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A locked knee is the medical term given to a range of conditions that limit or prevent the patient from bending or straightening their knee. There are a variety of potential underlying causes and different measures that can be taken to fix it, depending on the cause. For most people a locked knee can be treated, and their mobility issues can be fixed, although it can be a painful condition in the meantime. A summary of knee pain statistics can be found in the infographic attachment to this post.

In one rare case, a 70-year old woman presenting with symptoms of locked knee was found to have a traumatic isolated rupture of the popliteus tendon. This lady presented with the same symptoms as locked knee but had no history of significant trauma or features of instability. The cause was diagnosed using arthroscopy.

A literature review co-authored by Ali Ghoz (one of his many publications) looks at this particular case study. In most cases, a physician should be able to evaluate the causes of locked knee effectively and prescribe a treatment or course of treatment to regain mobility in the knee joint. Cases of locked knee fall into one of two categories: true knee locking and pseudo knee locking.

True Knee Locking

True knee locking refers to any incident where the patient cannot bend or straighten the knee joint due to the presence of a physical blockage preventing that movement. True knee locking can occur when a piece of bone has broken off and become a loose body in the joint, getting caught in part of the joint mechanism. This might happen due to a fall, a chip fracture, degenerative joint disease or some form of trauma. It can cause pain and swelling that might come and go as the loose body moves around, or stiffness of the joint. The patient may also be able to physically feel the loose shard as a bump under the skin and may be able to manipulate it.

One of the most common types of knee injuries that can cause locked knee is a meniscus tear. This is a tear to the bucket handle-shaped cartilage in the knee joint that cushions it from the thigh and shin bones. Meniscus tears usually happen when people are performing activities that require them to forcefully rotate or twist the knee, particularly when their full weight is on the knee.

Characteristics of this may include a popping sensation, stiffness, swelling, difficulty straightening the leg fully and pain, which will be worse when trying to rotate or twist the knee. If the torn part of the cartilage gets in the way of movement it can cause knee lock.

Some of the possible available treatments for locked knee can be found in the PDF attachment to this post.

Pseudo Knee Locking

Pseudo knee locking is where there is no physical obstruction to regular movement of the knee, but the patient has limited movement in the joint due to pain. Pain in or around the knee can trigger a muscle spasm which prevents the individual from moving the joint. Along with pain and an inability to move the joint, other symptoms of pseudo knee locking include brief locking or catching sensations and open or free sensations within the knee joint.

Pseudo knee locking can be caused by injuries such as fractures, tendonitis, bursitis, tears to the tendon, or subluxation or dislocation, particularly of the patella. Swelling and inflammation can also cause pseudo locked knee.

This type of knee locking can sometimes be fixed using physical therapy; you can find out more in the short video attachment to this post.