Meniscal Tears of the Knee
Diagnosis and Individualized Treatment
Joseph Bernstein, MD, MS
THE PHYSICIAN AND SPORTSMEDICINE - VOL 28 - NO. 3 - MARCH 2000
In Brief: Meniscal tears are very common sports injuries. Typical symptoms include pain, catching, and buckling. Signs on physical exam include joint-line tenderness, effusion, and, possibly, a click when the knee is taken through full range of motion. MRI is often needed to confirm tears and differentiate pain from that caused by other injuries such as articular cartilage damage. Treatment comprises physical therapy and rest, partial meniscectomy, or, in special instances, surgical repair. Therapeutic goals, which are often achieved, are to restore a high level of pain-free function and to prevent premature joint degeneration.
Knee meniscal tears are among the most common injuries seen in sports medicine. Twisting motions with the knee flexed, which are common in sports, place high stresses on the menisci. Many times the injury occurs when the athlete attempts a pivot; contact with another player typically does not occur, nor does lunging or landing awkwardly. A single "wrong step" is sufficient.
Meniscal tears among active patients are clinically significant on two counts. First, they cause pain, mechanical symptoms such as catching or locking, and effusion. Even if athletes can continue to play, they are rarely at top form with a tear. Second, healthy menisci are needed to prevent damage and degeneration of the joint. Thus, even if the patients are able to ignore symptoms, they should be dissuaded from doing so, especially if the tear is repairable.
Meniscus Anatomy and Function
Gross anatomy. The shape of the meniscus (figure 1) and its microanatomy are tailored to absorbing shock, distributing load, and stabilizing the joint (1). The meniscus consists of cartilage, but its composition is slightly different from the articular cartilage that lines the ends of bone. Meniscal cartilage is configured to be springy and resist shearing. Each knee has a medial and lateral meniscus that are attached by ligaments to the proximal tibia. The word meniscus means "little moon" in Greek—when viewed from above, the meniscus has a crescent shape. The meniscal ring is thickest at the periphery and tapers off centrally, creating a shallow cup to hold the round condyles of the femur. In cross-section, the meniscus has a triangular wedge shape.
Function. For many years, it was thought that the meniscus had no function. Accordingly, painful tears were treated by open meniscectomy (complete removal); however, this practice was abandoned after Fairbank (2) noted that x-rays in a large percentage of patients who had meniscectomies showed progressive flattening of the femur, narrowing of the joint space, and formation of bone spurs, some of the cardinal signs of osteoarthritis. These radiographic findings after meniscectomy are now known as Fairbank's changes (2).
The menisci play important roles in the biomechanics of the knee (3). The tapered-ring geometry of the meniscus promotes the "mating" of the rounded edge of the femur and the flat edge of the tibia. Without a meniscus, weight transmitted by the femur would concentrate on a single contact point on the tibia, under high pressure. (Pressure is defined as force divided by area; thus, a constant force on a smaller area creates higher pressure.) The meniscus allows the femur to rest effectively on nearly the entire tibial plateau, distributing the force and preventing excess stress on any single area. In addition, the meniscus functions as a shock absorber, dampening the forces that the femur may apply to the tibia under high-load activities such as jumping or running.
The meniscus also helps the anterior cruciate ligament (ACL) to stabilize the knee. Just as a block placed behind the wheel of a car prevents it from rolling, the body of the meniscus prevents the femur from gliding too far off the tibia. The posterior oblique ligament on the medial side of the knee tethers the posterior horn of the meniscus to ensure that this stabilizing wedge is kept in place. Patients who tear the posterior meniscal horn may feel instability—even if their cruciate ligament is intact—because this stabilizing effect is lost (4).
Tears of the menisci occur in two distinct settings. The first occurs when a healthy meniscus is traumatized and is characteristic of the young athlete. The mechanism of injury is commonly a twisting motion with the knee bent, and such tears can be found either within the body of the meniscus or at the junction of the meniscus and the inner lining of the knee, an area known as the joint capsule. When a large piece of the meniscus tears from the capsule, it can flip over within the joint creating a so-called a "bucket-handle" tear: attached at two ends, with the middle flipped upward in the center. The movable flap of meniscus can block motion and is one of the rare causes of a truly "locked" knee.
A different injury is seen in older patients. Because the tissue is no longer as strong or resilient, less force is needed to tear the meniscus. Accordingly, the older patient may not even recall when the injury occurred. Rather, the symptoms may appear gradually. Finally, since a degenerative tear cannot be repaired in the older patient, the urgency for treatment is much lower than that required when treating a bucket-handle tear in a young person, in which the objective is to prevent damage to potentially repairable tissue.
History and physical. Diagnosis of meniscal tears can often be made clinically (table 1). In the young athlete, there is usually a history of twisting injury that prevented continuation of play. An older athlete may note a more gradual onset of symptoms. If no other structures were damaged, pain localizes at the joint line and worsens with hyperflexion. In the early course, patients may limp as they find full weight bearing too painful. An effusion is common but may be absent if the tear occurs as an isolated injury.
Specific tests. An aspiration may help identify the underlying cause of the effusion. Blood in the knee is an ominous sign: Since the meniscus itself is avascular, hemarthrosis should not be attributed to a meniscal tear. Rather, the physician should assume that other structures in addition to the meniscus (such as the ACL) may have been injured (5). The lone exception to this rule is when the meniscus is torn from the capsule, a vascularized structure. Such an injury will produce blood in the joint. The presence of blood in this situation is a significant finding, but for beneficial reasons; it implies that the meniscus may be repairable. Accordingly, all patients with a bloody effusion after trauma should be referred to an orthopedic surgeon.
Special diagnostic maneuvers exist for identifying meniscal tears on physical examination, but they are not particularly sensitive. For example, the McMurray test, which attempts to detect a click as a torn meniscus is moved with knee extension, will miss at least 40% of all meniscal tears (6,7). Thus, the best diagnostic steps are general ones: Establish a history consistent with the injury, localize the symptoms to the joint line, and exclude other injuries such as cruciate or collateral ligament tears. If the clinician suspects a meniscal tear and determines that it needs to be treated, magnetic resonance imaging (MRI) can confirm the diagnosis.
MRI. The use of MRI is a hotly debated topic. The clinician should be aware of the strengths and limitations of MRI, and use it when the technique can be helpful. The advantages of MRI are that it involves minimal risk to the patient (since no ionizing radiation is used) and that it paints a fairly accurate picture of soft tissues of the knee (figure 2). MRI is both sensitive and specific for meniscal tears—accuracy is approximately 90% (8). Finally, MRI may reveal abnormalities that were not suspected on the clinical exam and thus may influence treatment.
One disadvantage of MRI is its high cost. In addition, patients may insist on treatment for a lesion discovered on MRI, even if the clinician is certain that such a lesion is not the source of the patient's symptoms. Although MRI is very helpful for discovering abnormalities (9), it cannot differentiate lesions responsible for the patient's symptoms from incidental lesions. As such, MRI is not always helpful for determining a treatment plan.
The important clinical factors to consider in management include the severity and location of symptoms, the patient's preferences, and the overall impact of the tear on the function of the patient's knee. None of these is reflected on the MRI. As such, MRI cannot replace the history and physical and does not supplant medical judgment.
Clearly, an MRI is not necessary for all patients. Consider, for example, an athlete who has a locked knee after a twisting injury, medial joint-line tenderness, and bloody effusion. These findings strongly suggest a bucket-handle tear of the medial meniscus. This tear needs to be reduced and repaired, if possible. Urgent arthroscopy, without MRI, is warranted. On the other hand, if the patient had known osteoarthritis and was not, accordingly, a good candidate for arthroscopy, using MRI for diagnosing a tear is unnecessary because it would not influence the immediate treatment plan.
Radiographs. Omitting an MRI does not mean that all imaging studies should be skipped. Athletes who have had an injury and cannot fully bear weight or have tenderness along the tibia, femur, or patella should be sent for plain radiographs to rule out a fracture. Because x-rays show only bone, plain radiographs cannot detect a meniscal tear; however, they can often exclude other problems such as a fracture or an osteochondral defect. In addition, weight-bearing x-rays can help detect degenerative arthritis, a finding that may affect treatment.
Nonoperative therapy. Current treatment for meniscal tears can be grouped into three categories (table 2): nonoperative, partial meniscectomy, and meniscal repair. Nonoperative treatment includes the use of anti-inflammatory medications as well as physical therapy to prevent quadriceps weakness, stiffness, and other consequences of disuse. Conservative treatment is appropriate even when there is a documented meniscal tear as long as the tear is not repairable and the patient is willing to wait and monitor symptom progression. In older patients, symptoms may simply abate with time. In Europe, where some national health insurance plans require a long wait for surgery, many patients cancel their operations because they have recovered sufficiently (10,11).
Small tears are especially good candidates for nonoperative therapy (12). If the tear is small and peripheral, it may heal without intervention (13). The risk of neglecting a tear is that a second, perhaps trivial, injury may lengthen the original tear. This risk, however, is small. Nonoperative treatment should always include an exercise program as well as physical therapy to prevent muscle atrophy. There is no formal role for knee braces, but some patients report a subjective improvement wearing a wrap or sleeve, perhaps because of the retained body warmth or increased proprioception from skin stimulation.
Nonoperative treatment also can produce complications. The patient's function may deteriorate until the meniscus is removed. Muscles may atrophy from disuse, and the meniscal fragment can detach and block knee motion or injure the adjacent articular cartilage. Blocked motion, especially if it persists after the pain improves, indicates a need for specialist referral. Finally, a potentially repairable tear can be pulverized by the articular surfaces and become irrepairable.
Partial meniscectomy. Typically, meniscectomies are performed arthroscopically, as are most repairs (figures 3 and 4). This minimally invasive approach lessens the disruption of normal tissue and allows for rapid rehabilitation. Arthroscopy leads to less postoperative swelling, faster achievement of full flexion, quicker return to work and sports, and lower hospital costs compared with open surgery (14,15). Meniscectomy reliably treats the acute symptoms of the tear (16). In the absence of a second intra-articular problem, excellent results are the norm (17-19). Still, most patients will need supervised postoperative physical therapy to regain full muscle strength (20,21).
One disadvantage of partial meniscectomy relative to repair is that it eliminates some of the benefits provided by the cartilage in that area; eg, arthroscopic partial meniscectomy may lead to Fairbank's changes if a large fragment is removed (22). Repairable tears should thus be fixed and not removed. Also, meniscectomy is not appropriate in all patients: If there is extensive articular damage, simply removing the meniscus will not revitalize the joint (23-25).
Meniscal repair. Meniscal repair, on the other hand, may prevent Fairbank's changes (26). In this surgery, the torn edges of the meniscus are sutured to preserve the form and function of the cartilage. Short-term follow-up shows that approximately 90% of sutured peripheral meniscal tears do, in fact, heal (27,28). Better still, some evidence suggests that repaired menisci can prevent articular degeneration (29).
In one 10-year study (30) of 50 arthroscopically repaired meniscal tears, only 8% of surgically treated knees had minimal joint changes, as compared with 3% in the uninjured knee. This finding represents a dramatic improvement over that noted by Fairbank (2) and suggests that the repaired cartilage can prevent degenerative changes. This potential benefit prompts some surgeons to advocate attempted repair of even those tears that have a fairly low chance of healing (31).
Not all patients are candidates for meniscal repair (32). Sometimes the tissue is too damaged to save. Also, since the meniscus itself is avascular, only tears at the periphery of the meniscus, adjacent to the synovial blood supply and capsule, are likely to heal. This region near the capsule is called the "red zone" because of its proximity to the capillaries of the synovium. The more central area is called the "white zone." It may be possible to repair a tear in the white zone under special circumstances. For instance, if a repair were undertaken at the same time as a ligament reconstruction, a white-zone tear may heal (33). It is thought that the intra-articular bleeding caused by drilling tunnels for ligament reconstruction provides the biological factors that can stimulate healing. When the tear is not quite in the red zone and no ligament surgery is done, creating vascular channels or placing a fibrin clot in the tear may increase the healing potential (34-36).
Rehabilitation and Education
If none of the signs that warrant orthopedic consultation are present, the primary care physician should recommend a program of physical therapy and perhaps medication for pain such as an anti-inflammatory drug or acetaminophen. Relative rest, but not complete inactivity, may also be helpful. It is also important to reassess the patient after a few days. At this point, the acute pain should have subsided, and a more accurate physical examination will be possible. Rehabilitative exercises, including stretching, flexion and extension strengthening, and stamina building can speed the patient's return to function, both as a primary treatment modality and as part of the postoperative regimen.
The final consideration is to educate patients about their injury. Some older patients may be very hampered initially by their symptoms, but they need to know that recovery is possible without surgery. On the other hand, a young athlete may be inclined to persevere despite the injury, which may damage a potentially repairable meniscal tear. Remember that an anatomic diagnosis does not define the treatment. Rather, the unique features of each patient's case—age, activity, symptom severity, etc—dictate the care required.
Dr Bernstein is director of sports medicine at the University of Pennsylvania, in Philadelphia. Address correspondence to Joseph Bernstein, MD, MS, Sports Medicine Service, University of Pennsylvania, 424 Stemmler Hall, Philadelphia, PA 19104-6081; e-mail to [email protected].