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INTRODUCTION ? A torn meniscus is a disruption of the fibrocartilage pads located between the femoral condyles and the tibial plateaus [1]. The medial and lateral meniscus provide shock absorption and play a role in joint lubrication.
Tears are classified as partial or complex; anterior, lateral, or posterior; traumatic or degenerative; and horizontal, vertical, radial, parrot-beak, or bucket handle. Significant tears lead to loss of smooth motion of the knee (locking), knee effusion, and premature osteoarthritis. Meniscal tears may occur in isolation or in association with a medial collateral ligament (MCL) or anterior collateral ligament (ACL) tear [2].
PRESENTATION ? The most common cause of meniscal injury is a twisting injury with the foot fixed; this frequently occurs in football and basketball. Older individuals may have degenerative tear with a history of minimal or no trauma.
The degree of pain at the time of injury is variable; most patients can ambulate after a small tear occurs and may continue to participate in the activity that caused the injury. The acute event is then followed by an insidious onset of pain and swelling over 24 hours. The pain is exacerbated by twisting or pivoting movements. Severe tears are usually associated with more significant pain and early restriction of knee motion. Some patients describe a tearing or popping sensation at the time of injury.
Patients with untreated meniscal tears can present weeks after the injury complaining of popping, locking, catching, and the knee "giving out," or may simply report a vague sense that the knee is not moving properly. This feeling of instability is related to the proprioceptive misinformation that occurs when a fragment (eg, meniscal tear) floats between the two articular surfaces, creating the sensation that the knee is not in the position in which it was anticipated to be. "Locking" is not true locking in the sense of not being able to move at all, but rather reflects the inability to fully extend the knee because of interference from the torn meniscus.
Effusions are common in patients with meniscal injury, particularly with large or complex tears and tears associated with degenerative arthritis. Patients typically complain of stiffness rather than swelling due to the effusion.
DIAGNOSIS ? The symptoms and signs of meniscal tear are often vague and nonspecific; the pain is not well localized or defined. A tentative diagnosis is based upon the history of mechanical catching or locking along with corroborating signs of physical examination. The diagnosis is confirmed by MRI or arthroscopy, although this is not necessary in most patients; the decision to proceed to MRI depends of the patient's age and whether or not surgery is considered. Arthroscopy is the definitive diagnostic and therapeutic test.
Physical examination ? Patients with certain types of meniscal tears can have a completely normal knee examination. Partial tears, horizontal tears, and anterior tears may not produce abnormal knee signs because of their size and anatomic location. These types of tears do not interfere with normal knee mechanics and are therefore less likely to compromise function or cause mechanical locking.
Patients with suspected meniscal injury are examined for:
Loss of passive smooth motion of the knee
Inability to squat or kneel
Palpably popping on the joint line (McMurray maneuver)
Joint effusion
The sensitivity and specificity of these tests for the diagnosis of meniscal injury is highly variable; one meta-analysis concluded that there is little evidence that the diagnosis of meniscal lesions is improved by these physical examination techniques [3]. However, the authors cautioned that these results be interpreted with care since the methods of the majority of studies included in the analysis were flawed. A positive McMurray test result had the most diagnostic significance in this report.
A subsequent literature review found mean estimates of sensitivity and specificity of 52 and 97 percent for the McMurray test (show table 1) [4]. In contrast to the above analysis, this subsequent review found that the overall physical exam showed good sensitivity and specificity for medial (86 and 72 percent, respectively) and lateral (88 and 92 percent, respectively) meniscal pathology (show table 2).
General knee function ? Screening tests for significant meniscal tears begin with an assessment of general knee function.
Gait is observed in order to assess the impact of the knee condition on the ability to ambulate. The patient is asked to walk in the examination room; this can be enhanced by asking the patient to toe and heel walk.
Passive and active flexion and extension of the knee are observed and compared with the opposite side. Loss of smooth motion is consistent with meniscal injury, although is a nonspecific finding.
The patient's ability to squat is observed to assess the flexibility of the knee, quadriceps muscle strength, and the influence of the patient's pain on his or her overall mobility. The patient is asked to squat as far as the pain allows, either performed free standing or holding onto the examination table. Squatting can be impaired by any cause of an effusion, moderate to advanced knee arthritis, injury to the supporting ligaments, and any condition reducing the effective strength of the supporting quadriceps mechanism.
The objective of observing the patient duck waddle is to assess the stability of the knee and ability to perform complex tasks (show picture 1). Duck waddling is virtually impossible with large, complex, vertical, or bucket-handle tears.
McMurray maneuver ? The McMurray maneuver, which involves passive flexion and extension of the knee, is used to assess the smooth motion of the joint (show picture 2). The maneuver should be performed several times. The tibia is internally rotated (relative to the femur) to trap the lateral meniscus and externally rotated to trap the medial meniscus. Full flexion and rotation of the tibia relative to the femur traps either posterior or posterolateral tears of the meniscus. A painful click or popping sensation in early or midextension noted under the examiner's fingers held firmly along the joint line is considered abnormal.
The sensitivity of the McMurray maneuver is limited since the test is incapable of trapping most anterior and anterolateral tears. A literature review found mean estimates of sensitivity and specificity of 52 and 97 percent for diagnosing meniscal tears (show table 1) [4]. Thus, a negative test does not exclude a meniscal tear. As mentioned above, a meta-analysis suggested that a positive test may have the most diagnostic significance of the physical examination maneuvers [3].
Detection of an effusion ? As mentioned above, an effusion may be detected in patients with meniscal tears, particularly large or complex tears and tears associated with degenerative arthritis. There are several ways to evaluate for an effusion (see "Evaluation of the patient with knee pain", section on Detection of an effusion, for a more complete discussion of the physical examination for effusion):
Small effusions (5 to 10 mL) will fill the peripatellar dimples with the knees extended and quadriceps muscles relaxed.
"Milking" the knee detects highly viscous effusions.
The ballottement sign is positive when there is at least 10 to 15 mL of intraarticular fluid.
Large effusions (20 to 30 mL) fill the suprapatellar space.
Knee flexion, as assessed by heel-to-buttock measurement (show picture 3) is also reduced in the presence of an effusion.
Joint aspiration is the definitive test for a knee effusion (show picture 4). Aspiration is indicated if infection is in the differential diagnosis. Joint aspiration may also be considered in patients who have the rapid development of a large effusion (eg, within three hours of injury) to rule out hemarthrosis. Hemarthrosis is unusual in patients with an isolated meniscal tear, and should raise the suspicion of an associated ACL tear or intraarticular fracture [5]. (See "Hemarthrosis").
Radiography ? X-rays of the knee, including sunrise, tunnel, posteroanterior, and lateral views, are appropriate in some patients with suspected meniscal tear. In patients with acute trauma to the knee, the Ottawa Knee Rules have been shown to be nearly 100 percent sensitive and 49 percent specific in the detection of clinically significant fractures (any bone fragment at least 5 mm in breadth or any avulsion fracture associated with complete disruption of tendons or ligaments) [6,7]. These rules state that radiographs of the knee should be obtained after acute injury only in patients who meet one of the following criteria [8]:
Age 55 years
Isolated tenderness of patella (with no other bony tenderness of the knee)
Tenderness at the head of the fibula
Inability to flex the knee to 90 degrees
Inability to bear weight both immediately and in the emergency department for four steps, regardless of limp (ie, unable to transfer weight onto each lower limb two times)
Plain films of the knee may also show degenerative change, calcification of the meniscus, or calcified loose bodies. The tunnel view demonstrates the intercondylar notch and may show a sequestered loose body.
MRI can define the extent and type of meniscal tear, although is usually not necessary unless surgery is being considered (see below). Nevertheless, it is the most sensitive imaging modality for detecting even the most subtle tears, with reported accuracy between 89 and 98 percent [9,10]. The negative predictive value of MRI in the exclusion of meniscal tears has approached 100 percent in some studies [2,11]. However, a subsequent review of the literature found that MRI had somewhat lower sensitivity and specificity for medial (89 and 80 percent, respectively) and lateral (79 and 91 percent, respectively) meniscal pathology (show table 2) [4].
MRI must be interpreted cautiously. Mucinoid degenerative change (increased signal arising from the center of the meniscus) is a common finding. This is a normal part of the aging process of the meniscus and should not be misinterpreted as a traumatic meniscal tear. This problem was illustrated in a study of 74 asymptomatic volunteers without a history of knee injury [12]. The incidence of MRI findings of a meniscal tear increased from 13 percent in individuals under the age of 45 to 36 percent in older patients. Additionally, asymptomatic tears are common in the contralateral knees of patients with symptoms in one knee apparently attributable to a meniscal tear. A study that performed MRI on both knees of 100 patients with unilateral findings suggesting a meniscal tear found that 57 patients had tears on the symptomatic side; of those 57, 36 also had tears on the contralateral side while none of the 43 patients without tears on the symptomatic side had contralateral tears [13].
TREATMENT ? The goals of treatment are:
Define the type and extent of the tear
Strengthen the muscular support of the knee
Determine the need for surgery
The management of meniscal tears depends upon the type of tear (eg, intrasubstance, horizontal, or vertical), the presence of significant mechanical symptoms, and the presence of persistent knee effusion. Small intrasubstance and vertical tears that cause infrequent symptoms and do not interfere with general knee function can be managed medically with rest, activity restriction, and exercises. Large, complex tears that are associated with persistent effusion, tears with frequently disabling symptoms, and vertical tears (in contact with the articular cartilage) should be referred for surgical repair or removal.
Factors that may suggest that conservative therapy is likely to be successful include [14]:
Symptoms develop over 24 to 48 hours after injury (as opposed to immediate)
The patient is able to bear weight
There is minimal swelling
There is full range of movement with pain only at the end of range of motion
Pain on McMurray's test is only in the inner range of flexion
Factors that may suggest that surgery will be required include:
There was a severe twisting injury and activity could not be continued
The knee is locked or motion is severely restricted
Pain on McMurray's test with minimal knee flexion
Presence of an associated ACL tear
Little improvement in symptoms after three weeks of conservative treatment
Acute therapy ? In the absence of hemarthrosis and gross instability, the initial management of meniscal tear includes the following: (See "Patient information: Physical therapy for knee problems")
Restrict activities and all sports. Avoid positions and activities that place excessive pressure on the knee joint until the pain and swelling resolve, including squatting, kneeling, twisting and pivoting, repetitive bending (eg, stairs, getting out of a seated position, clutch and pedal pushing), jogging, jazzercize, swimming using the frog or whip kick, and bicycling.
Apply ice to the knee for 15 minutes every four to six hours with the leg elevated
Encourage the use of crutches if the pain is severe
Prescribe a patellar restraining brace if quadriceps tone is poor and the knee frequently "gives out"
Patients should begin straight leg raising exercises without weights as the pain begins to wane with the goal of strengthening the quadriceps and hamstring muscles to provide support to the joint (show figure 1). Begin with sets of 10 leg lifts and gradually work up to 20 to 25 lifts, each held for 5 seconds. With improvement, weight can be added to the ankle, beginning with a two pound weight (eg, a heavy shoe, fishing weights or coins in a sock, a purse with a book in it) and gradually increase to a weight of 5 to 10 pounds.
Weighted leg lifts with the knee bent can begin if the above do not aggravate knee symptoms. Initially the knee is bent to 30º using weights and repetitions as described above. The amount of bending is gradually increased as tolerated in increments of 30º to 45º to 60º to 90º of bending.
Exercise on equipment such as the stair stepper, stationary bicycle, rowing machine, and universal gym utilizing leg extensions should be avoided until pain and swelling resolve. Exercises to encourage include fast walking, water aerobics, swimming using the crawl stroke, cross-country ski glide machines, soft platform treadmill, and trampoline.
Persistent symptoms ? Patients with symptoms that persist for two to four weeks despite the above should have any persistent effusion aspirated for diagnostic studies and to relieve pain. An MRI should also be obtained if mechanical symptoms and an effusion persist. Corticosteroid injection is recommended only in patients who have osteoarthritis complicated by a degenerative meniscal tear.
Referral ? Consultation with an orthopedic surgeon is considered if patients continue to have an effusion, frequent locking, and disabling symptoms after four to six weeks. Some data suggest that early surgical repair (eg, within three months of injury) improves outcomes compared with later repair [15].
Arthroscopic or open surgery ? The decision to undergo surgery for a meniscal tear depends upon a number of factors:
Frequency of symptoms (eg, daily)
General knee function (eg, unable to squat, unstable knee)
Type of tear (eg, complex tear extending to the articular surface)
Likelihood that leaving it unrepaired may lead to further damage to the articular cartilage
Surgical options include partial or total meniscectomy and repair of the meniscal tear. Open or arthroscopic surgery can be performed. A review that compared these options concluded that a lack of randomized trials precludes an evidence-based recommendation regarding meniscal repair versus excision [16]. Randomized trials have found no evidence of difference in radiological or long term clinical outcomes between arthroscopic and open meniscal surgery, or between total and partial meniscectomy. Partial meniscectomy may be preferable to total removal of the meniscus in terms of recovery and overall functional outcome in the short term.
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