Meniscal Injury

The meniscus has unique anatomic properties. An understanding of its anatomy is essential to comprehending the important functions of the meniscus, which include load bearing, load and force distribution, joint stability, joint lubrication, and proprioception.[6, 7, 8] One of the primary functions is to provide load bearing across the knee joint. Fifty percent of the compressive load in the knee is transferred by the menisci in extension, whereas up to 85% of the load is transferred at 90° of flexion.

Load and forces are distributed across a much larger surface area because of the menisci, which (1) decrease focal contact pressure by increasing the contact area and (2) protect the underlying articular cartilage. Resection of 15-34% of a meniscus may increase contact pressure by more than 350%. Normal knees have 20% better shock-absorbing capacity than meniscectomized knees.

Joint stability is increased because of meniscal structure, which allows increased congruence and conformity between the femoral condyles and tibial plateaus.[6, 7] The wedge-shaped meniscus attached to the tibia serves as a secondary stabilizer. For example, the posterior horn acts as a shim to resist anterior tibial translation relative to the femur. Meniscectomy alone may not increase knee laxity, but it has been shown that in association with anterior cruciate ligament (ACL) deficiency, greater anterior laxity results. Meniscal lubrication occurs from  fluid exudation across the surface, much like with articular cartilage.

Anatomy

The menisci are C-shaped wedges of fibrocartilage located between the tibial plateau and the femoral condyles. The larger, semilunar medial meniscus is attached more firmly than the loosely fixed, more circular lateral meniscus.[9] The anterior and posterior horns of both menisci are secured to the tibial plateaus. Anteriorly, the transverse ligament connects the two menisci; posteriorly, the meniscofemoral ligament helps to 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.

The microanatomy of the meniscus is dense fibrocartilage composed of cells and an extracellular matrix of collagen fibers in network. The cells are termed fibrochondrocytes because they appear to be a mixture of fibroblasts and chondrocytes. These cells are responsible for the synthesis and maintenance of the extracellular fibrocartilaginous matrix.

The most abundant component of the menisci is collagen (75%)—mainly type I collagen (>90%), although they also contain types II, III, V, and VI. Collagen fibers are arranged mostly along a longitudinal or circumferential direction, with some interwoven radial and oblique fibers. The circumferential fibers are related directly to the menisci's functional ability to dissipate compressive loads. The other fibers act primarily as ties to enhance structural rigidity and to help prevent longitudinal splitting. The extracellular matrix also includes proteoglycans, glycoproteins, and elastin.

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 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 spreading 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.[10]

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.[11]

The potential for vascular ingrowth is essential for successful meniscal healing and surgical repair. Various zones of the meniscus are described based on the blood supply; the red zone is the well-vascularized periphery, the red-white zone is the middle portion with vascularity peripherally but not centrally, and the white zone is the central avascular portion. Arnoczky, in 1982, proposed a classification system that categorizes lesions in relation to the meniscal vascular supply, as follows[12] :

• An injury resulting in a lesion 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 a 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

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.

Neuroanatomy

The neuroanatomy of the meniscus is not well described. However, the distribution of neural elements has been demonstrated in essentially the same anatomic distribution as the vascular supply. The anterior and posterior horns are the most richly innervated, and the body innervation follows the pattern along the periphery. Although not entirely clear, these nerve endings are believed to play a role in sensory feedback and proprioception. The greater innervation of the horns of the meniscus reflects the need for feedback at the extremes of flexion and extension, when the meniscal horns are compressed and neural elements are activated.[6, 7, 13]

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.[10] During extension, the femoral condyles exert a compressive force that displaces 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 tearing 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.[9]

Frequency

United States

Although the exact incidence and prevalence of meniscal injury are unknown, it is a fairly common sports-related injury among adults. Knee meniscal injuries also occur in individuals who are skeletally immature, but less commonly than in adults. Meniscal injuries are rare in children younger than 10 years with morphologically normal menisci.[14]

Mortality/Morbidity

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

A study by Yasuda et al suggested that medial meniscus tears cause spontaneous osteonecrosis of the knee (SONK). Specifically, the investigators found medial meniscal extrusion and the femorotibial angle to be significantly associated with SONK stage and volume in the medial femoral condyle.[15]

Race

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

Sex

Meniscal injuries are more common in males, which may be a reflection of greater involvement by males 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 persons older than 55 years; this is secondary to a degenerate meniscus being susceptible to injuries with minor trauma.[16] As previously stated, meniscal injuries are rare in children younger than 10 years with morphologically normal menisci.[14]

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 to 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. Stanitski et al studied 70 young patients with hemarthrosis after acute trauma and found that 47% had ACL tears and 47% had meniscal tears. In adolescents (aged 13-18 y), the rates were 65% and 45%, respectively. ^{[17, 18]}
• 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.

During clinical examination, use the uninvolved leg for comparison with qualitative and quantitative findings for the involved leg. Examination should include inspection, palpation, ROM, gait, girth measurements, and tests for integrity of menisci and other structures of the knee joint.[19]

Inspection

Look for effusion, and check the state of healing of any scars or incisions. Effusion occurs in approximately 50% of the patients presenting with a meniscal tear. The presence of an effusion is suggestive of a peripheral tear in the vascular, or red, zone (especially when acute); an associated intra-articular injury; or synovitis.

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; this is 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; along with the other objective findings, however, it can help to 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.

Only 57% of meniscal root tears result in a positive McMurray test.[20]

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 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 meniscal 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.

Thessaly test

This maneuver is performed with the patient standing on one leg and the knee flexed to 5° and 20°, while the patient holds the examiner’s hand for balance. From this position, the patient is asked to internally and externally rotate the knee. Pain or a locking or catching sensation at the medial or lateral joint line is suggestive of meniscal tears.

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.[9, 21]

A Danish study investigated whether an association exists between meniscal injuries and occupations that require kneeling.[22] 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.

If arthrocentesis is performed (see Procedures), send the fluid for analysis, though a hemarthrosis associated with acute injury often is evacuated only for patient comfort.

Send nonbloody fluid to the laboratory for cell count and determination of glucose and protein levels, Gram stain, bacterial culture, and special tests (eg, crystals), as indicated.

Posttraumatic aspiration of bloody fluid is suggestive of a cruciate ligament tear or an injury to the peripheral vascular part of the meniscus. Association of the bloody aspirate with fat globules is highly suggestive of associated fractures.

Plain radiography

An anteroposterior weight-bearing view, posteroanterior 45° flexed view, lateral view, and Merchant patellar view should be obtained to rule out degenerative joint changes (arthritis) or fractures.

Arthrography

Historically, arthrography was the standard imaging study for meniscal tears, but it has been replaced with MRI.

MRI

This is the criterion standard study for imaging meniscal pathology and all intra-articular disorders.[2, 3] MRI is not routinely required for the diagnosis of meniscal tears before proceeding with arthroscopic surgery; however, it helps to confirm the diagnosis and provides additional information concerning the status of the ligaments and articular cartilage (see images below).[4]

Normal menisci have a homogeneous low signal. Abnormal meniscal signals are classified into the following 3 groups:

• Grade I – Small area of increased signal within the meniscus
• Grade II – Linear area of increased signal that does not extend to an articulating surface
• Grade III – Abnormal increased signal that reaches the surface or edge of the meniscus

Grade I and II changes are common in older patients as evidence of the normal degenerative aging process and in young patients as a demonstration of normal perforating vascular channels. Grade I and II changes are not usually seen arthroscopically and do not represent meniscal tears, but grade III changes do.

MRI has proven to be an effective technique for evaluating menisci, with sensitivity, specificity, and accuracy being as follows:

• Average sensitivity - 95% medial, 81% lateral
• Average specificity - 88% medial, 96% lateral
• Average accuracy - 92% medial, 92% lateral

Meniscal root tears are directly or indirectly diagnosed via MRI by assessing the amount of meniscal extrusion, defined as at least 3 mm of coronal translation beyond the margin of the tibia.[23, 24]

A study by Furumatsu et al indicated that existence of the giraffe neck sign on MRI is helpful in diagnosing medial meniscus posterior root tears (MMPRTs). The study found the sign in 81.7% of MMPRTs but in only 3.3% of other medial meniscus tears and suggested that a combination of giraffe neck, cleft, ghost, and radial tear signs may play an important role in the MRI diagnosis of MMPRT.[25]

Arthrocentesis

Arthrocentesis can be used as a diagnostic tool and a therapeutic procedure.

Not all effusions require aspiration, though drainage of the bloody effusion provides symptomatic relief, improves examination accuracy, and helps to confirm the severity of the injury.

Arthrocentesis can be accomplished quickly and easily with minimal patient discomfort. The knee is prepared in sterile fashion and anesthetized with local anesthetic to facilitate the use of a large-bore needle. The choice of the site of aspiration is a matter of operator preference. Accepted locations include the level of the joint line, which is 1 cm medial or lateral to the patellar tendon when the patient is seated. Alternatively, a location 2 cm medial or lateral to the anterior-superior patella when the patient is supine can be used. An 18-gauge needle is needed for aspiration of the viscous or bloody fluid.

Arthroscopy

In the hands of a competent arthroscopist, arthroscopy is considered the best tool for meniscal tear diagnosis, with sensitivity, specificity, and accuracy approaching 100%.

Arthroscopy is therapeutic and diagnostic and thus offers the advantage of immediate treatment of most disorders.[3, 26, 27] (See image below.)

Most meniscal tears do not heal without intervention. If conservative treatment does not allow the patient to resume desired activities, his or her occupation, or a sport, surgical treatment is considered. Surgical treatment of symptomatic meniscal tears is recommended because untreated tears may increase in size and can abrade articular cartilage, resulting in arthritis.

Physical therapy

The goals of the physical therapy program are to minimize effusion, normalize gait, normalize pain-free ROM, prevent muscular atrophy, maintain proprioception, and maintain cardiovascular fitness.

A report by El Ghazaly et al indicated that in patients with symptomatic, unstable meniscal tears, better treatment results can be achieved with arthroscopic partial meniscectomy (APM) than with physical therapy. The study, on 70 patients, found that although pain and swelling were reduced in the physical therapy patients, their injured knees continued to have limited ROM, with greater knee function and treatment satisfaction found in the APM patients.[28]

On the other hand, a study by Stensrud et al reported that in middle-aged patients with degenerative meniscal tears, a 12-week supervised exercise therapy program can yield similar results to APM. Indeed, isokinetic knee extension peak torque was a mean 16% greater in the exercise group.[29]

When a meniscal repair is performed, the rehabilitation is typically more intensive. Many different protocols are described in the literature. Three main issues are considered in the rehabilitation of meniscal repairs: knee motion, weight bearing, and return to sports.[5]

The protocols for rehabilitation of a meniscal injury take into consideration biomechanical principles and the results of the physical examination. Factors such as the extent and location of the lesion, the amount of articular cartilage degeneration on weight-bearing surfaces, the duration of injury, and joint stability affect the pace and aggressiveness of the rehabilitation program. No preset duration for any phase of rehabilitation is described in this section, and phases may overlap, depending upon the patient's progress and symptoms. The protocols should be adjusted to each patient's status, progress, and goals.

Initial phase

When the patient first reports to outpatient physical therapy 4-7 days after surgery, he or she usually is able to bear full weight or as much weight as tolerated on the involved leg. Modalities are used as needed to decrease pain or swelling, including heat/ice contrasts, ice alone, transcutaneous electrical nerve stimulation (TENS), electric galvanic stimulation, and phonophoresis. As needed, the patient should perform flexibility exercises for the lower extremity musculature, including the hamstrings, quadriceps femoris, hip flexors, hip adductors, and calf muscles.

During the initial stage, the emphasis should be placed on overcoming any limitations to ROM. To increase passive flexion ROM, the patient should complete exercises such as wall slides. The uninvolved leg is used to control the speed of descent and to push the involved leg back up into extension. The patient does not have to use the quadriceps muscle of the involved leg for this exercise, but he or she can use it if there is no pain.

After the patient attains 110-115° of flexion, he or she may substitute heel slides for supine wall slides to increase flexion ROM. Isometric exercises for the quadriceps muscle assist in strengthening the quadriceps muscle, especially the VMO segment. Electrical muscle stimulation may be used to help retrain poorly contracting VMO or quadriceps femoris muscles. Short-arc quadriceps femoris muscle exercises strengthen the quadriceps femoris muscle.

Additional exercises to strengthen the lower extremity musculature (eg, hamstrings, hip adductors, hip abductors, calf muscles) are included in the program. The patient can begin isotonic strengthening exercises for the hamstring muscles when he or she can flex the knee to at least 80-90°. Hip abduction strengthening may begin when VMO muscle contraction and strength are adequate. If the patient begins hip abduction exercises before the quadriceps femoris muscle is strong enough, the exercises may contribute to increased lateral tracking of the patella. The tensor fasciae latae muscle inserts into the iliotibial band distally, and contraction of this muscle increases the tightness of the fascial sheath, contributing to lateral patellar tracking.

Depending on weight-bearing ability and other symptoms, the patient can begin toe raise exercises to strengthen the lower leg. Proper foot placement is important, as it influences the stresses at the knee. Supination of the foot causes tibial external rotation and a varus force at the knee joint, resulting in increased pressure in the medial compartment. Pronation causes tibial internal rotation, a valgus force at the knee joint, and increased lateral compartment pressure.

Stationary bicycling may be implemented into the rehabilitation program when the patient attains 115-120° of knee flexion. This exercise increases joint lubrication, which helps to improve ROM. Tension and resistance should be adjusted according to the presence of effusion or the patient's complaints of pain. If the patient's ROM is not adequate, bicycling may cause forced motion and increased pressure, irritating the knee.

Intermediate phase

The patient should have full ROM to begin this phase. Modalities are continued as indicated by symptoms. Flexibility and strengthening exercises are continued, increasing resistance as tolerated. The patient may progress to isokinetic strength and endurance training.

The patient also may begin closed kinetic chain exercises during this phase. If the quadriceps femoris muscle is strong enough (ie, if the patient can lift 10 lb during short-arc quadriceps femoris muscle exercise), the running program may be initiated. The first stage of the running program is jogging in place on a trampoline. Unless pain or swelling occurs, the patient gradually progresses to jogging for 10-15 minutes.

Advanced phase

During the advanced phase, the patient continues to progress in strength-training exercises while beginning to return to sports activities. Track running may start when the patient is able to run on the treadmill for 10-15 minutes at a pace of 7-8 minutes per mile (depending upon the patient's previous activity level). Once mileage on the track has reached 2-3 miles, agility drills and sport-specific activities may be performed.

The program for rehabilitation following meniscal repair is similar in principle to the program that follows meniscectomy; however, more limitations are put on the patient's weight-bearing status, and the duration of each phase of rehabilitation is longer to allow for healing. Full weight bearing is postponed until 4-6 weeks after surgery to reduce the tensile and compressive forces on the repair site. During the initial phase of rehabilitation, more attention should be paid to applying modalities to decrease pain and effusion. ROM exercises are performed with caution so that the healing process is not delayed. Mobilization of the patella may be required to ensure proper mechanics of the patellofemoral joint. Stretching exercises include calf stretches to reduce the possibility of Achilles tendinitis when the patient resumes weight bearing on the involved leg. Ankle ROM exercises also may be required to maintain adequate ankle ROM before weight bearing begins.

Open kinetic chain strengthening exercises may begin during the initial phase, but caution must be used, and the exercises must be reduced or suspended if the patient reports pain. Isokinetic training should not begin until the patient is able to lift 10 lb on the short-arc quadriceps muscle exercise. The running program may begin when the quadriceps femoris and hamstring muscles of the involved leg have reached approximately 70% of the strength of the same muscles of the uninvolved leg, as demonstrated by an isokinetic strength test.

The program for nonoperative rehabilitation is similar in principle to the program that follows meniscectomy. Cryotherapy and nonsteroidal anti-inflammatory drugs (NSAIDs) play a very important role in the management of nonoperative meniscal injury. These medications help to control the amount of swelling and provide some pain relief. Sometimes, aspiration is useful to decrease the effusion, and, rarely, an athlete may need a judicious one-time corticosteroid injection. Although not routinely advocated, an injection may provide an athlete with a way to control the irritation within the knee so that performance may not falter. Maintenance of ROM of the knee is important, as are muscular strength and endurance.

A reasonable goal before return to athletic activity is strength of the injured lower extremity within 20-30% of the contralateral side. Initially, activity modification is useful, particularly in athletes who are "weekend warriors." The time frame for return to activity depends on a number of factors. Returning to competition depends on the demands and motivation of the athlete, as well as on the severity of the meniscal tear.

Operative versus nonoperative treatment

Multiple factors are involved in making decisions regarding the management of an athlete with a known or suspected meniscal tear.[30] Factors such as the severity of the symptoms, the ability to perform one's activity, and the timing of possible surgery must be taken into account. The need for surgical management is quite evident in an individual with significant symptoms, such as a locked knee or debilitating pain with clinical or MRI evidence of a meniscal tear. A treatment decision may be much more difficult to make for an individual who has relatively mild symptoms of a meniscal tear and who is participating in a sporting event that is in the middle-to-late part of the season.

The severity of the symptoms can vary for different types of meniscal tears. A bucket-handle tear may cause the knee to lock and be quite painful, whereas a small vertical or radial tear that displaces may cause occasional symptoms of giving way and only mild pain. If the symptoms are infrequent and locking does not occur, then an initial period of conservative management may be indicated, depending on the activity level and demands of the athlete. If the athlete's ability to compete is impaired because of the symptoms, then nonoperative management is unlikely to be satisfactory and arthroscopic surgery should be helpful, although it may mean a delay of 1-4 weeks in returning to competition.

Delayed surgery

An athlete with recurrent mild symptoms but without impairment in the ability to compete may be a suitable candidate for delayed operative management. Thorough consultation between the athlete, the physician, and the athletic trainer must be undertaken before any decision is made. The athlete must be given a clear explanation of what a meniscal tear is and what the potential ramifications of delaying surgery are. Such ramifications include the possibility of propagation of the tear or significant symptoms during a competition, which may preclude further participation at a particular event. Few published studies have examined the results of nonoperative treatment of meniscal tears.

Operative plus physical therapy

A study by Gauffin et al indicated that in middle-aged patients with meniscal injury, arthroscopic knee surgery combined with physical therapy brings greater pain relief than does physical therapy alone. In the prospective, randomized, single-blind trial, 150 patients aged 45-64 years who had been suffering from meniscal symptoms for more than 3 months were treated with physical therapy, including a 3-month exercise program. Within this group, however, some patients were also treated with arthroscopic resection of meniscal injury, performed within 4 weeks of inclusion in the study. At 12-month follow-up, evaluation using the Knee Injury and Osteoarthritis Outcome Score determined that pain reduction was significantly greater in the patients who had been treated with physical therapy and surgery than in those treated only with physical therapy.[31]

A literature review by Thorlund et al for the Danish Society of Sports Physical Therapy found moderate-level evidence that self-reported pain and function in degenerative meniscal tears can be improved as much with exercise as with surgery, with muscle strength improved to an even greater extent. In contrast to the Gauffin study, the investigators also stated that in cases of degenerative meniscal tears, high-quality evidence showed that using surgery in addition to exercise did not have a clinically significant impact on pain and function.[32]

Arthroscopic surgery

Despite the Gauffin study’s findings, a systematic review and meta-analysis found that arthroscopic surgery for patients with degenerative meniscal tears and mild or no osteoarthritis provided no benefit when compared with nonoperative management.[33]

A study by Kise et al that included 140 adults looked to determine if exercise therapy is as effective as arthroscopic partial meniscectomy for knee function in middle-aged patients with degenerative meniscal tears. The subjects were randomly assigned to the treatment groups. The study found no differences at 2 years between the exercise therapy group and the arthroscopic surgery group in knee function and found greater muscle strength in the exercise group at 3 months and 12 months.[34, 35]

The results from this study led to the formation of an expert multidisciplinary panel to review the literature for or against the use of arthroscopy for patients with degenerative knee disease. A clinical practice guideline released by an international panel strongly recommended, based on a systematic review, that almost no patients with degenerative knee disease be treated with arthroscopic surgery. The panel included orthopedic surgeons, a rheumatologist, physical therapists, a general practitioner, general internists, epidemiologists, methodologists, and patients with degenerative knee disease who had or had not undergone arthroscopic treatment. It cited, with regard to the surgery, “a modest probability (< 15%) of small or very small improvement in short term pain and function that does not persist to 1 year,” as well as the postoperative limitations and, in rare cases, serious adverse effects that can occur.[36]

Operative management

Once a decision has been made to proceed with operative management, further decisions regarding the surgical treatment of the meniscus tear need to be made (see images below). Surgical options include partial meniscectomy or meniscal repair (and in cases of previous total or subtotal meniscectomy, meniscus transplantation). Arthroscopy, a minimally invasive outpatient procedure with lower morbidity, improved visualization, faster rehabilitation, and better outcomes than open meniscal surgery, is now the standard of care. One study found that arthroscopic pullout repair of a medial meniscal root tear provided better results than partial meniscectomy.[37] As previously stated, however, some controversy is now associated with arthroscopic treatment, with an international panel recommending that in most cases, such surgery not be used for degenerative knee conditions and finding the procedure to lack effectiveness.[36]

Numerous factors are involved in the determination of treatment of a meniscal tear. In assessing these factors, the clinician must be cognizant of meniscal biomechanics, including the role in load transmission and congruity of the knee joint. Because of the importance of intact functional meniscal tissue, the first goal is to preserve as much of the viable tissue as possible. Many factors (eg, the location, length, pattern, stability, and chronicity of the tear; the athlete's age; presence of degenerative changes; concurrent intra-articular injuries; desired timing of return to competition) need to be taken into consideration during the decision-making process.[4, 38]

The basic principle of meniscal surgery is to save the meniscus.[39] Tears with a high probability of healing with surgical intervention are repaired. However, most tears are not repairable, and resection must be restricted to only the dysfunctional portions, preserving as much normal meniscus as possible.

Partial meniscectomy is the treatment of choice for tears in the avascular portion of the meniscus or complex tears that are not amenable to repair. Torn tissue is removed, and the remaining healthy meniscal tissue is contoured to a stable, balanced peripheral rim.

Meniscal repair is recommended for tears that occur in the vascular region (red zone or red-white zone), are longer than 1 cm, are root tears, involve greater than 50% of the meniscal thickness, and are unstable to arthroscopic probing. A stable knee is important for successful meniscal repair and healing. Thus, associated ligamentous injuries must be addressed.

The most commonly associated ligamentous disruption is complete tear of the ACL, which must be reconstructed to prevent recurrent meniscal tears. Fortunately, the increased blood and growth factors in the knee during meniscal repair combined with cruciate reconstruction significantly improves the outcome of the meniscal repair. In ACL-intact knees with isolated meniscal tears, healing rates are less than those in ACL-reconstructed knees, but they are higher than those in ACL-deficient knees.

The principles of repair include smoothing and abrading the torn edges and bordering synovium to promote bleeding and healing. Likewise, needle trephination of the meniscal body (poking holes to create vascular channels) can be performed.

Meniscal repair fixation techniques are numerous and variable. Fixation can be accomplished with outside-in, inside-out, or all-inside arthroscopic procedures.[6, 40, 41, 5] The outside-in and inside-out methods are usually performed with sutures and require additional incisions. Suture repair can be accomplished with vertical or horizontal stitches. The all-inside method is very popular, and there is a plethora of commercially available meniscal repair devices (eg, biodegradable arrows or darts, sliding knot sutures with extracapsular anchor fixation).

Meniscal root tears have been investigated as a unique type of meniscal tear that requires special attention. Multiple biochemical studies have shown that the joint contact mechanics of a posterior root tear are almost identical to those of a complete meniscectomy and that repair restores normal mechanics.[42, 43] The global loss of circumferential hoop tension caused by root tears is believed to be the source of the increased joint contact forces observed in affected patients. Therefore, there has been an increased focus to surgically repair root tears more aggressively.

Surgical repair of root tears, however, poses a unique challenge in that the meniscus must be repaired to bone. The root is fixed to bone by either arthroscopically assisted bone suture anchors (all-inside technique) or an intraosseous suture technique (pullout technique).[44, 45, 46, 47, 48]

In a study comparing the results of the pullout technique with partial meniscectomy, investigators showed that repair improved functional outcomes and decreased progression of arthritic changes.[37] A separate study that compared the results of the all-inside and pullout techniques showed no difference in function or repair characteristics between the two procedures;[49] complete structural healing was observed in 86% of patients who underwent the all-inside technique and in 65% of those who underwent the pullout technique (P >0.05). In another study, investigators assessed the results of the all-inside repair and reported significant improvement in the amount of sagittal extrusion; however, improvement of coronal extrusion was not observed.[50]

Future prospective, randomized, controlled trials are needed to compare the effectiveness of these procedures with respect to healing rates and prevention of arthritic changes.

Human allograft meniscal transplantation is a relatively new procedure but is being performed with greater frequency. Specific indications and long-term results have not yet been clearly established. Meniscus transplantation requires further investigation to assess its efficacy in restoring normal meniscus function and preventing arthrosis.

The goals of pharmacotherapy are to reduce morbidity and prevent complications.

Class Summary

Pain control is essential to quality patient care. Analgesics ensure patient comfort and have sedating properties, which are beneficial for patients who have sustained injuries.

Acetaminophen (Tylenol, Feverall, Tempra, Aspirin-Free Anacin)

DOC for pain in patients with documented hypersensitivity to aspirin or NSAIDs, with upper GI disease, or who are taking oral anticoagulants.

Class Summary

Have analgesic, anti-inflammatory, and antipyretic activities. Their mechanism of action is not known, but they may inhibit cyclooxygenase (COX) activity and prostaglandin synthesis. Other mechanisms may exist as well, such as inhibition of leukotriene synthesis, lysosomal enzyme release, lipoxygenase activity, neutrophil aggregation, and various cell membrane functions.

Ibuprofen (Motrin, Ibuprin)

DOC for patients with mild to moderate pain. Inhibits inflammatory reactions and pain by decreasing prostaglandin synthesis.

Naproxen (Naprelan, Anaprox, Naprosyn)

For relief of mild to moderate pain; inhibits inflammatory reactions and pain by decreasing activity of COX, which results in a decrease of prostaglandin synthesis.

Diclofenac (Voltaren, Cataflam)

Designated chemically as 2-[(2,6-dichlorophenyl)amino] benzeneacetic acid, monosodium salt, with an empirical formula of C14 H10 Cl2 NO2 NA. One of a series of phenylacetic acids that has demonstrated anti-inflammatory and analgesic properties in pharmacological studies. Believed to inhibit COX, which is essential in biosynthesis of prostaglandins. Can cause hepatotoxicity; hence, monitor liver enzyme levels in first 8 wk of treatment.

Rapidly absorbed; metabolism occurs in liver by demethylation, deacetylation, and glucuronide conjugation. Delayed-release, enteric-coated form is diclofenac sodium, and immediate release form is diclofenac potassium. Has relatively low risk for bleeding GI ulcers.

Celecoxib (Celebrex)

Primarily inhibits COX-2. COX-2 is considered an inducible isoenzyme, induced during pain and by inflammatory stimuli. Inhibition of COX-1 may contribute to NSAID GI toxicity. At therapeutic concentrations, COX-1 isoenzyme is not inhibited, thus GI toxicity may be decreased. Seek lowest dose of celecoxib for each patient.

Class Summary

Narcotic analgesics should be used sparingly in the conservative treatment period. The use of these agents is warranted only in special cases in which intolerable pain is present that cannot be controlled by first-line medications. However, these drugs are commonly used in the postoperative period when surgical treatment is necessary. Many options are available, and narcotic analgesics are commonly combined with drugs from the above categories. Common examples are listed.

Hydrocodone and acetaminophen (Vicodin, Lortab, Lorcet)

Drug combination for moderate to severe pain.

Oxycodone (OxyIR, OxyContin, Roxicodone)

Indicated for moderate to severe pain.

Patients with meniscal injuries (operative or nonoperative) are recommended to receive outpatient physical therapy for rehabilitation. Please refer to the Physical Therapy section for appropriate treatment goals and guidelines.

Return to play after a meniscus injury is expected. The timing varies and depends on the injury, treatment, and rehabilitation protocol. In many cases, athletes can return to their sport as soon as 2-3 weeks status post arthroscopic partial meniscectomy or 6-8 weeks status post meniscal repair.

Over the long term, meniscal repairs fail to heal in 5-10% of patients. Failure rates are lower when the tears are repaired in patients with concomitant ACL reconstruction.

Also over the long term, meniscal injuries predispose to osteoarthritis secondary to increased loads on the articular surfaces of the knee.[51] However, the degree of correlation between meniscal injuries and osteoarthritis has not been well established in the literature.

A study by Everhart et al indicated that in middle-aged adults, meniscal tears and lateral meniscal extrusion accelerate loss of joint space. Patients with medial meniscal tears, regardless of whether or not extrusion had occurred, suffered an additional mean medial space loss of 0.05 mm/year, while those with lateral tears underwent an additional mean lateral space loss of 0.09 mm/year. Moreover, lateral extrusion was associated with an additional mean lateral space loss of 0.1 mm/year. Patients without lateral extrusion had a 0.5% annual incidence of knee arthroplasty, compared with a 1.5% rate for those with a lateral extrusion of less than 2.0 mm, and a 3.7% rate for those with an extrusion of 2.0 mm or more.[52]

A retrospective, dual-center study by Ronnblad et al of 918 patients who underwent meniscal repair indicated that surgeries using bioabsorbable arrows are more likely to fail than those employing all-inside sutures with anchors (hazard ratio [HR] = 1.8), with the failure rate also being higher for medial, rather than lateral, meniscal repairs (HR = 3.7).[53]

Unfortunately, most injuries to menisci occur during accidents that are, at times, not preventable. However, the following may help in avoidance of these injuries:

• Having strong thigh and hamstring muscles
• Gently stretching the legs before and after exercise
• Wearing shoes that fit properly when exercising and ensuring the shoes are appropriate for the activity being performed
• When skiing, ensuring that ski bindings are set correctly by a trained professional so that the skis release when a fall occurs