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Health condition · Clinically reviewed

Patella instability, from a first dislocation to a lasting fix.

A kneecap that slips or gives way isn’t something to just tape up and ignore. Most first episodes settle with physiotherapy - some need more.

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A radiographer guides a patient onto the bed of an advanced 3 Tesla MRI scanner in a London imaging suite

Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a registered UK clinician before publication.

  • 02

    Sourced from guidance

    Checked against NICE, BOA and peer-reviewed orthopaedic sources you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK practice including MPFL reconstruction thresholds and physiotherapy-first rehab.

Key facts

Patella instability at a glance.

The essentials, in plain English - what it is, who it affects, and how it’s treated in the UK today.

  • What it is

    The kneecap (patella) slips partly or fully out of its groove (the trochlea) during bending or twisting movements.

  • Who it affects

    Most common in adolescents and young adults, and more frequent in females than males.

  • Main causes

    A shallow trochlear groove, a high-riding kneecap, loose ligaments, or misaligned lower limbs raise the risk.

  • First episode

    Usually managed with a short period of bracing followed by physiotherapy rather than surgery.

  • Recurrence

    Common after a first dislocation - roughly one in three young patients has another episode.

  • When surgery helps

    MPFL reconstruction is considered for recurrent instability or high-risk anatomy identified on MRI.

Why this guide matters

The first dislocation shapes everything after it.

What happens in the weeks after a first patellar dislocation - and how carefully the anatomy is assessed - influences whether it happens again.

  • Most first episodes don’t need surgery

    Bracing followed by focused physiotherapy is the standard first step for the great majority of first-time dislocations.

  • Anatomy drives the risk of recurrence

    A shallow trochlear groove, a high-riding kneecap or loose ligaments make another episode more likely - MRI helps identify these.

  • Recurrent instability deserves a specialist opinion

    Repeated dislocations, or high-risk features on imaging, are a reasonable trigger to discuss surgical options.

How the diagnosis is made

From a giving-way knee to a clear plan.

The steps a UK GP, physiotherapist or orthopaedic specialist will normally follow, in order - so you know what to expect and why.

  1. 01

    Assessing

    History and mechanism

    What the knee was doing at the moment it gave way - twisting, pivoting, or direct contact - and whether it has happened before.

  2. 02

    Assessing

    Apprehension test

    The clinician gently pushes the kneecap sideways - a flinch or muscle guard supports a diagnosis of instability.

  3. 03

    Assessing

    Alignment and gait assessment

    Looking at knee position, foot posture and how the kneecap tracks as the knee bends and straightens.

  4. 04

    Confirming

    X-ray after a dislocation

    Checks for a fracture, loose bone fragment, or bony abnormality that needs urgent attention.

  5. 05

    Confirming

    MRI scan

    Assesses the medial patellofemoral ligament (MPFL), cartilage surfaces and the shape of the trochlear groove.

  6. 06

    Preparing

    Specialist orthopaedic referral

    Recommended after a first dislocation with high-risk features, or after any recurrent episode.

  7. 07

    Preparing

    Surgical planning if needed

    For recurrent or high-risk cases, imaging findings guide the choice between MPFL reconstruction, osteotomy or trochleoplasty.

Typical timeline: a first assessment to a settled rehab plan in one to two weeks.

Symptoms

What patella instability actually feels like.

From a subtle sense of apprehension to a visible, painful dislocation - and the features that mean it’s time to escalate.

  • A feeling the knee will give way

    A sense of instability or apprehension, particularly when twisting, pivoting or descending stairs.

  • Visible dislocation

    The kneecap appears displaced to one side, usually the outer side of the knee, after a twisting injury.

  • Sudden, severe pain

    Sharp pain at the front of the knee at the moment of dislocation, often followed by an inability to straighten the leg.

  • Rapid swelling

    The knee often swells within hours of a dislocation as blood collects inside the joint.

  • Recurrent instability

    Repeated episodes of the kneecap slipping or dislocating after a first-time injury.

  • Anterior knee pain

    Aching or discomfort at the front of the knee, especially with squatting, kneeling or climbing stairs.

  • Onset in adolescence

    Symptoms often begin during growth spurts, when bone and ligament development can affect kneecap tracking.

  • Red flag - locked or unable to weight-bear

    A knee that will not straighten or bear weight after a dislocation needs urgent assessment.

Treatment

How patella instability is treated in the UK.

Bracing and physiotherapy first for most first-time dislocations - surgery reserved for recurrent or high-risk cases.

  • Closed reduction

    If the kneecap has not gone back into place on its own, a clinician repositions it under gentle traction, usually with pain relief.

  • Brief bracing or immobilisation

    A short period in a knee brace protects the joint while early swelling and pain settle, typically one to three weeks.

  • Physiotherapy - quadriceps strengthening

    Targeted strengthening of the quadriceps, particularly the VMO (vastus medialis obliquus), improves how the kneecap tracks in the groove.

  • Patellar taping and bracing

    Taping techniques and functional braces support tracking during rehabilitation and return to activity.

  • Activity modification

    Temporary changes to pivoting sports or high-twist activities while the knee regains strength and control.

  • MPFL reconstruction

    Surgical reconstruction of the medial patellofemoral ligament for recurrent instability or high-risk anatomical features.

  • Tibial tuberosity osteotomy

    Repositions the attachment point of the patellar tendon for select cases with significant malalignment.

  • Trochleoplasty

    Reshapes a markedly shallow or dysplastic trochlear groove in complex, carefully selected cases.

What this guide is based on

The sources behind every claim on this page.

UK national guidance and orthopaedic society standards, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your GP or orthopaedic specialist knows your knee and history and can tell you which parts apply to you. If in doubt, get seen.

  • NICE Clinical Knowledge Summaries. Knee pain - assessment.

  • British Orthopaedic Association (BOA). Patellofemoral instability guidance.

  • British Journal of Sports Medicine. Management of first-time and recurrent patellar dislocation.

  • Royal College of Surgeons. Patellar instability - surgical management overview.

Red flags

When a kneecap injury needs urgent attention.

Most dislocations can be managed calmly. These are the situations that need same-day or emergency assessment.

  • Locked knee

    A knee that will not straighten after a dislocation may have a loose cartilage or bone fragment trapped in the joint - seek urgent assessment.

  • Open wound over the knee

    Any break in the skin over a dislocated joint needs emergency care to rule out an open (compound) injury.

  • Loss of sensation or pulse below the knee

    Numbness, pallor or a weak pulse in the foot after dislocation can signal nerve or blood vessel injury and needs immediate emergency review.

  • Visible bony deformity

    A grossly deformed knee, or suspicion of an associated fracture, warrants same-day X-ray and orthopaedic assessment.

  • Recurrent dislocation with instability

    Multiple episodes without improvement point towards a structural cause that a specialist opinion should assess.

  • Significant haemarthrosis

    Rapid, tense swelling within hours suggests bleeding inside the joint and should be reviewed promptly.

  • Failure to weight-bear

    Inability to put any weight through the leg after injury needs same-day assessment to exclude a fracture.

  • Fever or hot, red knee

    Warmth, redness and fever after injury or aspiration raise concern for joint infection and need urgent review.

  • Progressive cartilage damage

    Worsening grinding, catching or swelling over time may indicate ongoing cartilage injury that needs specialist reassessment.

Living with it

A treatable condition, with a clear rehab path.

Four things that make the biggest difference day to day - sticking with rehab, easing back into sport, using bracing when it helps, and knowing when to ask for more.

A quiet reminder

Strength rebuilds confidence, not the other way round.

A knee that feels strong stops feeling unstable - which is exactly why the physiotherapy matters as much as any brace.

  1. 01 Rehab

    Stick with the physiotherapy plan

    Consistent quadriceps and hip strengthening over several months meaningfully lowers the chance of another dislocation.

  2. 02 Movement

    Ease back into twisting sports

    Return to pivoting or contact sport gradually, guided by strength and confidence rather than a fixed calendar date.

  3. 03 Support

    Use bracing during higher-risk activity

    A patellar stabilising brace can add confidence and support while strength is rebuilt.

  4. 04 Escalate

    Ask about surgery if it keeps happening

    Repeated dislocations despite good rehabilitation are a reasonable trigger for a specialist surgical opinion.

Frequently asked

Everything we get asked about patella instability.

Quick answers on dislocation, physiotherapy, MPFL reconstruction and recurrence.

  • What is patella instability?

    It is a condition where the kneecap moves abnormally, or dislocates, from its normal groove (the trochlea) during knee movement. It ranges from a feeling of the knee giving way to a full, visible dislocation.

  • Who gets patella instability?

    It is most common in adolescents and young adults, and occurs more often in females. Risk factors include a shallow trochlear groove, a high-riding kneecap, loose ligaments, and abnormal alignment of the lower limb.

  • What should I do if my kneecap dislocates?

    Seek assessment promptly. If the kneecap has not gone back into place, a clinician can perform a closed reduction. An X-ray is usually taken afterwards to check for a fracture or bony injury.

  • Will I need surgery after a first dislocation?

    Most first-time dislocations are managed without surgery - a brief period of bracing followed by physiotherapy focused on quadriceps strengthening. Surgery is considered for recurrent instability or when imaging shows high-risk anatomical features.

  • What is MPFL reconstruction?

    It is a surgical procedure that reconstructs the medial patellofemoral ligament, the main soft-tissue restraint that keeps the kneecap in its groove. It is typically offered for recurrent instability or significant ligament damage.

  • How likely is the kneecap to dislocate again?

    Recurrence after a first dislocation is common, particularly in younger patients and those with underlying anatomical risk factors. This is why physiotherapy and, where appropriate, specialist referral matter after the first episode.

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