History of the Meniscus
One of the earliest descriptions of the menisci was recorded by Bland-Sutton in 1897. At that time, the menisci were thought to be vestigial tissue and were depicted as “the functionless remnants of intra-articular leg muscles.” Further advances in our understanding of the menisci have demonstrated that the menisci provide mechanical support and secondary stabilization, localized pressure distribution and load sharing, lubrication, and proprioception to the knee joint.
In 1936, King initially documented meniscal healing at the meniscosynovial junction in a canine model. He also documented minimal healing with intrasubstance tears. Significant articular chondral degeneration was documented in the setting of partial or complete meniscectomy. These data suggested that the available vascular supply may serve a crucial role in meniscal healing and that the menisci may have a role in chondroprotection.
Fairbank substantiated this chondroprotective role in 1948 using radiographic evaluation of patients after a total meniscectomy. This study documented specific radiographic “Fairbank changes,” including formation of an anteroposterior ridge extending from the femoral condylar margin, marginal flattening of the femoral articular surface, and joint space narrowing. These radiographic findings were identified as early as 5 months after a complete meniscectomy and demonstrated time-dependent progression. These observations led to the conclusion that the menisci may have a function during weight bearing and that a complete meniscectomy may contribute to intraarticular degenerative changes. This awareness, in conjunction with further substantiating data, increased the focus on meniscal preservation through limited partial meniscectomy, meniscal repair, biologic stimulation procedures, and an advanced algorithm to guide the effective use of these treatment options.
Meniscus Anatomy and Structure
The menisci are fibrocartilaginous structures that are semilunar in shape and wedge-shaped in cross-section. Two menisci (medial and lateral) exist between the femoral and tibial articulation. The femoral articulating meniscal surface is concave, whereas the tibial articulating surface is convex. These surfaces conform to the convex and concave opposing chondral surfaces, respectively. The conforming articulation provides perfect congruency between the femoral condyle, meniscus, and tibial plateau, which establishes the foundation for the biomechanical function of the menisci.
The medial and lateral menisci are significantly different in shape largely because of the structural differences between the medial and lateral femoral condyles and tibial plateau ( Fig. 96-1 ). Both the macroscopic and microscopic anatomy of the menisci determine its function. The medial and lateral menisci are two C-shaped fibrocartilaginous structures attached anteriorly and posteriorly to the tibial plateau. The medial meniscus is longer in the anteroposterior direction compared with the lateral meniscus. The anterior horn of the medial meniscus is smaller in sagittal cross-section compared with the posterior horn. The anterior and posterior horns of the lateral meniscus, on the other hand, are similar in size. Approximately 50% of the medial tibial plateau is covered by the medial meniscus, compared with 59% coverage of the lateral tibial plateau by the lateral meniscus.
Anchoring of the menisci occurs through insertional fibers and ligament attachments. Insertional fibers anchor both menisci to the subchondral bone at their anterior and posterior horns. The intermeniscal ligament also directly attaches the anterior horns of both menisci in most patients. The medial meniscus is continuous with the deep fibers of the medial collateral ligament and medial joint capsule, rendering it less mobile than the lateral meniscus. Nevertheless, the posterior horn of the medial meniscus remains mobile up to 5 mm to accommodate femoral rollback. The lateral meniscus, on the other hand, has significantly fewer capsular and ligamentous attachments and thus is more mobile. Normal lateral meniscal excursion has been documented up to 11 mm and may partially explain the reduced incidence of lateral meniscal injuries. The intraarticular portion of the popliteus tendon can be identified at the popliteal hiatus located between the posterolateral border of the lateral meniscus and the posterior knee capsule. This area of potential hypermobility is stabilized by the superior and inferior popliteomeniscal fasciculi that secure the posterolateral meniscus to the popliteus and posterior joint capsule ( Fig. 96-2 ). Fascicular injury can produce lateral meniscus hypermobility and may require meniscocapsular repair to reestablish meniscal stability.
In addition to the fasciculi, additional lateral meniscal stability may be achieved through accessory meniscofemoral ligaments in up to 66% of patients. Two accessory ligaments are frequently encountered: the ligament of Humphrey and the ligament of Wrisberg. Although uncommon, a Wrisberg ligament variant may also exist in the setting of a discoid lateral meniscus, in which there is deficiency of the meniscocapsular attachments, with only a stout Wrisberg ligament stabilizing the posterior horn (see Figs. 96-1 and 96-2 ). The ligament of Humphrey extends from the medial femoral condyle to the posterior horn of the lateral meniscus and courses anterior to the posterior cruciate ligament (PCL). The ligament of Wrisberg and Wrisberg’s variant have similar attachments but course posterior to the PCL.
Histologically, dense fibrocartilage is composed of collagen fibers that are arranged circumferentially (to disperse compressive loads or “hoop stresses”) with some radial fibers as well (to resist longitudinal tearing). At the surface, collagen fibers are arranged randomly to disperse shear stress associated with flexion and extension of the knee joint ( Fig. 96-3 ). Proteoglycan macromolecules hold and retain water, which is paramount to the compressive, shock-absorbing properties of the menisci and augments its ability to aid in lubrication of the knee joint.
The blood supply of the menisci originates at the periphery in the perimeniscal capillary plexus, which are tributaries of the medial and lateral geniculate arteries. Importantly, only the peripheral 25% to 30% of the meniscus is vascularized ( Fig. 96-4 ). The gradient attenuation in vascularity from the periphery to the central portion of the menisci is gradual, but the need for ease of clinical classification led to the designation of three vascular “zones.” The outer third is known as the “red-red zone” because of its relatively high concentration of vascular channels. In this zone, bleeding at the site of injury promotes fibrovascular scar formation and migration of anabolic cells in response to cytokines released during the inflammatory response. As a result, tears in this zone have the highest healing potential. The middle vascular zone is termed the red-white zone . This zone has intermediate vascularity, which leads to a less predictable result with regard to healing of meniscal tears. If a repair is attempted in this zone, ancillary techniques such as synovial abrasion, vascular access channels, and a fibrin clot may be used to increase local blood flow and maximize healing potential. The red-red and red-white zones combine to form the outer 4 mm of the meniscus. The remainder of the meniscus is avascular in adults and is therefore called the white-white zone . Nutrition of this tissue is achieved solely from the synovial fluid via passive diffusion, which is aided by motion of the knee joint. Consequently, injury in the white-white zone of the meniscus does not stimulate a healing response, and the prognosis for healing after attempted repair is poor.
Meniscal neuroanatomy and vascular anatomy are extremely similar both in density and location. The periphery and anterior and posterior horns of the menisci have a significantly higher density of neural components compared with the central regions. Both mechanical and sensory fibers have been identified in these locations and may contribute to pain and proprioception during knee range of motion. Dye et al. substantiated these basic science data through clinical study with use of neurosensory meniscal mapping. This study documented significant neural activity at the meniscocapsular junction and meniscal periphery, compared with limited activity in the central region. These data suggest that mechanical loading of the peripheral meniscal rim and meniscocapsular junction may be responsible for most of the pain experienced after a meniscal injury.
Meniscus Biomechanics and Function
The medial and lateral menisci function to provide mechanical support and secondary stabilization, localized pressure distribution and load sharing, lubrication, and proprioception to the knee joint. Mechanically, the menisci also transmit at least 50% to 75% of the axial load in knee extension and up to 85% with the knee in 90 degrees of flexion ( Fig. 96-5 ). The femoral and tibial radii of curvature are significantly different and thus are poorly congruent at the point of articulation. The menisci provide the congruency necessary for both load transmission and knee stability. They decrease the peak contact stresses at the articular surface by 100% to 200%. Removal of the menisci during partial or total meniscectomy results in increased point contact loading at the femorotibial articulation and significantly increased contract stresses focused in a small area. A recent biomechanical study by Lee et al. highlighted this function by documenting increased contact stress with incrementally increasing meniscectomy in a dose-response fashion. Moreover, resection of 75% of the posterior horn can increase contact stresses similar to those present after a total meniscectomy.
This process is particularly notable in the lateral compartment because of its specific anatomic differences. The femoral and tibial articulation is a convex-convex articulation that is buffered by the lateral meniscus, which covers up to 70% of the tibial surface area. This articulation is in direct contrast to the convex-concave femorotibial articulation in the medial compartment. For this reason, partial or complete removal of the lateral meniscus results in greater contact stresses and increased risk for progression of osteoarthrosis compared with the medial compartment.
The menisci perform a crucial role in shock absorption in addition to contact stress distribution. The meniscal collagen ultrastructure is organized in a circumferential fashion with radial linking fibers, thereby allowing conversion of axial loads to horizontal “hoop” stresses. This shock absorption is also aided by the reduced meniscal cartilage stiffness, increased elasticity, and biphasic structure. Prior data have demonstrated that total meniscectomy results in a 20% decrease in shock absorption, and thus preservation of meniscal integrity is crucial to minimize chondral damage.
The role of the meniscus as a secondary stabilizer of the knee has also been well documented. Bedi et al. noted that transection of the anterior cruciate ligament (ACL) and meniscectomy resulted in nearly double the anterior tibial translation in both Lachman and pivot shift testing compared with that of the ACL alone, as measured with knee-specific computer navigation software. The secondary stabilizing effect is primarily due to the posterior horn of the medial meniscus in resisting anterior tibial translation as demonstrated during a Lachman maneuver. Prior data have demonstrated that deficiency of the posterior horn of the medial meniscus in the setting of primary ACL reconstruction is associated with a higher risk of graft elongation and recurrent joint laxity. In this setting, the posterior horn of the medial meniscus functions as a wedge buttress to inhibit anterior tibial translation. Prior data have documented a 58% increase in anterior tibial translation with medial meniscectomy in the flexed ACL-deficient knee.
The biomechanical stabilizing effect of the lateral meniscus has also been well documented. Lateral meniscal deficiency may significantly reduce knee stability, specifically with tibial internal rotation (and subsequent pivot shift). Musahl et al. used computer-assisted navigation in a cadaveric model to document a significant 6-mm increase in anterior tibial translation after a lateral meniscectomy in ACL-deficient knees during the pivot shift but not Lachman maneuvers. These data demonstrate the importance of the lateral meniscus as a stabilizer during axial, rotatory loading of the knee.
Acute and chronic tears of the menisci are very common orthopaedic injuries that affect patients of various ages and activity levels. Meniscal injury often causes pain and physical impairment, and clinical symptoms such as catching, locking, and decreased range of motion may frequently require surgical intervention for relief. The treatment for meniscal tears has evolved over the course of several decades with both technological and intellectual advances in orthopaedic surgery.
Since 1936, when total meniscectomy was the treatment of choice, abundant research has led to the understanding that meniscal tissue should be retained whenever feasible. For this reason, recent measures have attempted to preserve as much of the meniscus as possible. These measures have evolved from open total meniscectomy to open partial meniscectomy and finally to arthroscopic partial meniscectomy or repair. Meniscal injury was recently noted to be the most common musculoskeletal injury, occurring with a frequency of 23.8/100,000 per year. The American Academy of Orthopedic Surgeons estimates that arthroscopy procedures of the knee total 636,000 cases per year in the United States as of 1999. Within this cohort, arthroscopic treatment of meniscal injury is among the most common procedure performed, accounting for 10% to 20% of all surgeries at some centers.
Improved understanding of the etiology, management, and outcomes for meniscal injury has been obtained from epidemiologic data regarding gender, age, activity level and type, and patient comorbidities. Men are up to four times more likely than women to sustain a meniscal tear. Cutting and pivoting sports requiring knee flexion at high activity levels generate the highest risk for meniscal injury, including basketball, soccer, gymnastics, wrestling, football, and skiing. Additionally, lateral meniscal tears are less common than medial meniscal tears for most of these activities and all age groups.
Recent advances in radiology including magnetic resonance imaging (MRI) have significantly improved the diagnosis of meniscal injury. However, improved imaging has also increased the frequency of incidental meniscal pathology that does not necessarily correlate with clinical symptoms. Prior data have documented a 5.6% incidence of asymptomatic meniscal tears in a young patient population (mean age: 35 years). Abnormal signal characteristics were also identified in the posterior horn of the medial meniscus in 24% of patients. These incidental findings significantly increase with age, with a 76% prevalence of meniscal tears in asymptomatic older patients (mean age, 65 years).
Advanced imaging techniques have also aided in diagnosing meniscal pathology in the setting of concomitant ligament injury. Injury to the ACL has been associated with a significantly increased risk of lateral and medial meniscal tears due to the mechanism of acute ACL injury and secondary stabilizing effects in chronic ACL tears, respectively. Prior data have documented a 60% to 70% prevalence of meniscal tears in the setting of acute ACL injury. Lateral meniscal tears more commonly occur as a result of the rotational and translational mechanism of injury. Previous data in a young population with acute ACL ruptures documented a 57% and 36% prevalence of concomitant lateral and medial meniscal tears, respectively. However, medial meniscal tears are more commonly identified in the setting of chronic ACL tears.
Meniscal Injury: Classification
Multiple types of tears have been described, including vertical (longitudinal or circumferential), radial, horizontal (transverse or cleavage), degenerative, and complex tears and horn detachment ( Fig. 96-6 ). Vertical, oblique, and longitudinal patterns are most common in the younger population, whereas complex degenerative tears are more often seen in patients older than 40 years. Numerous authors have observed that tear type and configuration were predictive of outcome, with complex unstable tears (i.e., those with >3-mm displacement upon examination with an arthroscopic probe) faring worse than simple vertical-longitudinal tear types.
Vertical (longitudinal or circumferential) meniscal tears are frequently due to a traumatic etiology such as an ACL tear. These tears are also termed bucket handle tears when they are large (>1 cm), displaced, and unstable. Bucket handle tears may frequently cause mechanical symptoms, including locking and the inability to fully extend the knee. They more frequently occur in the medial meniscus because of the limited motion afforded by the strong peripheral meniscocapsular attachments. Smaller, incomplete vertical tears more commonly occur and are frequently identified at the time of arthroscopy. These incomplete tears do not require intervention in the setting of concomitant ACL injury if they are determined to be stable when manually probed.
Oblique (parrot beak or flap) tears commonly occur at the junction of the posterior and middle body of the meniscus. These unstable tears frequently cause mechanical symptoms including locking and catching during knee motion that may or may not produce pain. The associated pain has been hypothesized to be associated with irritation of the meniscocapsular junction and surrounding synovium. This tear type is not typically amenable to repair because it most commonly occurs in the white-white meniscal region. Excision of the unstable fragment is effective in addressing the mechanical symptoms.
Radial tears are oriented perpendicular to the circumferential fibers and are commonly identified in the lateral meniscus after an acute ACL rupture. Again, variability exists in the length of these tears, which range from small to large tears that extend from the white-white zone through to the periphery. A small radial tear involving less than 60% of the meniscus does not significantly influence compartment biomechanics, whereas a large radial tear that extends through more than 90% of the meniscus to the periphery results in a significant increase in peak compartment pressures. Partial tears preserve the crucial peripheral circumferential fibers and thus the load distribution ability of the meniscus. This radial tear subtype can be debrided to a stable edge in most circumstances. Complete tears, on the other hand, result in complete circumferential fiber disruption, which not only compromises the function of the meniscus but also increases the biomechanical tendency for repair diastasis with axial load. Although diastasis significantly impairs healing, repair of this tear type should be attempted, because the only alternative treatment is effectively a near-total meniscectomy. Strict non–weight-bearing rehabilitation should be instituted after repair of complete radial tears to reduce the potential for tear diastasis.
Horizontal tears often develop from variable shear stress between the superior and inferior meniscal regions in the early stage of meniscal degeneration. This tear type is typically a degenerative tear and may be associated with meniscal cyst formation that may communicate with the periphery. These tears have been commonly identified on MRI; however, their presence is not necessarily linked to clinical symptoms. Although some data suggest that cyst aspiration and suture repair of the horizontal tear may obviate the need for meniscectomy, in our opinion, most horizontal tears, including associated flaps, can be treated with a partial meniscectomy.
Complex tears of the meniscus occur in a stellate pattern and propagate through multiple planes, although the horizontal cleavage plane is most common. These tears most commonly occur at the posterior root, are degenerative in nature, and should be treated with partial meniscectomy if surgical management is indicated.
A meniscal tear zone classification has been documented and divides each meniscus into three radial and four circumferential zones. This classification system permits improved clinical documentation and comparison of outcomes ( Fig. 96-7 ).
Meniscal tears can be either traumatic or degenerative. Degenerative tears have been closely associated with osteoarthritis. Acute tears are often related to trauma, most frequently as a result of a twisting motion. Early diagnosis and treatment of acute meniscal tears can significantly affect the short-term meniscal viability and subsequent long-term articular chondral protection. This treatment is particularly critical in a younger population given the high incidence of acute, traumatic meniscal tears and the importance of joint preservation at an early age.
A carefully completed history, physical examination, and diagnostic imaging evaluation facilitates efficient and accurate diagnosis and guide appropriate treatment. The aforementioned epidemiology should aid in guiding the patient history with regard to age, mechanism of injury, activity level, concomitant pathology, and previous ipsilateral injury or surgery. Additionally, fundamental questions should also be asked, including the location and duration of symptoms, exacerbating activities, and alleviating mechanisms, including medication and activity modification.
Patients may or may not be able to recall a single traumatic event. These events typically include twisting or hyperflexion with or without a mild effusion that may be noticed the day after injury. Notably, this effusion is nonspecific for meniscal pathology. Pain is often localized to the joint line and is usually intermittent. Constant pain or pain at rest usually indicates separate or additional pathology, such as osteoarthritis. Mechanical symptoms may also herald an unstable flap or bucket handle meniscal tear; these symptoms include catching, locking, popping, pinching, or the feeling of having to move the knee through a specific range of motion to “reset” the joint. Clear evidence of locking due to an incarcerated torn meniscal fragment must be described as an inability to achieve full extension. Unlike traumatic tears, degenerative, chronic meniscal tears are atraumatic and are rarely associated with an acute effusion. Instead, patients may describe mild intermittent effusions, infrequent mechanical symptoms, and generalized joint-line pain. These tears more commonly affect an older, less active population and may exist with concomitant osteoarthrosis.
Physical examination of the patient with a possible meniscus tear should include an evaluation of gait, standing alignment, range of motion and strength testing of the hip and knee, ligament stability testing, and a careful inspection and palpation of the knee with particular attention directed to the joint line. Additional specialized tests including the McMurray and Apley grind tests may also be included. The contralateral extremity should also be examined for comparison because of the variability and patient-specific nature of these physical examination findings.
Physical examination may reveal an antalgic gait with varus or valgus alignment. This alignment may prove to be pertinent to the etiology and treatment of the meniscal tear. Displaced tears may present with a mechanical block to range of motion that is also associated with distinct pain at that end point. Pain with deep knee flexion is nonspecific but is common for posterior horn injuries. Cruciate and collateral ligament stability should then be evaluated. A visible knee effusion may also exist that can be exaggerated with “milking” or manipulation of the suprapatellar pouch to maximize the size of the effusion inferiorly. At this time, palpation for point tenderness should be performed with a focus on ligamentous and tendinous origins and insertions and the joint line. We prefer to perform the palpation component of the examination with the patient in a supine position with the hip externally rotated and the knee flexed to 90 degrees. Notably, palpable joint line tenderness has been repeatedly identified as the most sensitive and specific physical examination finding for meniscal pathology. However, joint-line tenderness is significantly less accurate for identifying meniscal pathology in the setting of an ACL injury.
Provocative maneuvers that cause meniscal fragment impingement between the femoral and tibial surfaces have also been described. The McMurray test is performed on the medial meniscus by flexing the knee, creating a varus stress by internally rotating the tibia, and bringing the knee into full extension. Reproducible pain with a palpable mechanical click or pop indicates a positive examination. Conversely, the lateral meniscus is tested with an applied valgus stress and external tibial rotation. Another commonly performed test is the Apley grind test, in which an axial load is created with concurrent internal and external rotation (“grind”) with the patient positioned prone and the affected knee flexed to 90 degrees. A positive examination is defined as pain at the medial and/or lateral joint line. A new clinical test, termed the Thessaly test, has been used to increase the diagnostic accuracy of the physical examination for meniscal tears by dynamically reproducing the load transmission in the knee joint at 5 and 20 degrees of knee flexion. The Thessaly test is performed with the examiner holding the patient’s outstretched hands while he or she performs a single leg stance flat-footed on the affected extremity and axially rotates three times with the knee in 5 degrees and then 20 degrees of flexion. A positive test is documented with the presence of medial or lateral joint-line pain and possible mechanical symptoms. When this test is performed in 20 degrees of flexion, a 94% and 96% accuracy has been documented for medial and lateral meniscal tears, respectively, with low false-positive and false-negative results.
Isolated meniscal pathology can be accurately diagnosed in more than 90% of patients with history and physical examination alone. Nevertheless, diagnostic imaging, including plain radiographs and MRI, is critical to confirm clinical suspicions, evaluate alignment, and identify concomitant pathology. Imaging is particularly useful when concomitant chondral or ligament pathology exists because the history and physical examination are far less accurate in this setting.
Plain radiographs should be the first-line radiographic study but are not sensitive or specific to meniscal pathology. Weight-bearing anteroposterior, lateral, and 45-degree flexed posteroanterior views should be obtained. A Merchant patellar view allows evaluation of patellofemoral pathology. Standing knee alignment can be assessed and correlated with meniscal pathology and, if a significant concern exists for abnormal alignment, a full-length, standing, long cassette, anteroposterior hip to ankle view of both lower extremities should be obtained. Degenerative joint disease may indicate a degenerative meniscal tear, but acute tears have no specific radiographic findings.
MRI is the ideal radiographic study for visualizing soft tissue pathology, including injury to the meniscus, capsule, ligaments, and articular cartilage. Arthrography was historically used prior to MRI to identify meniscal tears and may be considered in the setting of a contraindication to MRI. MRI is a noninvasive study that is performed without exposure to ionizing radiation and is able to image in multiple planes, thereby providing a three-dimensional depiction of soft tissue and osseous structures. Previous studies have documented a very high accuracy for MRI identification of meniscal abnormalities.
We routinely obtain MRI imaging for evaluation of meniscal pathology using both fat-suppressed and diffusion-weighted fast spin-echo (cartilage sensitive) axial, coronal, and sagittal images ( Fig. 96-8 ). Normal meniscal architecture is demonstrated by uniform low signal intensity on both fast spin-echo and fat-suppressed images. A high signal within the meniscal substance but not extending to the articular surface frequently exists as a result of intrasubstance degeneration. This signal may lead to an overinterpretation of a meniscal tear. Grading of the meniscal high signal can minimize this overinterpretation (see Fig. 96-8 ). Grade I is characterized by a nonfocal intrasubstance high signal without articular extension. Grade II is a focal linear high-signal region without articular extension. Grade III is a focal linear high-signal region located at the free edge of the meniscus with superior or inferior articular extension. A grade III signal that is identified on two or more MRI images has 90% sensitivity for representing a true meniscal tear. Nevertheless, careful evaluation of the surrounding structures, including the meniscofemoral and intermeniscal ligaments and popliteus tendon, should be conducted because they may mimic a meniscal tear.
Sagittal meniscal windows may aid in identifying acute, vertical meniscal tears and bucket handle tears, whereas coronal images are most helpful for identification of horizontal degenerative tears. Axial imaging may further confirm the existence of radial and flap tears. Bucket handle tears should be carefully evaluated at the intercondylar notch with the classic double PCL sign where the displaced meniscal tissue may be identified as a second low-signal line parallel and anterior to the PCL.
Despite the high sensitivity and noninvasive attributes of MRI, significant limitations exist, including higher cost and technical errors in both imaging technique and interpretation. Multiple studies have shown a high percentage of asymptomatic meniscal tears on MRI examination ranging from 36% to 76%. This percentage increases significantly with patient age. Prior MRI data from asymptomatic patients older than 65 years documented a 67% prevalence of meniscal tears. This prevalence increased to 86% in the setting of symptomatic osteoarthritis. For this reason, it is important to correlate MRI findings with the history and physical examination and, when indicated, findings on arthroscopy.
Nonoperative management of meniscal tears is not designed to facilitate healing of the tear but rather is directed at symptom management. Although prior data have documented spontaneous healing of stable, isolated peripheral meniscal tears, this outcome is a rare exception. Most unrepaired meniscal tears will not progress to healing, and therefore nonoperative management must be directed at reducing symptoms in carefully selected patients. Our experience suggests that most symptomatic meniscal lesions in the absence of significant concomitant osteoarthrosis do not respond well to nonoperative management, especially in the setting of mechanical symptoms, despite some evidence that symptom resolution may occur with this approach. However, nonoperative treatment is frequently used in the setting of associated medial or lateral compartment osteoarthrosis with concomitant meniscal tears and the absence of mechanical symptoms.
Nonoperative management should include rest, use of ice and nonsteroidal antiinflammatory medications, and activity modification for 6 to 12 weeks. Intraarticular injections of corticosteroids, analgesic medications such as lidocaine or bupivacaine, and viscosupplementation may also be used if concomitant osteoarthrosis is present. We do not suggest this methodology in the absence of osteoarthrosis, and it should be noted that corticosteroids may impair meniscal healing and that bupivacaine may lead to chondral damage. It is important to note that nonoperative management of an unstable, repairable meniscal tear may also result in tear propagation, thereby producing an irreparable tear that must be excised.
The definitive treatment of meniscal tears involves either repair or excision of the pathologic tissue. Surgery is indicated in patients who have persistent mechanical symptoms and/or pain and have not responded to a course of nonoperative treatment. The indications for arthroscopy include (1) symptoms of meniscal injury that affect activities of daily living, work, and/or sports participation, such as instability, locking, effusion, and pain; (2) positive physical findings of joint-line tenderness, joint effusion, limitation of motion, and provocative signs, such as pain with squatting, a positive pinch test, or a positive McMurray test; (3) failure to respond to nonsurgical treatment, including activity modification, medication, and a rehabilitation program; and (4) ruling out other causes of knee pain identified by patient history, physical examination, plain radiographs, or other imaging studies.
Timing of the injury and surgical management must also be considered. Acute tears have a higher rate of successful healing compared with chronic ones; it is understood that repairs of tears less than 8 weeks old heal more frequently compared with older tears. Additionally, patients undergoing repairs of traumatic meniscal tears have better 6-year functional results than do persons with degenerative meniscal tears. The majority of these studies, however, combine traumatic meniscal tear and concomitant injury. Stein et al. recently compared long-term outcomes after arthroscopic meniscal repair versus partial meniscectomy for traumatic meniscal tears and documented no difference in function score. However, the meniscal repair group demonstrated a higher rate of return to preinjury and sporting activity levels. Additionally, only 40% of the meniscal repair group demonstrated osteoarthritic progression at 8-year follow-up compared with 81% of the partial meniscectomy group. For these reasons, a recent traumatic history should be considered a good prognostic factor for meniscal healing within the meniscal repair algorithm.
The influence of patient age on meniscal repair outcome has been well documented. Prior data have documented a reduced cellularity and healing response in patients older than 40 years. Increased repeat tear rates have also been documented in patients older than 30 years, although failure occurred later in older patients. The association between increased age and worse outcome seems to be negated in the setting of avascular tears and meniscal tears with concomitant ACL rupture. No difference between younger patients and older patients (>40 years) has been found with regard to clinical success after meniscal repairs performed for tears with relative avascularity. Kalliakmanis et al. recently documented no difference in repair failure between older or younger patients younger than 35 years of age in the setting of a concomitant ACL tear. Although prognostic factors including avascular tears, concomitant ACL rupture, and continued ligamentous instability seem to play identical roles in younger patients, the consequence of postmeniscectomy arthritis remains significantly greater.
From the aforementioned variables, one may synthesize surgical indications for meniscal repair that can predict healing prognosis. Contraindications for repair include older or sedentary patients or patients who are unable to perform the necessary postoperative rehabilitation. Additionally, isolated inner third white-white tears with a remaining rim greater than 6 mm should not be repaired. Borderline tears including middle third white-white tears should only be considered for repair if extension exists into the red-white or red-red region. Degenerative or stable longitudinal (<12 mm in length) tears should also not be repaired. Meniscal tears with a peripheral rim less than 4 mm should be considered for repair, because removal of this large tear will result in biomechanical alterations similar to a total meniscectomy. Particular consideration should be given in this circumstance to patients younger than 40 years of age and those with active lifestyles. Meniscal repair is ideal in younger patients with acute traumatic tears. The adverse sequelae of meniscectomy are most marked after a lateral meniscectomy in young, active women, with some patients demonstrating a relatively rapid progression to lateral compartment arthrosis. Thus aggressive attempts should be made to repair the lateral meniscus in this setting.
Arthroscopy can be used both to confirm the diagnosis and to treat meniscal pathology. Careful evaluation of the meniscal tear configuration should aid in preoperative planning regarding potential meniscectomy, meniscal repair, or even transplantation. Nevertheless, a complete diagnostic arthroscopy with careful probing of all intraarticular structures remains the gold standard for diagnosis of meniscal injury and should be conducted to confirm the preoperative diagnosis and identify other potential intraarticular pathology.
Meniscal Root Tears
Diagnosis and treatment of a tear in the anterior or posterior root of the medial or lateral meniscus is extremely important because of the biomechanical role that these attachments play in meniscal stability. These tears often occur with concomitant ligamentous injury, including ACL ruptures and multiligamentous knee injury. Unstable posterior root tears of the lateral meniscus may be identified with high-energy acute ACL tears because of the translation and impaction of the posterolateral meniscus and the tibial plateau that occur during the traumatic pivot shift.
Anterior or posterior root tears can be repaired through an arthroscopic approach. Bone tunnel and suture anchor repairs have been described with good success. Both techniques should include preparation of the anatomic insertion site with osseous abrasion to stimulate a vascular footprint. The first step of the bone tunnel repair requires passing nonabsorbable sutures through the anterior or posterior root tissue. An arthroscopic guide can then be used to facilitate the creation of a bone tunnel from the anterior tibial cortex to the meniscal root footprint. The nonabsorbable sutures should then be retrieved through the tunnel and secured at the anterior tibial aperture over a bone bridge or other preferred cortical fixation device. The suture anchor repair is performed by placing a suture anchor in the footprint of the meniscal root followed by passing the loaded sutures through the meniscal root and subsequent reduction and fixation. A posteromedial or posterolateral accessory portal is required to place the suture anchor in the correct position for posterior horn tears.
Lateral Meniscus Fascicular Tears
Tears of the fascicular attachments to the lateral meniscus represent a unique injury to the lateral meniscus. Stabilization of the lateral meniscus differs from the medial meniscus because of the intraarticular position of the popliteus tendon. For this reason, direct meniscocapsular attachment is not possible in this region. Two popliteomeniscal fasciculi that anchor the lateral meniscus to the popliteus tendon have been described. Fascicular tears can produce an unstable posterolateral meniscus and mechanical symptoms. Repair of these anchoring fasciculi can be achieved using an inside-out or all-inside repair because of the vascular nature of these peripheral attachments. Incarceration of the popliteal tendon should be avoided during suture placement.
Meniscal cysts may also be identified in conjunction with an adjacent meniscal tear. Meniscal tears may lead to the formation of meniscal cysts, likely because of a one-way valve mechanism that allows extravasation and capture of synovial fluid. This mechanism is particularly prevalent with horizontal cleavage tears in the anterior meniscal region. Prior data have suggested that cysts are up to seven times more common in the lateral compartment, but recent MRI data have documented an equivalent prevalence.
Treatment of both the cyst and the associated meniscal tears is important to effectively address the one-way valve mechanism by which the cyst likely occurred. Arthroscopic partial meniscectomy and debridement remove the one-way valve mechanism created by the opposing flaps and provide access to and decompression of the associated cyst. Intraarticular extravasation of the cyst fluid may be observed during the arthroscopic debridement and can serve as a confirmatory sign of effective management. Open cystectomy may also be performed in rare cases with no associated meniscal pathology or an unusually large fluid collection. Both surgical techniques have been associated with good outcomes. Ultrasound-guided aspiration of the cyst is rarely a definitive treatment, because the fluid in the cyst may reaccumulate.
Discoid Meniscus and Meniscal Variants
Young first identified the discoid meniscus during a cadaveric dissection in 1889. This variant likely occurs as a congenital anatomic variant but has been previously thought to occur because of abnormal embryologic apoptosis of the central meniscus during development. The prevalence of the discoid meniscus variant is approximately 5% but may be increased in the Asian population. Both medial and lateral discoid menisci have been described, but the lateral side is much more common. Bilateral discoid menisci may also occur in up to 20% of cases.
Three main lateral discoid meniscal variants exist according the classification system described by Watanabe et al. This system was developed from arthroscopic observations of the lateral meniscus and its tibial attachments ( Fig. 96-9 ). Type I describes a discoid variant that fully covers the lateral tibial plateau and has intact peripheral attachments. This type is the most common of the three variants. Type II is an incomplete variant that also has intact peripheral attachments but does not fully cover the tibial plateau. Type III, or the Wrisberg ligament type, is lacking the normal posterior meniscal attachments and is posteriorly anchored solely by the meniscofemoral ligament of Wrisberg. For this reason, this type has increased mobility of the posterior meniscal body and subsequent clinical instability. This instability has been termed snapping-knee syndrome . Fortunately, this unstable variant has a low prevalence of between 0 and 33%. Notably, the posterior meniscal instability has been most commonly identified in younger patients with complete discoid morphology. Absence of capsular attachments of the anterior aspect of a discoid meniscus with resultant instability of this portion of the meniscus has also been described. Other classification systems also exist that attempt to provide a more specific description of the stability and structure and may prove more useful in guiding treatment.
The majority of discoid menisci are incidentally identified and asymptomatic and thus do not require treatment; however, some discoid menisci require operative intervention because of symptomatic tears that occur from high intraarticular sheer stress. Common symptoms include mechanical snapping or clicking with type III discoid menisci or tears in previously stable type I or II variants. These mechanical symptoms may be associated with lateral joint-line pain and swelling. The patient may or may not be able to recall a specific traumatic event that was associated with the symptoms. Joint-line palpation may reveal focal tenderness at the location of the tear with or without a palpable click during motion. Diagnostic imaging should be performed, including plain radiographs, which can demonstrate lateral joint space widening and tibial plateau concavity, a flattened lateral femoral condyle, tibial spine hypoplasia, meniscal calcification, and concomitant lateral femoral condyle osteochondritis dissecans. MRI evaluation should also be used to specifically evaluate the morphology of the meniscus and identify any tears. An absent “bow-tie” sign may be identified, demonstrating meniscal continuity between the anterior and posterior horns in three or more consecutive 5-mm coronal images ( Fig. 96-10 ). Although this sign can be easily used to identify type I and II discoid variants, it is less effective for the type III variant. The type III variant can only be identified by the absence of small peripheral attachments because of the otherwise normal meniscal morphology. Diagnostic arthroscopy should be used to confirm a clinical suspicion in this case.
Symptomatic type I and II variants should be treated with arthroscopic “saucerization” or partial meniscectomy with contouring to mimic normal meniscal morphology (see Fig. 96-9 ). A motorized shaver or arthroscopic biter can be used to resect the abnormal central tissue and other associated torn or degenerative tissue. A peripheral 6- to 8-cm meniscal rim should be maintained and contoured to avoid potential repeat tearing. Careful technique should be used to avoid iatrogenic chondral injury, because the discoid meniscus is frequently associated with a tight, narrow joint space and thickened meniscus. The techniques previously described for partial meniscectomy should also be applied in this case. If a large meniscal tear that extends to the periphery or an unstable peripheral detachment is present, the surgeon should consider repair and stabilization according to the techniques described in the meniscal repair section.
The combination of saucerization and peripheral repair is particularly suited for treatment of a symptomatic, unstable type III discoid lateral meniscus. Careful evaluation of the stability of the peripheral rim should be performed to confirm an adequate repair and stabilization, because this variant can be significantly unstable. We suggest using an inside-out repair technique for these cases because of the young age and significant instability of this variant. Nevertheless, continued improvements in all-inside implants may increase the utility of the all-inside technique in this setting.
A total meniscectomy should be avoided, if possible, because of the clear association with early compartmental arthrosis. Long-term data after a total meniscectomy have documented increased compartmental degeneration and arthrosis. Saucerization and repair, on the other hand, have been correlated with good to excellent early clinical and radiographic results. Unfortunately, a total meniscectomy is required in some circumstances because of significant tissue degeneration or tearing without the possibility of repair. Patients in whom total meniscectomy is required should be observed carefully for early signs and symptoms of meniscal deficiency (i.e., early arthrosis) to optimize the potential for a future meniscal transplant when indicated.
Meniscal Allograft Transplantation
Although recent improvements in the understanding of meniscal biomechanics and pathology and advancement in surgical techniques have resulted in more focused attempts to preserve the meniscal integrity and structure, this goal is not possible in many cases. Severe cases may require total meniscectomy or segmental meniscal excision with subsequent chondral deterioration and osteoarthrosis. This degeneration can result in significant pain, activity limitation, and functional impairment. In these circumstances, a meniscal allograft transplant has been used as a surgical management option. Clinical and radiographic evaluation, surgical indications and techniques, and postoperative management for meniscal allograft transplantation are discussed later in this chapter.
We believe that the history and physical examination are the most important components for optimizing the management of a patient with meniscal pathology. The specific age, activity level, occupation, and sport-specific requirements must be carefully considered when developing an individualized treatment plan.
We routinely obtain an MRI for any patient with potential meniscal pathology. Noncontrast cartilage-specific MRI is used to carefully evaluate the menisci, ligaments, and articular cartilage. Although performing MRI routinely can be costly, we believe that the information provided is crucial for diagnosis and management. MRI can provide confirmation of a meniscal tear or identify mimicking pathology such as an articular chondral injury. Tailored nonoperative management or preoperative planning can be carefully constructed on the basis of these diagnostic imaging data. A concomitant articular chondral injury may also be identified and, when indicated, addressed at the time of surgery.
We believe that early diagnosis and management of a meniscal injury optimizes the biologic and clinical outcome. This early intervention is particularly important for younger patients. We perform most meniscal surgery procedures on an outpatient, ambulatory basis with use of a regional anesthetic. We typically use the anteromedial and anterolateral portals for most meniscal procedures but may create accessory posteromedial or posterolateral portals for improved visualization and instrumentation. We do not routinely use a superomedial or superolateral outflow portal because it is rarely required for visualization and can unnecessarily injure the quadriceps muscle.
In our institution, we use isolated trephination and synovial abrasion for partial-thickness tears and stable, vertical tears less than 10 mm in length. The remaining reparable tears undergo formal repair. Improvements in instrumentation have allowed a transition to an all-inside technique for most vertical posterior and midbody tears using the FasT-Fix suture system (Smith & Nephew, Andover, Massachusetts). Nevertheless, we continue to use the formal inside-out technique for a subset of patients, including those of a younger age and those who have large bucket-handle tears and unstable type III discoid variants. These techniques do not need to be used in isolation, and thus we frequently perform an all-inside repair for the posterior component of a tear followed by use of inside-out and outside-in techniques for anterior tear extension. We only consider repairing meniscal tears in the avascular zone in young patients who have a large fragment, particularly in the setting of concomitant ACL reconstruction.
Partial meniscectomy is reserved for irreparable tears, including radial, horizontal, oblique, and degenerative tear configurations. We carefully limit the meniscal resection to only that which is necessary to maintain a stable construct. Both ipsilateral and contralateral portals are used to maximize visualization and instrument access. A motorized shaver is used for final contouring of the meniscectomy. We prefer to use a curved shaver because the shaving edge can be easily mobilized with rotation and it provides excellent access to the posterior meniscal tissue.
The most important surgical decision regarding a meniscal injury is whether to excise or repair the lesion. This decision is directly dependent on the aforementioned vascular supply of the meniscal region in which the tear occurs—red-red, red-white, or white-white zones. Vertical tears are particularly amenable to repair if they occur at the meniscal periphery in the red-red zone. Repair of a centrally located red-white tear, on the other hand, is less successful because of the presence of vascular supply for only half of the meniscal substance. Nevertheless, meniscal repair may be considered in this region depending on the tear type. White-white tears, on the other hand, have an exceedingly low likelihood for successful repair, and thus a partial meniscectomy should be performed in this region.