Meniscus Tears

Meniscal tears are among the most common knee injuries. They occur at every age, but the pattern follows the mechanism: the young athlete tears a healthy meniscus with a twist, the middle-aged patient tears a degenerate one with minor trauma or none at all. The menisci are C-shaped fibrocartilaginous structures with critical roles in load transmission, shock absorption and joint stability.

Why preservation matters. The menisci transmit 70% of the knee's load in extension and 50% in flexion, and they increase the contact area by 50%, which lowers peak stress. Take one away and contact pressure rises by 200-300%. The clinical price is osteoarthritis: after meniscectomy for a degenerative tear, the relative risk of radiographic and symptomatic OA at 16 years was approximately 7 (Englund 2003). Repair, even when technically challenging, gives better ten-year outcomes than resection, and a young patient with a repairable tear should be offered one.

The shift in practice. The historical approach was arthroscopic partial meniscectomy for every symptomatic tear. Two randomised trials published in the NEJM in 2013, FIDELITY (Sihvonen et al) and METEOR (Katz et al), found no benefit from arthroscopic partial meniscectomy for degenerative tears, whether against sham surgery or against physiotherapy alone; the trials are set out under management. Repair techniques improved over the same period, and the modern position is to preserve meniscal tissue whenever possible.

Two populations. The traumatic tear and the degenerative tear are different diseases in different patients, and almost every decision on this page depends on which one is in front of you.

Gross anatomy. The two menisci differ in shape, mobility and attachment.

Microstructure. The meniscus is fibrocartilage: type I collagen makes up 90% of it, with proteoglycans and fibrochondrocytes. The collagen runs as circumferential fibres, which resist hoop stress, and radial tie fibres. Structurally there are three zones: a superficial zone in contact with femur and tibia, a deep transitional zone and a central lamellar zone.

Hoop stress. Load on the meniscus becomes circumferential hoop stress in those fibres, like the hoops on a barrel. A radial tear or a root tear cuts the circumferential fibres and abolishes that function: the meniscus becomes a washer with a cut in it, unable to resist extrusion and no longer load-bearing. That is why those two patterns are so damaging.

Blood supply. The perimeniscal capillary plexus, fed by the superior and inferior geniculate arteries, enters at the periphery and penetrates radially. In the adult only the outer 10-25% is vascular. Repair in the white-white zone succeeds in only 20-30%, which is why central tears are generally resected rather than sutured.

Why children heal better. Paediatric menisci carry their blood supply further toward the centre; in young children the red-white zone may extend to 50%. Tears in children therefore have better healing potential, and repair should be attempted even for more central tears.

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Function. The meniscus has five jobs.

• Load transmission
• Shock absorption: energy dissipation during loading
• Joint stability: a secondary stabiliser, especially the lateral meniscus in the ACL-deficient knee
• Joint lubrication: distribution of synovial fluid
• Proprioception: mechanoreceptors provide feedback

Tears are described first by morphology, because pattern predicts both the symptoms and the chance of repair, and then by location, depth, length and tissue quality.

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ISAKOS ClassificationBucket-Handle TearsRoot TearsDiscoid Meniscus

The ISAKOS system (International Society of Arthroscopy, Knee Surgery and Orthopaedic Sports Medicine) is the most comprehensive and widely accepted classification. Its strength is that it integrates the three things the surgical decision turns on: pattern, which determines load-bearing, location, which determines vascularity, and tissue quality, which determines healing.

Vertical

Description

Parallel to circumferential fibres, longitudinal

Mechanism

Acute trauma, twisting

Repairability

Good if peripheral

Horizontal

Description

Cleavage tear, parallel to tibial plateau

Mechanism

Degenerative, chronic

Repairability

Poor - usually resect

Radial

Description

Perpendicular to circumferential fibres

Mechanism

Acute or chronic

Repairability

Difficult - consider if root

Complex

Description

Combination of patterns

Mechanism

Chronic, degenerative

Repairability

Variable, usually poor

ISAKOS Meniscus Tear Patterns

Type	Description	Mechanism	Repairability
Vertical	Parallel to circumferential fibres, longitudinal	Acute trauma, twisting	Good if peripheral
Horizontal	Cleavage tear, parallel to tibial plateau	Degenerative, chronic	Poor - usually resect
Radial	Perpendicular to circumferential fibres	Acute or chronic	Difficult - consider if root
Complex	Combination of patterns	Chronic, degenerative	Variable, usually poor

Beyond pattern, ISAKOS records the location (anterior horn, body or posterior horn), the depth (partial, on the superior or inferior surface, or full-thickness), the length in millimetres and the tissue quality (traumatic, with good tissue, or degenerative, with poor tissue).

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Definition. A complete vertical longitudinal tear whose inner fragment has displaced into the intercondylar notch.

Presentation. Mechanical symptoms: locking, catching and an inability to extend fully, with an extension deficit of 10-30 degrees, joint line tenderness and a positive McMurray test.

Locked Knee Emergency

A locked knee from a displaced bucket-handle tear needs urgent arthroscopy, within days. The displaced fragment rubs against the femoral condyle, and prolonged displacement can damage the cartilage. Do not delay with prolonged conservative management.

Surgery. Repair is strongly preferred if the tissue quality allows, typically with 3-5 vertical mattress sutures, inside-out for the posterior horn. 40% have an associated ACL tear and may need ACL reconstruction as well. Repair succeeds in 80-85% when the tear is peripheral, under 3mm from the rim, and the long-term result is significantly better than resection, which is why repair should be attempted for a displaced bucket-handle tear.

Definition. A complete radial tear or avulsion at the root attachment to the tibia. The posterior medial root is much the commonest site, 80% of root tears; the posterior lateral root is next, and the anterior roots are rare.

What it does. The root anchors the circumferential fibres, so a root tear means complete loss of hoop stress. Functionally it is a total meniscectomy, with contact pressures comparable to total meniscectomy (LaPrade 2015) and rapid progression to OA. The meniscus extrudes, and that extrusion is what MRI shows.

Recognition. On MRI the root is discontinuous, which is a complete root tear, and the meniscus is extruded, which is the loss of hoop stress made visible. At arthroscopy the finding is a radial tear at the root with its anchorage disrupted. Either finding is an indication for urgent arthroscopy and transtibial pullout repair to restore hoop stress, the technique described under management.

Root Tears Don't Heal Without Surgery

Unlike peripheral tears, which may stabilise, root tears progressively worsen because of extrusion: the meniscus moves outward with each step, increasing contact stress. Early repair, within 3-6 months, has the best outcomes.

Definition. A developmental variant: an abnormally thick, disc-shaped meniscus, lateral in nearly every case and rarely medial. Watanabe classifies it by coverage and attachment:

• Type I (complete): the meniscus covers the entire lateral plateau
• Type II (incomplete): partial coverage, but wider than normal
• Type III (Wrisberg variant): no posterior meniscotibial ligament attachment

Presentation. Often asymptomatic until it tears. The Wrisberg type produces the snapping knee syndrome in children; otherwise the complaint is lateral knee pain with joint line tenderness.

Management. An asymptomatic discoid meniscus is observed; do not operate because it is discoid. A symptomatic tear is treated by arthroscopic saucerisation with repair of the tear, the goal being a normal C-shaped meniscus with the peripheral rim preserved: tissue kept, and a stable, functional meniscus made.

A parameniscal cyst is a collection of synovial-like fluid beside the meniscus. It almost always communicates with a meniscal tear, characteristically a horizontal cleavage tear, through a one-way valve that pumps fluid peripherally, and it is a recurring exam favourite because of how it must be treated.

Where and how it presents. Lateral cysts are commoner and more often palpable; medial cysts tend to be larger and more posterior. The patient has joint-line pain and a firm joint-line swelling, which in the lateral cyst is classically most prominent near extension and reduces with flexion.

Imaging. MRI shows the cyst contiguous with the underlying meniscal tear, which is usually horizontal.

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History. The first task is to place the patient in one of the two populations in the overview table, traumatic or degenerative. Then the questions that change management:

• True locking or pseudo-locking: true locking is an inability to extend fully
• Mechanical symptoms: catching or clicking with specific movements
• The swelling pattern, immediate or delayed
• Previous knee injuries or surgery
• Activity level and goals

Examination. Inspect for effusion, for quadriceps wasting in the chronic case, and for alignment. Palpate the joint line, tenderness there being the most sensitive single finding. Check the range of motion for an extension deficit, the bucket-handle sign, and for a painful arc, then perform the special tests, and finish with stability, Lachman for the ACL and valgus stress for the MCL, for the associated injuries.

Differential diagnosis. The symptoms attributed to a meniscal tear (joint-line pain, catching, giving way, effusion) overlap with several other conditions, and a tear seen on MRI is frequently incidental in middle-aged and older patients (Englund, NEJM 2008). Consider the breadth of differentials before blaming the meniscus.

Radiographs first. AP standing, lateral and skyline patella, with a long-leg alignment film if surgery is being considered. Radiographs cannot show a meniscal tear; their job is to exclude bony injury and the differentials, fracture, OA and loose body, and to grade the OA and the alignment. Standing films are essential if a meniscal transplant or realignment surgery is contemplated.

MRI is the gold standard, with sensitivity 90-95% and specificity 85-90%. A tear is increased signal within the meniscus on T2, graded by how far it reaches:

• Grade 0: normal
• Grade I: intrasubstance signal, no tear
• Grade II: linear signal that does not reach the surface, no tear
• Grade III: signal reaching the articular surface, a tear

Only grade III is a tear. Grades I and II are intrasubstance degeneration, are not surgical indications, and are often seen in asymptomatic patients over 45. Read the signal on two orthogonal planes, then report morphology, location, extrusion, associated chondral disease and whether the tear looks repairable, and look for the ACL, the MCL and bone marrow oedema. Extrusion of more than 3mm means a root tear or severe degeneration.

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Arthroscopy is the true gold standard when it is performed, but it is invasive, and with modern MRI it is used therapeutically more than diagnostically.

Other tests. Ultrasound is operator-dependent but can identify peripheral tears. Arthro-CT is rarely used and is reserved for patients who cannot have an MRI.

Algorithm

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The decision. Everything follows from one principle: preserve meniscal tissue wherever possible, because meniscectomy accelerates osteoarthritis. Then ask the algorithm's three questions in order, locked knee, root tear, degenerative tear in an older knee, each of which has its own answer. Only the traumatic tear that has passed all three needs the repair-versus-resection judgement that follows.

Conservative ManagementSurgical Decision-MakingRepair TechniquesRoot Repair

Who. Non-operative treatment is the first line for:

• Degenerative tears in patients over 45 years (FIDELITY and METEOR trials)
• Small stable tears without mechanical symptoms
• Grade I-II MRI signal, which is intrasubstance degeneration
• Patient choice or medical comorbidity

Conservative Treatment Protocol

AcuteInitial Phase (0-6 weeks)

• Activity modification: avoid twisting, pivoting and squatting
• Ice and NSAIDs for symptom control
• Quadriceps strengthening: straight leg raises, quad sets
• Gentle flexion-extension range of motion

ProgressiveRehabilitation (6-12 weeks)

• Comprehensive physiotherapy programme
• Progressive resistance strengthening of quadriceps and hamstrings
• Proprioception training: balance exercises
• Functional, sport-specific training

OngoingMaintenance

• Continue strengthening
• Avoid deep squatting
• Weight management to reduce knee load
• Corticosteroid or hyaluronic acid injection if symptoms persist

A degenerative or complex tear in the white-white zone is given six months of this programme before partial resection is considered for the patient who fails it.

FIDELITY and METEOR Trials - Changed Practice

Two NEJM 2013 randomised trials reshaped management of degenerative tears. FIDELITY (Sihvonen et al, n=146, age 35-65, no OA) found arthroscopic partial meniscectomy no better than sham surgery at 12 months. METEOR (Katz et al, n=351, age 45+, with mild-to-moderate OA) found surgery plus physiotherapy no better than physiotherapy alone at 6 and 12 months, though 30% of the physiotherapy-only group crossed over to surgery within 6 months. Together they support a trial of physiotherapy first for degenerative tears.

Clear indications. Surgery is the answer for:

• A locked knee from a bucket-handle tear (urgent)
• Significant mechanical symptoms, catching or locking, despite conservative treatment
• A young patient with a traumatic tear, where repair is attempted
• A root tear with meniscal extrusion, to restore hoop stress
• A repairable tear in the vascular zone, to preserve the meniscus

Conservative first. A degenerative tear in a patient over 45, a small stable tear without mechanical symptoms, and the patient with advanced OA, whom surgery will not help.

Repair or resect. For the tear that needs surgery, the choice is set by where it is, what shape it is, what the tissue is like and who the patient is. A symptomatic radial or posterior root tear in the 30-50 age group is repaired to preserve the meniscus. In the young patient with an ACL injury and a repairable peripheral tear, the ACL is reconstructed and the meniscus repaired together, because the stable knee protects the repair.

Location

Repair

Peripheral (under 3mm from rim)

Resection

Central (white-white zone)

Pattern

Repair

Vertical, longitudinal

Resection

Horizontal, complex, degenerative

Tissue quality

Repair

Good (traumatic)

Resection

Poor (degenerative, frayed)

Length

Repair

Over 10mm

Resection

Short or flap tear

Age

Repair

Young (prefer repair)

Resection

Older (accept resection)

Stability

Repair

Stable rim

Resection

Unstable, fragmented tissue

Repair vs Resection Decision

Factor	Repair	Resection
Location	Peripheral (under 3mm from rim)	Central (white-white zone)
Pattern	Vertical, longitudinal	Horizontal, complex, degenerative
Tissue quality	Good (traumatic)	Poor (degenerative, frayed)
Length	Over 10mm	Short or flap tear
Age	Young (prefer repair)	Older (accept resection)
Stability	Stable rim	Unstable, fragmented tissue

Mnemonic

REPAIRREPAIR - Indications for Meniscus Repair

R

Red-red or red-white zone

Peripheral location with blood supply

E

Edge distance under 3mm

Within 3mm of meniscocapsular junction

P

Pattern vertical/longitudinal

Tear orientation favourable for sutures

A

Acute or traumatic

Better healing than chronic degenerative

I

Intact peripheral rim

Stable tissue quality for suture purchase

R

Rim stability maintained

No significant extrusion or instability

Hook:REPAIR guides you to save the meniscus - check all criteria before deciding

Inside-out. The gold standard for the posterior horn and body, and the strongest fixation. It needs an accessory posteromedial or posterolateral incision, which gives direct visualisation of the neurovascular structures, and its risk is to the saphenous nerve medially and the peroneal nerve laterally.

Outside-in. Suited to the anterior horn and anterior body: the sutures are passed from skin into the joint and back out. It is less commonly used.

All-inside. Implants of various designs, arrows, darts and suture anchors, placed without an accessory incision, so faster and technically easier. The risk is neurovascular injury if the device penetrates too far. Outcomes are similar to inside-out.

Protect the Nerves

Always use a safety incision and protect the neurovascular structures when tying inside-out sutures.

Medial repair: the saphenous nerve and vein are at risk posteriorly. Make a safe accessory incision and use a spoon retractor to displace the neurovascular bundle away from the capsule while tying.

Lateral repair: the peroneal nerve is at risk posterolaterally. Keep the knee flexed to 90 degrees to displace the nerve away from the joint line, and use a lateral safety incision.

The steps. Whatever the device, the sequence is the same:

1. Arthroscopic examination and assessment of the tear
2. Debride the tear edges: remove unstable flaps and roughen the surfaces
3. Create vascular access channels by trephination or rasping to promote healing
4. Pass the sutures in a vertical mattress pattern, 3-5mm apart
5. Tie with the knee at 20 degrees of flexion
6. Confirm a stable repair on probing

Augmentation. A fibrin clot placed in the repair site improves healing in the red-white zone; platelet-rich plasma injection is of controversial benefit; marrow venting creates bone marrow channels from the tibia to enhance the vascular response. These adjuncts may improve healing rates, especially for red-white zone repairs.

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Transtibial pullout is the gold standard, and the operation is a sequence:

1. Arthroscopic assessment: identify the root tear or avulsion, assess the tissue quality and confirm the location, medial or lateral, posterior
2. Debride the root stump to healthy tissue
3. Pass non-absorbable sutures (FiberWire) through the root tissue
4. Mark the anatomic root insertion on the tibia, 7mm anterior to the PCL
5. Drill a 6-7mm tibial tunnel at the insertion, angled to exit the anteromedial tibia
6. Pass the sutures through the tunnel and reduce the meniscus to its anatomic position
7. Tie over a cortical button or bridge on the anterior tibia
8. Confirm the reduction arthroscopically

What it achieves. An anatomic repair restores the hoop-stress mechanism, significantly reduces extrusion and slows the progression of OA. The best results come from repair within 6 months of injury: early repair is the best chance of functional restoration and OA prevention.

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After repair. Nerve injury is the significant risk of the inside-out technique. With medial repair the saphenous nerve is injured in 2-5%, presenting as numbness or paraesthesia over the posteromedial leg and usually resolving over 6-12 months. Peroneal nerve injury with lateral repair is under 1% but more serious, because it risks a foot drop, and a complete injury may need nerve exploration. Prevention is the retractor, the safe accessory incision and the flexed knee described under repair technique.

Repair failure runs at 10-20% depending on location and technique, 10-15% in the red-red zone and 20-30% in the red-white zone; the risk factors are a white-white location, poor tissue quality and non-compliance with rehabilitation. The other complications of repair are persistent pain in 5-10%, stiffness in 5%, which usually responds to physiotherapy, and, rarely, a postoperative meniscal cyst.

After resection. Haemarthrosis occurs in 5-10% and usually resolves. Residual symptoms may mean an incomplete resection or other pathology, chondral damage or a ligament injury; if they persist beyond 3 months, consider an MRI. The long-term complication is accelerated OA, the figures for which are in the overview: progressive joint space narrowing, increasing pain and functional limitation, and a higher long-term rate of progression to total knee arthroplasty. Prevention is to preserve every possible millimetre, to attempt repair in the red-red and red-white zones, to counsel patients about the long-term risk, and to consider meniscal transplant in the young patient who has already had a total meniscectomy. Understanding the OA risk is essential to shared decision-making.

General. Infection is usually superficial: oral antibiotics for a superficial infection, arthroscopic washout for a deep one, and prophylactic cefazolin 2g IV before the operation. DVT is rare because of early mobilisation; routine thromboprophylaxis is not indicated for isolated meniscal surgery and is considered for high-risk patients, obesity, thrombophilia or prolonged immobilisation. Regional anaesthesia, a nerve block or a spinal, is preferred: it reduces opioid requirements and allows same-day discharge. At the portals, numbness from the infrapatellar branch of the saphenous nerve is common and usually resolves; scar sensitivity occurs, and keloid rarely. These general complications are shared by all arthroscopic procedures and their overall rates are low.

What predicts a successful repair. The same things that made the tear repairable: a peripheral location, a vertical longitudinal pattern, acute trauma and healthy tissue. The poor-prognosis tear is central, horizontal, complex or radial, chronic and degenerate, with frayed tissue. Age counts in its own right, under 30 good and over 50 poor, and so does the ACL: an intact or reconstructed ACL protects the repair, and the ACL-deficient knee is a poor-prognosis setting.

The long term. After partial meniscectomy the OA risk is substantially higher, and more extensive resection and a degenerative rather than traumatic tear are associated with worse radiographic and symptomatic outcomes. After a successful repair the OA risk approaches that of a normal knee, the joint is preserved and the long-term quality of life is better.

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The medial meniscus is torn more often, but losing the lateral one costs the knee more, and the table says why: a less congruent compartment and a meniscus carrying a greater share of its load, so that lateral meniscectomy raises peak contact stress more.

Global epidemiology

Meniscal tears are among the most common knee injuries worldwide and arthroscopic partial meniscectomy has historically been one of the highest-volume orthopaedic procedures in many health systems. The population burden is dominated by degenerative tears in middle-aged and older adults: in the population-based Framingham MRI study (Englund et al, NEJM 2008; PMID 18784100), the prevalence of a meniscal tear or destruction rose from 19% in women aged 50-59 to 56% in men aged 70-90, and 61% of those with a tear were asymptomatic in the preceding month. Traumatic tears predominate in younger, athletic populations and are commonly associated with ACL rupture.

Guidelines side-by-side

International guidance has converged against routine arthroscopy for degenerative tears since the FIDELITY and METEOR trials, although surgery retains a clear role for true mechanical locking, repairable traumatic tears and root tears.

Registry and practice variation

There is no dedicated international meniscus registry comparable to arthroplasty registries (e.g. AOANJRR, NJR), so population-level evidence comes from administrative datasets and RCTs rather than implant-style registry survival data. Despite consistent guidance, large practice variation persists: arthroscopic partial meniscectomy rates differ several-fold between and within countries, and uptake of the FIDELITY/METEOR evidence into routine practice has been slow. This gap between evidence and practice is a recognised low-value-care target and a common exam discussion point.

The evidence above is drawn from FIDELITY (DOI), METEOR (DOI), Englund 2008 (DOI), Englund 2003 (DOI), Paxton 2011 (DOI), LaPrade root classification 2015 (DOI) and LaPrade root biomechanics 2015 (DOI).