Locked knee: Causes and what to do

The knees are two of the most important joints in the human body. Aside from supporting a person's body weight, the knees enable everyday activities, such as standing up, walking, and climbing stairs.

As a result of such frequent use, the knees are prone to injury and degeneration. Both can lead to locked knee, which is where a person cannot bend or straighten their knee.

There are two types of locked knee: pseudo and true locked knee. Keep reading for more information about their causes, symptoms, and treatments.

What is locked knee?

Locked knee occurs when a person is unable to either bend or straighten their knee. There are two types.

Pseudo locked knee

Injury is a possible cause of a locked knee.

Pseudo locked knee occurs when severe knee pain triggers the knee muscles to spasm and contract.

It is an automatic defense mechanism that the body uses to discourage movement of the knee. Restricting the knee in this way helps prevent further damage.

Although muscle tightening and swelling make bending or straightening the knee painful, the knee joint itself is not physically incapable of moving.

True locked knee

True locked knee occurs when something physically prevents the knee from straightening. When a person has true locked knee, their knee joint gets stuck in one position and cannot move at all.

Causes

The causes of locked knee vary depending on the type.

Causes of pseudo locked knee

Some potential causes of pseudo locked knee include:

• pain from a knee injury
• inflammation from injury or degenerative joint disease (osteoarthritis)
• plica syndrome, which is inflammation of the knee joint tissue
• patellar maltracking, where the kneecap does not move correctly

Causes of true locked knee

Some potential causes of true locked knee include:

Meniscal tear

The menisci are two pieces of 'c'-shaped cartilage that sit either side of the knee joint. They act as a cushion between the bones of the shin and thigh.

If a meniscus tears, a fragment can break away and become stuck in the knee joint, causing the joint to lock.

A meniscal tear can occur during forceful twisting or rotation of the knee. Other causes include overuse and degenerative changes to the knee.

Loose bodies in the knee

Like cartilage, bone fragments can also embed themselves in the knee joint, causing it to lock.

Loose bodies such as cartilage and bone fragments can occur due to injury or osteoarthritis.

Patella dislocation

Certain injuries to the knee can cause the kneecap, or patella, to move out of position. This is called patella dislocation. It can cause the knee to lock during extension.

Knee joint inflammation

If the structures within the knee joint become swollen and inflamed, they may prevent extension of the knee. Swelling could occur as a result of injury, overuse, or osteoarthritis.