Keywords

Anatomy and Basic Science

Function

  • To disperse the load transmitted through the knee joint by increasing the contact surface area:

    • Knee extension – up to 50% of joint reactive force absorbed

    • Knee flexion – up to 90% of joint reactive force absorbed

  • Deepens the surface area of the joint – provides stability

  • Peripheral boarders attached to joint capsule and provides proprioception

  • Assists in joint lubrication and assists with cartilage nutrition

Histology

  • Fibrocartilage disks composed of collagen (95%), fibrochondrocytes, water, proteoglycans (1%), glycoproteins (1%), and elastin (0.6%)

  • Collagen components – type 1 (90%), types 2, 3, 5, and 6 (5–10%)

  • Cellular function – synthesizes extracellular matrix and limited anaerobic metabolism

Layers

  • Superficial – radially oriented fibers, woven in meshwork

  • Surface layer – random fiber orientation

  • Middle layer – fibers circumferential to disperse hoop stress and radial to hold the circumferential together

Vascular Supply

  • Superior and inferior medial and lateral geniculate arteries:

    • Branch circumferentially to form a plexus

  • Supply peripheral meniscus (medial has improved supply).

  • Central meniscus has limited nutrient supply – provided by synovial fluid.

  • Fibrochondrocyte primarily responsible for healing.

  • Three zones:

    • Red zone – 3 mm from the joint capsule (best chance of healing)

    • Red-white zone – 3–5 mm from the joint capsule

    • White zone – >5 mm from the joint capsule (most tears do not heal)

Innervation

  • Peripheral two-third:

    • Type 1 and 2 nerve endings

    • Anterior < posterior horn concentration

    • Limited in meniscal body

Medial Meniscus

  • C-shaped, broader posteriorly than anteriorly.

  • Anterior horn attaches to the tibial intercondylar area anterior to the ACL.

  • Posterior horn attaches to the tibial intercondylar area anterior to the PCL.

  • Medially attaches to the tibial collateral ligament.

Lateral Meniscus

  • Nearly circular and smaller/more mobile.

  • Tethered to the medial meniscus through the transverse ligament.

  • Popliteus tendon separates the lateral meniscus from the fibular collateral ligament.

  • Attached to the PCL and the medial femoral condyle by the posterior meniscofemoral ligament

Injury

Epidemiology

  • Tears are present in 32% of painful/symptomatic knees and 23% of asymptomatic knees.

  • Meniscal tears are the most common indication for knee surgery.

  • Risk increases in ACL-deficient knees.

  • Medial and lateral tears occur in equal frequency.

  • Lateral tears more common in traumatic setting and concurrent with acute ACL tears:

    • Longitudinal and transverse tears most common.

    • Mechanism of injury is usually rotation of the flexed knee as it begins extension.

    • Discoid menisci have increased tear rates.

  • Degenerative tears occur most commonly occur in the posterior horn of the medial meniscus:

    • Horizontal cleavage tears, flap tears, and complex tears.

    • Partial thickness tears involve inferior surface of the meniscus more commonly than the superior surface.

Patterns of Injury

  • Longitudinal:

    • Very common with ACL tears, repair when peripheral

  • Radial:

    • High-energy tears perpendicular to the long axis of the meniscus

  • Horizontal:

    • More common in the elderly as degenerative changes make the meniscus less mobile

    • Associated with meniscal cysts which are found more common on the lateral side

  • Oblique:

    • May cause mechanical locking symptoms

  • Bucket handle:

    • Subtype of longitudinal tear that may displace into the intercondylar notch

    • Can progress to pedunculated if one side detaches

Presentation and Physical Exam

Symptoms

  • Knee pain – can be generalized or localized to affected side.

  • Mechanical symptoms mostly occur with longitudinal tears and bucket handle lesions:

    • Not pathognomonic for meniscal tear

  • Knee effusion – can be after acute event or recurrent with activity.

  • Sensation of the leg giving away.

Physical Exam Maneuvers (Sensitivity, Specificity)

  • Apley grind test (97%, 87%):

    • Patient lies prone with the knee flexed to 90°.

    • Examiner places own knee across the patient’s posterior thigh.

    • Tibia compressed onto the knee joint while externally rotated

    • Pain with External rotation = medial meniscus; internal rotation = lateral meniscus

  • Joint line tenderness (83%, 83%)

  • McMurray (61%, 84%):

    • Knee flexed to 90° with the foot in one hand and the other hand at joint line.

    • Induce varus stress with one hand pushing medial side of the knee laterally.

    • Use the second hand to rotate the leg externally.

    • If pain or click is felt, test is positive for medial meniscal tear.

    • Similar signs with valgus stress indicate lateral meniscal tear.

  • Thessaly test (75%, 87%) – dynamic test of joint loading:

    • Patient stands on one knee with the examiner holding arms for support.

    • Patient flexes weight-bearing knee to 5° and rotates body internally and externally three times.

    • Procedure then repeated with the knee in 20° of flexion.

    • Joint line discomfort, locking, or catching indicate positive test.

Diagnostic Studies

  • Radiographs – likely normal in meniscal pathology

  • MRI – most sensitive test:

    • High rate of false positives.

    • Grade III signal indicates a tear.

    • Parameniscal cyst – fluid collection that indicates concurrent tear.

    • Double PCL sign – indicates bucket handle pathology.

Treatment

Nonoperative

  • Indications – first-line treatment for degenerative tears:

    • Incomplete tears, <5 mm peripheral tear, and no other pathology

  • Management – activity modification, rest, NSAIDs, and rehabilitation

Operative

Partial Meniscectomy

  • Indications – irreparable tears with no healing potential

  • Occurs in the white zone of the meniscus

  • Outcomes – >80% satisfaction and function at follow-up:

    • 50% have radiographic changes (osteophytes, flattening, joint space narrowing) postoperatively.

    • Improved outcomes:

      • Age <40, normal alignment, minimal arthritis, and single tear

    • Causes slight increase in joint laxity.

    • Medial partial meniscectomy has better results than lateral.

  • Total meniscectomy – historical procedure as meniscus thought to have been inconsequential:

    • 20% progression to arthritic lesions.

    • 70% have radiographic changes within 3 years of surgery.

    • 100% arthritis at 20 years.

    • Severity directly correlated to amount removed.

Meniscal Repair

  • Indications – peripheral tear in the red zone:

    • Rim width – distance from the tear to the blood supply (i.e., peripheral junction with capsule)

    • Improved healing potential:

      • Lower rim width

      • Vertical or longitudinal tears

      • 1–4 cm in length

      • Acute repair with ACL reconstruction concurrently

  • Outcomes – 70–95% success rate, highest with ACL reconstruction:

    • 30% success rate with untreated ACL deficiency.

    • Healing occurs by fibrocartilaginous scar at 10 weeks.

    • Maturation occurs for several months following repair.

Meniscal Transplant

  • Indications – young patient (< 50 years) with near total meniscectomy.

  • Contraindications – instability, obesity, malalignment, significant arthritis, inflammatory arthritis, chondrosis, and immunodeficiency.

  • Weight-bearing with patient in full extension for first 6 weeks.

  • Gradually increase flexion between 6 and 12 weeks.

  • Requires 8–12 months for full graft maturation.

  • Return to full activity in 6–9 months.

  • A 10-year follow-up demonstrates improved pain and function:

    • Lateral and medial survival of 70% and 74%, respectively

    • Poor results if advanced cartilage degeneration has begun

  • Re-tears, extrusion, and progressive radiographic changes common

Complications

  • Saphenous neuropathy (7%)

  • Arthrofibrosis (6%)

  • Sterile effusion (2%)

  • DVT (1.2–4.9%)

  • Peroneal Neuropathy (1%)

  • Infection (0.23–0.42%)