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Translating Science into Effective Knee Rehabilitation Strategies

Injuries to the anterior cruciate ligament (ACL) of the knee have become fairly common, especially in athletes. Medical professionals agree that rehabilitation for ACL injuries requires a structured program of exercises. But there is some debate about which kinds of exercises are best. Studies like this one help rehabilitation professionals translate scientific findings about knee movement into effective ACL rehab programs.

The ACL connects the femur bone in your thigh with the tibia bone in your lower leg. The ACL also keeps a check on how far the tibia can slide forward--or translate--under the femur bone. The further forward the tibia translates, the bigger the force on the ACL. Some types of exercise cause the tibia to translate more than others.

The authors measured how far the tibia moved during two forms of exercise. One form is called open kinetic chain exercise, where the arm or leg is free to move in various directions. The example in this study is the standard knee extension exercise. Closed kinetic chain exercise is the term used to describe a newly popularized method for rehabilitating certain injuries. In this form, the limb is fixed to a surface as the joints closer to the body work. The authors chose the squat exercise as the closed chain exercise used in this study to measure tibia movement.

The subjects were divided into two groups of 12 people. The control group had healthy knees. All the members of the other group had an ACL injury. The control group did leg extensions and three different kinds of squat exercises while knee movements and muscle activity were measured in one leg. The injured group did the same exercises but had measurements taken for both legs.

As might be expected, there weren't many differences comparing results of the uninjured knees. But when patients who had ACL injuries did leg extensions, they had notably more forward translation of the tibia.

But doing a squat exercise posed a much smaller risk of strain on the injured ACL. In fact, doing a squat with the body centered over the feet or slightly behind the feet showed only a minor amount of tibia movement. From this, the authors confirm that closed kinetic chain exercises like squats are much safer for rehabilitation from ACL injuries than open kinetic chain exercises like leg extensions.

The authors also found that doing squats activated leg muscles more than a standard leg extension exercise. This was especially true of the quadriceps muscle on the front of the thigh and the gastrocnemius muscle of the calf. When these two muscles work together during the squat exercise, the body is able to keep the tibia from translating forward. Researchers used to credit the hamstring muscles for this action, but this study shows that the gastrocnemius and quadriceps work together to keep the tibia aligned.

The authors' translation of this new information is conclusive: closed kinetic chain exercises, such as the squat exercise, are safe and effective when used during rehabilitation for an injured ACL.

References: Joanna Kvist, RPT, PhD, and Jan Gillquist, MD, PhD. Sagittal Plane Knee Translation and Electromyographic Activity During Closed and Open Kinetic Chain Exercises in Anterior Cruciate Ligament-Deficient Patients and Control Subjects. In The American Journal of Sports Medicine. January/February 2001. Vol. 29. No. 1. Pp. 72-82.

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