I am 41 years old and have had problems with both knees for the past three years. My symptoms are popping, locking and swelling of both knees. These symptoms occur only on occasion and in one knee at a time. When my knees lock, I am unable to bend them at all and the pain is excruciating. When I experience the popping, my knees then become very tender and I am unable to walk comfortably.
The knee joint, above almost all others, is subject to powerful mechanical forces and prone to injury and instability. The design may be a bit flawed, but what choice do we have? It is the one we are stuck with and we must make the best of it. The design actually dictates that the knee bend only in one direction, and that direction must be unrestricted. It should not extend much beyond a full straightening, and should certainly not bend side to side. Finally, there should be little in the way of rotation or twisting allowed in the knee.
It might help to consider a very different joint, the hip, for additional perspective. The hip allows the leg to swing forward and back and side to side, and also allows the leg to rotate (pointing the toes in different directions.) This is an impressive range of motion and yet the hip is remarkably stable and much less likely to have problems compared to the knee.
So what can go wrong with the knee? Quite a few things actually. The most common are wear and tear injuries. For example, the incessant movement of the kneecap back and forth along its groove can result in chondromalacia patellae, a roughening of the cartilage beneath the kneecap causing pain. Like most other joints, there can be tendinitis, bursitis and the most serious of the “itis” group, arthritis. Degenerative arthritis is very common in the knee. Joint cartilage breaks down over the years, and pain and disability result from bone grinding on bone. The knee may look enlarged, knobby and will be stiff and uncomfortable. But arthritis alone does not usually cause the locking that you describe.
As a doctor there are certain symptoms I look for in assessing a patient with knee problems, signs that might indicate a need for orthopedic referral. Locking of the knee is one of them. You have described the sensation well. Imagine then, a small bone chip, or a torn piece of cartilage, a flap of tissue perhaps, that gets trapped or interposed between the two large articulating bones of the knee. Smooth movement of the knee requires smooth cartilage and bone surfaces as well as lubricating joint fluid that causes the surfaces of the joint to appear shiny and glistening on the inside. All it takes is a small piece of bone or cartilage to jam the joint and lock the knee. It is the proverbial monkey wrench in the gears, the extraneous object that screws everything up.
The locking is usually momentary. With minor movement and adjustments, the object is freed and slides back to its usual anatomical position or slips over to a less critical roomier part of the joint. Quite often the locking seems to occur at random. It may be hard to figure just what it was that triggered the locking, and therefore hard to predict or prevent the next episode.
A magnetic resonance image of the knee will reveal in glorious detail the cartilage, bones and tendons on the knee, and may be the chosen diagnostic test. Alternatively, or sometimes additionally, an arthroscopy is performed. Arthroscopic surgery, familiar to many people, is basically a lighted scope that is inserted into the knee joint, allowing for the repair of torn cartilage or ligaments, and irrigation to remove loose bodies such as bone chips.
Your symptoms do not sound like something that will go away on their own, and it also seems unlikely that they will respond to anti-inflammatory medications. I would think an orthopedist consultation would be your next step.
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