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Knee Locking : What Causes Locked Knee and How is it Treated?

What is Knee Locking or Locked Knee?

“Knee Locking” or “Locked Knee” is the term used to describe a painful condition that occurs as result of knee extension at certain angle.1 During extension of knee joint, extension is restricted at 10 to 30 degree to prevent pain. Patient is unable to achieve optimum normal extension. Any further extension beyond the restricted angle causes severe intractable knee pain. Most common cause of locked knee or knee locking is meniscus tear, congenital defect, injury or disease like osteoarthritis.

Lock Knee or Knee Locking

Knee Locking: What Can Cause Your Knee To Get Locked?

Knee Locking or Locked knee is caused by mechanical obstruction of knee joint movements. Locking up of the Knee causes severe knee pain during the act of knee joint extension.

Mechanical Obstruction as a Cause for Knees to get Locked Up:

  • Cartilage or Bony Fragments that are physically caught within knee joint can cause Knee Locking or Locked Knee.2
  • A “Bucket Handle” or “Meniscus Tear” – Causes restriction of knee joint extension and is one of the main cause for knees to get locked up.3
  • Fracture of Tibia or Fibula at knee joint can cause knee locking or locked knee joint.
  • Surgical Complications – Complications arising after surgery can cause knee locking or locked knee. Anterior cruciate ligament reconstruction sometimes causes knee locking despite satisfactory surgical outcome.
  • Osteoarthritis – Locked knee joint in patients suffering with arthritis of knee joint causes severe pain because of restricted knee extension. Arthritis and natural aging can increase the risk for knee locking up. Overtime, the cartilage that surrounds the bones in the knee will wear out and begins to break off.
  • Ligament Injury as a Cause for Knees to get Locked Up- Ligament injury causes unstable knee and knee giving way, a condition sometimes referred to as trick knee. Knee pain becomes severe with extension and weight bearing.
  • Loose Tissue Fragments Can Cause Knee Locking or Locked Knee- Severe pain is caused by loose tissue fragments other than cartilage when lodged inside the joint.
  • Inflammation of Knee Joint – Knee joint inflammation causes swelling of knee joint. Swelling and edema of knee joint restrict extension and causes pain leading to muscle spasm and locked knee.
  • Patellar Dislocation – Superior dislocation of patella causes restriction of knee joint extension and severe pain with extension restricting knee joint movements and causing the knees to get locked up.
  • Tear of Mediopatellar Plica – Knee joint synovitis causes mechanical damage of plica inside the knee joint resulting in severe pain and restricted extension of knee joint causing locked knee.
  • Osteochondritis Dissecans – Knee joint cartilage is completely worn out, which follows fragment of chipped bone to dislodge in joint. The condition restricts movements of knee joint and causes severe pain along with locked knee.

Pathophysiology of Knee Locking or Locked Knee

Knee joints are comprised of:

  • Cartilages – Medial and Lateral Meniscus.
  • Ligaments – Anterior and Posterior Cruciate Ligaments.
  • Synovial Membrane.
  • Bones – Distal end of femur and proximal end of tibia.

Knee locking or knees getting locked up is a condition caused by inflammation of synovial membrane, cartilage damage, ligamental tear or fracture of patella, tibia, or fibula. Knee joint is a compact joint. Space within the knee joint is limited and thin. Trauma, injury and disease causing hematoma, mucosal edema or inflammation of synovial membrane within the joint can compromise the joint space and restrict the knee joint extension.

Extension and flexion of knee joint depends on alignment of medial and lateral meniscus as well as stability of anterior and posterior ligament. Knee joint during flexion and extension maintains an optimum horizontal or oblique vertical position of meniscus. Tear of meniscus or fragments within knee joint interferes with achieving optimum resting position in extension of knee.

Knee joint has two tough cartilaginous menisci. Medial meniscus lies inside of the knee joint and lateral meniscus lies outside of knee joint. Both menisci lies between femur and tibia. Meniscus tear causes large fragment of the torn meniscus wedged within the knee joint. A torn meniscus fragment obstructs the extension of knee joint by locking the knee and prevents normal movement of the knee joint.

A misalignment of the muscles or bones due to muscle strain or an injury also can cause knees to lock. In either situation, the knee can become stiff and frozen, which is accompanied by extreme pain. To treat knee locking or locked knee, it is important to know what caused the initial symptoms.

Signs and Symptoms of Knee Locking or Locked Knee

  • Fever – Knee joint infection or abscess of knee joint
  • Severe Pain on extension is one of the symptoms of locked knee
  • Restricted Knee Joint Movements – Knee locking often causes difficulty to stand on affected leg.
  • Knee Examination – Tender and painful knee joint on palpation.
  • In Locked knee, Flexion of Knee Joint is fixed in position, often at a 45 degree angle.
  • Extension of Knee Joint – Person suffering from knee locking or locked knee will be unable to straighten the leg. Leg can be cautiously and manually placed to complete extension position using both hands.
  • Rubbing and Grinding Sounds can be one of the sign and symptoms of locked knee. Knee joint movement creates a sound because of the rubbing of the fragment of torn meniscus which is caught in the joint. Abnormal sound is associated with intense pain.
  • Stump Impingement Reflex Sign is observed in anterior cruciate ligament tear.

Investigations to Diagnose Knee Locking or Locked Knee

Blood Examination to Diagnose the Cause of Knee Locking or Locked Knee:

  • White Blood Cell Count – Increased white blood cell count in case of knee joint infection.
  • Rheumatoid Factor is elevated in patient suffering with rheumatoid arthritis.
  • Elevated Erythrocyte Sedimentation Rates – Seen in inflammatory arthritis, rheumatoid arthritis or systemic lupus erythematosus.
  • Elevated Uric Acid levels in the blood may indicate gout.

Watch 3D Video of Knee Joint Rheumatoid Arthritis:

Synovial Fluid Study to Diagnose the Cause of Knee Locking or Locked Knee:

Synovial Fluid Study – Tested for red blood cells in case of bleeding in knee joint, tested for white blood cells to rule out infection, tested for cartilage cells (seen in osteoarthritis) and uric acid crystals (in gout).

X-Rays To Diagnose the Cause of Knee Locking or Locked Knee:

X-rays are useful in diagnosing degenerative arthritis in knee joint, which could be the cause for knees to get locked up.4

MRIs for to Diagnose the Cause of Locked Knee

MRIs are useful in diagnosis of following disease which can be causing the knees to get locked:

  • Meniscus tear.
  • Fracture or dislocation of cruciate ligament.
  • Fracture or dislocation of patella.
  • Fracture of tibia or fibula at knee joint.

Treatment for Knee Locking or Locked Knee

Treatment for Knee Locking or Locked Knee

  • NSAIDs – Anti-inflammatory medications are prescribed for inflammation, pain and fever associated with knee locking or locked knee.
  • Muscle Relaxants are prescribed to ease knee pain, reduce knee stiffness and relax muscles.
  • Heat and Cold Application.
  • Physical Therapy for Locking Knee – PT is directed towards exercise, stretching, massage and knee manipulations.
  • Surgery of Locking Knee or Locked Knee:
    1. Removal of Fragments in Knee Joint Which Cause Knees to Get Locked- Torn cartilage is removed so it no longer interferes with knee joint mobility.
    2. Surgery – Meniscectomy. This is done to remove all parts of torn meniscus that can cause knees to get locked
    3. Meniscus Repair. It is an outpatient surgical procedure to repair torn knee cartilage that can be causing the knees to get locked
    4. Meniscus Transplantation.
    5. Knee Replacement.


Pramod Kerkar, M.D., FFARCSI, DA
Pramod Kerkar, M.D., FFARCSI, DA
Written, Edited or Reviewed By: Pramod Kerkar, M.D., FFARCSI, DA Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:August 11, 2022

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