Meniscal Tears

• Two populations: a traumatic tear in a younger patient from twisting on a loaded, flexed knee; and a degenerative tear in an older patient, often with little or no trauma and coexisting osteoarthritis.
• Presentation: joint line pain, effusion developing gradually over a day (contrast the rapid haemarthrosis of an ACL tear), catching or clicking, and true locking — an inability to fully extend — which suggests a displaced bucket-handle fragment and warrants urgent referral.
• Examination: joint line tenderness (the most useful single sign), McMurray test, Thessaly test, and pain on deep squatting.
• Imaging: radiographs to assess for osteoarthritis and exclude fracture or loose body; MRI is the standard for characterising the tear.
• Management is where the evidence has shifted. For degenerative tears with osteoarthritis, structured physiotherapy performs as well as arthroscopic partial meniscectomy in multiple randomised trials, and surgery is no longer routine. Reserve arthroscopy for mechanical locking, displaced bucket-handle tears, and failure of a genuine trial of conservative care.
• Repair rather than resection is preferred where the tear is peripheral and vascular, because meniscectomy accelerates later osteoarthritis.

Traumatic (acute) mechanism

• Axial load plus rotation on a flexed, weight-bearing knee: the classic stem is a pivot, cut, or twist in football, soccer, basketball, or skiing; the femoral condyle grinds the trapped meniscus against the tibial plateau.
• Deep squatting or kneeling and rising from a squat: maximal posterior horn compression produces posterior horn tears, common in labourers, plumbers, and wrestlers.
• Concurrent ligament injury: acute ACL rupture frequently tears the lateral meniscus; chronic ACL deficiency, with repetitive anterior tibial translation, shears the medial posterior horn over time (the classic O'Donoghue unhappy triad of ACL, MCL, and meniscal injury is still tested with the medial meniscus as the answer).

Degenerative mechanism

• Mucoid degeneration of an ageing meniscus: horizontal cleavage and complex tears occur with trivial or no trauma, typically after age 40, and are best understood as one feature of osteoarthritis rather than a discrete injury.
• Meniscal root avulsion: often spontaneous in middle-aged or older patients during a minor squat, and functionally equivalent to total meniscectomy.

Non-modifiable risk factors

• Age and male sex (for traumatic tears); prior meniscectomy in either knee.
• Discoid lateral meniscus: a congenital broad, thickened meniscus that tears easily in children and adolescents — snapping knee.
• Varus or valgus malalignment and generalised ligamentous laxity, which concentrate compartment load.
• Medial predominance: the medial meniscus is tethered to the deep MCL and capsule and is relatively immobile, so it absorbs shear rather than translating out of harm's way; the lateral meniscus is mobile (interrupted at the popliteus hiatus) and tears less often overall.

Modifiable risk factors

• Obesity, which raises compressive and hoop stress and is also a driver of coexisting osteoarthritis — the ACR 2019 osteoarthritis guideline treats weight loss as a core intervention.
• Occupational kneeling, squatting, stair climbing, and heavy lifting.
• Quadriceps weakness and poor neuromuscular control, which reduce dynamic knee stability during landing and pivoting.

• Normal load transfer: circumferentially oriented type I collagen bundles convert axial compression into hoop stress, which is resisted by the anterior and posterior root attachments to the tibia. Intact menisci transmit a substantial share of load across the knee and deepen the tibial plateau, adding secondary stability.
• Loss of hoop tension: a radial tear that crosses the circumferential fibres, or a root avulsion, uncouples the ring. The meniscus is squeezed peripherally out of the joint (meniscal extrusion) and stops distributing load, so tibiofemoral contact area falls and peak cartilage contact pressure rises — the mechanical basis for accelerated osteoarthritis after root tears and after meniscectomy.
• Vascular anatomy dictates healing: the perimeniscal capillary plexus from the geniculate arteries supplies only the peripheral third. Red-red and red-white zone tears can mount an inflammatory-reparative response with fibrin clot and fibrovascular scar; white-white zone tears have no vascular access, so they cannot heal and are debrided rather than repaired.
• Why it hurts: nociceptors and mechanoreceptors are concentrated in the peripheral rim and the horns. Pain from an inner-zone tear is largely referred through traction on the innervated periphery and adjacent synovium, which localises to the joint line and is reproduced by rotation and compression manoeuvres.
• Why the effusion is slow: a torn meniscus provokes reactive synovitis and a serous effusion that accumulates over roughly a day. Contrast with cruciate rupture or osteochondral fracture, where torn vessels produce a tense haemarthrosis within a couple of hours.
• Why the knee locks: a longitudinal tear that propagates and displaces into the intercondylar notch (bucket-handle) acts as a physical doorstop, producing a springy block to terminal extension and a fixed flexion deformity — true mechanical locking, distinct from pain-inhibited pseudo-locking.
• Degenerative tears: proteoglycan-rich mucoid change and collagen disorganisation let the tissue fail under physiologic load. Because the tear is a marker of a diseased joint rather than the sole pain generator, removing it does not reliably remove the pain.

The two stems examiners write

• Young athlete: twisting on a planted foot during a pivot, an audible pop or tearing sensation, ability to finish the play or walk off, then progressive pain and swelling over the following hours.
• Patient over 40: insidious medial joint line pain after a squat, minor step, or nothing at all, with morning stiffness, crepitus, and radiographic osteoarthritis.

Symptoms

• Joint line pain localised to the medial or lateral line, worse with twisting, pivoting, deep squatting, and stairs — the loads that compress and shear the torn fragment.
• Delayed effusion over 12–24 hours from reactive synovitis; recurrent swelling after activity is typical.
• Catching, clicking, or a sense of giving way, from an unstable flap intermittently interposing between the condyles. Giving way here is a buckling from pain and quadriceps inhibition, not the frank instability of ACL rupture.
• True locking: the knee is stuck short of full extension and the patient cannot passively straighten it. This signals a displaced bucket-handle fragment and, as noted above, warrants urgent orthopaedic referral rather than a watchful trial of therapy.

Physical findings

• Joint line tenderness: palpate with the knee flexed to 90°; the single most useful sign, sensitive but not specific.
• McMurray test: with the hip and knee flexed, apply valgus and external rotation while extending to test the medial meniscus (varus and internal rotation for the lateral); a palpable thud or clunk with pain is positive.
• Thessaly test: single-leg stance at about 20° of flexion with the patient rotating the body over the fixed foot; reproduction of joint line pain or catching is positive.
• Apley grind: prone, knee at 90°, axial compression plus rotation reproduces pain; distraction relieves it, separating meniscal from ligamentous pain.
• Loss of terminal extension, effusion, and quadriceps (vastus medialis) atrophy in chronic cases; pain on deep squat.
• Always test ACL, PCL, and collateral integrity — Lachman, pivot shift, and varus/valgus stress — since combined injury changes management.

Step 1 — clinical assessment

• History plus a composite of examination signs outperforms any single test. Joint line tenderness, a positive McMurray or Thessaly, effusion, a mechanical history, and pain on squatting together make the diagnosis probable; no single manoeuvre is definitive.

Step 2 — plain radiographs

• **Apply the *Ottawa Knee Rule*** to decide on radiography after acute injury: age 55 or older, isolated patellar tenderness, tenderness at the fibular head, inability to flex to 90°, or inability to bear weight for four steps both immediately and in the emergency department.
• Obtain weight-bearing views, including a flexed posteroanterior (Rosenberg) view, plus lateral and skyline. Radiographs do not show the meniscus; they exclude fracture, loose body, and tumour and grade the joint space narrowing and osteophytes that reclassify the problem as osteoarthritis with a degenerative tear.

Step 3 — MRI, the confirmatory imaging standard

• Non-contrast MRI is the test of choice, consistent with the ACR Appropriateness Criteria for chronic knee pain and acute knee trauma. It is highly sensitive and specific for meniscal tears and simultaneously assesses cruciates, collaterals, and cartilage.
• Signal grading: intrasubstance globular or linear signal that does not reach an articular surface is degeneration (grade 1–2); grade 3 signal contacting an articular surface on two or more images is a tear.
• Characteristic patterns: the double PCL sign and absent bow-tie sign on sagittal images indicate a displaced bucket-handle tear; a ghost meniscus and increased radial extrusion of the meniscal body suggest a root tear; a horizontal cleavage tear with a parameniscal cyst is typical of degeneration.
• Caution: asymptomatic meniscal tears on MRI are common in middle-aged and older adults, so an MRI finding does not by itself justify surgery.

Adjuncts

• Arthrocentesis if the effusion is tense or infection is suspected — bloody aspirate with fat globules points to intra-articular fracture, not an isolated meniscal tear.
• Diagnostic arthroscopy remains the true gold standard but is now performed only when intervention is already planned.

Immediate measures

• A truly locked knee is the exception to conservative care: urgent orthopaedic referral for arthroscopic reduction and repair of a displaced bucket-handle fragment, because prolonged locking causes fixed flexion contracture and chondral damage.
• Otherwise: relative rest, ice, compression, elevation, and crutches with weight bearing as tolerated; early range of motion to prevent stiffness and quadriceps inhibition.

First-line non-operative therapy

• Structured physiotherapy: quadriceps and hip abductor strengthening, neuromuscular and proprioceptive retraining. The AAOS clinical practice guideline on non-arthroplasty management of knee osteoarthritis and the ACR 2019 osteoarthritis guideline both make exercise a core, strongly supported intervention, and randomised trials of degenerative tears show physiotherapy matches arthroscopic partial meniscectomy in outcome.
• NSAIDs: topical first in older or comorbid patients (e.g. diclofenac gel), oral otherwise (e.g. naproxen); ACR 2019 conditionally recommends topical over oral NSAIDs for the knee.
• Weight loss where BMI is elevated, to reduce compartment load.
• Intra-articular glucocorticoid (e.g. triamcinolone) for a painful effusion, conditionally recommended by ACR for short-term relief.

Escalation and surgery

• Meniscal repair — inside-out, outside-in, or all-inside sutures — for peripheral red-zone vertical/longitudinal tears, bucket-handle tears, and in young patients; healing rates are best when repair accompanies ACL reconstruction, which restores stability and floods the joint with marrow elements.
• Transtibial pull-out repair of root tears, to restore hoop tension and prevent extrusion-driven arthritis.
• Arthroscopic partial meniscectomy, resecting only unstable irreparable fragments back to a stable rim, when white-zone tears cause persistent true mechanical symptoms despite a genuine trial of therapy.
• Meniscal allograft transplantation in selected young, aligned, non-arthritic patients with a prior subtotal meniscectomy.

Avoid

• Routine arthroscopic partial meniscectomy for degenerative tears with osteoarthritis — not recommended by AAOS.
• Opioids and intra-articular hyaluronic acid for knee osteoarthritis, both recommended against by ACR 2019.
• Attempting repair of an avascular white-zone degenerative tear, which will not heal.

Of the untreated or treated tear

• Post-meniscectomy osteoarthritis: loss of load distribution raises peak cartilage contact pressure; radiographs show Fairbank changes — joint space narrowing, condylar flattening, and ridging. Risk rises with the volume of meniscus resected, which is why repair is preferred over resection.
• Meniscal extrusion after root tear or radial tear: rapid compartment collapse, sometimes with subchondral insufficiency fracture of the knee (historically called spontaneous osteonecrosis of the knee) — sudden severe medial pain in an older patient with focal marrow oedema on MRI.
• Fixed flexion contracture from a chronically locked bucket-handle fragment, with secondary quadriceps atrophy and altered gait.
• Parameniscal cyst, classically with a horizontal cleavage tear of the lateral meniscus, presenting as a firm joint line mass most prominent in extension.
• Loose body from a detached fragment, causing unpredictable locking episodes.

Of surgery

• Re-tear or failure of repair, especially in white-zone tears, smokers, and repairs performed without concurrent ACL reconstruction; recurrent locking or effusion signals it.
• Septic arthritis — an emergency. Fever, an exquisitely painful hot knee, and refusal to move the joint days after arthroscopy; aspirate immediately, expect a markedly elevated synovial white cell count with neutrophil predominance, and proceed to urgent surgical washout with antibiotics.
• Venous thromboembolism — a potential emergency; calf pain and swelling, or pleuritic chest pain and hypoxaemia with PE.
• Nerve injury: the infrapatellar branch of the saphenous nerve during medial portals or inside-out medial repair (numb patch below the knee, sometimes painful neuroma); the common peroneal nerve during lateral repair (foot drop, first web space numbness).
• Popliteal neurovascular injury: rare but catastrophic with posterior horn instrumentation — expanding haematoma, absent distal pulses, requires emergent vascular assessment.
• Arthrofibrosis and persistent haemarthrosis, both presenting as failure to regain extension after an uneventful operation.

• Effusion timing is the discriminator: swelling over hours to a day equals meniscus; a tense haemarthrosis within about two hours equals ACL rupture, patellar dislocation, or osteochondral fracture.
• True locking = displaced bucket-handle = urgent orthopaedic referral, and it is the one meniscal scenario where "physical therapy" is the wrong answer. On sagittal MRI look for the double PCL sign and the absent bow-tie sign.
• Joint line tenderness is the single most useful physical finding; McMurray, Thessaly, and Apley grind add to it but none is diagnostic alone.
• The single best next step after a suspicious history and exam in an acute injury is plain radiographs (guided by the Ottawa Knee Rule) to exclude fracture, then MRI to characterise the tear. Jumping straight to MRI or to arthroscopy is the classic distractor.
• The association examiners test: medial meniscus tears with the unhappy triad of O'Donoghue, because the medial meniscus is tethered to the deep MCL and cannot escape shear. Chronic ACL deficiency likewise shears the medial posterior horn.
• Red zone repairs, white zone resects. Peripheral vascular tears in young patients get sutured — especially alongside ACL reconstruction; inner avascular tears cannot heal.
• Degenerative tear plus osteoarthritis in a patient over 40 → structured physiotherapy, not arthroscopy, per the evidence reflected in the AAOS knee osteoarthritis guideline; asymptomatic meniscal tears are common on MRI at this age, so the MRI finding does not license surgery.
• A child or adolescent with a painless snapping knee and a clunk on extension has a discoid lateral meniscus — saucerisation rather than excision if surgery is needed.
• The commonest trap: choosing arthroscopic partial meniscectomy for an older patient with mechanical-sounding but pain-driven pseudo-locking; only an inability to fully extend the knee counts as true locking.