INTRODUCTION — Meniscal injuries of the knee are common. Acute meniscal tears occur most often from twisting injuries; chronic degenerative tears occur in older patients and can occur with minimal twisting or stress. Tears are classified as partial or complex; anterior, lateral, or posterior; traumatic or degenerative; and horizontal, vertical, radial, “parrot-beak,” or “bucket handle.”
Left untreated, large complex tears impair smooth motion of the knee (locking), cause joint effusions, and lead to premature osteoarthritis. Meniscal injuries can occur in isolation or in association with collateral or cruciate ligament tears. The diagnosis and treatment of meniscal injuries will be reviewed here. Undifferentiated knee pain in the adult, physical examination of the knee, and other specific knee injuries are discussed separately.
ANATOMY — The two menisci contained within the knee joint are crescent-shaped pads of fibrocartilage located between the femoral condyles and the tibial plateaus. They aid in dissipating loading forces placed on the knee, stabilizing the knee during rotation, and lubricating the knee joint.
In cross section, the medial and lateral menisci are wedge-shaped with the thicker portion along the joint periphery, where they attach to the joint capsule of the knee. The medial meniscus is firmly attached to the medial collateral ligament; the lateral meniscus is not rigidly attached to the lateral collateral ligament and therefore more mobile. This may contribute to its lower injury rate.
The menisci receive blood from branches of the geniculate arteries. However, arterial flow to the inner portions of the menisci is limited compared to the peripheral or outer portions. This explains in part why tears of the inner menisci often do not heal.
PRESENTATION — The most common cause of a meniscal tear is a twisting injury with the foot fixed; this frequently occurs in football (soccer), basketball, American football, and other sports that involve sudden deceleration and change in direction. Older individuals can develop a degenerative tear with minimal or no trauma. When it does occur, such trauma may be so minor that the patient omits it from the history.
The degree of pain at the time of injury is variable; most patients can ambulate after a small tear occurs and can continue to participate in the activity that caused the injury. The acute event is then followed by the 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 patients 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 meniscal fragment floats between the two articular surfaces, creating the sensation that the knee is not in the position it should be. “Locking” does not mean being completely unable to move the knee, but rather the inability to extend the knee fully 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 with an effusion typically complain of stiffness rather than swelling.
DIAGNOSIS — The symptoms and signs of meniscal tear are often vague and nonspecific, as the pain may not be well localized or defined. A presumptive diagnosis is based upon the mechanism of injury, characteristic symptoms, such as mechanical catching or locking, and corroborating signs from the physical examination. Clinicians with experience using musculoskeletal ultrasound often use such imaging to assist in diagnosis. The diagnosis may be confirmed by MRI or arthroscopy, although this is unnecessary in many patients, particularly those with findings suggesting that nonoperative management will be successful.
The decision to proceed to MRI depends upon the patient’s age and whether surgery is being considered. Arthroscopy is the definitive diagnostic and therapeutic test.
In older patients, osteoarthritis of the knee may be the cause of symptoms, rather than a chronic degenerative tear of the meniscus. Therapy for osteoarthritis should be maximized.
Overview — The accuracy of the physical examination for meniscal tear varies depending upon the type and location of the tear. Patients with partial, horizontal, or anterior meniscal tears can have a completely normal knee examination. Such tears often do not interfere with normal knee mechanics and are therefore less likely to compromise function or cause mechanical symptoms.
Performance of the knee examination is described in detail separately; concepts and tests of particular importance to the evaluation of meniscal injury are reviewed here.
Patients with suspected meniscal injury should be examined for:
- Joint line tenderness
- Abnormal knee motion: look for loss of smooth passive motion or an inability to fully extend the knee
- Inability to squat or kneel
- Palpable catching at the joint line as detected by the McMurray maneuver
- Pain elicited by specific provocative tests (eg, Thessaly test)
- Joint effusion
Multiple positive examination findings in the setting of a suggestive mechanism make the diagnosis of meniscal injury likely.
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 upon ambulation.
- Flexion and extension of the knee, both passive and active, are assessed and compared with the unaffected side. Loss of smooth motion is consistent with meniscal injury, although it is a nonspecific finding.
- Squat: The patient’s ability to squat is observed to assess the flexibility of the knee, quadriceps muscle strength, and the effect of the patient’s pain on overall mobility. The patient is asked to squat as deeply as pain and mobility allow. The patient may perform the squat free standing or while holding onto the examination table for support.
Squatting can be impaired by an effusion, moderate to advanced knee arthritis, injuries to supporting ligaments, and any condition that reduces quadriceps strength.
Having the patient duck waddle while in a squatting position allows the clinician to assess knee stability and the ability to perform complex motor tasks. Duck waddling is virtually impossible with large complex vertical or bucket-handled meniscal tears. Older patients often cannot perform this maneuver and other provocative tests may be more useful in this patient population.
Provocative testing — The Thessaly, McMurray, Apley compression, and bounce home tests are provocative maneuvers designed to elicit discomfort or a catching sensation in patients with meniscal tears.
- Thessaly test – The Thessaly test attempts to simulate the loading forces placed upon the knee. It involves having the patient hold an examiner’s hand and then stand on one leg with the knee flexed to 20 degrees. From this position, the patient then internally and externally rotates their knee. Pain or a locking or catching sensation constitutes a positive test.Two prospective studies of 116 and 213 patients referred to sports medicine clinics for possible meniscal tear found the Thessaly test to have a sensitivity of approximately 90 percent and a specificity of 96 percent for meniscal tear. A third prospective study of 109 patients found the sensitivity to be only 61 percent for medial meniscal tear but 80 percent for lateral tear. Further study of the Thessaly test in a wider patient population is needed.
- McMurray test – The McMurray maneuver, which involves passive flexion and extension of the knee, is used to assess joint motion. Full flexion and rotation of the tibia relative to the femur traps either posterior or posterolateral tears of the meniscus. A painful click in early- or mid-extension is suggestive of a meniscal tear.The sensitivity of the McMurray maneuver is limited since the maneuver is incapable of trapping most anterior and anterolateral tears. Three systematic reviews found the sensitivity of the test to range from 51 to 53 percent, but specificity varied widely, ranging from 59 to 97 percent. Clinicians should be aware that a negative test does not exclude a meniscal tear.
- Apley test – The Apley test is performed with the patient prone and the affected knee flexed to 90 degrees. The clinician can stabilize the patient’s thigh with a knee or hand. The maneuver is performed by pressing the patient’s heel directly toward the floor while internally and externally rotating the foot, thereby compressing the meniscus between the tibial plateau and the femoral condyles. Focal pain elicited by compression marks a positive test. The sensitivity of the Apley test was found to be only 38 and 41 percent, respectively, in a systematic review and a subsequent prospective trial.
- Bounce home test – Although not well studied, the bounce or bounce home test is used by some clinicians to help determine the presence of intraarticular pathology, particularly meniscal tear. It is performed by holding the heel of a relaxed supine patient with their legs extended and gently bouncing the leg. A normal knee falls into full extension while an abnormal knee does not.
Detection of an effusion — An effusion may be detected in patients with meniscal tears, particularly large or complex tears and tears associated with degenerative arthritis. Signs of an effusion are mentioned here, but a more complete discussion of the examination for knee effusion is found separately.
There are several ways to evaluate for an 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, is reduced in the presence of an effusion.
Joint aspiration is the definitive test for a knee effusion. Aspiration is indicated if the knee joint may be infected. Joint aspiration may also be helpful in patients who rapidly develop 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 suspicion for an associated ACL tear or intraarticular fracture.
Plain radiographs — X-rays of the knee, including sunrise, tunnel, posteroanterior, and lateral views, are appropriate in some patients with suspected meniscal tear. The Ottawa knee rule provides useful guidance for determining whether x-rays are indicated following an acute injury. This rule is discussed separately.
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 reveal a sequestered loose body.
Ultrasound — Bedside ultrasound is being used more frequently to assess patients with acute knee injuries. Ultrasound allows the skilled practitioner to examine the knee dynamically and to compare injured and uninjured joints. Several small prospective studies have found the sensitivity of ultrasound for meniscal tear to range from 83 to 86 percent. Larger studies are needed to determine the accuracy and appropriate use of ultrasound in the evaluation of meniscal tear.
Magnetic resonance imaging — Magnetic resonance imaging (MRI) can define the extent and type of meniscal tear and is the most sensitive imaging modality for detecting small tears. However, MRI is usually not necessary unless surgery is being considered. According to a systematic review, MRI has a sensitivity and specificity of 89 and 80 percent, respectively, for medial meniscal tear and of 79 and 91 percent, respectively, for lateral meniscal tear.
MRI findings 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 and should not be misinterpreted as a traumatic meniscal tear. In addition, asymptomatic tears are common in the contralateral knees of patients with symptoms attributable to a meniscal tear.
The need for careful MRI interpretation has been illustrated in several observational studies.
- In a study of 74 asymptomatic volunteers without a history of knee injury, 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.
- In a population-based sample of 991 subjects, the prevalence of meniscal tears evident on MRI was even higher among patients aged 70 to 90 years, with 40 percent of women and 50 percent of men showing signs of injury.
- In another study, MRI was performed on both knees of 100 patients with unilateral findings suggesting a meniscal tear. Fifty-seven patients had meniscal tears on the symptomatic side and of those 57, 36 also had tears on the asymptomatic side. None of the 43 patients without a meniscal tear on the symptomatic side had a contralateral injury.
Initial management — In the absence of hemarthrosis and gross instability, the initial management of a meniscal tear includes the following:
- Rest the knee.
Avoid positions and activities that place excessive pressure on the knee joint until pain and swelling resolve. Such activities include: squatting, kneeling, twisting and pivoting, repetitive bending (eg, stairs, getting out of a seated position, clutch and pedal pushing), jogging, exercise classes, dancing, swimming using the frog or whip kick, and bicycling.
- Apply ice to the knee for 15 minutes every four to six hours, while keeping the leg elevated.
- Encourage the use of crutches if the pain is severe.
- Prescribe a patellar restraining brace if quadriceps strength 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. Begin with sets of 10 leg lifts and gradually work up to 20 to 25 lifts, each held for five seconds. With improvement, light weights can be added to the ankle, beginning with a two pound weight and gradually increasing the weight to 5 to 10 pounds. In lieu of exercise weights, a heavy shoe, fishing weights or coins placed in a sock, or a purse containing a book may be used.
Exercise on equipment that requires deep knee bends against resistance, such as the stair stepper, stationary bicycle, and rowing machine, should be avoided until pain and swelling resolve. Suitable exercises may include walking, swimming using a limited crawl kick, water aerobics, walking or light jogging on a soft platform treadmill, and using a cross-country ski glide machine.
Approach to treatment and orthopedic referral — Definitive treatment of meniscal tears includes:
- Strengthening the muscular support of the knee
- Defining the type and extent of the tear
- Determining 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 effusions. 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 physical therapy. Many knowledgeable clinicians try to exhaust conservative management options before referring such patients for surgery.
The following factors suggest conservative therapy will be successful:
- Symptoms develop over 24 to 48 hours after the acute injury (as opposed to immediately after)
- The patient is able to bear weight
- There is minimal swelling
- The knee has full range of movement with pain only at or near full flexion
- Pain on McMurray testing occurs only with deep knee flexion
Large, complex tears associated with persistent effusions, tears that frequently cause disabling symptoms, and large vertical tears in contact with the articular cartilage should be referred to an orthopedist without delay.
The following factors suggest surgery will be required:
- A severe twisting injury occurred and activity could not be resumed thereafter
- The knee is locked or motion is severely restricted
- Pain develops with McMurray testing involving minimal knee flexion
- An associated anterior cruciate ligament tear exists
- There is little improvement in symptoms after three weeks despite proper conservative treatment
Persistent symptoms — An MRI of the knee should be obtained for any patient with notable mechanical symptoms or recurrent effusions that persist for three to four weeks despite the initial management described above. Any significant persistent effusion is aspirated for diagnostic studies and pain relief.
A glucocorticoid injection is useful only in patients who have osteoarthritis complicated by a degenerative meniscal tear.
Consultation with an orthopedic surgeon is needed if the MRI demonstrates a large or complex meniscal tear or the patient continues to develop joint effusions, frequent locking of the knee, or other disabling symptoms after four to six weeks of conservative management. Some observational data suggest that early surgical repair (eg, within three months of injury) improves outcomes compared with later repair.
Knee “locking” — “Locking” of the knee can occur when some portion of a torn meniscus, or some other body (eg, cartilage fragment), interposes between the femur and the tibia preventing motion. In rare instances, a torn anterior cruciate ligament may be responsible. Locking typically occurs suddenly and may resolve spontaneously equally suddenly. Some patients with a torn, interposed meniscus may not have a mechanical impediment to movement but may be apprehensive about moving the knee or having it manipulated. Such patients, as well as those with a truly locked joint, may benefit from icing or an intra-articular injection of anesthetic (eg, lidocaine). MRI may help determine whether a true mechanical lock is present.
Release of a locked knee can sometimes be accomplished by applying longitudinal traction to the leg while simultaneously rotating the leg gently both internally and externally. If the knee cannot be released after several hours of treatment and rest, referral to an orthopedic surgeon is needed. If the knee is released and motion restored, the need for surgical referral depends upon the frequency of locking and the degree to which it is interfering with daily activities.
Surgery is often needed in patients with knee locking, but some patients accommodate. Surgical repair of the meniscus is often less successful in older patients with severe osteoarthritis of the knee and degenerative meniscal tearing. Some clinicians wait until locking is recurrent and debilitating in such patients before referring them for surgery. Patients can reduce the risk of locking by avoiding activities that involve full flexion of the knee.
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 meniscus unrepaired will lead to further damage of the articular cartilage
Surgical options include partial or total meniscectomy and repair of the meniscal tear. Open or arthroscopic surgery can be performed. An important surgical principle is to retain as much functioning meniscus as possible.
Functional rehabilitation plays an important role in recovery. Patients with chronic tears generally require more time for recovery following surgery than those with acute injuries.
Chronic degenerative meniscal injury — Tears associated with chronic degeneration of the meniscus occur in older patients and may not be associated with an acute injury. Meniscectomy does not appear to help in such cases, but physical therapy may.
In a small randomized trial, patients with tears associated with chronic degeneration of the meniscus improved their knee function and decreased their pain through participation in a rigorous rehabilitation program. The addition of partial meniscectomy did not improve clinical outcomes.
OUTCOMES — The long-term outcome of patients with meniscal tears varies according to the type of tear and the underlying condition of the knee. The prognosis is good for patients with tears amenable to nonsurgical management.
Among patients treated surgically, younger patients with isolated tears generally do well. According to a retrospective review of 362 medial and 109 lateral isolated arthroscopic meniscectomies, factors associated with a favorable prognosis include: age less than 35 years, a vertical tear, no cartilage damage, and an intact meniscal rim upon completion of the procedure.
Degenerative tears appear to be associated with a worse prognosis. In a small retrospective study of patients over 50 who underwent arthroscopic meniscectomy, 90 percent of those with nondegenerative tears (ie, acute meniscal injury) had good results at six year follow-up, compared with only 20 percent of patients with degenerative tears (ie, chronic meniscal injury).
Meniscal injury does predispose patients to the development of osteoarthritis over the long term.
- The most common mechanism for meniscal tear is a twisting injury with the foot fixed. Older individuals may develop a degenerative tear with minimal or no trauma.
- The degree of pain at the time of injury is variable; most patients can ambulate after incurring a small tear. Swelling may develop over the subsequent 24 hours. 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, catching, locking, the knee “giving out,” or the knee not moving properly.
- The symptoms and signs of meniscal tear are often vague and nonspecific; the pain may not be well localized or defined. Often a presumptive diagnosis is made based upon the history and physical examination. The diagnosis may be confirmed by MRI or arthroscopy, but this is unnecessary in most patients; the decision to proceed to MRI depends upon the patient’s age and whether surgery is being considered. Arthroscopy is the definitive test.
- Partial tears, horizontal tears, and anterior tears may not produce abnormal signs because of their size and location. Such tears do not interfere with normal knee mechanics and are less likely to compromise function or cause mechanical locking.
- Patients with suspected meniscal injury are examined for:
- Joint line tenderness
- Inability to squat or kneel
- Loss of passive smooth motion of the knee; inability to extend the knee fully
- Palpable catching on the joint line (McMurray maneuver)
- Pain elicited by specific tests (eg, Thessaly test)
- Joint effusion