Knee locking

Your knee suddenly stops at a certain angle as it moves, and it feels as though you need to apply some force or gently jiggle it to release it. Some people describe discomfort because their knee stays partly bent and will not straighten fully.

'Locking' is not a diagnosis, but a term for a sensation in the knee. The same feeling can have different causes, so it helps to understand the two types.

• True locking — Something catches between the joint surfaces, physically blocking movement.
• Pseudo-locking — Nothing is catching, but pain or swelling causes the muscles to stop movement on their own, making the knee feel locked.

True locking happens when something gets trapped within the knee joint. A common example is a tear in the meniscus, the cushion between the thighbone and shinbone, with a torn fragment shifting into the joint space and getting caught. In particular, when the meniscus tears lengthwise and a segment shifts into the center of the joint, the knee may be unable to straighten fully. You can see the different tear shapes in Meniscal tear patterns. An intra-articular loose body, a piece of cartilage or bone floating inside the joint, can also get trapped and cause catching.

Pseudo-locking happens when the body limits movement on its own because the knee is painful or swollen. Plica syndrome, in which a fold of tissue inside the knee becomes irritated, is often discussed in this context. In these cases, movement becomes stiff without anything physically catching, and it often eases as the swelling subsides.

• The knee may catch, then release with a 'pop' after you bend and straighten it a few times or gently jiggle it, and feel fine again.
• Catching may come with clicking sounds (knee crepitus) or a snapping sensation.
• Subluxation, in which the kneecap slips slightly to one side and then returns, can also feel like catching and releasing, so the descriptions overlap.

• Do not rush when your knee catches. Rather than trying to force it straight, sit down, relax your leg, and try gently jiggling your knee to release it.
• Rest if your knee is swollen. Swelling makes movement stiffer. Elevate your leg and use cold compresses and ice packs.
• Temporarily cut back on squatting and deep knee bends. These movements place considerable strain on the meniscus.
• Keep a record of which movements cause catching. Remembering the angle and circumstances—on stairs, when standing up, or when twisting—can help when looking into it later.
• Try gently strengthening the muscles at the front of your thigh. Strong quadriceps femoris muscles help make the knee more stable.

• Your knee remains unable to straighten or bend fully for a while
• Catching keeps recurring and becomes increasingly frequent
• Your knee is swollen and warm, or you cannot bear weight on it
• Your knee does not release after catching, or it gives way as though losing strength even after it releases