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Health condition · Clinically reviewed

Knee dislocation, a limb-threatening emergency, not a bad sprain.

A true tibiofemoral dislocation tears at least three of the four major knee ligaments and puts the popliteal artery and peroneal nerve at risk. Every case needs urgent reduction, imaging and specialist care.

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 BOAST, BOA and peer-reviewed orthopaedic sources you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK trauma pathways including CT angiography, staged multi-ligament reconstruction and specialist commissioned care.

Key facts

Knee dislocation at a glance.

The essentials, in plain English - what it is, why it is different from a dislocated kneecap, and why every case is an emergency.

  • What it is

    True tibiofemoral dislocation - the tibia displaces on the femur, tearing at least three of the four major knee ligaments. A limb-threatening injury, distinct from a patellar dislocation.

  • Why it matters

    Up to a third involve popliteal artery injury and around a quarter involve peroneal nerve injury. Missing either can cost the limb.

  • Directions

    Anterior, posterior, medial, lateral or rotatory - direction predicts which structures are torn and which vessel is at risk.

  • Schenck classification

    KD I to KD V - grades by the number and pattern of ligaments torn, and whether there is fracture, vascular or nerve injury.

  • Aetiology

    High-energy - road traffic collisions, falls from height and sport - and low-energy (ultra-low-velocity) dislocations in morbidly obese patients.

  • Not the same as patellar

    A patellar dislocation is far more common, often reduces spontaneously and is a soft-tissue injury of the extensor mechanism - it is not a knee dislocation.

Why this guide matters

Three things a knee dislocation absolutely needs.

It is rare, missed easily when reduced, and unforgiving of delay. The three points below shape everything else on this page.

  • Urgent reduction, then reassessment

    Reduce the joint as a trauma emergency, then re-check pulses and nerves before and after - a normal foot on arrival does not rule out injury.

  • Routine CT angiography, every time

    BOAST is clear - image the popliteal artery in every knee dislocation, not just those with absent pulses. Late vascular injury is limb-threatening.

  • Staged multi-ligament reconstruction

    Definitive ligament work is planned in a specialist commissioned knee unit once soft tissues have settled and the vascular picture is clear.

How the diagnosis is made

From the emergency call to a specialist plan.

The steps a UK trauma team will follow in a specialist commissioned centre, in order - so you know what to expect and why.

  1. 01

    Assessing

    Emergency assessment

    Airway, breathing, circulation and mechanism - a knee dislocation is a trauma call, not a sprain. Documented as an orthopaedic emergency from the outset.

  2. 02

    Assessing

    Vascular examination

    Pulses (dorsalis pedis, posterior tibial), colour, temperature, capillary refill and ankle-brachial pressure index - repeated serially, before and after reduction.

  3. 03

    Assessing

    Neurological examination

    Peroneal nerve (foot drop, dorsal-foot sensation) and tibial nerve (plantar flexion, sole sensation) - documented before any manipulation.

  4. 04

    Confirming

    Plain X-rays

    AP and lateral views confirm direction of dislocation, associated fractures and the reduced position after manipulation.

  5. 05

    Confirming

    CT angiography

    The BOAST-recommended investigation of choice for vascular injury - performed routinely, not only when pulses are absent, in a specialist commissioned centre.

  6. 06

    Confirming

    MRI - the gold standard

    Delineates cruciate, collateral, posterolateral and posteromedial corner injuries plus meniscal and chondral damage - the map for ligament reconstruction.

  7. 07

    Planning

    MDT specialist review

    Trauma, vascular, plastic and knee-reconstruction surgeons plan reduction, vascular repair, external fixation and staged ligament work in a specialist commissioned unit.

Typical timeline: emergency reduction on arrival, definitive ligament reconstruction weeks later.

Symptoms

What a knee dislocation looks like.

Obvious in most, silently reduced in some - the features that tell a trauma team this is a limb-threatening injury and not a simple sprain.

  • Obvious deformity

    Visible malalignment of the tibia on the femur - though some dislocations reduce spontaneously and look almost normal on arrival.

  • Severe pain and swelling

    Immediate, severe pain with rapid haemarthrosis and gross swelling of the whole knee.

  • Inability to weight-bear

    The knee is completely unstable - patients cannot stand or move the limb without support.

  • Absent or asymmetric pulses

    A cold, pale foot with absent dorsalis pedis or posterior tibial pulses is a vascular emergency requiring immediate specialist input.

  • Foot drop or numbness

    Inability to dorsiflex the foot or altered sensation on the dorsum suggests common peroneal nerve injury.

  • Multi-ligament instability

    Gross laxity in more than one plane - anterior, posterior, valgus and varus - reflects torn cruciates and collaterals.

  • Ultra-low-velocity mechanism

    A simple stumble in a morbidly obese patient can produce a full knee dislocation - a well-recognised specialist pattern.

  • Red flag - suspected reduced dislocation

    Any high-energy knee injury with gross swelling and multi-ligament laxity should be treated as a reduced knee dislocation until proven otherwise.

Treatment

How a knee dislocation is treated in the UK.

The BOAST and BOA pathway - reduce, image, protect and rebuild - delivered by a specialist commissioned trauma and knee team.

  • Urgent closed reduction

    The first priority - performed under sedation or general anaesthesia as an orthopaedic emergency, with immediate re-check of pulses and nerves.

  • Post-reduction neurovascular check

    Pulses, ABPI, sensation and motor function reassessed after reduction - deterioration triggers immediate vascular imaging and surgical review.

  • CT angiography

    Routine imaging of the popliteal artery in every knee dislocation, per BOAST - specialist commissioned pathway not a discretionary test.

  • Emergency vascular repair

    Popliteal artery injury is repaired within hours by a vascular surgeon - delay beyond six to eight hours dramatically increases amputation risk.

  • External fixation or splinting

    A knee-spanning external fixator or a well-padded above-knee splint holds the joint safely reduced while soft tissues settle and further surgery is planned.

  • Fasciotomy for compartment syndrome

    Rising compartment pressures after reduction or vascular repair are treated with immediate four-compartment lower-leg fasciotomy.

  • Staged multi-ligament reconstruction

    Definitive repair or reconstruction of the cruciates and corners is planned in a specialist commissioned knee unit - see /treatments/knee-multi-ligament-reconstruction/.

  • Rehabilitation and physiotherapy

    A prolonged, protocol-driven programme with a specialist orthopaedic physiotherapy team - see /treatments/spinal-physiotherapy/.

What this guide is based on

The sources behind every claim on this page.

UK trauma standards and orthopaedic society guidance, 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.

If you suspect a knee dislocation, call 999. Every case belongs in a specialist commissioned trauma centre without delay.

  • BOAST (British Orthopaedic Association Standards for Trauma). The management of knee dislocations.

  • British Orthopaedic Association (BOA). Standards for trauma and orthopaedics.

  • NHS England. Specialist commissioned major trauma network standards.

  • Schenck RC. The dislocated knee - classification and management principles.

Red flags

When a knee dislocation becomes a limb-threatening emergency.

Every knee dislocation is urgent - these are the features that make it a race against the clock.

  • Absent or asymmetric pedal pulses

    A cold, pale or pulseless foot after a knee injury is a limb-threatening popliteal artery injury - immediate vascular surgery input in a specialist commissioned centre.

  • Expanding calf or worsening pain

    Escalating pain, tense swelling and pain on passive stretch after reduction suggest compartment syndrome - urgent fasciotomy is limb-saving.

  • Foot drop or dense numbness

    Common peroneal nerve palsy is common after knee dislocation - documented early and monitored, with specialist nerve review if recovery is slow.

  • Open dislocation

    Any wound over the joint turns this into an open injury - urgent debridement, antibiotics and combined orthoplastic care.

  • Ultra-low-velocity mechanism

    A knee dislocation after a trivial fall in a morbidly obese patient still carries the full vascular and nerve risk - do not under-investigate.

  • Spontaneously reduced dislocation

    Marked instability with a "normal" X-ray after a high-energy injury still needs CT angiography and MRI - the vascular risk is unchanged.

  • Delayed vascular repair

    Beyond six to eight hours of warm ischaemia, amputation rates rise sharply - a hard stop for delay in the emergency pathway.

  • Bilateral or polytrauma presentation

    Multiple injuries can mask a dislocated knee - a low threshold for examination and imaging under anaesthesia is essential.

  • Fixed dislocation that will not reduce

    Dimple sign over medial skin suggests a posterolateral dislocation with buttonholed femur - never repeatedly force reduction; go to theatre.

Living with it

A serious injury, with a long but real recovery.

Four things that make the biggest difference in the months after a knee dislocation - patience, specialist physiotherapy, vigilance for late problems, and realistic goals.

A quiet reminder

Rehabilitation is where the outcome is made.

Surgery reduces and reconstructs; a structured, months-long physiotherapy programme decides how well the knee actually works.

  1. 01 Recovery

    A long road, but a real one

    Full recovery from a multi-ligament knee injury is measured in months to a year or more - progress is real but rarely quick.

  2. 02 Rehab

    Physiotherapy is the treatment

    Structured, specialist-led physiotherapy is as important as the surgery - range of motion, strength and proprioception rebuilt in sequence.

  3. 03 Vigilance

    Watch for late vascular problems

    Claudication, cold foot or ulceration months later can signal a late arterial issue - report new symptoms promptly.

  4. 04 Realistic

    Return to sport is possible

    Many patients return to work and recreational sport - high-impact competitive sport is possible but individualised with the specialist team.

Frequently asked

Everything we get asked about knee dislocation.

Quick answers on emergency care, vascular risk, surgery and recovery.

  • What is a knee dislocation?

    A true knee dislocation is a tibiofemoral dislocation - the tibia displaces on the femur, tearing at least three of the four major knee ligaments (usually both cruciates and one or both collaterals). It is a limb-threatening emergency, distinct from a patellar dislocation.

  • How is it different from a dislocated kneecap?

    A patellar dislocation is a soft-tissue injury of the extensor mechanism - the kneecap slips out of its groove, often reduces on its own and is far more common. A tibiofemoral (knee) dislocation is a high-energy multi-ligament injury with a real risk to the popliteal artery and peroneal nerve.

  • Why is it treated as an emergency?

    Because up to a third involve injury to the popliteal artery. Beyond about six to eight hours of warm ischaemia, amputation rates rise sharply. Around a quarter also involve the common peroneal nerve. Every knee dislocation needs urgent reduction, serial neurovascular checks and routine CT angiography in a specialist commissioned centre.

  • What happens in the emergency department?

    The knee is reduced as an orthopaedic emergency, usually under sedation or anaesthesia. Pulses, sensation and motor function are documented before and after reduction. CT angiography is performed to assess the popliteal artery, X-rays confirm the reduced position and MRI later maps the ligament damage. The patient is admitted under a specialist trauma team.

  • Will I need surgery?

    Almost always. Vascular injury needs immediate repair. External fixation or splinting stabilises the joint while soft tissues settle. Definitive multi-ligament reconstruction is planned in stages by a specialist commissioned knee unit - see our guide to knee multi-ligament reconstruction.

  • How long is the recovery?

    Rehabilitation is prolonged - typically many months, and often a year or more before full function returns. Structured specialist orthopaedic physiotherapy is central to the outcome. Many patients return to work and recreational sport; high-impact competitive sport is possible but individualised with the surgical team.

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