It doesn't take very many miles for your knees to start feeling the stress. Running this way could eventually hyperextend the medial ligaments and tendons of your kneecap.
What to Do
Learn to run with your feet pointed in the direction you're headed. But don't just point your foot forward. Rotate your entire leg in towards your centerline until your feet are parallel and pointing forward. This will strengthen your adductors (the muscles that run along your inner thighs) and straighten out your legs. This allows your knees to hinge in the direction they were designed to, instead of twisting as they bend.
Running with your feet turned out will also affect the illiotibial band, which is attached at its lower end to the lateral side of your tibia just below your knee. Lateral pain in your knees is more often an illiotibial problem and is often mistaken for a knee problem.
If your feet turn out, your heel will strike on the lateral side and your ankle will pronate as your ankle supports your weight. If your feet splay out a lot, it will probably feel like you're pigeon-toed when you try to point your feet forward. If that's the case, rotate your legs medially only as far as you can, without feeling discomfort.
Increase the amount you rotate your legs inward in small increments over a number of weeks or months, to give the muscles, tendons and fascia in your legs, feet and knees time to adjust to the new direction of movement. Changing the biomechanics of your body takes time and persistence, but it's well worth it if you never have to deal with knee pain again.
Taking good care of your knees should be a high priority, especially if you want to continue running year after year. Reducing torque and impact are the two best places to build a life insurance policy for your knees.
For more on how to take the pain out of running and make any running distance enjoyable, check out Chi Running.
Get your knees ready for a running event.