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News about Bracing ACL-Deficient Knees

What effect does knee bracing have on muscle control for patients with a damaged anterior cruciate ligament (ACL)? Bracing is often prescribed for athletes who want to keep playing sports but who have a weak ACL. The players say the brace gives them needed support and improved performance. No one knows how this works.

Researchers at the Mayo Clinic Sports Medicine Center studied the effects of bracing on muscle control. They tested 10 subjects with chronic ACL problems. All of the subjects in this study had been wearing a brace for at least 30 months. Each one hopped on one leg with and without a brace. Muscle activity for the hamstrings (back of thigh), quadriceps (front of thigh), and gastrocnemius (calf) muscles was measured by electromyography.

Research has shown that the normal muscle-firing pattern is hamstrings first, then quadriceps, and finally the gastrocnemius. According to this study, the order of muscle firing is the same for most patients using a knee brace. The timing changes somewhat. There may be a delay before the muscle starts to contract. This delayed response is measured in units of time and is called latency. Onset latency is common among brace wearers.

Without the brace, the order of muscle-firing changes, but not all the time. Each person seems to have his or her own pattern. The authors of this study think there are several reasons for these findings. Electromyography measurements for the same muscle performing the same activity varies widely. There may be other factors to blame such as age, gender, brace fit, and muscle strength. It's possible that the effect of bracing lessens over time. Perhaps bracing works better early on, right after the leg is first injured.

The researchers also suggest it's possible that bracing works for other reasons than preventing a delay in muscle firing. Maybe the brace changes the entire leg's function and that, in turn, helps stabilize the knee. Until it's known how bracing works, doctors will have to continue prescribing them according to their own experience and observations.

References: Jay Smith, MD, et al. Effects of Functional Knee Bracing on Muscle-Firing Patterns about the Chronic Anterior Cruciate Ligament-Deficient Knee. In Archives of Physical Medicine and Rehabilitation. November 2003. Vol. 84. No. 11. Pp. 1680-1686.

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