Meniscal injury

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Menisci distribute load, contribute stability, lubricate and support proprioception. An acute traumatic tear in younger healthy tissue differs from a degenerative tear discovered during osteoarthritis assessment. Ask about loaded twist, pop, immediate or delayed swelling, joint-line pain, catching and the precise nature of locking. A true locked knee has a persistent mechanical block, often to extension; transient hesitation or movement limited by pain is different. Establish sport, occupation, previous injury and goals.

Inspect gait, alignment and effusion and assess active and passive range. Palpate medial and lateral joint lines and test meniscal compression or rotation only when pain permits. Examine ACL, PCL and collateral ligaments and the patellofemoral joint because combined injury changes treatment. Document ability to straight-leg raise and distal neurovascular function. In a grossly swollen acute knee, repeat examination after protection and swelling control because guarding lowers diagnostic accuracy.

Plain radiographs are appropriate after significant trauma and in middle-aged or older adults where osteoarthritis, fracture or loose body is plausible. They do not show meniscal tissue but prevent MRI findings being interpreted without the whole joint. MRI maps tear pattern, displacement, root attachment, cartilage and associated ligaments. Use expedited MRI for a suspected locked tear when it facilitates surgery, but do not let scanning delay urgent arthroscopic management when the clinical block is clear and access is unsafe to postpone.

Degenerative meniscal tears are frequent in asymptomatic knees and coexist with osteoarthritis. Correlate side, compartment, joint-line findings and mechanical pattern rather than treating the report. Most non-locked presentations start with progressive quadriceps and hip strengthening, range restoration, aerobic activity, swelling control and graded return. Manage weight and osteoarthritis medicines where relevant. Set a review against extension, effusion, confidence and meaningful activity.

Acute repairable tears, displaced bucket-handle tears and root injuries need early specialist discussion because biology and tissue position can change. Surgery aims to preserve functional meniscus. Repair is favoured when pattern, vascular zone, tissue quality, stability and patient factors make healing credible. Partial meniscectomy removes only irreparable unstable tissue. Correct associated ligament instability when it threatens repair. Explain that repair has longer restrictions and possible failure, whereas resection recovers faster but sacrifices load-sharing tissue.

BASK consensus pathways distinguish locked knee, acute target lesions and advanced osteoarthritis. Advanced structural arthritis is generally not an arthroscopic meniscal indication. For persistent symptoms after adequate non-operative care, confirm a matching target and revisit pain sources. NICE advises against arthroscopic lavage or debridement for osteoarthritis. Shared decisions include no surgery, further rehabilitation, repair or limited resection, with realistic likelihood of benefit rather than a promise to remove all pain.

Immediate care uses relative protection, ice if helpful, compression, elevation, simple analgesia and early safe movement. Avoid prolonged immobilisation in a stable non-locked knee. NSAID choice follows gastrointestinal, renal, cardiovascular, pregnancy and anticoagulant risk. Intra-articular steroid is not treatment for an acute repairable tear and should never be injected into an unexplained hot effusion. Thromboprophylaxis is not routine for every minor knee injury but requires individual risk assessment when immobilisation is used.

Rehabilitation after repair follows tear and fixation-specific limits for weight bearing and flexion, then progresses extension, quadriceps activation, strength, landing and pivot control. Return is criteria based rather than time alone. Reassess recurrent locking, swelling or instability for re-tear, missed ligament injury, chondral lesion or infection after surgery. Long-term prevention protects meniscal tissue, restores neuromuscular control and manages whole-joint risk instead of repeating arthroscopy for every MRI change.

Key points

Clarify mechanism, timing of swelling, joint-line pain, catching and whether the knee is truly fixed or merely painful to extend.
Examine effusion, range, joint lines, McMurray or Thessaly only when tolerated, ligament stability, patella, hip and distal neurovascular status; no single manoeuvre is definitive.
Obtain plain radiographs after trauma or when osteoarthritis is plausible. MRI is the preferred soft-tissue study when a repairable acute tear or locked knee will change management.
A true locked knee receives urgent specialist assessment and should not be sent through a routine months-long rehabilitation pathway before the mechanical block is addressed.
Most non-locked degenerative tears begin with education, progressive strength and activity rehabilitation and osteoarthritis care where applicable.
Surgery should target a defined lesion after clinical and imaging correlation, with meniscal preservation and repair preferred over unnecessary resection when feasible.
Arthroscopic lavage or debridement is not treatment for uncomplicated osteoarthritis, and an incidental MRI tear is not itself an indication.
After repair, follow the surgeon's pattern-specific loading and range protocol; restore swelling control, extension, quadriceps strength and neuromuscular function before return to pivoting activity.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Acute rotational trauma

Loaded knee flexion with twisting can split healthy meniscal tissue, creating longitudinal, radial, root or displaced bucket-handle patterns.

Degenerative tissue failure

Age-related meniscal matrix change permits horizontal or complex tearing with modest everyday load and commonly accompanies established whole-joint osteoarthritis.

Ligament-associated injury

ACL rupture increases tibiofemoral shear and rotational instability and may produce concurrent lateral or medial meniscal and cartilage damage.

Root and extrusion injury

Posterior root disruption functionally removes meniscal hoop stress, permits extrusion and accelerates focal cartilage loading and compartment osteoarthritis progression.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Loss of hoop stress
Complete radial and root tears interrupt circumferential fibres, reducing meniscal load distribution and substantially raising focal articular contact pressure.
2
Displaced fragment
A longitudinal fragment can move into the intercondylar notch and physically block extension or cause reproducible catching.
3
Vascular-zone difference
Peripheral meniscus has a better blood supply than the central white zone, influencing repair potential alongside age, pattern and stability.
4
Synovial irritation
Unstable meniscal tissue and associated chondral damage provoke reactive effusion, quadriceps inhibition and pain that may fluctuate with activity.
5
Degenerative association
Many MRI tears are part of whole-joint osteoarthritis and are not the independent cause of pain or a surgical target.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

True locked knee

Persistent fixed extension loss after a twist suggests a displaced fragment and differs from voluntary guarding or pain-limited movement.

Acute traumatic tear

Joint-line pain and delayed effusion after loaded rotation in a previously normal knee supports a focal repairable injury.

Degenerative tear

Insidious pain with osteoarthritic features and no fixed mechanical block often reflects whole-joint disease rather than an isolated surgical lesion.

Root injury

A painful pop during deep flexion with posterior joint-line symptoms and meniscal extrusion on MRI may indicate loss of root function.

Combined ACL injury

Immediate haemarthrosis, pivot mechanism and laxity suggest cruciate rupture and change meniscal repair planning.

Postoperative infection

Increasing pain, fever, wound change or large effusion after arthroscopy requires urgent aspiration and infection care.

Red flags requiring action

A fixed inability to extend rather than pain-limited movement after a twist suggests a displaced tear and requires urgent specialist review.
Large immediate haemarthrosis, gross instability or high-energy injury suggests cruciate rupture, osteochondral fracture or knee dislocation and broadens imaging and vascular assessment.
Fever, erythema and severe passive pain indicates possible septic arthritis and requires aspiration before any steroid or routine rehabilitation.
Inability to bear weight with focal bony tenderness after trauma requires fracture imaging before attributing symptoms to a meniscus.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
First-line history and examinationFirst stepFirst line
Why
Separate fixed locking, traumatic target and degenerative pain.
Interpretation and limitations
Mechanism, effusion timing, extension block, joint line and ligament findings together outperform a single provocative test.
02
Plain radiographs
Why
Exclude fracture, loose body and established osteoarthritis.
Interpretation and limitations
Obtain trauma or weight-bearing views as appropriate; normal radiographs do not exclude soft-tissue injury.
03
MRI for a surgical target
Why
Define tear displacement, root, repair potential and associated injury.
Interpretation and limitations
Use when findings will change management; degenerative signal without clinical correlation is not an indication.
04
Urgent locked-knee imaging pathway
Why
Confirm a displaced fragment when this can be done without harmful delay.
Interpretation and limitations
A clear persistent mechanical block requires urgent soft-tissue knee ownership even if MRI access is limited.
05
Aspiration for a hot effusion
Why
Exclude infection and identify crystals.
Interpretation and limitations
Send cell differential, Gram stain, cultures and crystals; do not inject steroid before infection is excluded.
06
Arthroscopic assessment
Why
Directly identify and treat a confirmed mechanical lesion.
Interpretation and limitations
It is therapeutic rather than a routine diagnostic test and should preserve repairable tissue.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

ACL injury

Immediate haemarthrosis, pop and instability after pivoting suggests cruciate rupture with or without associated meniscal damage.

Osteochondral loose body

A mobile cartilage or bone fragment can lock the knee and may follow patellar dislocation, direct trauma or osteochondral disease.

Osteoarthritis flare

Activity-related pain, brief stiffness and fluctuating effusion with degenerative change may mimic a symptomatic degenerative meniscal tear.

Patellofemoral pain

Anterior or peripatellar pain during stairs, squatting or prolonged sitting without matching joint-line findings suggests a patellofemoral source.

Septic or crystal arthritis

An acute hot painful effusion requires urgent aspiration because apparent mechanical symptoms and identified crystals do not safely exclude bacterial infection.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01LockedUrgent mechanical pathwayFirst stepThe knee has a persistent fixed extension block after a plausible injury.

1Protect the knee, document range, effusion, ligament and neurovascular findings and obtain trauma radiographs.
2DefinitiveRefer urgently to a soft-tissue knee clinician and arrange expedited MRI if it does not delay definitive care.
3Treat a displaced repairable lesion arthroscopically with meniscal preservation where feasible.
4Use pattern-specific postoperative range, loading and strength rehabilitation.

02Non-lockedRehabilitate before elective surgeryPain or intermittent catching occurs without a fixed block or urgent associated injury.

1Identify degenerative OA, ligament, patellofemoral and referred contributors with radiographs when appropriate.
2Deliver progressive strength, range, aerobic and neuromuscular rehabilitation and manage whole-joint risk.
3Review persistence against objective function and ensure any MRI lesion matches the clinical compartment.
4Discuss arthroscopy only for a defined target after adequate non-operative treatment.

03CombinedProtect meniscus and stabilise the kneeA repairable tear occurs with ACL or other ligament instability.

1Map the meniscus, cartilage and all injured stabilisers on clinical assessment and MRI.
2Plan repair, ligament treatment and timing together rather than treating each report line separately.
3Avoid unnecessary resection and document healing and re-tear risks.
4Progress return to pivoting only after swelling, motion, strength and neuromuscular criteria are met.

Key medicines and prescribing safety2 treatments · regimens, roles and cautions

Reduces pain and synovial irritation during early rehabilitation without altering the mechanical tear itself.

Short-course NSAID when suitable

Use one licensed oral NSAID at the lowest effective adult dose for the shortest period needed to support movement and rehabilitation, or a licensed topical NSAID when local treatment is sufficient.

Assess gastrointestinal, renal, liver and cardiovascular disease, blood pressure, pregnancy, anticoagulants and concurrent NSAIDs; avoid masking worsening locking, infection or fracture and stop when no functional benefit remains.

Offers short-term analgesia while examination, swelling control and rehabilitation proceed.

Paracetamol for brief rescue

If suitable, use paracetamol 500–1,000 mg orally up to every 4–6 hours as needed, maximum 4 g in 24 hours for a healthy adult, with a lower maximum in low body weight, frailty, liver disease, malnutrition or hazardous alcohol use.

Check all combination products to avoid overdose and do not allow analgesia to postpone assessment of a locked, hot or traumatically non-weight-bearing knee.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Persistent locking

A displaced fragment can maintain fixed movement loss, muscle inhibition and cartilage injury until reduced or treated.

Meniscal tissue loss

Excessive partial or subtotal meniscectomy removes load-sharing tissue, raises compartment contact stress and materially increases later symptomatic osteoarthritis risk.

Repair failure

Unfavourable tear pattern, poor tissue biology, persistent instability, smoking and premature loading can cause non-healing, recurrent symptoms or re-tear.

Quadriceps deconditioning

Pain, effusion and prolonged avoidance reduce muscle control, creating ongoing giving way despite a stable knee.

Low-value surgery harm

Arthroscopy for incidental degenerative tears can add thrombosis, infection and recovery burden without improving osteoarthritis symptoms.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Track extension, flexion, effusion, joint-line symptoms and true locking rather than pain alone.
Measure quadriceps and hip strength, gait, confidence and return-to-work or sport tasks through rehabilitation.
Reassess persistent symptoms for ligament, patellofemoral, osteoarthritic and referred sources before surgery.
After repair, monitor wound, infection, range, loading adherence and recurrent catching or swelling.
Review NSAID and analgesic toxicity and discontinue medicines that do not improve function.
Use criteria-based return and protect repaired tissue while progressively restoring pivot control.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Locking is a physical claim

Ask the patient to describe and demonstrate whether the joint is fixed, because clicking and pain inhibition are often labelled locking.

The report may be incidental

Degenerative tears are common on MRI and require symptom, side and compartment correlation before treatment.

Meniscus preservation protects load

Repair or limited resection retains hoop function better than removing all abnormal-looking tissue.

Roots behave like absence

A complete root tear disrupts circumferential load transmission and can accelerate compartment degeneration.

Swelling timing adds information

Immediate haemarthrosis suggests ligament or osteochondral injury, while delayed effusion is more compatible with isolated meniscal irritation.

Arthroscopy is not an OA wash

Removing incidental degenerative tissue does not correct the whole-joint biology of osteoarthritis.

11Common pitfallsFrequent interpretation and management errors.

01
Calling any clicking a locked knee or missing a genuine fixed extension block.
02
Diagnosing and operating from MRI without matching history, examination and radiographs.
03
Sending an urgent locked knee through prolonged routine physiotherapy before specialist review.
04
Removing repairable meniscal tissue when preservation is technically credible.
05
Offering arthroscopic lavage for uncomplicated osteoarthritis.
06
Missing associated ACL injury, osteochondral fracture or septic effusion.