eMedicine Specialties > Physical Medicine and Rehabilitation > Lower Limb Musculoskeletal Conditions

Meniscal Injury

Author: Sarjoo M Bhagia, MD, Honorary Teaching Faculty, Charlotte Institute of Rehabilitation, Consulting Staff, Physical Medicine and Rehabilitation, OrthoCarolina
Coauthor(s): Michael Weinik, DO, Associate Chairman, Associate Professor, Physical Medicine and Rehabilitation, Temple University Hospital; Selina Yingqi Xing, MD, MS, Staff Physician, Department of Physical Medicine and Rehabilitation, Temple University
Contributor Information and Disclosures

Updated: Jun 30, 2009

Introduction

Background

Understanding of the importance of the menisci in the biomechanics of the knee has progressed steadily since 1968, when Jackson wrote, "The exact function of that structure (meniscus) is still a matter of some conjecture."¹ At that time, it was common to remove the entire substance if any doubt existed regarding the integrity of the meniscus. Today, it is known that the menisci are not optional or expendable structures; they have an integral role in normal knee joint mechanics. The physician treating an athlete with a known or suspected meniscal tear needs to understand the structure and function of the meniscus and the factors involved in treating an athlete with nonoperative versus operative treatment. This article presents a program for rehabilitation after meniscal injuries, meniscectomy, and meniscal repair based on current knowledge of knee biomechanics. (See images below and Images 1, 2.)

Pathophysiology

Anatomy

The menisci are C-shaped wedges of fibrocartilage located between the tibial plateau and femoral condyles. The menisci contain 70% type I collagen. The larger semilunar medial meniscus is attached more firmly than the loosely fixed, more circular lateral meniscus. The anterior and posterior horns of both menisci are secured to the tibial plateaus. Anteriorly, the transverse ligament connects the 2 menisci; posteriorly, the meniscofemoral ligament helps stabilize the posterior horn of the lateral meniscus to the femoral condyle. The coronary ligaments connect the peripheral meniscal rim loosely to the tibia. Although the lateral collateral ligament (LCL) passes in close proximity, the lateral meniscus has no attachment to this structure.

The joint capsule attaches to the entire periphery of each meniscus but adheres more firmly to the medial meniscus. An interruption in the attachment of the joint capsule to the lateral meniscus, forming the popliteal hiatus, allows the popliteus tendon to pass through to its femoral attachment site. Contraction by the popliteus during knee flexion pulls the lateral meniscus posteriorly, avoiding entrapment within the joint space. The medial meniscus does not have a direct muscular connection. The medial meniscus may shift a few millimeters, while the less stable lateral meniscus may move at least 1 cm.

In 1978, Shrive et al reported that the collagen fibers of the menisci are oriented in a circumferential pattern.² When a compressive force is applied in the knee joint, a tensile force is transmitted to the menisci. The femur attempts to spread the menisci anteroposteriorly in extension and mediolaterally in flexion. Shrive et al further studied the effects of a radial cut in the peripheral rim of the menisci during loading. In joints with intact menisci, the force was applied through the menisci and articular cartilage; however, a lesion in the peripheral rim disrupted the normal mechanics of the menisci and allowed it to spread when a load was applied. The load now was distributed directly to the articular cartilage. In light of these findings, it is essential to preserve the peripheral rim during partial meniscectomy to avoid irreversible disruption of the structure's hoop tension capability.

Blood supply

The blood supply to the menisci is limited to their peripheries. The medial and lateral geniculate arteries anastomose into a parameniscal capillary plexus supplying the synovial and capsular tissues of the knee joint. The vascular penetration through this capsular attachment is limited to 10-25% of the peripheral widths of the medial and lateral meniscal rims. In 1990, Renstrom and Johnson reported a 20% decrease in the vascular supply by age 40 years, which may be attributed to weight bearing over time.³

The presence of a vascular supply to the menisci is an essential component in the potential for repair. The blood supply must be able to support the inflammatory response normally seen in wound healing. Arnoczky, in 1982, proposed a classification system that categorizes lesions in relation to the meniscal vascular supply.⁴

• An injury resulting in lesions within the blood-rich periphery is called a red-red tear. Both sides of the tear are in tissue with a functional blood supply, a situation that promotes healing.
• A tear encompassing the peripheral rim and central portion is called a red-white tear. In this situation, one end of the lesion is in tissue with good blood supply, while the opposite end is in the avascular section.
• A white-white tear is a lesion located exclusively in the avascular central portion; the prognosis for healing in such a tear is unfavorable.

Repair of lesions in the red zone has yielded good results, according to Stone. Reports describe techniques for manufacturing a vascular access channel from the peripheral vasculature to improve the chance that tissue in the central region will repair itself.

Biomechanics

The menisci follow the motion of the femoral condyle during knee flexion and extension. Shrive et al presented a model of normal meniscal function.² During extension, the femoral condyles exert a compressive force displacing the menisci anteroposteriorly. As the knee moves into flexion, the condyles roll backward onto the tibial plateau. The menisci deform mediolaterally, maintaining joint congruity and maximal contact area. As the knee flexes, the femur externally rotates on the tibia, and the medial meniscus is pulled forward. Studies by Shrive, Fukubayashi, Walker, and Kurosawa state that the menisci directly influence the transmission of forces, distribution of load, amount of contact force, and pressure distribution patterns.

Mechanism of injury

Meniscal injuries, particularly sports-related injuries, usually involve damage due to rotational force. A common mechanism of injury is a varus or valgus force directed to a flexed knee. When the foot is planted and the femur is internally rotated, a valgus force applied to a flexed knee may cause a tear of the medial meniscus. A varus force on a flexed knee with the femur externally rotated may lead to a lateral meniscus lesion. According to Ricklin, the medial meniscus is attached more firmly than the relatively mobile lateral meniscus, and this may result in a greater incidence of medial meniscus injury.

Frequency

United States

Although the exact incidence and prevalence of meniscal injury are unknown, it is a fairly common sports-related injury among adults. Although less common than in adults, knee meniscal injuries do occur in individuals who are skeletally immature. Meniscal injuries are rare in children younger than 10 years with morphologically normal menisci.⁵

Mortality/Morbidity

Meniscal injuries usually are associated with pain that results in gait deviation and loss of time from work and/or sport.

Race

A correlation of race and meniscal injuries is not known to exist.

Sex

Meniscal injuries are more common in males, which may be a reflection of males being more involved in aggressive sporting and manual activities that predispose to rotational injuries of the knee.

Age

Meniscal injuries are common in young males who are involved in sporting or manual activities. A second peak of incidence is observed in elderly persons older than 55 years; this incidence is secondary to a degenerate meniscus being susceptible to injuries with minor trauma.⁶ Meniscal injuries are rare in children younger than 10 years with morphologically normal menisci.⁵

Clinical

History

A thorough subjective history can help the examiner choose the appropriate clinical tests to include in the physical examination. A complete understanding of the exact mechanism of injury helps determine what type of meniscal involvement to look for. Initial symptoms may include the following:

• Acute joint-line pain may be described.
• Joint effusion gradually develops over a few hours. Patients with peripheral tears of the meniscus occasionally develop effusion rapidly (in minutes), secondary to a tear that is associated with hemarthrosis and is in the vascular outer one third of the meniscus. In 1993, Stanitski et al studied 70 young patients with hemarthrosis after acute trauma and found that 47% had anterior cruciate ligament (ACL) tears and 47% had meniscal tears. In adolescents (aged 13-18 y), the rate was 65% and 45%, respectively.^7,8
• Locking is a common symptom after a meniscal lesion develops. Locking usually occurs at 20-45° of joint extension. If a torn fragment has been trapped within the joint, extension may feel limited against a rubbery resistance. Joint effusion or capsular involvement also may mimic signs of locking. A more reliable indicator of meniscal lesion is a click or snap after the joint unlocks.
• A sensation of giving way may occur. In true meniscal lesions, the fragment becomes lodged momentarily in the knee joint, causing a sense of buckling. This finding should be distinguished from the sensation of giving way due to joint instability (eg, ACL tear) or buckling secondary to decreased activity of the quadriceps femoris muscle.

Physical

During clinical examination, use the uninvolved leg as the reference for comparison with qualitative and quantitative findings of the involved leg. Examination should include inspection, palpation, range of motion (ROM), gait, girth measurements, and tests for integrity of menisci and other structures of the knee joint.⁹

• Inspection
  • Look for effusion, and check the state of healing of any scars or incisions.
  • Identify any signs of atrophy. Marked atrophy of the quadriceps femoris muscle, especially the vastus medialis oblique (VMO) segment, is sometimes an indication of long-standing meniscal injury because the patient may be unwilling or unable to achieve full extension, and most tension is required of the VMO muscle at or near full extension.
• Palpation
  • Localized palpable tenderness at the joint line often is present in patients with meniscal lesions because the coronary ligaments are irritated.
  • Assess joint lines for palpable pain. The location of the tenderness is not a sure sign of the type of lesion.
  • To assess effusion, perform the fluid shift test and evaluate for the presence of the fluctuation sign. The amount of effusion does not indicate the presence or absence of a meniscal lesion.
• ROM and gait
  • The patient may have difficulty extending the knee fully if a meniscal tear blocks the motion.
  • Full flexion, as in squatting, may be painful or impossible because of a tear.
  • Assess the gait pattern, looking for deviations or compensatory movements.
• Girth measurements
  • Girth (circumference) measurements allow for a general assessment of effusion and atrophy.
  • Swelling within the knee joint is measured grossly by a girth measurement taken at the joint line.
  • Measurements taken at 5 cm and 20 cm proximal to the base of the patella and 15 cm distal to the apex of the patella can provide an indirect indication of atrophy in the VMO segment, quadriceps femoris muscle, and calf muscles, respectively.
• Tests: Perform stability tests for anterior, posterior, and varus-valgus motion to rule out additional involvement of soft tissue. Several special tests may be used to assess meniscal involvement. A positive result of any test does not by itself establish the presence of a meniscal lesion, but, along with the other objective findings, such a test result can help differentiate a meniscal tear from other possible knee injuries.
  • McMurray test
    • This test indicates tears of the middle or posterior horn of the meniscus.
    • With the patient supine and the hip and knee fully flexed, apply a valgus force and externally rotate the tibia while extending the knee. An audible or palpable pop or snap indicates a medial meniscal tear.
    • Lesions of the lateral meniscus are tested by applying a varus force and internally rotating the tibia during knee extension. The snap is produced as the torn fragment rides over the femoral condyle during extension.
    • A snap in extreme flexion is indicative of a posterior horn tear; a click at 90° of flexion indicates a lesion in the middle section of the meniscus.
  • Apley test
    • This test is used to distinguish between meniscal and ligamentous involvement.
    • With the patient in a prone position, the knee flexed at 90°, and the leg stabilized by the examiner's knee, distract the knee while rotating the tibia internally and externally. Pain during this maneuver indicates ligamentous involvement.
    • Then, compress the knee while internally and externally rotating the tibia again. Pain during this maneuver indicates a meniscal tear.
  • Bragard sign
    • This test may be used if anterior joint-line point tenderness is present.
    • To test for a medial lesion, the examiner extends and externally rotates the tibia, which displaces a meniscal lesion forward, if one exists. Palpable tenderness along the anterior medial joint line is reduced with flexion and internal rotation.
  • Bounce home test
    • The patient is supine with his or her heel cupped in the examiner's hand.
    • The examiner fully flexes the knee and then passively extends the knee. If the knee does not reach complete extension or has a rubbery or springy end feel, the knee movement may be blocked by a torn meniscus.
  • Childress test
    • Instruct the patient to squat with the knee fully flexed and attempt to "duck walk."
    • If the motion is blocked, a meniscal lesion is indicated; however, pain in this position may indicate a meniscal tear or patellofemoral joint involvement.
  • Merkel sign
    • Instruct the patient to stand with his or her knees extended and to rotate the trunk. This movement causes compression of the menisci.
    • Medial compartment pain during internal rotation of the tibia indicates a medial meniscal lesion. Lateral compartment pain occurring during external rotation of the tibia indicates a lateral meniscal lesion.
  • Modified Helfet test
    • While the patient is sitting on the edge of a table with the knee flexed 90°, instruct him or her to extend the knee.
    • If knee mechanics are within normal limits, the tibial tuberosity can be seen in line with the midline of the patella in full flexion; during extension, the tibia rotates and the tibial tubercle moves into line with the lateral border of the patella.
    • Failure of the tibia to rotate during extension indicates a meniscal lesion or cruciate ligament involvement.
  • O'Donoghue test
    • With the patient prone, the examiner flexes the knee 90°. The examiner rotates the tibia internally and externally twice, then fully extends the knee and repeats the rotations.
    • Increased pain during rotation in either or both knee positions indicates a meniscal tear or joint capsule irritation.
    • With a valgus force to a flexed and laterally rotated knee, the medial meniscus, medial collateral ligament (MCL), and the ACL all may be injured, representing the O'Donoghue triad.
  • Payr sign
    • With the patient sitting cross-legged, the examiner exerts downward pressure along the medial aspect of the knee.
    • Medial knee pain indicates a posterior horn lesion of the medial meniscus.
  • First Steinmann sign
    • With the patient supine and the knee and hip flexed at 90°, the examiner forcefully and quickly rotates the tibia internally and externally.
    • Pain in the lateral compartment with forced internal rotation indicates a lateral meniscus lesion. Medial compartment pain during forced external rotation indicates a lesion of the medial meniscus.
  • Second Steinmann sign
    • This test is indicated when point tenderness is located along the anterior joint line.
    • When the examiner moves the knee from extension into flexion, the meniscus is displaced posteriorly, along with its lesions. The point of tenderness also shifts posteriorly toward the collateral ligament.

Causes

Most commonly, meniscal injuries are due to a traumatic event (especially in athletes) or degenerative changes in older individuals. Meniscal tears are caused by twisting motions with the knee in a flexed position (eg, pivoting in basketball). Chronic or repetitive stress also may cause degenerative tears of the menisci.

A Danish study investigated whether an association exists between meniscal injuries and occupations that require kneeling.¹⁰  Magnetic resonance imaging (MRI) of the knees was conducted in 92 male floor layers and compared with MRI scans from referents, in this case 49 male graphic designers. (The mean age for all persons in the study was 55.6 years.) The incidence of degenerative tears of the medial meniscus was significantly higher in floor layers than in graphic designers, the odds ratio (OR) being 2.28. Medial tears in both knees also occurred more frequently in floor layers (OR 3.46). Tears in the lateral meniscus, however, were no more prevalent in floor layers than in graphic designers.

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