.