Introduction / Definition

Meniscal tears represent the most common intra-articular pathology of the knee joint, with an estimated annual incidence of 60 to 70 per 100,000 population. Historically regarded as vestigial embryonic remnants and routinely managed with total open meniscectomy, the critical biomechanical role of the menisci in load transmission, shock absorption, joint congruity, and secondary joint stabilisation is now well recognised. Following the landmark observations by Fairbank in 1948 highlighting rapid chondral degeneration and joint space loss following total excision, the modern paradigm prioritises meniscal preservation whenever feasible.

Epidemiology & Aetiology

The distribution of meniscal tears follows a bimodal presentation:

• Young, active patients (acute traumatic tears): Typically aged 15–40 years, resulting from high-energy axial loading combined with torsional strain on a flexed knee. Often associated with concomitant ligamentous disruption; acute anterior cruciate ligament (ACL) ruptures are associated with lateral meniscal tears in over 50% of cases, whereas chronic ACL deficiency predisposes to secondary medial meniscal tears due to repetitive shear stress from anterior tibial translation.
• Older patients (degenerative tears): Typically aged >40 years, presenting after trivial rotational stress or insidious onset. These reflect age-related fibrocartilaginous desiccation and mucoid degeneration.

Relevant Anatomy & Biomechanics

Gross Structure & Attachments

• Medial Meniscus: C-shaped (semi-lunar), broader posteriorly than anteriorly, covering approximately 60% of the medial tibial plateau. It features firm peripheral attachments to the deep medial collateral ligament (meniscotibial/coronary ligaments), rendering it considerably less mobile (translating only 2–5 mm during flexion-extension) and more susceptible to entrapment and tearing.
• Lateral Meniscus: More circular (covering ~80% of the lateral plateau), with uniform width and closely approximated anterior and posterior root insertions. It is interrupted posterolaterally by the popliteus hiatus and popliteus tendon, conferring substantially greater excursion (9–11 mm), which confers protective compliance against shear stresses.
• Meniscofemoral Ligaments: The posterior horn of the lateral meniscus frequently connects to the medial femoral condyle via the anterior meniscofemoral ligament of Humphrey and the posterior meniscofemoral ligament of Wrisberg.

Microarchitecture & Vascularity (Cooper Zones)

• Composition: Extracellular matrix consists of 70% water, with dry weight predominantly composed of Type I collagen (90%) arranged primarily in a circumferential orientation to dissipate axial compressive loads into tensile "hoop stresses". Radial "tie fibres" interlace between circumferential bundles to resist longitudinal splitting.
• Vascularity: Derived from the superior and inferior medial and lateral genicular arteries, creating a perimeniscal capillary plexus:
  • Red-red zone: Peripheral outer 10–25% (up to 30% medially); rich vascularity with robust intrinsic healing capacity driven by fibrochondrocytes.
  • Red-white zone: Intermediate border zone (middle third); variable vascular arborisation with intermediate healing potential.
  • White-white zone: Central inner 70–80%; completely avascular, nourished purely by synovial fluid diffusion. Tears within this zone lack intrinsic regenerative healing capacity.
• Innervation: Mechanoreceptors (Ruffini, Pacinian, and Golgi tendon-like organs) and free nociceptive nerve endings are concentrated within the peripheral vascular third and the anterior and posterior root horns.

Classification

Morphological Classification

1. Longitudinal / Vertical Tears: Run parallel to circumferential collagen bundles. When extensive, they may displace into the intercondylar notch as a bucket-handle tear, classically blocking terminal knee extension.
2. Radial Tears: Transverse division perpendicular to the tibial plateau and circumferential fibres. Complete radial tears interrupt hoop stress transmission, conferring biomechanical consequences equivalent to a total meniscectomy.
3. Horizontal Cleavage Tears: Divide the meniscus into superior and inferior leaves; predominantly degenerative and strongly associated with parameniscal cyst formation due to fluid extrusion through a capsular breach.
4. Oblique / Flap / Parrot-Beak Tears: Combine vertical and radial planes; mechanical flaps can intermittently subluxate into the femorotibial joint space.
5. Complex Tears: Multiplanar disruptions displaying two or more patterns, typically degenerative.
6. Root Tears: Avulsion or radial disruption within 1 cm of the meniscal bony insertion. Posterior root tears disrupt hoop continuity entirely, resulting in rapid meniscal extrusion (>3 mm on coronal MRI) and accelerated chondrolysis.

Vascular Zone Classification (Cooper)

• Zone 1: Red-red (peripheral capsular margin, <3 mm from periphery).
• Zone 2: Red-white (3–5 mm from periphery).
• Zone 3: White-white (>5 mm from periphery).

Clinical Presentation & Examination

Symptoms

Patients typically report an acute twisting injury or progressive mechanical discomfort. Hallmarks include:

• Well-localised joint line pain aggravated by deep flexion or impact.
• Intermittent joint effusion (delayed, developing over 12–24 hours, in contrast to the rapid haemarthrosis of acute ACL tears).
• Mechanical symptoms: popping, catching, true locking (inability to achieve terminal extension pathognomonic of an entrapped bucket-handle tear), or "giving way".

Physical Examination

• Joint Line Tenderness (JLT): The most sensitive physical sign (~75–85%).
• Effusion / Ballotable Patella: Moderate reactive synovitis.
• McMurray Test: Internal/external tibial rotation coupled with extension from deep flexion; a painful palpable click indicates entrapment of a meniscal fragment.
• Apley Grind Test: Prone patient with knee flexed to 90°; axial compression and rotation reproduce discomfort.
• Thessaly Test: Dynamic single-leg rotation at 20° flexion; high diagnostic accuracy for catching.
• Extension Deficit: Springy end-feel block in acute locked bucket-handle tears.

Investigations

Plain Radiographs

Standard series: Weight-bearing AP, lateral at 30°, Rosenberg view (bilateral 45° flexion posteroanterior), and axial skyline views. Essential to rule out osteochondral lesions, tibial spine avulsions, loose bodies, and pre-existing osteoarthritis. Classic Fairbank changes following meniscal loss include:

1. Ridge formation (marginal osteophytes).
2. Flattening of the involved femoral condyle.
3. Joint space narrowing.

Magnetic Resonance Imaging (MRI)

Gold standard non-invasive imaging modality (sensitivity 90–95%, specificity 85–90%).

• Diagnostic Criteria: Intra-meniscal high signal on T2/proton-density sequences that clearly intersects the articular surface on at least two consecutive slices (or a clear distortion of meniscal morphology).
• Specific Signs:
  • Double PCL sign: Bucket-handle fragment displaced anterior/inferior to the posterior cruciate ligament in the notch (seen on sagittal views; diagnostic of displaced medial bucket-handle tear with intact ACL).
  • Ghost sign: Absence of normal dark meniscal signal on sagittal slices indicating a root tear.
  • Radial tear truncation: Abrupt loss of the meniscal triangle on coronal imaging.

Management

Non-Operative Management

• Indications: Asymptomatic tears; stable, partial-thickness tears (<5 mm length) in the red-white or white-white zones; and primary degenerative horizontal/complex tears without mechanical locking.
• Evidence: High-level randomised trials (e.g. FIDELITY, METEOR) demonstrate that arthroscopic partial meniscectomy provides no sustained clinical superiority over structured exercise therapy and physical conditioning for degenerative tears in middle-aged and older individuals.
• Regime: Analgesia/NSAIDs, activity modification, unloader bracing (if associated with early compartment overload), quadriceps/hamstring strengthening, and intra-articular corticosteroid or hyaluronic acid injections for secondary inflammatory synovitis.

Operative Management

1. Arthroscopic Partial Meniscectomy (APM)

• Indications: Symptomatic, mechanically disruptive tears not amenable to repair (e.g. macerated white-white tears, flap tears, complex degenerative lesions failing 3–6 months of conservative care).
• Principles: Excised tissue should be minimised. Preserve a stable, contoured, smooth peripheral rim to sustain circumferential hoop continuity.

2. Meniscal Repair

Preservation is mandatory for repairable tears, particularly in young patients or with concomitant ligament reconstructions.

• Indications: Vertical longitudinal tears >10 mm within the red-red or red-white zone (<4 mm from periphery), reducible bucket-handle tears, and acute root disruptions.
• Techniques:
  • Inside-Out: The gold standard for middle-third and posterior tears. Cannulated double-barrel guides deliver flexible sutures from inside the joint across the tear, tied over the outer capsule via accessory posteromedial or posterolateral open incisions. Caution: Retract the medial head of gastrocnemius to protect the saphenous nerve/vein medially, and retract biceps femoris and gastrocnemius to protect the common peroneal nerve laterally.
  • Outside-In: Ideal for anterior horn and anterior mid-body tears. Spinal needles are introduced percutaneously perpendicular to the tear, passing monofilament or braided sutures across the repair line.
  • All-Inside: Uses dedicated suture devices (e.g. anchor-based sliding knot constructs) wholly via arthroscopic portals; optimal for posterior horn and root regions without supplementary skin counter-incisions.
  • Root Repair: Trans-osseous transtibial pull-out repair drilling through the tibial plateau, or suture anchor fixation into the anatomical root footprint.
• Biological Augmentation: Trephination (needle fenestration of the parameniscal capsule), vascular access channels, microfracture of the intercondylar notch, and application of platelet-rich plasma (PRP) or autologous fibrin clot significantly enhance healing rates.

3. Concomitant ACL Reconstruction

Meniscal repair performed simultaneously with ACL reconstruction achieves higher union rates (~90%) compared to isolated meniscal repair (~60–70%), driven by the haemarthrosis and extensive intra-articular release of mesenchymal stem cells and growth factors.

4. Meniscal Allograft Transplantation (MAT)

Indicated for young (<50 years), active, normo-aligned or realigned knees with near-total or total meniscectomy suffering symptomatic compartmental unicompartmental overload, without advanced (Kellgren-Lawrence grade 3/4) osteoarthritis.

Complications

• Neurovascular Injury: Saphenous nerve / infrapatellar branch entrapment (medial inside-out repairs); common peroneal nerve neuropraxia (lateral inside-out repairs); popliteal neurovascular bundle penetration (posterior capsular all-inside instrumentation if depth limiter is improperly set).
• Repair Failure / Non-Union: 10–25% re-operation rate over 5–10 years.
• Chondral Scuffing: Iatrogenic articular cartilage damage during instrument passage.
• Implant Migration / Cyst Formation: Prominent hardware from all-inside anchors leading to localized synovitis.
• Accelerated Osteoarthritis: Proportional to the volume of meniscal rim resected during partial or subtotal meniscectomy.

Exam Pearls

• Biomechanical Equivalent: A complete radial tear or meniscal root tear completely dissipates hoop stress and is biomechanically equivalent to a total meniscectomy.
• Double PCL Sign: Characteristic MRI sign seen on sagittal view signifying an anteriorly and medially displaced bucket-handle fragment lying anterior and parallel to the posterior cruciate ligament (indicates an intact ACL).
• ACL Association: Lateral meniscal tears occur more frequently in acute ACL ruptures, whereas medial meniscal tears predominate in chronic ACL-deficient knees.
• Degenerative Cleavage Evidence: Landmark randomised controlled trials (FIDELITY, METEOR) have demonstrated that partial meniscectomy offers no long-term functional superiority over sham surgery or physical therapy for non-obstructive degenerative meniscal tears in older cohorts.
• Zone Boundaries: The red-red vascular zone extends 0–3 mm from the meniscocapsular junction; red-white is 3–5 mm; white-white is >5 mm from the periphery.
• Nerve Hazards: The common peroneal nerve lies intimately adjacent to the posterolateral capsule (jeopardised during lateral inside-out repair); the saphenous nerve and its infrapatellar branch cross posteromedially (jeopardised during medial inside-out approaches).