Why Does My Knee Lock When I Run?

Q  This past Saturday, I ran five easy kilometres on the treadmill (first time using one) and experienced a locked sensation in my right knee after I finished my run. By that evening, it was swollen and I could not bend or straighten it. I iced my knee through the weekend and hoped for the best. By Monday, the visible swelling was gone and I regained full range of motion with no pain. I went for a slow 2.5km run and experienced no ill effects. I’ve never had knee problems and am worried about this. I have a half-marathon later this year and training is right around the corner. – ESTER


A  A locking knee can suggest problems inside the knee. The usual culprit is the meniscus cartilage – the crescent shaped cartilage on the medical and lateral compartments of the knee that help cushion and stabilise the joint. The meniscus is often damaged in younger people during trauma that results in a tear of the cartilage. You often read about this in football or soccer players. In older runners and others, the cartilage can thin and wear out with time resulting in a degenerative tear. Most of us have some degenerative change in the later decades of life; some will cause symptoms, some will not. The meniscus is a mobile structure and sometimes the meniscus can “shift” and get “stuck” a bit out of its usual position. This shift can cause pain. The meniscus can return to its usual spot spontaneously or can be moved back to its normal position by a manual therapist.

The patellofemoral joint (kneecap) can sometimes produce a locking sensation if it is irritated on the underside by exercise or trauma. More often knee cap irritation produces pain when the undersurface contacts the femur with stair climbing or squatting, rather than a locking sensation.

Whatever caused your knee immobility and swelling was likely due to the changes in your running mechanics on the treadmill compared to your free running form. Fortunately it seems to have resolved on its own. As long as the pain and swelling do not return, I would just continue with your training program. I would stay off the treadmill until after your race and then try it again if you feel the need. If the locking or swelling returns, you should have your knee evaluated by your physician or physical therapist. – BILL

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