Back

The Knee Muscle That Wouldn't

All it takes is a good whack to your knee, and the surrounding muscles may decide to stop doing their job. Your injury is called a patellar contusion--a blow to the kneecap. You will have pain and most likely weakness in the quadriceps (the big muscle on the front of your thigh). What is the best way to get your quadriceps strong again?

That depends on whether the weakness is caused by quadriceps atrophy or inhibition. Atrophy means that the muscle is weak and shrunken. In this case, atrophy could happen because the pain in the knee causes you to use that leg less. Inhibition means that the muscle just can't engage when you try to move it. The pain and swelling are believed to throw the nervous system off, keeping the muscle from working.

The difference between atrophy and inhibition is important, because the two conditions need to be treated differently. Atrophy is treated by strengthening the muscles. Inhibition requires that the muscle be "re-educated" using specialized therapy, such as electrical stimulation.

If clinicians could easily tell the difference between inhibition and atrophy, they could design better rehabilitation programs. These authors set out to identify inhibition in people with patellar contusions. Sixteen patients who had been injured less than four months earlier were tested. Patients answered questions about their activities and knee function. Researchers then used a special kind of electrical test as the patients contracted their quadriceps. The test was also run on each patient's uninjured leg as a comparison. Inhibition was documented if the muscle could give a bigger effort when the electricity kicked in.

The authors expected to find that most of the patients had quadriceps inhibition. All the patients had weaker quadriceps muscles on their injured legs. But the results showed that less than one-third (a total of 5) of the patients showed signs of actual inhibition. And the questionnaires about pain and activity didn't give any clues as to which patients had quadriceps inhibition, either. (People with inhibition would be expected to have lower scores on these types of questionnaires.)

So the search is still on for a good way to diagnose inhibition after patellar contusion. As it is, it's not an easy task to tell the difference without high-tech testing equipment. Knowing the difference could help patients get the best treatment right away-- turning the knee muscle that wouldn't into the knee muscle that could.

References: Tara J. Manal, MPT, OCS, and Lynn Snyder-Mackler, ScD, PT. Failure of Voluntary Activation of the Quadriceps Femoris Muscle After Patellar Contusion. In Journal of Orthopaedic & Sports Physical Therapy. November 2000. Vol. 30. No. 11. Pp. 654-663.

Back