The meniscus is a C-shaped pad of cartilage that acts as a shock absorber between the femur (thighbone) and the tibia (shinbone). It also helps stabilize the knee joint and nourish the cartilage. There are two menisci in the human knee a medial (inner) one and a lateral (outer) one.
The medial meniscus is the one most commonly torn. If the tear is small and is not located in the region where the meniscus has an active blood supply, the doctor can simply remove the torn part and sculpt the edges of the meniscus until they're smooth and stable. This is called partial medial meniscectomy. If you have this procedure, you must simply wait for the arthroscopic wounds to heal and for the knee's swelling to go down before resuming running.
For most of my patients, this takes about three weeks, at which point they can go back to light jogging on a track or a soft, grassy surface. By six weeks, many are able to start fairly intensive road running and interval workouts.
If the tear to the meniscus is large or near the edge of the meniscus, where there is good blood supply, your surgeon may elect to stitch the meniscus to hold it in place while it heals. In this case, wait six weeks before resuming a running program.
In the meantime, avoid kneeling or squatting. By six weeks the repair should be stable enough for you to begin jogging lightly on flat surfaces, and by 12 weeks you should be able to run over any surface, including trails and rugged terrain.
When I start my runners back in training after knee surgery, I recommend they run every other day and bike or swim on off days. After three weeks of running on alternate days, your knee should be conditioned well enough for you to resume your normal training program.
If your knee begins to swell after you run, you know you've done a little too much. Ice your knee, use anti-inflammatories and back off your running a bit. If you rehab sensibly and gradually after knee surgery, you should be able to run just as fast and as far as you did before surgery.