The knee is one of the most complex joints in the human body. It connects the thigh bone (femur) to the shin bone (tibia), and also includes a smaller bone, the fibula, which is located next to the tibia, and the knee cap (patella). Tendons connect these bones to the leg muscles, while ligaments connect the knee bones to each other and make the knee stable. In addition, two C-shaped pieces of cartilage-the medial and lateral menisci-provide a cushion between the femur and tibia, acting, in effect, as shock absorbers.
Knees are designed to bend up and down, and to rotate slightly. When a knee is unable to perform those functions, it impacts mobility and the ability to complete daily living activities, such as sitting, standing, squatting, or kneeling. When a knee cannot be bent or straightened, it is called a locked knee. There are two types of locked knees. A true locked knee occurs when the knee joint is literally locked into place and cannot move. A pseudo locked knee occurs when pain makes it difficult to move the knee joint.
The most common cause of a locked knee is a tear in the cartilage that cushions the knee joint. Typically, once the cartilage has been torn or damaged, it gets stuck in the joint, making it difficult to move the knee. In addition, the knee may swell, make a popping sound, stiffen, and/or cause pain during standing, bending, or kneeling. Torn cartilage in the knee can be caused by either a sudden physical trauma or gradual wear and tear on the joint.
A true locked knee may also be caused by decreased blood supply to the knee, or by what's known as a "loose body" in the knee joint. The most common type of loose body is a detached fragment of bone. When a loose body becomes wedged in the knee joint, it causes it to lock. A loose body may result from a knee fracture, or from an underlying condition, such as arthritis of the knee. Foreign objects left in the body during past surgery can also act as loose bodies and cause joint locking.
While a locked knee is primarily characterized by the inability to fully extend the leg, the condition can also be accompanied by swelling, a small bump that moves when touching the knee, and joint stiffness.
The primary symptom of a pseudo locked knee is pain that prevents movement of the knee. This pain may be accompanied by a sensation that the knee is locking up or catching when moved. There may also be a sensation that the joint frees up when moved a certain way.
A pseudo locked knee can have many causes. For example, the knee may be fractured, dislocated, or affected by bursitis or tendonitis. A degenerative disease, such as rheumatoid arthritis or gout, may also cause inflammation and swelling that impedes knee movement. When there is a fold in the knee joint tissue-called plica syndrome-the tissue becomes irritated and causes the knee to ache, swell, lock, click, catch, or become painful. Plica syndrome may make the knee feel unstable, as if it's going to collapse.
Pseudo locked knee may also be caused by the inability of the kneecap to move correctly. This is called patellar maltracking. When this happens, pain occurs at the front of the knee when running, ascending, or descending. Pain may also occur when sitting for a lengthy period of time, and the knee joint may feel unstable or lock.
When a knee locks repeatedly or is so painful that movement is impeded, it is important to consult with a physician. The doctor will examine the joint, review the relevant medical history, and, if necessary, request imaging, such as an X-ray, CT scan, or MRI.
When a true locked knee is diagnosed, surgery may be required to remove the damaged cartilage or bone fragment. Typically, this surgery is performed arthroscopically. Several small incisions are made in the knee, and a tiny camera is inserted to locate the exact site of the tear or damage. The camera is also used to guide the use of tiny instruments that repair or remove the damaged cartilage. When the surgery is completed, the cuts are sutured and covered with a bandage. Most patients leave the hospital after the surgery and use crutches or a brace to keep pressure off of the knee until the cartilage heals.
Pseudo locked knee is most often resolved by effective management of the pain. The cause behind the knee locking up will determine the appropriate treatment. Icing, over-the counter anti-inflammatory medications, and resting the knee may be recommended. If those treatments fail to alleviate the pain, cortisone or a local anesthetic may be injected into the knee joint. Due to possible side effects, prescription pain medications are rarely employed in cases of pseudo locked knee.
“Knee Locking Up,” Knee Pain Explained, https://www.knee-pain-explained.com/knee-locking.html.
“Picture of the Knee,” WebMD, https://www.webmd.com/pain-management/knee-pain/picture-of-the-knee#1.
“Why Is My Knee Locking?,” Healthline, https://www.healthline.com/health/locked-knee#causes.
“Why Your Knee Locks and What You Can Do About It,” verywellhealth, https://www.verywellhealth.com/locked-knee-unable-to-bend-joint-2548655.
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