Knee sprains aren't common in mountain biking. But it can occur when you "part company" with your bike and try to "run it out." If the foot catches on the ground while the leg is rotated outward (so the toes are pointing away from the other leg), it can put stress on the inner side of the knee, resulting in a sprain.
A sprain is a stretching injury to ligaments (the bands of tough tissue that control which direction joints can bend). The usual knee sprain is on the inner side of the knee, involving a ligament called the medial collateral ligament (MCL). With a minor knee sprain (one you could treat at home), there should be NO swelling, no discoloration, and you should be able to walk on the leg normally.
Internal structures can be injured when the knee is twisted. If there's an internal injury, the knee will puff up with fluid. If the knee looks normal, functions normally, and only hurts directly over a small area on the inner side of the knee, chances are it's just a sprain. But the signs of an internal injury can develop a day or two later, particularly with small cartilage tears.
This biker trapped her leg in the frame of the bike while falling across the bike (falling to the left while the right foot was caught). Note the smoothness of the skin around the kneecap. The normal contour has "rounded out" because of fluid in the knee, indicating an internal injury.
|See the doctor if:
there's any swelling or deformity
there's pain when the knee is resting (after the first hour)
you can't move the joint fully
you can't put your full weight on the leg
there's pain with small motions of the knee
there's numbness or weakness below the injured area.
From the side, notice the bulge above the kneecap and the outward curve in the area of the patellar tendon (the tendon below the knee). A simple knee sprain should have NO outward sign of injury.
The treatment of a sprain is "RICE:" Rest, Ice, Compress, and Elevate. Immediately elevate the injured part and apply an ice bag. Once the area is thoroughly cooled, apply an elastic wrap to compress the injury.
For the first 48 hours, repeat ice and elevation 1/4 of the time (for example, 30 minutes of ice every two hours). As the pain subsides, return to activities. The rule is: "If it hurts, don't do it." You can usually stop using the elastic wrap after 2 to 3 days. If the knee remains weak or painful in routine use, go to the doctor.
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Isometric strengthening: Sit in a chair. Hold the injured leg up so the foot is at hip level. Bend the knee a tiny bit. Now pretend your big toe is a piece of chalk, and draw the entire alphabet (in the air) with your foot. Repeat four times daily.
Active quads strengthening: Once you're walking pain-free, begin active strengthening. You can use the quads machine at your favorite gym. Start light (around 20 pounds), then progress up to 1/4 of your body weight. Do 10 lifts at each weight setting. High-performance athletes should try to reach 1/3 of their body weight. If you don't have access to a weight machine, you can do "short arc dips" at home. Stand on the injured leg, while touching a wall for balance. Slowly dip down about 6 inches, so the knee bends to an angle of around 135-150 degrees (30 to 45 degrees off of straight), then rise up as quickly as you can. Repeat 20 times.
If the injured area doesn't improve promptly, see the doctor.
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