Meniscal injury of the knee

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.

Left untreated, large complex tears can impair smooth motion of the knee, cause joint effusions, and may lead to premature osteoarthritis. Meniscal injuries can occur in isolation or in association with collateral or cruciate ligament tears. (See "Medial (tibial) collateral ligament injury of the knee" and "Anterior cruciate ligament injury".)

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. (See "Approach to the adult with unspecified knee pain".)

ANATOMY AND TEAR TYPES — The two menisci contained within the knee joint are crescent-shaped pads of fibrocartilage located between the femoral condyles and the tibial plateaus (figure 1 and figure 2) [1]. 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 (sometimes referred to as root attachments). 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 the lower injury rate of the lateral meniscus.

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.

Meniscus tears can be classified as simple or complex; anterior, lateral, or posterior (based on location); traumatic or degenerative; and horizontal, vertical, radial, "parrot-beak," or "bucket handle" (figure 3) [2]. Occasionally, the meniscus can tear off the tibia at its anterior or posterior end, which is referred to as a "meniscus root tear."

MECHANISM AND PRESENTATION — Acute meniscal tears typically occur when a person changes direction in a manner that involves rotating or "twisting" the knee while the knee is flexed and the corresponding foot is planted [3-5]. Such a maneuver places compressive, rotational, and shear stresses on the meniscus, which if they are excessive cause the meniscus to tear.

This mechanism frequently occurs in football (soccer), basketball, American football, and other sports that involve rapid 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. Meniscal tears are rare in children below the age of 10 years [6]. (See 'Chronic degenerative meniscal injury' below and "Approach to acute knee pain and injury in children and skeletally immature adolescents", section on 'Meniscal tear'.)

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.

Although traditionally ascribed to meniscal injury, mechanical symptoms such as popping, catching, or giving out may be caused by articular cartilage damage or other knee injury [7]. (See 'Differential diagnosis' below and "Approach to the adult with knee pain likely of musculoskeletal origin".)

Effusions are common in patients with meniscal injury, particularly with large or complex tears, and can occur intermittently from tears associated with degenerative arthritis. Patients with an effusion typically complain of stiffness rather than swelling.

PHYSICAL EXAMINATION

Overview — The accuracy of the physical examination for meniscal tear varies depending upon the type and location of the tear [8-11]. 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. (See "Physical examination of the knee".)

Patients with suspected meniscal injury should be examined for [3,4,12]:

●Joint line tenderness (a sensitive but nonspecific finding)

●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 (picture 1). 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 are likely to be more useful in this patient population. Limited evidence suggests the duck waddle test is neither sensitive nor specific for meniscal tear [13].

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 (movie 1). To perform the test, the patient and examiner face each other and hold hands for support. The patient then stands on one leg with their knee flexed to 20 degrees and rotates the knee and body, while maintaining knee flexion. This internally and externally rotates the knee, while loading the meniscus. Pain or a locking or catching sensation constitutes a positive test. The test should always be performed on the normal knee first so the patient can be trained and so a comparison to the affected knee can be made.

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 [14,15]. 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 [9]. Further study of the Thessaly test in a wider patient population is needed.

●McMurray test – The McMurray maneuver, which involves repeated passive flexion and extension of the knee, is used to assess joint motion and meniscal injury (picture 2). A painful click in early- or mid-extension that is typically felt but sometimes heard is suggestive of a meniscal tear. Pain along the joint line during the maneuver also suggests a meniscal tear. We perform the test as follows:

•Grasp the patient's heel with one hand and place the fingers and thumb of the other hand along the joint line of the knee.

•Passively flex the knee as much as possible and internally rotate the tibia.

•Gradually extend the knee as much as possible while maintaining internal rotation of the tibia.

•Smoothly repeat full passive flexion and extension of the knee a few times, while keeping the tibia in internal rotation.

•Then, passively flex the knee as much as possible and externally rotate the tibia.

•Smoothly repeat full passive flexion and extension of the knee a few times, while keeping the tibia in external rotation.

Full flexion of the knee during the McMurray maneuver tests the posterior and middle portions of the meniscus; 90 degrees and more of knee flexion allows testing of the more anterior portions of the meniscus, although anterior tears are more difficult to detect.

During the McMurray maneuver, the clinician may apply slight valgus pressure to the lateral aspect of the knee while it is flexed and extended a few times, and then slight varus pressure to the medial aspect of the knee while the maneuver is repeated a few times. Both internal rotation of the tibia and application of a varus (medial) stress are performed to assess the lateral meniscus; both external rotation and application of a valgus (lateral) stress are performed to assess the medial meniscus. While not part of McMurray's original description and not well studied, varus or valgus pressure may increase the stress applied to the injured meniscus and elicit pain [16].

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 [4,17,18]. 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 [19]. 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 [17,18].

●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 (figure 4) [3]. 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. (See "Physical examination of the knee", section on 'Detection of an effusion'.)

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 (picture 3).

Joint aspiration is the definitive test for a knee effusion (picture 4). 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 [20]. The presence of fat globules in aspirate may be indicative of a fracture [21]. (See "Overview of hemarthrosis" and "Anterior cruciate ligament injury".)

IMAGING

Plain radiographs — Radiographs of the knee, possibly including sunrise, tunnel, posteroanterior, weightbearing anteroposterior, and lateral views, are appropriate in some patients with suspected meniscal tear. The Ottawa knee rule provides useful guidance for determining whether radiographs are indicated following an acute injury. This rule is discussed separately. (See "Approach to the adult with knee pain likely of musculoskeletal origin", section on 'Ottawa Knee Rule (OKR)' and "Radiologic evaluation of the acutely painful knee in adults".)

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 or an osteochondral defect.

Ultrasound — Office based ultrasound is being used more frequently to assess patients with acute knee pain. Ultrasound is safe, inexpensive, and allows the skilled practitioner to examine the knee dynamically and to compare injured and uninjured joints. The main limitation of ultrasound is its inability to visualize completely deep, internal structures of the knee. Performance of the standard knee ultrasound examination is reviewed separately. (See "Musculoskeletal ultrasound of the knee".)

A series of small observational studies evaluating the use of ultrasound to diagnose meniscal tears report sensitivity ranging from 83 to 100 percent, and specificity ranging from 71 to 89 percent [22-28]. In these studies, ultrasound was compared to arthroscopy and magnetic resonance imaging (MRI) findings. Further study is needed to determine the overall accuracy of ultrasound in the evaluation of meniscal tears.

Magnetic resonance imaging — MRI can define the extent and type of meniscal tear (figure 3) and is the most sensitive imaging modality for detecting small tears (image 1) [11,19,29,30]. However, MRI is usually not necessary unless surgery is being considered. According to a systematic review, MRI has a sensitivity and specificity of 91.4 and 81.1 percent, respectively, for medial meniscal tear, and of 76 and 93.3 percent, respectively, for lateral meniscal tear [31]. MRI has limited capacity for determining which tears are amenable to surgical repair [32-34].

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 [35].

●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 [36].

●In another study, MRI was performed on both knees of 100 patients with unilateral findings suggesting a meniscal tear [37]. 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.

DIAGNOSIS — Diagnosing an acute meniscal tear can be difficult because the symptoms and signs are often vague and nonspecific, and pain may not be well localized or defined. In addition, chronic degenerative tears not associated with a discrete traumatic incident can develop in older patients. A presumptive diagnosis of meniscal tear is based upon the mechanism of injury in the case of acute tears (often involving twisting the knee while the foot is planted), common symptoms, such as mechanical catching or locking, and corroborating signs from the physical examination, including joint line tenderness and positive provocative tests (eg, McMurray, Thessaly). (See 'Mechanism and presentation' above and 'Physical examination' above.)

Clinicians with experience using musculoskeletal ultrasound sometimes use such imaging to assist in diagnosis. The diagnosis may be confirmed by magnetic resonance imaging (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. (See 'Approach to treatment and orthopedic referral' below.)

In older patients, osteoarthritis of the knee often coexists with chronic degenerative tear of the meniscus. Therapy for osteoarthritis should be maximized. (See 'Chronic degenerative meniscal injury' below and "Overview of surgical therapy of knee and hip osteoarthritis" and "Management of knee osteoarthritis".)

DIFFERENTIAL DIAGNOSIS — While no single symptom or examination test can definitively diagnose a meniscus tear, the presence of a combination of suggestive historical features (eg, knee locking) and examination findings (eg, focal joint line tenderness, positive Thessaly test) significantly increases the likelihood of meniscus injury, while reducing the likelihood of other conditions. Nevertheless, several knee conditions can present with symptoms and signs that overlap with meniscal tear. Some symptoms traditionally associated with meniscus tears, such as catching, locking, and popping, may be caused more often by damaged articular cartilage [7]. (See "Approach to the adult with knee pain likely of musculoskeletal origin".)

The mechanical symptoms (eg, loss of smooth knee flexion and extension; giving out; catching or locking) can be caused by osteoarthritis (OA) in its advanced stages, anterior cruciate ligament (ACL) tears, intraarticular loose bodies (eg, osteochondral lesions off the femur or patella), tibial plateau fracture, pigmented villonodular synovitis [38], chondrocalcinosis, and congenital discoid meniscus. Abnormal clicking and popping can also be caused by patellofemoral pain and OA. Acute hemarthrosis is most commonly caused by tears of the ACL or a fracture of the tibial plateau or patella. In some cases, a meniscus tear can also cause an acute hemarthrosis. (See "Anterior cruciate ligament injury" and "Proximal tibial fractures in adults" and "Patellofemoral pain" and "Patella fractures" and "Clinical manifestations and diagnosis of osteoarthritis", section on 'Knee'.)

OA is distinguished from an acute meniscal tear on the basis of patient demographics, mechanism of injury, clinical findings more consistent with degenerative change of the knee joint, and radiographic appearance (if radiographs are obtained). Acute meniscal tears typically occur in younger adults playing higher risk sports, are caused by a sudden injury involving twisting of the knee while the foot is planted, and do not manifest the typical sequelae of OA on plain radiographs. However, OA and degenerative meniscal tears often coexist, in which case magnetic resonance imaging (MRI) or arthroscopy is necessary to make a definitive diagnosis, if this is necessary.

ACL tears cause knee laxity, as demonstrated by positive Lachman and anterior drawer tests, but may be accompanied by a meniscus tear. Isolated meniscal tears do not cause knee laxity.

Fractures of the tibial plateau or patella often involve significant trauma to the knee and generally are visible on plain radiographs. Distinguishing a loose intraarticular body, discoid meniscus, or pigmented villonodular synovitis from a meniscal tear is difficult and often requires imaging or arthroscopy.

Patellofemoral pain is often gradual in onset, typically causes vague symptoms around the patella rather than the joint line, does not cause true locking of the knee, may be consistently associated with particular activities (eg, prolonged sitting, going up and down stairs), and is often associated with weak quadriceps and hip abductors. When the physical examination demonstrates a significant knee effusion, a large isolated meniscus tear is a possible cause, but often other intraarticular structures are injured. Aspiration of a knee with an effusion may reveal blood or crystals, findings that suggest diagnoses other than meniscus injury.

TREATMENT

Initial management — In the absence of hemarthrosis and gross instability, the initial management of a meniscal tear includes the following (table 1):

●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, dancing, and swimming using the frog or whip kick.

●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.

●A patellar restraining brace may be helpful 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 to provide support to the joint (picture 5). 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 2 pound weight and gradually increasing the weight to 5 to 10 pounds. In lieu of exercise weights, a heavy shoe or a bag containing one or more books may be used.

Exercise on equipment that requires deep knee bends against resistance, such as the stair stepper and rowing machine, should be avoided until pain and swelling resolve. Suitable exercises may include walking, swimming using a limited freestyle 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 (figure 3)), 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. Studies have reported no greater improvement in short-term functional outcomes from surgery, and many clinicians try to exhaust conservative management options before referring such patients for surgery [39,40].

The following factors suggest conservative therapy will be successful [5,41]:

●Symptoms develop over 24 to 48 hours after the acute injury (as opposed to immediately after)

●Swelling is minimal

●The knee has full range of movement with pain only at or near full flexion

●Pain with McMurray testing occurs only with deep knee flexion

Large, complex tears associated with persistent effusions, tears that frequently cause disabling symptoms, and large tears in contact with the articular cartilage should be referred to an orthopedist. In addition, if the patient is unable to extend their knee completely ("locked knee"), immediate referral to an orthopedist is necessary.

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 (see "Anterior cruciate ligament injury")

●There is little improvement in symptoms after three to six weeks despite proper conservative treatment

Persistent symptoms — A magnetic resonance image (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. A glucocorticoid injection may be useful 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, 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 [42].

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. 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. MRI may help determine whether a true mechanical lock is present [43,44].

Release of a locked knee can sometimes be accomplished by applying longitudinal traction to the leg while simultaneously rotating the lower extremity (hip joint) gently both internally and externally.

Surgery is often needed in patients with knee locking, but some patients accommodate. Surgical repair of the meniscus is less successful in older patients with severe osteoarthritis of the knee and degenerative meniscal tearing [45,46]. 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 several factors, including:

●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)

●Presence of osteoarthritis or damage to the articular cartilage or other structures

●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 when performing meniscectomy is to retain as much functioning meniscus as possible [47-49].

Few high-quality, randomized clinical trials have been performed to determine best surgical practice [50]. A 2022 meta-analysis of 27 studies (primarily small case series) involving 1630 meniscal repairs reported an overall success rate of 80.5 percent at five years when modern surgical techniques were employed [51]. Repairs of lateral meniscus tears were more successful than medial (87.4 versus 76.1 percent). Among young, active patients with uncomplicated tears who opt for surgery, meniscus repair is the preferred treatment. Surgical repair of complex meniscal tears (eg, horizontal cleavage, radial, involving meniscal root) is being performed with increasing frequency, but outcomes data are limited [52-54].

Regardless of procedure type, cautious postoperative care is required, including a period of modified weightbearing and well-supervised physical therapy. Functional rehabilitation plays an important role in recovery [55,56]. Patients with chronic tears generally require more time for recovery following surgery than those with acute injuries [57].

Chronic degenerative meniscal injury — Meniscal tears associated with chronic degeneration of the meniscus occur in older and some middle-aged adults and may or may not be associated with an acute injury. In a meta-analysis of 63 studies involving MRI examination of over 5000 asymptomatic knees in adult patients, the prevalence of meniscal tears in participants 40 years of age and older was 19 percent [58].

Arthroscopic treatment with partial meniscectomy or debridement does not appear to be of greater benefit than physical therapy in cases of nonobstructive degenerative meniscal tear (ie, tear does not cause locking of the knee). In addition, the use of physical therapy to treat degenerative meniscal injuries is supported by observational studies showing an association of the condition with diminished quadriceps strength and lower extremity function [41,56,59,60]. Therefore, in patients without persistent knee effusion or mechanical dysfunction, we recommend initial treatment with physical therapy. (See "Rehabilitation of common knee injuries and conditions", section on 'Meniscal injury (nonoperative and/or postoperative)'.)

A meniscal tear that causes persistent joint effusions or recurrent mechanical dysfunction (eg, locking) warrants referral to an orthopedic surgeon. Up to one third of patients may need surgery, despite adequate physical therapy and strengthening [61]. The treatment of degenerative meniscal injury in the setting of significant knee osteoarthritis is discussed separately. (See 'Outcomes' below and 'Approach to treatment and orthopedic referral' above and "Overview of surgical therapy of knee and hip osteoarthritis", section on 'Arthroscopic debridement'.)

A systematic review, a meta-analysis involving 805 patients, and multiple randomized trials report no clinically significant improvements in function or pain among patients with nonobstructive, degenerative meniscal tears and without severe osteoarthritis who are treated with arthroscopic surgery compared with those managed with a well-designed physical therapy program [61-73]. In one trial, partial meniscectomy for a degenerative medial meniscal tear not associated with osteoarthritis was compared with sham surgery, and no clinically significant difference in knee function or pain was found [69]. These findings are consistent with the results of a meta-analysis of nine randomized trials that found no additional improvement in function or symptom relief from arthroscopic surgery involving debridement or partial meniscectomy in middle-aged and older patients with knee pain associated with degenerative knee disease [70-73]. Another meta-analysis restricted to randomized trials of partial meniscectomy reported similar results in patients with degenerative meniscal tears [68]. Overall, the available research indicates that surgical treatment for degenerative meniscal tears not causing mechanical symptoms is ineffective both over the short and longer term [66,67,72-77].

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 nondegenerative tears amenable to nonsurgical management [72,78].

Among patients treated surgically, younger patients with isolated tears generally do well [49,79,80]. 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 [79].

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) [45,72].

Depending upon the type and extent, meniscal injury may predispose patients to the development of osteoarthritis over the long term. Meniscus repair leads to higher rates of return to sport and a lower long-term risk of osteoarthritis compared to partial meniscectomy [54,81,82]. (See "Epidemiology and risk factors for osteoarthritis", section on 'Joint injury'.)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Knee pain" and "Society guideline links: Meniscal injury".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topics (see "Patient education: Knee pain (The Basics)" and "Patient education: Meniscal tear (The Basics)" and "Patient education: How to use crutches (The Basics)")

●Beyond the Basics topic (see "Patient education: Knee pain (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

●Mechanism and presentation – The most common mechanism for a meniscal tear involves twisting of the knee while the foot is planted. Older individuals may develop a degenerative tear with minimal or no trauma. (See 'Mechanism and presentation' above.)

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. 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. Articular cartilage damage and other structural abnormalities can present similarly. (See 'Differential diagnosis' above.)

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. Partial tears, horizontal tears, and anterior tears (figure 3) 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. (See 'Overview' above.)

●Physical examination – Patients with suspected meniscal injury are examined for:

•Joint line tenderness

•Inability to squat or kneel

•Loss of smooth passive knee motion; inability to extend the knee fully

•Palpable catching on the joint line (eg, McMurray maneuver)

•Pain elicited by specific tests (eg, Thessaly test)

•Joint effusion

Multiple positive findings suggest the diagnosis. (See 'Physical examination' above.)

●Diagnostic imaging and arthroscopy – The Ottawa knee rule provides useful guidance for determining whether radiographs are indicated. Diagnosis may be confirmed by magnetic resonance imaging (MRI) or arthroscopy. The decision to proceed to MRI depends upon the patient's age and whether surgery is being considered. Arthroscopy is the definitive test. MRI and arthroscopy are usually not necessary for patients with osteoarthritis in the affected knee. (See "Approach to the adult with knee pain likely of musculoskeletal origin", section on 'Ottawa Knee Rule (OKR)' and 'Imaging' above and 'Diagnosis' above.)

●Management – The management of meniscal tears depends upon the type of tear, the presence of significant mechanical symptoms (eg, knee locking), the presence of a persistent knee effusion, age, activity level, and the presence of osteoarthritis or other structural knee damage. (See 'Treatment' above.)

Small intrasubstance and vertical tears that cause infrequent symptoms and do not interfere with general knee function can be managed nonoperatively. Many clinicians try to exhaust conservative management options before referring such patients for surgery. Factors associated with successful and unsuccessful conservative management are described in the text. (See 'Approach to treatment and orthopedic referral' above.)

Orthopedic referral is needed for meniscal tears associated with persistent effusions or disabling symptoms and those involving large, complex tears or vertical tears in contact with the articular cartilage.

Chronic degenerative meniscal injuries occur in older patients and are managed nonoperatively in most cases. (See 'Chronic degenerative meniscal injury' above.)