The Hyperextended Knee

Overly flexible knees can cause injury, but yoga can help stabilize loose tendons and ligaments by strengthening the muscles around the joint.

By Julie Gudmestad

Many yoga students are quite surprised to learn that joints can become too flexible. But in many joints, ligaments and tendons play a major role in preventing excessive motion; if those tissues become too loose, the joint can move in ways that cause damage or set the stage for injury. A joint with such laxity is said to be hypermobile, and the knee is particularly vulnerable to this problem. In fact, this joint is more or less just one long bone (the femur, or thighbone) stacked on top of another long bone (the tibia, or shinbone). Ligaments and tendons are all that holds these bones together.

Most people are all too aware of how easily and dramatically the knee's connective tissues can be injured by twisting. But fewer people are aware that knee hyperextension--too much opening at the back of the knee--also creates misalignment and bad movement habits that can pave the way for arthritis and more serious knee injuries.

Do You Hyperextend?

Wearing minimal or tight-fitting clothes so you can clearly discern the alignment of your legs, stand sideways in front of a full-length mirror, far enough away that you can see your whole body. In normal standing alignment, the leg forms a straight line from ankle to hip, with knee over ankle and hip over knee. If your knee is hyperextended, however, the leg will appear to curve back, with the knee behind an imaginary straight line drawn from ankle to hip.

Since hyperextended knees are basically a problem of too-loose ligaments and tendons around the knee, you can cause or exacerbate such looseness through poor alignment in yoga poses. The soft tissues at risk of being overstretched include the cruciate ligaments deep inside the knee, the medial and lateral collateral ligaments on the inner and outer surfaces of the knee, and the popliteal ligaments, which cross the back of the knee. There are also several large tendons that cross the back of the knee and normally help prevent hyperextension: the hamstring tendons coming down from the back of the thigh and the gastrocnemius tendons coming up from the calf.

If you look at the hyperextended knee pictured at left, you can see that these tendons are overstretched. The overstretched knee ligaments and tendons are also usually accompanied by changes in adjacent muscle groups, including the soleus muscle, which is deep in the calf. The soleus originates on the upper tibia and fibula, then runs down the calf to attach to the heel. If it is short and tight, it will pull the upper ends of the tibia and fibula backward, contributing to hyperextension. So if you have hyperextended knees, it's important to regularly practice bent-knee calf stretches, like Malasana (Garland Pose) and simple squats.

Though yoga probably will not shorten overstretched knee ligaments, it can help stabilize your knees by strengthening the surrounding muscles.

Protecting Your Knees

Of course, you want to practice your poses in a way that won't increase hyperextension and knee instability. If you tend to hyperextend, typical calf and hamstring stretches done with a straight knee can aggravate the problem unless you take care to engage your quadriceps (front thigh muscles). People with hyperextended knees usually have weak quadriceps, or do not tend to engage them fully in straight-legged poses like Tadasana (Mountain Pose) and Trikonasana (Triangle Pose). Instead of engaging the quads to stabilize and protect the knees, people who hyperextend usually just push their knee joints back. To overcome this habit, they need to strengthen the quads in bent-knee postures such as Virabhadrasana I and II (Warrior Poses I and II) and Parsvakonasana (Side Angle Pose) and train the quads to be active and strong in straight-knee poses.

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