Knee Locking – Causes & How to Treat?
Knee locking or “locked knee” is a condition in which the knee gets stuck during extension such that an individual cannot attain optimal extension or straightening of the knee.
In knee locking, the extension of the knee joint is stopped and restricted at an angle of 10 to 30 degrees and any further extension of the knee causes a severe knee pain.
Knee locking may last for a few seconds to some minutes, depending on the cause. The locking of the knee may be due to a physical or mechanical obstruction to the movements of the structures within the knee joint or a functional limitation placed by the knee on itself to protect it from an external factor such as pain.
Knee locking is categorized, based on the mechanism underlying it, into true knee locking and pseudo-knee locking and both have different characteristics and causative factors as outlined below.
True Knee Locking
In the case of true knee locking, there is a mechanical obstruction in the affected knee joint impeding its extension.
In true knee locking, there is severe difficulty in moving the knee any further up and it may take gentle waggling of the knee to get the obstruction away and in severe cases, surgical intervention to relieve the knee of the physical obstruction.
This is also referred to as false knee locking, not because the knee does not get “locked”, but because the movement of the knee is not locked by any physical or mechanical obstruction, but as a protective mechanism placed on itself.
Pseudo Locking of the knee occurs in cases where an individual already has severe knee pain, the body’s protective mechanisms are then triggered to lock the knee’s movements in an attempt to prevent further damage to the knee. It usually happens by causing the muscles moving the knee to contract and tighten.
There are other key differences between true knee locking and pseudo locking. In the latter, both flexion and extension of the knee are impeded while in the former, only extension of the knee is locked. Additionally, while the knee gets unlocked quickly in pseudo knee locking, it often takes some time for it to unlock in true knee locking.
To understand knee locking, one needs to understand the anatomy or structure of the knee joint. The knee joint is formed by two bones: the thigh bone (the femur), the shin bone (the tibia). A third bone, the patella or knee-cap joins with the femur to protect the front of the knee joint.
The knee joint is surrounded by a capsule and it has tough tissues called ligaments which hold the inside and outside of the joint in place as well as crossing the inside of the joint. These are called the collateral and the cruciate ligaments respectively. These ligaments stabilize and strengthen the knee joint.
Another group of tissues that form the knee joint is the meniscus (plural: menisci). There are two menisci in each knee joint and they are tough cartilages that pad between the joint surfaces of the thigh bone and the shin bone. The menisci provide a smooth surface on which both bones move as well as act as shock absorbers for the knee.
For descriptive purposes and clarity, the causes of knee locking are best divided into those that cause true knee locking, that is, in which there is a mechanical obstruction in the knee joint, and those that cause pseudo locking.
Causes of True Knee Locking
If the meniscus gets torn, its loose fragment may get stuck within the knee joint, impeding the gliding of the thigh bone over the shin bone causing the knee joint to lock.
The “bucket handle” tear is the commonest type of meniscal tear that causes true knee locking. In this case, when the meniscus gets torn, the partially attached flap gets wedged in a wrong position locking further movement of the knee.
Meniscal tear may be caused by trauma or degenerative changes from overuse of the knee and it is one of the commonest causes of knee locking. Meniscal tears are common in sports such as soccer, volleyball and football.
Loose bodies include bone fragments or cartilages that break off from the joint due to trauma or chronic inflammation and remain within the joint structure floating around. In time, these fragments may move into a wrong position, impeding movement of the knee, locking it consequently.
Osteoarthritis is a degenerative disease of the joint resulting from wear and tear or excessive strain or use of a joint. Knee locking from osteoarthritis often occurs as a result of breaking off or weakening of the joint cartilages.
A ligament sprain often causes the knee to become unstable and the adjoining bones may become unable to glide against each other because of the looseness of the injured ligament.
Certain injuries may cause the kneecap to be moved out of position altering the machinery and restricting the mobility of the knee joint. This causes extension of the knee to get locked
Inflammation of the Knee Joint
Inflammation comes with swelling, and oedema of structures within the knee joint may impede full extension of the joint, thereby, locking it.
This is a condition in which the cartilages in the knee joint are worn out, this may cause the adjoining bones to glide directly over each other causing them to break off releasing small fragments which may lock the knee.
Causes of Pseudo Knee Locking
The following are causes of pseudo locking of the knee;
Joint inflammation or arthritis of all types come with pain and swelling within the joint due to excess fluid accumulation in the joint capsule.
While the swelling may impede movement of the knee joint, the pain triggers spasm of the thigh muscles and knee muscles to contract suddenly in an attempt to protect the joint when moving it.
The medial plica is a fold in the tissue lining the joint surfaces, the synovium. If this fold is inflamed, it often causes excruciating pain which limits and locks the movement of the knee joint.
Acute Knee Injury
Any injury to the knee which causes significant pain would trigger the muscles of the thigh and leg to spasm limiting the movement of the injured knee.
Pathophysiology of Knee Locking
This answers the question: How does Knee Locking happen? The knee is a compact joint, that is, the space within the joint is limited.
Trauma, fractures, loose bodies, or meniscal tears may compromise this small space within the joint impeding the free gliding of the femur and tibia against each other restricting extension of the knee.
When the knee is extended, the articular or joint surfaces of the tibia and fibula are brought together and the joint space is reduced and held in place by the ligaments.
In flexion or bending of the knee, the articular surfaces are separated and the joint space widened. If the joint space has been occupied by an abnormal structure such as bone fragments, cartilages, or swelling from inflammation, full articulation of the tibia with the femur becomes impossible and full extension of the knee is locked.
In Pseudo knee locking, as explained earlier, pain is the main inciting factor, causing spasm of the strong flexor and extensor muscles of the knee, locking the knee transiently.
Signs and Symptoms of Knee Locking
Several signs and symptoms accompany locking of the knee and these depend on the cause of the locked knee. The following are common symptoms associated with knee locking;
- Pain – Pain is usually the hallmark of knee locking. Although it may not always be present in true knee locking, pain is the main trigger for a pseudo knee locking. Knee locking, however, is generally associated with severe pain on extending the knee.
- Reduced range of motion of the knee: When there is an impediment to the movement of the knee joint, activities such as squatting, running, and walking which require strong flexion and extension of the knee become extremely difficult.
- Fever: In acute knee joint infections, abscesses, and infective arthritis, the individual may present with elevated body temperature.
- Clicking Sounds on moving the knee: This occurs when the articular structures of the knee glide against the mechanical obstruction such as the loose fragment of a torn meniscus. The sound may also be rubbing or grinding in character.
Treatment of Knee Locking
Treatment of a “locked knee” depends on the cause.
After careful physical examination and history taking by your doctor, several investigations may be ordered to narrow the options and determine the actual cause of your locked knee.
Essential investigations in the diagnosis of locked knee include the following;
- White blood cell count to check for knee joint infection,
- Rheumatoid factor to exclude rheumatoid arthritis,
- Serum uric acid level to exclude gouty arthritis.
- X-rays of the Joint – This is useful in diagnosing degenerative joint diseases such as osteoarthritis.
- Magnetic Resonance Imaging (MRI) efficiently detects meniscus tear, fracture and dislocation of the patella, ligament tear, and fracture of the articular aspects of the tibia or fibula in the knee.
- Synovial Fluid Study – The synovial fluid or joint fluid is collected by aspiration with a special needle. The fluid is then analysed for the count of red blood cells and white blood cells in it, and the presence of proteins, abnormal cells, crystals, and microorganisms in it. The analysis of this fluid helps diagnose bleeding into the joint (hemarthrosis), joint infection, gouty arthritis, as well as degenerative joint diseases.
Essentially, locked knee can be treated by conservative and surgical management. Conservative management of a locked knee includes the following;
- Heat and Cold Application – This is aimed at reducing the inflammation within the joint, thereby suppressing the trigger of the knee locking. Ice packs can be applied alternatively with warm pads on the affected knee to achieve this.
- Muscle Relaxants: In cases where muscle spasms cause or contribute to the locking of the knees, muscle relaxants cause the knee to relax and move easily.
- Analgesics – Non steroidal anti-inflammatory drugs (NSAIDSs) help relieve the swelling and pain in the knee, eliminating the triggers of the knee locking.
- Physical therapy – This consists of stretch exercises, massages, and knee manipulations to relax the muscles of the knee, as well as allow more space for the articular structures to glide against each other easily.
In severe cases, and in those situations where conservative treatment does not resolve the knee locking, you may be referred to an orthopaedic specialist for further management.
Surgical treatment options for locked knee include the following;
- Arthroscopic removal of fragments- In this case, the fragments are manually removed using surgical instruments to allow free movement of the articular structure against each other.
- Meniscus repair – The torn meniscus are repaired and reattached to the bones
- Meniscectomy – There are some cases where a torn meniscus is irreparable and the best option is to remove the damaged meniscus so it does not impair joint function.
- Arthroplasty – Here, the knee is replaced with a metal or plastic prosthesis in severe where the knee is badly damaged.
How to prevent Knee Locking
Besides the fact that knee locking may be severely painful, stress is transferred from the knee muscles to the knee itself when it happens, and this could cause injury to the knee. Here are tips to help prevent locking of your knee.
- Do not exercise beyond your limit
Performing strong leg and standing exercises such as squats and leg presses beyond your tolerance level may cause your knee to lock.
- Strengthen your leg muscles
Perform resistance-training exercise on your quadriceps, calf muscles, and hamstrings. Stronger calf muscles reduce the stress placed on the knee during activity.
Weak muscles make the knee do more work, making it prone to being locked.
- Build a stronger core
Building your core improves the alignment of the feet and legs, ensuring proper use of the leg muscles, consequently reducing stress on the knee.
A weak core tilts the pelvis off its centre, causing distortion of movement and strength of the leg muscles.
- Keep your muscles flexible
This can be achieved by regularly stretching the calves, iliotibial band, and thigh muscles. Having tight calves, for example, before exercise causes them to be activated slowly consequently placing extra stress on the knee, causing it to lock.
While knee locking may be treated using conservative means such as application of ice compresses and warm pads, use of analgesics and muscle relaxants, some cases such as meniscal tears may require surgical management.
You can prevent knee locking by building stronger core muscles, strengthening and stretching your calves, and not exercising beyond your tolerance level.