The meniscus is one of the most commonly injured structures in the knee. Meniscal injuries can occur in any age group, but causes are somewhat different for each age group. In younger people, the meniscus is fairly tough and rubbery, and tears usually occur as a result of a fairly forceful twisting injury. In the younger age group, meniscal tears are more likely to be caused by athletic activity (Sutton, 1999). In older people, the meniscus grows weaker with age. The tissue that makes up the meniscus becomes degenerative and much easier to tear.
Meniscal injuries in older people occur as a result of a fairly minor injury, even from the up and down motion of squatting. Degenerative tears of the meniscus are commonly seen as a part of the overall condition of osteoarthritis of the knee in the older population. In many cases, there is no one associated injury to the knee that leads to meniscal tears (Sutton, 1999). In order to understand how the menisci can be injured, you must understand the basic anatomy of the menisci and why they are important.
The menisci are two oval (semilunar) fibrocartilages that deepen the articular facets of the tibia and cushion any stresses placed on the knee joint. They enhance the total stability of the knee, assist in the control of normal knee motion, and provide shock absorption against compression forces between the tibia and the femur (Booher, 2000). Articular cartilage covers the ends of the bones that make up the joint. The articular cartilage surface is a tough, very slick material that allows the surfaces to slide against one another without damage to either surface.
This ability of the meniscus to spread out the force on the joint surfaces as we walk is important because it protects the articular cartilage from excessive forces occurring in any one area on the joint surface, leading to degeneration over time (Sutton, 1999). Blood is supplied to each meniscus by the medial genicular artery.
Each meniscus can be divided into three circumferential zones: the red-red zone is the outer or peripheral one third and has a good vascular supply; the red-white zone is the middle one third and has a minimal blood supply; and the white-white zone on the inner one third is avascular (Arnheim,1997).
The medial meniscus is larger and more oval or C-shaped in the outline than the lateral meniscus. The medial cartilage is also more firmly fixed to the tibia and the capsule than the lateral meniscus; as a result, it is much more frequently injured than the lateral cartilage. Because of its attachments to the medial collateral ligament, the medial meniscus may also be injured in conjunction with a sprain of this ligament (Arnheim, 1997).
The lateral meniscus is smaller and more round or O-shaped. It is not as firmly attached to the tibia and it is not attached to the lateral collateral ligament. Therefore, the lateral meniscus has greater freedom of movement, and it is not injured nearly as often as the medial meniscus (Booher, 2000). The lateral meniscus also attaches loosely to the lateral articular capsule and the popliteal tendon. The Wrisberg ligament is the part of the lateral meniscus that projects upward, close to the attachment of the posterior cruciate ligament.
Then the transverse ligament joins the anterior portions of the lateral and medial menisci (Arnheim, 1997). Meniscal tears are among the most common of all knee injuries. The menisci are frequently injured or torn as they become displaced, trapped, pinched, or crushed between the femoral condyles and tibial plateaus. The damaged sustained by the menisci varies, ranging from a very small tear along the periphery of the cartilage to a large longitudinal tear which is generally referred to as a “bucket-handle tear”.
The menisci are often injured by twisting activities during weight bearing, but also can be direct blows to the knee or chronic trauma (Booher, 2000). Acute injuries to the meniscus occur when the athlete suddenly twists or extends their knee. The athlete more often tears the medial meniscus which is less mobile with more peripheral attachments. Tears occur as the athlete cuts with their knee bent with their foot planted, thus rotating their upper leg. The joint traps the medial meniscus between the femur and tibia, pulling it towards the center and tearing it.
The lateral meniscus is more mobile with less peripheral attachment and commonly tears when the knee suddenly extends thus placing a sudden distraction force on the meniscus (Medical Multimedia Group, 1998). The athlete usually remembers the event that resulted in the acute tear, but does not in the case of a degenerative tear. They often complain of knee pain and swelling. They also repeatedly catch the torn fragment in their knee causing them to complain of catching, popping, and/or buckle and give way of their knee with activities.
Their knee occasionally locks and lacks full extension because of a trapped fragment in the joint (Sutton, 1999). Tears around the periphery of the meniscus or to the ligamentous attachments may heal because of the blood supply to this area. Tears involving the avascular body of the meniscus will not heal and usually result in persistent systems (Booher, 2000). Athletes with meniscal tears frequently have pain and tenderness along the joint line, pain with full extension, and clicking of the knee.
The athlete with a chronic or degenerative tear, symptoms and complaints are usually variable. Pain develops over time with no particular event leading to pain or swelling. The athlete with a degenerative tear usually does not remember injuring it (Medical Multimedia Group). During an initial evaluation it is often difficult to recognize a cartilage injury, because symptoms may be limited or vague. So it is important to get a careful and accurate history concerning meniscal injuries. In many cases suspected meniscal damage can be found in history alone.
Along with the mechanism of injury the athlete may relate a popping or tearing sensation felt at the time of injury, followed by pain. Pain and swelling is usually localized along the medial and lateral joint line. The athlete may also complain that the knee “gives out” or buckles. Walking up and down the stairs is frequently difficult, and squatting may be painful. The swelling associated with a damaged meniscus is usually caused by synovial irritation and occurs gradually over several hours (Booher, 2000) The most common symptoms of meniscal injuries are clicking and locking.
Clicking is an audible or palpable sensation often caused by a torn meniscal fragment rubbing against a femoral condyle. Locking is the mechanical blockage of complete range of motion. The most common cause of locking of the knee is that a fragment of an injured meniscus becomes caught between the femoral condyle and the tibial plateau, restricting complete extension (Booher, 2000). After taking a complete and accurate history it is important to perform a physical exam which will include: inspection, palpation, functional tests, ligamentous tests and special tests.
The major findings of a physical exam of a athlete with a meniscal tear are: joint effusion, tenderness over the medial and lateral joint line, limitation of the last few degrees of extension, a positive McMurray’s Test and positive Apley compression test. (Lincoln, 1998) Specific tests for the meniscus can assist in diagnosing a tear in them. All the meniscal tests are performed to attempt to trap, pinch, or displace the injured meniscus between the articular surfaces of the femur and the tibia by performing various circumduction or rotatory maneuvers.
The torn meniscus may cause pain or a clicking, grinding, or snapping sensation during these procedures. Three tests should be performed when assessing meniscal injuries: McMurray’s Test and Apley’s compression and distraction test (Arnheim, 1997). The McMurray Test is performed with the athlete lying supine and the hip and knee flexed maximally. Hold the athlete’s heel in one hand and palpate the medial and lateral joint line with your thumb and index finger of the other hand. Apply a valgus (lateral) stress and flex the knee, and then apply a varus (medial) stress back into extension.
Then repeat for two more rotations while internally and externally rotating the tibia (Booher, 2000). Apley’s Compression test is performed with the athlete lying prone with their leg in 90 degrees of flexion so the soles of their feet are parallel to the ceiling. Hold the athletes foot or heal, and press down firmly on the lower limb as you rotate it back and forth thus applying a compressive grinding force to the knee. Pain could indicate a meniscal injury, but in order to be sure perform the Apley’s distraction test.
Perform this test by pulling up on the tibia causes it to distract from the femur. The pain should be relieved when performing this test because the menisci are not compressed anymore (Booher, 2000). An MRI scan is very good at showing the meniscus. The MRI (Magnetic Resonance Imaging) machine uses magnetic waves rather than x-rays, to show the soft tissues of the body. With this machine, they are able to “slice” through the area they are interested in very clearly. An MRI is used to look for injuries, such as tears in the menisci or ligaments of the knee.
This test does not require any needles or special dye, and is painless. If there is a uncertainty in the diagnosis following the history and physical examination, or if other injuries in addition to the meniscal tear are suspected, the MRI scan may be suggested (Medical Multimedia Group). Initial treatment for a torn meniscus is usually directed towards rest, ice, compression, elevation, and early rehabilitation are recommended for many small tears that will heal on their own as well as the older player who has gradual onset to pain, without catching or locking.
If the knee is locked and cannot be straightened out, arthroscopic surgery will be required to either remove the torn portion of the meniscus or to repair the tear. During arthroscopic surgery, small incisions are made in the knee to allow the insertion of a small TV camera into the joint. Through another small incision, special instruments are used to remove the torn portion of the meniscus while the arthroscope is used to see what is happening. In some cases the torn meniscus can be repaired.
Sutures are then placed into the torn meniscus until the tear is repaired. Repair of the meniscus is not always possible. Young people with relatively recent meniscal tears are the most likely to have a successful repair. Degenerative type tears in older people are not usually repairable. It is very important to evaluate and manage a meniscal tear in order to prevent long term effects with in the knee. If the meniscal tear goes untreated it could cause constant rubbing of the torn meniscus on the articular cartilage, which could lead to degeneration of the joint.