CHAPTER 6 Meniscal Resection

Emilio Lopez-Vidriero, Donald H. Johnson

Joint line tenderness, locking, popping, or catching are the hallmark symptoms of the meniscal pathology. As the population becomes older and more active, the prevalence of degenerative meniscal tears increases. Meniscal injuries, mainly traumatic tears, represent one third of all athletic injuries. They usually involve a hyperflexion mechanism and prevent the patient from continuing his or her sports activity, and normal life. For these reasons, interest in the treatment of meniscal pathology has increased in the last century.

Knee joint stability is enhanced by the menisci in a similar manner to the glenoid or acetabular labrum. Basic and clinical research studies have shown that the main functions of the menisci are shock absorption and load transmission during knee joint movement and loading. In addition, the intact meniscus serves as a secondary restraint to anteroposterior knee motion. Finally, the menisci also have a role in proprioception and joint lubrication.

The menisci were once considered a vestigial tissue, without any function in the knee, and thus no treatment was required. Since then, in the last few decades, with the increasing information about the importance of the menisci, many treatment protocols have been described. The treatment options range from benign neglect to repair.

Meniscectomy is still the most frequent surgical procedure, almost 80% of operative cases. Arthroscopic meniscectomy achieves instant relief of pain caused by the mechanical symptoms resulting from the unstable fragments. The result is improvement of function of the knee joint.

The known advantages of arthroscopy over open surgery have now been widely recognized—day surgery without the need of hospital admission, less recovery time, less pain caused by the minimally invasive surgery, less global morbidity, more accurate resections because of better visualization, fewer complications, and less cost for the patient and/or the system. Thus, arthroscopic meniscectomy or repair has become the standard of care.

Arthroscopic surgery of the knee is a very common procedure. The American Academy of Orthopaedic Surgeons estimates that 636,000 are performed each year in the United States, and more than half are related to meniscal pathology.

This chapter reviews the main aspects of the basic science and clinical knowledge of the menisci. The classification of meniscal pathology related to the indications for its surgical treatment, emphasizing meniscectomy, are presented. We describe our surgical approach to the different configurations of meniscal tears, including special emphasis on the anterior cruciate ligament (ACL)–deficient knee with a meniscal tear. Rehabilitation programs and complications are also discussed. The literature on arthroscopic meniscectomy is reviewed to provide a scientific background to support the reader’s clinical decisions.

ANATOMY

Menisci are discs of fibrocartilage interposed between the femoral condyles and tibial plateau. The articular surface of the medial condyle of the tibia is oval, with the longer axis being in the anteroposterior plane (Fig. 6-1). The central portion of the articular surface is not covered by meniscus and represents the articular area. The lateral meniscus plateau is almost circular and less concave. The menisci cover the peripheral two thirds of the tibia, and serve to deepen its articular surface and stabilize the joint. The upper borders of the menisci are concave and the undersurfaces are flat. Peripherally, the menisci thicken and are attached to the synovium and capsule. Centrally, the border is thin and exists as a free edge.

FIGURE 6-1 Axial view of the tibial plateau showing both menisci. Note that the cruciate ligament’s insertion has been removed to allow better visualization (grey rectangle). Transverse ligament, dashed arrow; hiatus popliteus, arrow.

The medial meniscus is oval, 3.5cm in length, and wider posteriorly from its peripheral to its central aspects in the knee. Its anterior horn attaches to the tibial plateau just anterior to the attachment of the ACL. Some posterior fibers originating from the anterior horn cross the knee joint anteriorly, attaching to the lateral meniscus and forming the transverse ligament (see Fig. 6-1). Posteriorly, the meniscus is anchored to the intercondylar fossa of the tibia between the posterior cruciate ligament (PCL) and lateral meniscal attachment. Along its periphery, the medial meniscus is attached to the joint capsule and the deep medial collateral ligament (MCL). The medial meniscus has less mobility than the lateral meniscus, and moves almost 10 mm from extension to flexion.

The lateral meniscus is circular, covering a larger portion of the articular surface than its medial counterpart. It is the same width anteriorly and posteriorly. The anterior horn attaches near the intercondylar spine posterior to the attachment of the ACL, with which it partially blends (Fig. 6-2). The posterior horn attaches just posteriorly to the intercondylar spines, anterior to the attachment of the medial meniscus. The lateral meniscus does not attach to the lateral collateral ligament but is attached loosely to synovium along much of its length. The anterior (ligament of Humphrey) and posterior (ligament of Wrisberg) meniscofemoral ligaments run from the posterior horn of the lateral meniscus to anterior and posterior, respectively, to the PCL attachment on the medial femoral condyle. Moreover, the tendon of the popliteus muscle, on its way to insert into the lateral condyle, crosses the joint through a hole on the lateral meniscus called the hiatus popliteus (see Fig. 6-1). This area along the popliteal hiatus is described as the avascular region.

FIGURE 6-2 Oblique view of the tibia showing the insertion of the ACL. Note how the anterior horn of the lateral meniscus fibers blend with the ACL (arrow).

Vascular Anatomy of the Meniscus

Menisci are relatively avascular, having a limited peripheral blood supply originating from the superior and inferior genicular arteries. Some of its branches form a premeniscal capillary plexus within the synovial tissue of the knee. This plexus forms a circumferential vascular pattern, with radial branches extending to the central portions of the menisci. The vessels penetrate readily into the peripheral 10% to 30% of the medial meniscus and into the peripheral 10% to 25% of the lateral meniscus. It is important to note that the vascular outer third of the meniscus is maintained throughout life, and does not significantly decrease with age.

Biomechanics and Meniscal Function

The menisci distribute stress over a large area of the articular cartilage. When the knee is loaded, the tensile strength of the meniscal matrix (hoop tension) counteracts extrusion of the meniscus. Therefore, the healthy meniscus responds to load mainly with compression.

The menisci have been shown to accept approximately 50% of the weight-bearing load with the knee in extension and 85% of the load with the knee at 90 degrees of flexion. The menisci increase the tibiofemoral contact area significantly, and thus reduce the stress on the articular cartilage.

A complete meniscectomy has been shown to decrease the contact area by approximately 50%.¹ A partial or total meniscectomy has been clinically demonstrated to result in degenerative changes in the knee.² This has been postulated to result from the increase in contact pressures in the knee. Even a minor meniscectomy, removing 15% to 34% of the meniscus, increases contact pressures in the knee by up to 350% and can result in degenerative changes. In meniscectomized knees, a significant reduction in contact area of about 55% is observed, and peak contact pressures increase an average of 260.4% compared with those of nonmeniscectomized knees.³

In addition, menisci also perform a role in absorbing forces or shocks during locomotion, where they dampen these forces by approximately 20%. The loss of this function may further contribute to the development of degenerative arthrosis of the knee.

Knee joint stability is enhanced by the menisci in a similar manner to the glenoid or acetabular labrum. The intact meniscus serves as a secondary restraint to anteroposterior knee motion.⁴ The ACL-deficient knee can place abnormal stress on an intact medial meniscus, resulting in a meniscal tear. The increased anteroposterior motion created by meniscectomy in the ACL-deficient knee can lead to increased instability.

Thus, the function of the meniscus is to share in weight bearing, aid in lubrication, and help stabilize the compartment. The medial meniscus shares in 60% of the weight bearing of the medial compartment, compared with 70% of the lateral meniscus.

Regenerative Capacity of the Meniscus

King’s 1936 experiment on a canine model represents the historical origin of the interest in meniscal healing.⁵ Later experimentation demonstrated the necessity of a peripheral blood supply to support the inflammatory cascade required for meniscal healing.⁶

The reparative process of the meniscus involves a coalescence of blood from the peripheral vascular zone adjacent to the meniscal tear and formation of a fibrin clot. Undifferentiated mesenchymal cells accumulate in the clot, forming a cellular fibrovascular scar, which maintains the tear edges in a reduced position. The inflammatory reaction proceeds with ongoing invasion of cells from the synovial fringe and the fibrovascular scar tissue. This inflammatory cascade ultimately results in angiogenesis in the premeniscal capillary plexus, allowing vessels to proliferate throughout the repair tissue.

Studies have shown that when a radial tear extends into the synovium, it can heal spontaneously by 10 weeks.⁷ The strength of this tissue is 33% normal at 8 weeks, 52% at 4 months, and 62% at 6 months. It is this inherent healing ability of the meniscus that clinical initiatives exploit in efforts to preserve as much meniscal tissue as possible.

CLASSIFICATION

A meniscal tear may be classified by its location relative to its blood supply and vascular appearance. The peripheral and central surfaces can be clinically graded as white (relatively avascular) or red (vascular) at the time of arthroscopy. This classification is based on anatomic studies that have depicted a peripheral vascular zone.

A red-red tear is defined as a peripheral capsular detachment, and has the best prognosis for healing. Unfortunately, a significant portion of tears occur in the white-white zone, which lies in the central avascular portion of the meniscus. This area of the meniscus has minimal blood supply, and theoretically is unable to heal. The remainder exist as red-white tears. These are meniscal rim tears through the peripheral vascular zone of the meniscus. The central portion of this tear exists in the avascular zone, so theoretically, these lesions should have sufficient vascularity to heal by fibrovascular proliferation.

Conventional wisdom dictates that meniscal repairs be limited to the peripheral vascular area of the meniscus (i.e., red-red and red-white tears). Both experimental and clinical studies have suggested that white-white tears are incapable of healing, even in the presence of a surgical suturing. This has thus provided the rationale for partial meniscectomy. In an effort to extend the zone of repair more peripherally, techniques such as the creation of vascular access channels by trephination, synovial abrasion, and use of a fibrin clot have been developed.

In addition, meniscal tears can be classified depending on their stability (Box 6-1). A tear is considered unstable when it is more than half the length of the meniscus and subluxes under the femoral condyle when probed with a hook (Fig. 6-3A). This concept is especially important to help decide the treatment options—left alone, trephinated, resected, or repaired.

Box 6-1 Criteria For Arthroscopically Defined Stability Using the Probe

• Cannot be displaced into the intercondylar notch

• Inner edge of meniscus cannot touch central part of the femoral condyle

• Length of the tear <10 mm

FIGURE 6-3 A, Unstable longitudinal vertical tear. Note how it subluxes under the femoral condyle when probed. B, Stable incomplete longitudinal vertical tear. Stability should be assessed continuously with the probe. C, Stable complete longitudinal vertical tear. Some tears although complete may also be stable.

Stable tears, which occur particularly in the posterior aspect of the meniscus and do not subluxate into the joint may be left alone (see Fig. 6-3B and C). Fitzgibbons and Shelbourne⁸ have found that of 189 patients whose stable meniscal tears of the posterior horn of the medial meniscus were left alone, no patient was symptomatic at 2.6 years following surgery. Also, a stable longitudinal tear of the lateral meniscus, posterior to the popliteus, may be left alone, even in association with a torn ACL.

Tears can be described depending on their morphology and based on their configuration. Under these criteria, tears could be vertical or horizontal, according to whether the line of the lesion goes from superior to inferior (vertical) or from inside to outside (horizontal), commonly called open book or fishmouth tear (Fig. 6-4). Moreover, tears can be described as longitudinal if the pattern is from anterior to posterior (Fig. 6-5; also see Fig. 6-3), or transverse, also called a radial or parrot beak tear (Fig. 6-6). Combinations of these four basic patterns make up the others types of tears; the oblique tear is vertical and radial, and the so-called bucket handle tear is a vertical longitudinal tear that is unstable and subluxes completely under the condyle (Fig. 6-7; also see Fig. 6-3A). Finally, the complex tear is a combination of all of these, usually in a degenerative setting, located in the posterior horn of the medial meniscus (Fig. 6-8).

FIGURE 6-4 Horizontal degenerative tear. These tears may reach the vascular zone (arrow).

FIGURE 6-5 Diagram showing the longitudinal tear.

FIGURE 6-6 Radial tear. This is also called a parrot beak or flap tear.

FIGURE 6-7 Bucket handle tear dislocated into the intercondylar notch.

FIGURE 6-8 Complex tear. These tears are usually located in the posterior horn of the medial meniscus and are associated with degeneration.

Longitudinal vertical tears usually occur in the young patient in association with an anterior ACL tear, and more frequently in the medial meniscus because of its lower mobility. Oblique tears tend to appear in between the medial and posterior thirds of the meniscus. They may cause mechanical symptoms of entrapment and pain caused by the tension on the meniscus–capsular junction.

Horizontal-shaped tears usually begin as intrasubstance degeneration in the middle of the meniscus, and migrate toward the free surface. Often, they also extend to the capsular junction and can cause the formation of a cyst. Because of the increasing size of the cyst over time, the patient may experience pain and tenderness. They usually appear more frequently in the lateral meniscus and are filled with a gel-like substance chemically similar to synovial fluid. These cysts have been reported to be 1% to 10% of meniscal pathology.⁹

Complex tears appear mainly in older patients and are usually associated with cartilage degeneration. They are considered to be part of the process of arthrosis and degenerative arthropathy. Because of their complex pattern, the fragments can be unstable and cause mechanical symptoms. The pain associated with these tears is an added element to the generalized inflammation involved in the osteoarthritic knee. The associated histologic pathology is myxoid degeneration, hyaline acellular degeneration, and dystrophic calcification.¹⁰

Timing is also important in decision making. Tears can be acute, with more likelihood of healing, or chronic, which are usually associated with complex patterns and degeneration. These usually require resection. The time frame to consider a tear to be chronic is generally 8 to 12 weeks after the lesion has occurred.

The cause or mechanism of the tear should be determined. If the tear is traumatic, which usually happens in a young active patient, and is diagnosed acutely, there is an improved chance of success. On the other hand, degenerative complex tears usually occur in older patients and are associated with arthrosis. Whether they are a cause or consequence of the osteoarthritic process is still unknown.

Finally, tears can be classified depending on the side—that is, the medial or lateral meniscus. Metcalf and colleagues ¹¹ have observed that 69% of tears affected the medial meniscus, whereas the lateral was affected 24% of the time. In their review, both menisci were torn at the same time in 7% of patients. Moreover, 80% of the tears were vertical or oblique and affected the posterior medial part of the meniscus.

In summary, the most common meniscal tears are as follows:

Chronic, degenerative, horizontal, or complex in the medial meniscus (see Fig. 6-8)

Acute, traumatic, longitudinal, and vertical in the medial meniscus (see Fig. 6-3)

The degenerative horizontal type tear usually occurs insidiously in older patients, and generally requires resection. On the other hand, the traumatic vertical or longitudinal tear is seen more often in the younger patient, and potentially can be repaired.

PATIENT EVALUATION

History

The meniscus is commonly injured in sports, but can occur as a sequel of age-related degeneration. In these cases, there may be no trauma but, more typically, patients give a history of a twisting hyperflexion injury followed by pain. This acute episode may involve locking of the knee and moderate swelling that usually develops over the first 24 hours. Recurrent episodes of pain and swelling are occasionally accompanied by complaints of mechanical symptoms such as catching, popping, or locking in the knee. The pain tends to localize along the joint line, especially with deep flexion and twisting motions.

Is also important to inquire about symptoms of instability, because the menisci are a secondary restraint to anteroposterior translation and certain tears can worsen in the setting of an ACL-deficient knee.

Physical Examination

The patient is examined for signs of an effusion, loss of quadriceps bulk, and decreased range of motion. Tenderness to palpation along the medial or lateral joint line is among the most sensitive signs of a meniscal tear (Fig. 6-9A). Studies have shown it to be as sensitive as 74%, with a positive predictive value of 50%.¹² The collateral and cruciate ligaments need to be assessed to determine whether additional injury is present. In the setting of an ACL-deficient knee the sensitivity of joint line tenderness has been shown to decrease to approximately 50%.

FIGURE 6-9 A, Palpating for joint line tenderness. This is the most sensitive sign for meniscal tear. B, The McMurray test. As a mnemonic rule, the heel of the foot points toward the injured meniscus. The test is considered positive when the patient feels pain in the appropriate joint line, accompanied by a thud or click.

Special tests for assessing the meniscus, such as the McMurray, Steinmann, and Apley tests, are not conclusive but can aid in the diagnosis. The aim of all these maneuvers is to trap a fragment of meniscus between the tibia and femur, producing pain, a clunk, or both. Because the meniscus itself is fairly aneural, pain is caused by traction at the synovium-meniscal junction.

The McMurray test is preferred because it is easy, fast, and reliable. In addition, complementary knee tests may be done in the same position. This provocative test is performed with the patient supine, the hip flexed to 90 degrees, and the knee in forced maximal flexion. The foot is grasped by the heel, the knee is steadied, and the joint line is palpated with the other hand. As the knee is slowly brought into extension, an external rotation stress will test the medial meniscus and an internal rotation stress will test the lateral meniscus (see Fig. 6-9B). As a mnemonic rule, the heel of the foot points toward the injured meniscus. The test is considered positive when the patient feels pain in the appropriate joint line, accompanied by a thud or click. When the clunk is present, the test has a sensitivity of 98% but, because it is not always possible to evoke the clunk, its specificity is only 15%.¹³

In conclusion, the hallmarks of a meniscal tear are presence of an effusion, joint line tenderness, and a positive McMurray test. When the history and physical examination are considered together, the overall sensitivity to diagnose a meniscal tear, confirmed with arthroscopy, is approximately 95% and specificity is 88%.¹⁴

Diagnostic Imaging

Evaluation of the patient with a meniscal tear should include routine anteroposterior (AP) and lateral x-rays of the knee. If degenerative changes are expected, standing views, including a 45-degree flexion AP view, should be obtained to assess the degree of joint space narrowing. Assessing osteoarthritis is important to counsel the patient about expectations of success. It has been proven that the degree of arthrosis before surgery correlates with worse postoperative results in the short- and long-term periods.¹⁵^,¹⁶

Although not clinically indicated for all patients, magnetic resonance imaging (MRI) plays a valuable role in the evaluation of the full range of meniscal pathology, including the primary diagnosis of a meniscal tear, detection of a recurrent tear after resection or repair, and demonstration of associated injuries. MRI shows the relative locations of the tears, and is able to determine the presence of a meniscal tear with an accuracy of over 90%.¹⁷ These results indicate that MRI is an accurate noninvasive technique for evaluating meniscal tears.

Image results should be combined with pertinent history and physical examination. It has been proven that meniscal tears in young adults can be completely asymptomatic.¹⁸ In these cases, MRI may modify the therapeutic plan. For example, if an athlete suffers an ACL during the season and the MRI demonstrates no tear, one may be inclined to let the athlete finish the season with a brace. If there is a meniscal tear associated with the ACL tear, the preference would be for early reconstruction.

TREATMENT

Indications and Contraindications

Meniscectomy is indicated when the type of tear has no chance to heal spontaneously or repair is not possible. Although technology is improving and the indications for repair are increasing, arthroscopic partial meniscectomy is currently still indicated in 80% of tears (Table 6-1).

TABLE 6-1 Indications for Meniscectomy: Situations in Which Meniscectomy Is Preferred Over Repair

Factor	Features
Meniscal Tear Factors
Location	White-white
Morphology	Horizontal cleavage Radial lateral Degenerative bucket handle
Size	>20 mm
Chronicity	>8-12 wk
Patient Factors
Age	>40 years old
ACL acute deficient knee	Small posterior flap tear in lateral meniscus
ACL chronic deficient knee	All types of tears
Rehabilitation	Noncompliant patient