Locked Knee
A mechanical block where the knee joint becomes physically stuck in a bent or straight position and cannot be moved.
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What does this symptom mean?
True knee locking occurs when a piece of tissue—such as a torn meniscus fragment or a loose body of bone or cartilage—becomes physically wedged inside the joint, preventing movement. True mechanical locking must be distinguished from temporary stiffness or pain-induced restriction ('pseudo-locking'). Mechanical locking prevents full range of motion and warrants prompt medical assessment.
Anatomical Overview
Important — Educational Information Only
Pain location alone cannot determine the cause of knee symptoms. This map provides educational information about anatomical structures and possible associations. It is not a diagnostic tool. A clinical examination by a qualified specialist is required to determine the cause of your knee pain.
Knee Pain Location — Educational Guide
Select a view and tap a numbered hotspot on the photograph to view associated educational information.
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Select a numbered hotspot on the Front (Anterior) photograph or use the Prev/Next buttons below to browse.
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Front (Anterior) View
Around the Kneecap (Anterior)
Pain around or behind the kneecap (patella). Often worsened by stairs, squatting, or prolonged sitting.
Outer Joint Line (Lateral)
Pain along the outer joint line. Often related to sports injuries, pivoting movements, or lateral compartment problems.
Inner Joint Line (Medial)
Pain along the inner side of the knee joint line. The medial compartment bears the majority of weight-bearing load.
Back (Posterior) View
Behind the Knee (Posterior)
Pain, swelling, or fullness in the hollow behind the knee (popliteal fossa). Often secondary to an internal joint problem.
Inner (Medial) View
Medial (Inner) Compartment
Pain along the inner side of the knee. The medial compartment is the most commonly affected by arthritis and meniscal tears.
Outer (Lateral) View
Lateral (Outer) Compartment
Pain along the outer knee compartment. Lateral problems are less common but frequently sports-related.
Symptom-to-Recovery Pathway
Standard Patient Journey Pathway
How the symptom may present
Patients describe this symptom in various ways depending on its trigger and severity:
Possible causes
The possible causes listed below are not exhaustive. One symptom can have several underlying causes, and a clinical assessment is typically required to confirm a diagnosis.
Meniscal Tear
A tear in the shock-absorbing C-shaped cartilage discs of the knee, often caused by twisting forces or age-related changes.
Cartilage Injury
Focal damage to the protective articular cartilage lining the bones, leading to localized pain, clicking, or swelling.
Loose Bodies
Fragments of bone or cartilage that float freely within the knee joint, potentially causing locking, catching, or sudden pain.
Knee Arthritis
Degeneration of the knee joint cartilage leading to progressive pain, stiffness, and restricted mobility.
When to seek urgent advice
Certain symptoms (red flags) indicate the need for prompt clinical evaluation. Seek immediate assessment if you experience:
- The knee is physically locked and cannot be straightened even with gentle assist
- Locking occurred immediately after a twisting injury
- Frequent, painful locking episodes that cause you to fall or lose balance
How the symptom is assessed
Your consultant will carry out a thorough assessment to understand the triggers, location, and functional impact of the symptom.
- Detailed review of locking frequency, duration, and triggering movements
- Assessment of whether the joint is physically blocked or restricted by pain
- Physical examination checking range of motion and joint stability
- Evaluation of previous meniscus or cartilage injuries
Investigations that may be considered
Depending on the findings of your clinical assessment, your consultant may recommend imaging scans:
Standard X-rays
check for loose bone fragments or osteophytes
MRI scan (highly recommended)
identify meniscus tears or loose cartilage bodies
What may help initially
For non-urgent presentations, simple self-care and load management can help settle symptoms:
- Gentle, passive movement to see if the block releases naturally without force
- Avoiding forced straightening, which can cause further joint damage
- Physiotherapy to reduce swelling and maintain range of movement once unlocked
- Arthroscopic surgery (keyhole) to repair the meniscus or remove loose bodies if locking persists
When to arrange a professional consultation
You should arrange a specialist consultation if you experience any of the following:
- Your knee is currently locked and will not straighten (prompt review advised)
- You experience recurrent catching or locking episodes
- Locking is accompanied by joint swelling and instability
Frequently Asked Questions
Would you like an individual knee assessment?
A consultation can help clarify the possible cause of your symptoms and discuss appropriate next steps.
Face-to-face appointments are arranged through the reception team at the chosen clinic. Video consultations use Google Calendar where available.
Next Step: Explore Possible Conditions
Similar symptoms can occur with several different knee conditions. Learn about common diagnoses, how they are assessed, and how force transmission affects joint health.
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Medical Disclaimer
This website provides educational and general information about knee symptoms, conditions, and treatments. The content is for informational purposes only and does not constitute medical advice, diagnosis, or a treatment plan. It should not be used as a substitute for a professional consultation, examination, or clinical decision-making by a qualified orthopaedic specialist.
If you are experiencing symptoms or are concerned about a knee problem, please arrange a clinical consultation. If you have urgent symptoms, severe pain, or are unable to put weight on your leg, please read our urgent advice guidance or contact emergency services immediately (dial 999 or NHS 111).