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Sports Medicine

Causes of locking knee



I am a runner and had experienced sore, tired knees for approximately three weeks but no real pain or loss of function. But while bending down to pick up a package, I felt an intense pain in my kneecap in the area of my patellar tendon. Nothing popped, nothing snapped, it was just pain. Several days later the back of my knee ached, and a week later I was limping and my knee locks when standing. I am able to straighten the leg when sitting but not when standing. Besides a torn meniscus, what else causes a knee to lock? The other websites I have visited all list a torn meniscus as the #1 cause for locked knee but there is no #2, #3, etc. Can inflamation cause a knee to lock? Can a strain to the popliteus tendon cause the knee to lock and to cause pain at the back of the knee? Can a strained patellar tendon cause this? I welcome your response and appreciate it very much.


A question very similar to yours has just been answered today in the Sports Medicine section. Take a look at the question titled, "Meniscus Tear and Numb Toes" for more information.

However, to answer your additional questions:

First, it must be determined whether knee locking is "true" locking or "pseudolocking". Pseudolocking resembles true locking, but doesn't require a mechanical maneuver to get the knee to "unlock", whereas with true locking, a torn meniscus, loose fragment of articular cartilage (such as can result from osteoarthritis), or a fracture fragment becomes lodged between opposing knee joint surfaces and requires a twisting or jerking motion to dislodge this interposed tissue and thereby unlock the knee.

Knee joint inflammation by itself (called "synovitis") can result in painful knee motion, which could therefore conceivably cause pseudolocking, but not true knee joint locking.

Neither a strain of the popliteus tendon, nor of the patellar tendon, would cause true knee locking. Pain from patellar tendinitis is located anteriorly (so would not account for aching pain in the back of the knee)... pain from popliteus tenosynovitis is located laterally rather than posteriorly. I hope this helps!

For more information:

Go to the Sports Medicine health topic, where you can:

Response by:

Brian L Bowyer, MD Brian L Bowyer, MD
Clinical Associate Professor
Physical Medicine & Rehabilitation
College of Medicine
The Ohio State University