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Health condition · Clinically reviewed

Knee cartilage injury, graded, imaged and repaired on a specialist ladder.

From a twisted knee that will not settle to a full-thickness chondral defect, this guide walks through UK diagnosis and treatment - MRI, arthroscopy, microfracture, OATS and MACI.

Jump to treatment
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 UK-registered clinician before publication.

  • 02

    Sourced from guidance

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

  • 03

    Current for 2026

    Reflects modern UK cartilage repair pathways including microfracture, OATS and MACI at specialist commissioned centres.

Key facts

Knee cartilage injury at a glance.

The essentials, in plain English - what it is, how it is graded and how it is treated on the UK cartilage repair pathway.

  • What it is

    Damage to the articular (hyaline) cartilage lining the knee joint surfaces, ranging from softening to full-thickness defects exposing bone.

  • How it happens

    Traumatic (twisting injury, osteochondral fracture, patellar dislocation), overuse, osteochondritis dissecans (OCD), or degenerative wear.

  • Not a meniscal tear

    Meniscal cartilage is a separate structure and is graded and repaired differently - see our meniscal tear guide.

  • How it is graded

    Outerbridge and ICRS classifications grade 0 (normal) to grade 4 (subchondral bone exposed).

  • How it is diagnosed

    Specialist musculoskeletal MRI is the first-line imaging test; arthroscopy is both diagnostic and therapeutic.

  • How it is treated

    A stepped ladder from physiotherapy to microfracture, OATS and MACI - decided in a specialist commissioned cartilage repair MDT.

Why this guide matters

A staged pathway, not a one-shot fix.

Cartilage injuries are common, gradable and - with the right ladder - often treatable. Three principles shape the rest of this page.

  • Grading drives treatment

    Outerbridge and ICRS grades 0 to 4 sort softening from full-thickness loss and decide whether physio, microfracture, OATS or MACI is the right step.

  • MRI first, arthroscopy second

    Specialist musculoskeletal MRI is the first-line UK imaging test. Arthroscopy is used to confirm findings and treat at the same sitting.

  • Repair happens in centres

    Microfracture, OATS and MACI are specialist commissioned procedures with defined MDT pathways at UK cartilage repair centres.

How the diagnosis is made

From injury to a clear repair plan.

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

  1. 01

    Assessing

    History and mechanism

    A specialist takes a careful history - the twisting fall, the dislocated kneecap, the training load - to shortlist likely diagnoses.

  2. 02

    Assessing

    Clinical examination

    Effusion, joint-line tenderness, range of movement, patellar tracking and ligament stability all guide the next steps.

  3. 03

    Assessing

    Specialist musculoskeletal MRI

    MRI is the first-line imaging test - it detects cartilage lesions, subchondral bone injury and associated meniscal or ligament tears. See our private MRI scan guide.

  4. 04

    Confirming

    MRI arthrogram (selective)

    When standard MRI is inconclusive, a contrast MRI arthrogram gives a clearer picture of small chondral flaps and loose fragments.

  5. 05

    Confirming

    Diagnostic arthroscopy

    A specialist orthopaedic keyhole procedure - both diagnostic and often therapeutic - grading the defect under direct vision using ICRS.

  6. 06

    Planning

    Cartilage repair MDT

    Complex defects are discussed at a specialist commissioned cartilage repair centre where surgeons, radiologists and physiotherapists agree the plan.

  7. 07

    Planning

    Personalised treatment plan

    The MDT matches defect size, depth, location and your goals to the right intervention on the BASK ladder.

Typical timeline: a first specialist visit to a settled plan in weeks, not months.

Symptoms

What a cartilage injury feels like.

The classic mix of pain, swelling and mechanical symptoms - and the features that mean it is time for specialist review.

  • Activity-related knee pain

    A deep, aching pain worse with loading, stairs, squats and impact sport - often localised to one compartment.

  • Swelling and effusion

    Recurrent joint swelling after activity is a classic sign of a cartilage or subchondral injury.

  • Mechanical locking

    A loose osteochondral fragment can jam in the joint, producing true locking that stops the knee moving.

  • Catching and giving way

    A cartilage flap catches under the femoral condyle, giving a sharp sensation and a feeling of instability.

  • Reduced range of movement

    Loss of full flexion or extension - sometimes with a soft block - suggests loose bodies or intra-articular pathology.

  • Post-traumatic onset

    Symptoms often start after a specific twisting injury, patellar dislocation or a fall onto a flexed knee.

  • Progressive symptoms

    Untreated defects tend to enlarge over time and can accelerate post-traumatic osteoarthritis.

  • Red flag - true locked knee

    A knee stuck in flexion needs urgent specialist orthopaedic review - a displaced osteochondral fragment may be trapped.

Treatment

The UK cartilage repair ladder.

Physiotherapy and offloading first, selective injections and arthroscopy next - and dedicated repair procedures for larger defects at specialist commissioned centres.

  • Activity modification and physiotherapy

    The BASK first step - offloading the compartment, quadriceps and hip strengthening, and a graded return to sport with a specialist musculoskeletal physiotherapist.

  • NSAIDs and adjuncts

    Short-course anti-inflammatories for symptom control. Glucosamine and chondroitin have limited evidence but are used by some patients.

  • Hyaluronic acid or PRP injection

    Selective specialist injections that can settle symptoms in smaller defects or early osteoarthritis while other options are considered.

  • Arthroscopic debridement

    A specialist keyhole procedure to trim unstable cartilage flaps and remove loose bodies - useful for symptom relief in selected cases.

  • Microfracture

    A marrow-stimulation technique for small, contained defects performed at specialist commissioned centres - see our microfracture guide.

  • OATS - osteochondral autograft or allograft

    Transplantation of a cylindrical plug of bone and cartilage into the defect - suited to focal lesions of the femoral condyle at specialist commissioned centres.

  • MACI or ACI

    Matrix-assisted or autologous chondrocyte implantation - NICE-approved in 2017 for larger defects, performed at specialist commissioned centres.

  • Osteotomy for malalignment

    A high tibial or distal femoral osteotomy realigns the joint to protect the repaired compartment - a specialist commissioned procedure.

  • Partial or total knee replacement

    For end-stage disease where the joint surface cannot be salvaged - specialist commissioned unicompartmental or total knee arthroplasty.

  • Emerging biological therapies

    Stem cell and tissue-engineering approaches remain investigational and are only offered inside specialist commissioned research pathways.

What this guide is based on

The sources behind every claim on this page.

UK national guidance and specialist 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 specialist orthopaedic surgeon knows your knee and history and can tell you which parts apply to you. If in doubt, get seen.

  • British Association for Surgery of the Knee (BASK). Meniscal and cartilage repair standards of care.

  • NICE TA477. Autologous chondrocyte implantation using chondrosphere for treating symptomatic articular cartilage defects of the knee (2017).

  • NICE IPG379. Mosaicplasty for symptomatic articular cartilage defects of the knee.

  • International Cartilage Regeneration and Joint Preservation Society (ICRS). Cartilage injury classification.

  • NHS England. Specialised services clinical commissioning policy for cartilage repair.

Red flags

When a knee injury needs urgent attention.

Most cartilage injuries can be worked up in outpatients. These situations are not - and where a specialist opinion is needed sooner.

  • True locked knee

    A knee held in flexion that will not straighten - a displaced osteochondral or meniscal fragment may be trapped. Needs urgent specialist orthopaedic review.

  • Acute haemarthrosis

    A large, tense swelling within hours of injury suggests an osteochondral fracture, ACL tear or patellar dislocation. Seek same-day assessment.

  • Patellar dislocation

    A first-time dislocation can shear an osteochondral fragment from the trochlea or patella - request an MRI and specialist review.

  • Adolescent knee pain and swelling

    In young patients, osteochondritis dissecans (OCD) can cause progressive symptoms and needs specialist paediatric orthopaedic input.

  • Persistent effusion

    A knee that repeatedly swells over weeks - not just after heavy exercise - deserves specialist musculoskeletal imaging.

  • Post-traumatic osteoarthritis risk

    Untreated full-thickness cartilage loss accelerates arthritis - see our knee arthritis and knee joint osteoarthritis guides.

  • Instability after injury

    Giving way suggests combined ligamentous or meniscal pathology - a specialist should co-assess before rehabilitation.

  • Fever and hot swollen knee

    Septic arthritis is a surgical emergency and can mimic a mechanical flare - seek urgent care.

Living with it

A treatable condition, with a clear ladder.

Four things that make the biggest difference day to day - respect the compartment, build strength, manage weight, and escalate when mechanical symptoms arrive.

A quiet reminder

Consistency beats intensity, every time.

Small, steady habits - kept up for months - do more for a knee than a heroic week that does not last.

  1. 01 Load

    Respect the compartment

    Modify sport and daily loading around the affected compartment - your physiotherapist will guide impact, cycling and strength work.

  2. 02 Strength

    Quadriceps and hip work

    Well-drilled quadriceps and gluteal strength unload cartilage and improve symptoms - keep it up long after the pain settles.

  3. 03 Weight

    Body-weight optimisation

    Every extra kilogram multiplies joint load. A modest weight loss often translates into a large symptom improvement.

  4. 04 Escalate

    Do not accept locking

    Mechanical symptoms - locking, catching, giving way - deserve specialist orthopaedic review, not more time and hope.

Frequently asked

Everything we get asked about knee cartilage injury.

Quick answers on grading, MRI, arthroscopy and the UK repair ladder from microfracture to MACI.

  • What is a knee cartilage injury?

    It is damage to the articular (hyaline) cartilage that lines the ends of the femur, tibia and back of the patella. It ranges from softening and fibrillation to full-thickness defects that expose the underlying bone. It is separate from a meniscal cartilage tear, which affects the fibrocartilage wedges between the bones.

  • How is a cartilage injury different from a meniscal tear?

    The meniscus is a fibrocartilage shock absorber between the femur and tibia. Articular cartilage is the smooth hyaline lining on the bone ends. They can occur together but are graded and treated differently. See our meniscal tear guide for how meniscal injuries are managed.

  • How is the injury graded?

    Surgeons use the Outerbridge or ICRS grading system - grade 0 is normal, grade 1 is softening, grade 2 is partial-thickness fibrillation, grade 3 is deep fissuring and grade 4 is full-thickness loss exposing subchondral bone. The grade influences which treatment is offered.

  • Do I need an MRI or can I just have an arthroscopy?

    Specialist musculoskeletal MRI is the first-line imaging test in the UK because it is non-invasive and gives information about cartilage, bone, ligaments and menisci. Arthroscopy is used when the diagnosis is uncertain or when a therapeutic procedure is planned at the same time.

  • Will I need cartilage surgery?

    Not always. Many patients settle with activity modification, physiotherapy and selective injections. Surgery is considered when symptoms persist despite conservative care, when there is mechanical locking, or when a defect is large enough that a repair procedure is likely to help - decided at a specialist commissioned cartilage repair MDT.

  • What is the difference between microfracture, OATS and MACI?

    Microfracture stimulates the marrow to fill small defects with fibrocartilage. OATS transplants plugs of bone and hyaline cartilage into the defect. MACI (matrix-assisted autologous chondrocyte implantation) grows your own cartilage cells on a scaffold and implants them - NICE-approved in 2017 for larger defects. All three are performed at specialist commissioned centres.

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