Abstract
The most common knee injury is a meniscal tear. Up to one-third of symptomatic knees and one-fourth of asymptomatic knees possess meniscal tears with their prevalence increasing with patient age. Understanding meniscal anatomy and physiology is vital to appreciating their importance. Knowing physical exam maneuvers to illicit meniscal pathology is indispensable for every budding orthopedic surgeon. Classification of meniscal tear patterns and their epidemiology can also be helpful in determining treatment options for these patients. This chapter will succinctly cover these essentials to provide a holistic overview of meniscal pathology.
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Keywords
Anatomy and Basic Science
Function
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To disperse the load transmitted through the knee joint by increasing the contact surface area:
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Knee extension – up to 50% of joint reactive force absorbed
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Knee flexion – up to 90% of joint reactive force absorbed
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Deepens the surface area of the joint – provides stability
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Peripheral boarders attached to joint capsule and provides proprioception
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Assists in joint lubrication and assists with cartilage nutrition
Histology
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Fibrocartilage disks composed of collagen (95%), fibrochondrocytes, water, proteoglycans (1%), glycoproteins (1%), and elastin (0.6%)
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Collagen components – type 1 (90%), types 2, 3, 5, and 6 (5–10%)
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Cellular function – synthesizes extracellular matrix and limited anaerobic metabolism
Layers
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Superficial – radially oriented fibers, woven in meshwork
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Surface layer – random fiber orientation
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Middle layer – fibers circumferential to disperse hoop stress and radial to hold the circumferential together
Vascular Supply
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Superior and inferior medial and lateral geniculate arteries:
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Branch circumferentially to form a plexus
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Supply peripheral meniscus (medial has improved supply).
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Central meniscus has limited nutrient supply – provided by synovial fluid.
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Fibrochondrocyte primarily responsible for healing.
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Three zones:
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Red zone – 3 mm from the joint capsule (best chance of healing)
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Red-white zone – 3–5 mm from the joint capsule
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White zone – >5 mm from the joint capsule (most tears do not heal)
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Innervation
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Peripheral two-third:
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Type 1 and 2 nerve endings
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Anterior < posterior horn concentration
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Limited in meniscal body
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Medial Meniscus
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C-shaped, broader posteriorly than anteriorly.
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Anterior horn attaches to the tibial intercondylar area anterior to the ACL.
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Posterior horn attaches to the tibial intercondylar area anterior to the PCL.
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Medially attaches to the tibial collateral ligament.
Lateral Meniscus
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Nearly circular and smaller/more mobile.
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Tethered to the medial meniscus through the transverse ligament.
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Popliteus tendon separates the lateral meniscus from the fibular collateral ligament.
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Attached to the PCL and the medial femoral condyle by the posterior meniscofemoral ligament
Injury
Epidemiology
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Tears are present in 32% of painful/symptomatic knees and 23% of asymptomatic knees.
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Meniscal tears are the most common indication for knee surgery.
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Risk increases in ACL-deficient knees.
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Medial and lateral tears occur in equal frequency.
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Lateral tears more common in traumatic setting and concurrent with acute ACL tears:
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Longitudinal and transverse tears most common.
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Mechanism of injury is usually rotation of the flexed knee as it begins extension.
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Discoid menisci have increased tear rates.
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Degenerative tears occur most commonly occur in the posterior horn of the medial meniscus:
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Horizontal cleavage tears, flap tears, and complex tears.
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Partial thickness tears involve inferior surface of the meniscus more commonly than the superior surface.
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Patterns of Injury
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Longitudinal:
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Very common with ACL tears, repair when peripheral
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Radial:
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High-energy tears perpendicular to the long axis of the meniscus
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Horizontal:
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More common in the elderly as degenerative changes make the meniscus less mobile
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Associated with meniscal cysts which are found more common on the lateral side
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Oblique:
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May cause mechanical locking symptoms
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Bucket handle:
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Subtype of longitudinal tear that may displace into the intercondylar notch
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Can progress to pedunculated if one side detaches
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Presentation and Physical Exam
Symptoms
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Knee pain – can be generalized or localized to affected side.
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Mechanical symptoms mostly occur with longitudinal tears and bucket handle lesions:
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Not pathognomonic for meniscal tear
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Knee effusion – can be after acute event or recurrent with activity.
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Sensation of the leg giving away.
Physical Exam Maneuvers (Sensitivity, Specificity)
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Apley grind test (97%, 87%):
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Patient lies prone with the knee flexed to 90°.
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Examiner places own knee across the patient’s posterior thigh.
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Tibia compressed onto the knee joint while externally rotated
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Pain with External rotation = medial meniscus; internal rotation = lateral meniscus
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Joint line tenderness (83%, 83%)
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McMurray (61%, 84%):
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Knee flexed to 90° with the foot in one hand and the other hand at joint line.
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Induce varus stress with one hand pushing medial side of the knee laterally.
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Use the second hand to rotate the leg externally.
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If pain or click is felt, test is positive for medial meniscal tear.
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Similar signs with valgus stress indicate lateral meniscal tear.
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Thessaly test (75%, 87%) – dynamic test of joint loading:
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Patient stands on one knee with the examiner holding arms for support.
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Patient flexes weight-bearing knee to 5° and rotates body internally and externally three times.
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Procedure then repeated with the knee in 20° of flexion.
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Joint line discomfort, locking, or catching indicate positive test.
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Diagnostic Studies
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Radiographs – likely normal in meniscal pathology
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MRI – most sensitive test:
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High rate of false positives.
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Grade III signal indicates a tear.
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Parameniscal cyst – fluid collection that indicates concurrent tear.
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Double PCL sign – indicates bucket handle pathology.
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Treatment
Nonoperative
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Indications – first-line treatment for degenerative tears:
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Incomplete tears, <5 mm peripheral tear, and no other pathology
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Management – activity modification, rest, NSAIDs, and rehabilitation
Operative
Partial Meniscectomy
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Indications – irreparable tears with no healing potential
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Occurs in the white zone of the meniscus
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Outcomes – >80% satisfaction and function at follow-up:
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50% have radiographic changes (osteophytes, flattening, joint space narrowing) postoperatively.
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Improved outcomes:
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Age <40, normal alignment, minimal arthritis, and single tear
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Causes slight increase in joint laxity.
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Medial partial meniscectomy has better results than lateral.
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Total meniscectomy – historical procedure as meniscus thought to have been inconsequential:
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20% progression to arthritic lesions.
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70% have radiographic changes within 3 years of surgery.
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100% arthritis at 20 years.
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Severity directly correlated to amount removed.
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Meniscal Repair
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Indications – peripheral tear in the red zone:
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Rim width – distance from the tear to the blood supply (i.e., peripheral junction with capsule)
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Improved healing potential:
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Lower rim width
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Vertical or longitudinal tears
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1–4 cm in length
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Acute repair with ACL reconstruction concurrently
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Outcomes – 70–95% success rate, highest with ACL reconstruction:
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30% success rate with untreated ACL deficiency.
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Healing occurs by fibrocartilaginous scar at 10 weeks.
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Maturation occurs for several months following repair.
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Meniscal Transplant
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Indications – young patient (< 50 years) with near total meniscectomy.
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Contraindications – instability, obesity, malalignment, significant arthritis, inflammatory arthritis, chondrosis, and immunodeficiency.
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Weight-bearing with patient in full extension for first 6 weeks.
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Gradually increase flexion between 6 and 12 weeks.
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Requires 8–12 months for full graft maturation.
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Return to full activity in 6–9 months.
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A 10-year follow-up demonstrates improved pain and function:
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Lateral and medial survival of 70% and 74%, respectively
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Poor results if advanced cartilage degeneration has begun
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Re-tears, extrusion, and progressive radiographic changes common
Complications
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Saphenous neuropathy (7%)
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Arthrofibrosis (6%)
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Sterile effusion (2%)
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DVT (1.2–4.9%)
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Peroneal Neuropathy (1%)
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Infection (0.23–0.42%)
References
McCulloch, Patrick. Meniscal pathology. In: Orthobullets. N.p., 13 Sept. 2015. Web. 1 Nov; 2015.
Miller MD. In: Hart JA, editor. Review of orthopedics. Philadelphia: Saunders/Elsevier; 2008. Print
Moore KL, Agur AMR. Basic sciences. In:Essential clinical anatomy. Philadelphia: Lippincott Williams & Wilkins; 2007. p. 42–3. Print
Smith BE, Thacker D, Crewesmith A, Hall M. Special tests for assessing meniscal tears within the knee: a systematic review and meta-analysis. Evid Based Med Evidence Based Medicine. 2015;20(3):88–97. Web
Thompson JC, Netter FH. Netter's concise orthopedic anatomy. Philadelphia: Saunders Elsevier; 2010. p. 384–5. Print
Wiesel, Sam W. Part 1: sports medicine. In: Operative techniques in orthopedic surgery. 2nd ed. vol. 1. N.p.: n.p; n.d. p. 276–330. Print.
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Gillig, J., Pearsall, A. (2017). Meniscal Tear. In: Eltorai, A., Eberson, C., Daniels, A. (eds) Orthopedic Surgery Clerkship. Springer, Cham. https://doi.org/10.1007/978-3-319-52567-9_67
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DOI: https://doi.org/10.1007/978-3-319-52567-9_67
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