Dislocated Kneecap

Last updated: February 8, 2026Reviewed date: February 8, 2026Reading time: 8 min read
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A dislocated kneecap is a common injury that normally takes about 6 weeks to heal. Kneecap subluxation or dislocation may occur more than once. The first few times it happens will be painful, and you will be unable to walk. If subluxations continue to occur and are not treated,...

For severe symptoms, danger signs, pregnancy, child illness, or sudden worsening, seek urgent medical care.

বাংলা রোগী নোট এখনো যোগ করা হয়নি। পোস্ট এডিটরে “RX Bangla Patient Mode” বক্স থেকে সহজ বাংলা সারাংশ যোগ করুন।

এই তথ্য শিক্ষা ও সচেতনতার জন্য। এটি ডাক্তারি পরীক্ষা, রোগ নির্ণয় বা প্রেসক্রিপশনের বিকল্প নয়।

Article Summary

A dislocated kneecap is a common injury that normally takes about 6 weeks to heal. Kneecap subluxation or dislocation may occur more than once. The first few times it happens will be painful, and you will be unable to walk. If subluxations continue to occur and are not treated, you may feel less pain when they happen. However, there may be more damage to your knee joint each time...

Key Takeaways

  • This article explains Pathophysiology in simple medical language.
  • This article explains Causes in simple medical language.
  • This article explains Symptoms of a dislocated patella in simple medical language.
  • This article explains Diagnosis in simple medical language.
Educational health guideWritten for patient understanding and clinical awareness.
Reviewed content workflowUse writer and reviewer profiles for stronger trust.
Emergency safety firstUrgent warning signs are highlighted below.

Seek urgent medical care if you notice

These warning signs are general safety guidance. Local emergency numbers and clinical judgment should always come first.

  • Severe symptoms, breathing difficulty, fainting, confusion, or rapidly worsening illness.
  • New weakness, severe pain, high fever, or symptoms after a serious injury.
  • Any symptom that feels urgent, unusual, or unsafe for the patient.
1

Emergency now

Use emergency care for severe, sudden, rapidly worsening, or life-threatening symptoms.

2

See a doctor

Book a professional medical evaluation if symptoms persist, worsen, recur often, affect daily activities, or occur in a high-risk patient.

3

Learn safely

Use this article to understand possible causes, tests, treatment options, prevention, and questions to ask your clinician.

A dislocated kneecap is a common injury that normally takes about 6 weeks to heal. Kneecap subluxation or dislocation may occur more than once. The first few times it happens will be painful, and you will be unable to walk. If subluxations continue to occur and are not treated, you may feel less pain when they happen. However, there may be more damage to your knee joint each time it happens.

An athlete can dislocate his/her patella when the foot is planted and a rapid change of direction or twisting occurs. Usually, a pre-existence ligamentous laxity is required to allow a dislocation to occur in this manner. Direct blows to a knee can cause dislocations as well.

The initial injury can have lasting consequences, as these dislocations can cause loose fragments of cartilage or bone in the knee joint, and patients with a prior history of patellar dislocation are more likely to have repeat dislocations in the future, either in the same or opposite knee.

Pathophysiology

  • General
    • It is important to take a thorough history to determine if the occurrence was a first-time dislocation
    • Patients may describe a popping sensation without obvious dislocation suggesting subluxation or dislocation with spontaneous reduction
  • Lateral Dislocation
    • Most common by far
    • Occurs with contact during contact or collision sport
    • Without contact during aggressive cutting or pivoting maneuver
  • Other Directions
    • Medial dislocations, intra-articular and superior dislocations are rare
    • Associated with congenital conditions, quadriceps atrophy or iatrogenic

Causes

Sudden knee pain can result from a traumatic injury, stress injury, or flare-ups from another underlying condition. Remember that it doesn’t take a severe injury to cause a partial tear of your ligament or to wear down your cartilage.

  • Typically traumatic from:
    • Non-contact twisting injury to the knee
    • Direct blow to the medial aspect of the knee
    • Tibia is often externally rotated with foot planted, knee slightly flexed with a valgus position
  • Generalized ligamentous laxity
    • These patients may have more benign etiology
    • Often subluxation events rather than frank dislocation

Pathoanatomy

  • Vastus Medialis Obliquus (VMO)
    • The most distal portion of the medial quadriceps muscle
    • Exerts a medially directed force that helps keep the patella in position
  • Medial retinaculum
  • Medial Patellofemoral Ligament (MPFL)
    • Primary static restraint to lateral instability during the first 30° of flexion
    • Prevents excessive lateral movement of the patella
    • Almost universally torn during dislocations

Associated Conditions

  • Miserable Malalignment Syndrome
  • Osteochondral Defect Knee
  • Patellar Instability
  • Patellofemoral Pain Syndrome
  • General
    • Female > male
    • Younger age
  • Muscle related factors
    • Weakness or atrophy of Vastus Medialis Obliquus
    • The excessive tone of the Vastus Lateralis or Iliotibial band
  • Anatomic factors
    • Increased Q Angle
    • Patella Alta or high riding patella
    • Trochlear dysplasia
    • Excessive lateral patellar tilt
    • Lateral femoral condyle hypoplasia
    • Laterally located tibial tubercle
  • Generalized ligamentous laxity
  • Connective Tissue Disorder
    • Marfan Syndrome
    • Ehlers Danlos Syndrome
  • Down Syndrome
    • Due to congenitally small patella, hypoplastic condyle

diagnosis: Differential diagnosis is a list of possible conditions that may explain symptoms. সহজ বাংলা: একই লক্ষণের সম্ভাব্য রোগের তালিকা।" data-rx-term="differential diagnosis" data-rx-definition="Differential diagnosis is a list of possible conditions that may explain symptoms. সহজ বাংলা: একই লক্ষণের সম্ভাব্য রোগের তালিকা।">Differential Diagnosis

  • Fractures
    • Distal Femur Fracture
    • Patellar Fracture
    • Tibial Plateau Fracture
  • Dislocations & Subluxations
    • Patellar Dislocation (and subluxation)
    • Knee Dislocation
    • Proximal Tibiofibular Joint Dislocation
  • Muscle and Tendon Injuries
    • Quadriceps Contusion
    • Iliotibial Band Syndrome
    • Quadriceps Tendonitis
    • Patellar Tendonitis
    • Popliteus Tendinopathy
    • Extensor Mechanism Injury
      • Patellar Tendon Rupture
      • Quadriceps Tendon Rupture
      • Patellar Fracture
  • Ligament Pathology
    • ACL Injury
    • PCL Injury
    • MCL Injury
    • LCL Injury
    • Meniscal Pathology
    • Posterolateral Corner Injury
    • Multiligament Injury
  • Arthropathies
    • Knee pain and stiffness. সহজ বাংলা: বয়স/ক্ষয়ের কারণে জয়েন্টের ব্যথা।" data-rx-term="osteoarthritis" data-rx-definition="Osteoarthritis is wear-and-tear joint disease causing pain and stiffness. সহজ বাংলা: বয়স/ক্ষয়ের কারণে জয়েন্টের ব্যথা।">Osteoarthritis
    • Septic pain, swelling, stiffness, or reduced movement. সহজ বাংলা: জয়েন্টের প্রদাহ।" data-rx-term="arthritis" data-rx-definition="Arthritis means joint inflammation causing pain, swelling, stiffness, or reduced movement. সহজ বাংলা: জয়েন্টের প্রদাহ।">Arthritis
    • Gout
  • Bursopathies
    • Prepatellar Bursitis
    • Pes Anserine Bursitis
    • MCL Bursitis
    • Infrapatellar Bursitis
  • Patellofemoral Pain Syndrome (PFPS)/ Anterior Knee Pain)
    • Chondromalacia Patellae
    • Patellofemoral pain and stiffness. সহজ বাংলা: বয়স/ক্ষয়ের কারণে জয়েন্টের ব্যথা।" data-rx-term="osteoarthritis" data-rx-definition="Osteoarthritis is wear-and-tear joint disease causing pain and stiffness. সহজ বাংলা: বয়স/ক্ষয়ের কারণে জয়েন্টের ব্যথা।">Osteoarthritis
    • Osteochondral Defect Knee
    • Plica Syndrome
    • Infrapatellar Fat Pad Impingement
    • Patellar Instability
  • Neuropathies
    • Saphenous Nerve Entrapment
  • Other
    • Bakers Cyst
    • Patellar Contusion
  • Pediatric Considerations
    • Patellar Apophysitis (Sinding-Larsen-Johansson Disease)
    • Patellar Pole Avulsion Fracture
    • Tibial Tubercle Avulsion Fracture
    • Tibial Tuberosity Apophysitis (Osgood Schalatters Disease)

Symptoms of a dislocated patella

  1. An audible pop.
  2. Buckling of the knee.
  3. Intense pain.
  4. Sudden swelling.
  5. Bruising at the knee.
  6. Locking of the knee.
  7. Inability to walk.
  8. The kneecap is visually out of place.
  9. A popping sensation.
  10. Swelling or stiffness.
  11. Pain, especially when twisting or rotating your knee.
  12. Difficulty straightening your knee fully.
  13. Feeling as though your knee is locked in place when you try to move it.
  14. Feeling of your knee giving way.

Diagnosis

Clinical example of the laterally dislocated patella
  • History
    • Most describe the pain and potentially a noticeable deformity of the knee
    • Usually preceded by direct trauma to the knee or a sudden change in direction
    • Many describe a sense of giving way or instability when the dislocation occurs
    • Feel a pop or multiple pops and there may be generalized pain in the anteromedial knee
  • Exam: Physical Exam Knee
    • The acutely dislocated patella is typically easy to see
    • May have joint effusion or hemarthrosis (#2 cause in pediatrics behind ACL[6])
    • Carefully identify the patellar poles, medial and lateral joint lines, and retinaculum
    • Palpable tenderness along the medial retinaculum or MPFL may be appreciable
    • Patellar laxity, looseness, or increased motion may be noted
    • Important to stress other structural ligaments if possible
    • Range of motion is very limited in dislocation, may be intact in subluxation
    • Strength testing can be limited in knee extension, hip abduction
    • Normal patellar glide medially and laterally is between 25-50% of the width of the patella
    • Other findings include femoral anteversion, patella Alta, tibial torsion, genu recurvatum, genu valgum or varum, pes planus, and general ligamentous laxity
  • Special tests
    • Special tests may need to be deferred in the acute setting depending on how symptomatic the patient is
    • Consider evaluating for ligamentous laxity using the Beighton Score[7]
    • Patellar Apprehension Test: Apply medial and lateral pressure to the patella testing for apprehension
    • Patellar J Sign: Evaluate path of the patella during flexion and extension

Radiographs

  • Standard Radiographs Knee
    • Ideally, standard AP and lateral weight-bearing views, as well as sunrise view
    • It May not be possible in the setting of acute dislocation
  • Plain radiography
    • Help identify fractures of the patella, avulsion fractures, loose bodies, and sometimes large cartilage defects
    • PA radiographs at 45 degrees flexion may aid in the assessment of the coronal alignment of the tibiofemoral joint
  • Lateral views and Sunrise or Merchant views
    • Provide information to trochlear morphology, patellar height, and patellar tilt
  • Lateral patellar Tilt
    • Assessed by the lateral patellofemoral angle on sunrise or merchant view
    • Angle is measured between a line along the subchondral bone of the lateral trochlear facet and posterior femoral condyles
    • Normal: angle greater than 11° that opens laterally
    • Abnormal angles: parallel or open medially
  • Patellar height
    • Can be measured by both direct and indirect methods
    • The Insall-Salvati Ratio: ratio measuring the length of the patella ligament, patellar length
      • A normal ratio is 1.0; a ratio of 1.2 suggests patella Alta and 0.8 patella Baja
    • Caton-Deschamps index: distance between the distal point of the patellar articular surface and the anterior superior margin of the tibia, divided by the patellar articular surface length
      • A normal ratio is 1.0; a ratio of less than 0.6 suggests patella baja and a ratio of 1.3 suggests patella alta
    • Blackburne-Peel method (BP): ratio of the height of the lower pole of the articular surface above a tibial plateau line to the articular surface length of the patella
      • Normal between 0.54- 1.06; A ratio of less than 0.54 is considered to be patella Alta
    • The technique described by Blumensaat uses the roof of the intercondylar notch as a reference line and is one of the most commonly used direct methods for the assessment of patellar height
  • True lateral radiographs and sunrise views can help identify other risk factors
    • The trochlear findings were elucidated by Dejour and Le Coultre and were subsequently revised to create the trochlear dysplasia classification system [10]
    • Crossing sign: occurs when the trochlear groove lies in the same plane as the anterior border of the lateral condyle, which represents a flattened trochlear groove
    • Double contour sign: occurs when the anterior border of the lateral condyle lies anterior to the anterior border of the medial condyle, which represents a convex trochlear groove or hypoplastic medial condyle
    • A supratrochlear spur can arise from the proximal aspect of the trochlea and can also indicate a risk factor

CT

  • Computed tomographic (CT)
    • Can more accurately characterize the morphology of the trochlea
    • Assess femoral and tibial torsion
  • Tibial tubercle to trochlear groove (TT-TG) distance
    • Assesses relative rotation of femur to the tibia
    • The TT-GG distance is between two perpendicular lines; one from the posterior cortex to the tibial tubercle and one from the posterior cortex to the trochlear groove
    • Average 8-10 mm in pediatric and adult patients; a TT-TG distance of greater than 20 is highly associated with patellar instability.

MRI

  • Indicated if any evidence of loose body or Osteochondral Lesion on radiographs
  • Common Findings[11]
    • The bruising pattern of the lateral femoral condyle, medial patella
    • Disruption of the MPFL (at the medial femoral epicondyle insertion)
    • Articular cartilage injuries if present

Classification

Dejour Classification of Trochlear Dysplasia

  • Type A: flatter than normal with a sulcus angle greater than 145°
  • Type B: which is flat
  • Type C: which is convex
  • Type D: which is convex with a supratrochlear spur

Treatment

Patellar Dislocation Reduction

  • Acute dislocations require reduction
  • Consideration should be made to transfer the patient to the emergency department depending on the clinical context
  • The patient will require some degree of analgesia, possibly procedural sedation
  • Procedure
    • A dislocation should be obvious
    • The patient should have his knee in a resting position of slight flexion
    • With a distal hand gently extend the knee
    • Simultaneously, the proximal hand applies gentle medial pressure to the patella
    • As the knee extends, the patella should slide over the lateral femoral condyle and pop into the groove
    • Patients typically feel much better after reduction is complete

Nonoperative

  • Indications
    • First-time dislocation
    • No evidence of osteochondral defect, intra-articular damage
  • Relative rest from offending activities
  • NSAIDS, Ice Therapy
  • Patellar J Brace
    • Often helpful initially to provide additional stability
  • Kinesiology Tape can be considered
    • Especially McConnell technique
  • Physical Therapy
    • Begin around 2-4 weeks

Operative

  • Indications
    • Presence of osteochondral defect or loose body
    • Subluxation of the patella on sunrise view
    • Failure to improve with conservative management
    • Anatomic factors predisposing to dislocation
    • Recurrent Dislocation
  • Technique
    • Arthroscopy with or without open debridement
    • MPFL repair (re-attachment) or reconstruction (proximal realignment)
    • Lateral release (distal realignment)
    • Tibial Osteotomy (distal realignment)
    • Trochleoplasty
Doctor visit helper

Prepare before seeing a doctor

A simple rural-patient checklist to help you explain symptoms clearly, ask better questions, and avoid unsafe self-treatment.

Safety note: This is not a prescription or diagnosis. For severe symptoms, pregnancy danger signs, children with serious illness, chest pain, breathing difficulty, stroke-like weakness, or major injury, seek urgent care.

Which doctor may help?

Orthopedic doctor, rheumatologist, or physiotherapist depending on cause.

What to tell the doctor

  • Write which joints hurt, swelling, morning stiffness duration, fever, injury, and walking difficulty.
  • Bring X-ray, uric acid, ESR/CRP, rheumatoid factor, or previous reports if available.

Questions to ask

  • Is this injury, osteoarthritis, rheumatoid arthritis, gout, infection, or another cause?
  • Which exercises, supports, or lifestyle changes are safe?
  • Do I need blood tests or X-ray?

Tests to discuss

  • Joint examination and range of motion
  • X-ray when chronic arthritis or injury is suspected
  • ESR/CRP, uric acid, rheumatoid tests when inflammatory arthritis is suspected

Avoid these mistakes

  • Do not ignore hot swollen joint with fever.
  • Avoid repeated steroid injections/tablets without a clear diagnosis and follow-up.

Medicine safety and first-aid guide

This section is for patient education only. It does not replace a doctor, pharmacist, or emergency care.

Safe first steps

  • Rest, drink safe water, and observe symptoms carefully.
  • Keep a written note of symptoms, duration, temperature, medicines already taken, and allergy history.
  • Seek medical care quickly if symptoms are severe, worsening, or unusual for the patient.

OTC medicine safety

  • For mild pain or fever, ask a registered pharmacist or doctor before using common over-the-counter pain/fever medicines.
  • Do not combine multiple pain medicines without advice, especially if you have kidney disease, liver disease, stomach ulcer, asthma, pregnancy, or take blood thinners.
  • Do not give adult medicines to children unless a qualified clinician advises it.

Avoid these mistakes

  • Do not start antibiotics without a proper medical decision.
  • Do not use steroid tablets or injections casually for quick relief.
  • Do not delay emergency care because of home remedies.

Get urgent help if

  • Severe symptoms, confusion, fainting, breathing difficulty, chest pain, severe dehydration, or sudden weakness need urgent medical care.
Medicine names, dose, and timing must be decided by a qualified clinician or pharmacist after checking age, pregnancy, allergy, other diseases, and current medicines.

For rural patients and family caregivers

Patient health record and symptom diary

Write your symptoms, medicines already taken, test results, and questions before visiting a doctor. This note stays on your device unless you print or copy it.

Doctor to discuss: Doctor / qualified healthcare provider
Tests to discuss with doctor
  • Basic vital signs: temperature, pulse, blood pressure, oxygen level if needed
  • Relevant blood, urine, imaging, or specialist tests only after clinical assessment
Questions to ask
  • What is the most likely cause of my symptoms?
  • Which warning signs mean I should go to emergency care?
  • Which tests are really needed now?
  • Which medicines are safe for my age, pregnancy status, allergy, kidney/liver/stomach condition, and current medicines?

Emergency warning signs such as chest pain, severe breathing difficulty, sudden weakness, confusion, severe dehydration, major injury, or loss of bladder/bowel control need urgent medical care. Do not wait for online information.

Safe pathway to proper treatment

Care roadmap for: Dislocated Kneecap

Use this simple roadmap to understand the next safe steps. It is educational and does not replace examination by a doctor.

Go to emergency care if you notice:
  • Severe or rapidly worsening symptoms
  • Breathing difficulty, chest pain, fainting, confusion, severe weakness, major injury, or severe dehydration
Doctor / service to discuss: Qualified healthcare provider; specialist depends on symptoms and examination.
  1. Step 1

    Check danger signs first

    If danger signs are present, seek emergency care and do not wait for online information.

  2. Step 2

    Record the symptom story

    Write when symptoms started, severity, medicines already taken, allergies, pregnancy status, and test results.

  3. Step 3

    Visit a qualified clinician

    A doctor, nurse, or qualified healthcare provider can examine you and decide which tests or treatment are needed.

  4. Step 4

    Do only useful tests

    Do tests after clinical assessment. Avoid unnecessary tests, random antibiotics, or repeated medicines without diagnosis.

  5. Step 5

    Follow up and return early if worse

    If symptoms worsen, new warning signs appear, or treatment is not helping, return for review quickly.

Rural patient practical tips
  • Take a written symptom diary and all previous prescriptions/test reports.
  • Do not hide medicines already taken, even herbal or over-the-counter medicines.
  • Ask which warning signs mean urgent referral to hospital.

This roadmap is for education. A real diagnosis and treatment plan requires history, examination, and clinical judgment.

RX Patient Help

Ask a health question safely

Write your symptom story. A health professional or site editor can review it before any answer is prepared. This box is not for emergency care.

Emergency first: Severe chest pain, breathing trouble, unconsciousness, stroke signs, severe injury, heavy bleeding, or rapidly worsening symptoms need urgent local medical care now.

Frequently Asked Questions

Is this article a replacement for a doctor?

No. It is educational content only. Patients should consult a qualified clinician for diagnosis and treatment.

When should I seek urgent care?

Seek urgent care for severe symptoms, rapidly worsening condition, breathing difficulty, severe pain, neurological changes, or any emergency warning sign.

References

Add references, clinical guidelines, textbooks, journal articles, or trusted medical sources here. You can edit this area from the RX Article Professional Blocks panel.

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