The meniscus is a fibrocartilage component of some synovial joints. The menisci (commonly referred to as cartilage) of the knee are the most widely known examples. Another joint containing fibrocartilage is the A-C joint. This discussion will be concerned with the knee.
The menisci of the knee have unique shape. They are a wedged, “C” shape. The “C” shape corresponds to the surface area of the femur that would contact the surface of the tibia if the menisci were not present. The wedge shape corresponds to the shape of the heads of the femur as well. The ends of the femur are rounded for maximal flexion of the knee. The menisci act like a wedge to assist with the rotational stability created by the anterior cruciate ligament; like a wooden block placed behind the wheel of a car prevents the car from rolling.
The menisci also act as a shock absorber. As we walk, run, and jump the knee absorbs tremendous forces. The menisci help to absorb these forces so that the joint surfaces are not damaged. The compressive forces on the knee have been described as equivalent to the “amount of compression that would be exerted on the skin if a 300 pound person would hang from a ledge by a fingertip.” The amount of force increases exponentially as the speed of movement increases from walking to running to jumping. The menisci disperse the compressive forces over the entire knee rather than isolating them.
Mensical blood supply is limited: the menisci get nutrition from blood and synovial fluid. The outside border (red zone) of the meniscus has a blood supply that proliferates from the synovial capsule while the inside border (white zone) gets its nutrition from the synovial fluid. Due to this tears nearer the middle of the knee (white zone) do not heal due to a lack of blood supply to trigger an inflammatory response. Because of this many meniscal tears do not heal.
The meniscus in the knee is usually torn, in young adults, by a twist occurring on a slightly flexed knee. In the older adult, the tear may be due to a natural degeneration of the menisci that occurs with age. The traumatic type of injuries are quite common in the athletic setting. The meniscus can be torn anterior to posterior, radially, or can have a bucket handle appearance. Due to this, repair of the meniscus can be a complicated issue. If the meniscus tear is large enough and not addressed surgically, the torn flap of cartilage can cause further damage by causing degenerative arthritis (Fairbank’s changes).
Diagnosing a meniscal tear begins with a complete history. Often, the history alone will be the indicator of a meniscal tear. The athlete may also complain of clicking, popping, or locking of the knee. These symptoms are usually accompanied by pain along the joint line and a joint effusion. If the surgeon aspirates (drains) the knee and the fluid is bloody, further studies need to be done to rule out possible ACL damage. If there is no other damage, this could be an indicator of a tear in the red zone of the meniscus. These injuries are excellent candidates for repair rather than resection.
Physical examination may reveal point tenderness along the joint line, a positive McMurray test, positive meniscal compression test, or pain with squats. Manual tests for meniscal tears are only about 50% reliable even for the most experienced orthopaedists. Due to this an MRI may be ordered to rule out a meniscal tear. The image shows a normal meniscus in the left pane and a torn meniscus in the right pane (red arrow). The normal meniscus appears as a solid black wedge, while the torn meniscus has an area of white with in the black wedge.
A meniscal tear that is symptomatic (painful with activities of daily living) needs to be addressed surgically. There are two treatment options available, depending upon the location of the meniscus tear. Surgery is performed arthroscopically (a fiber-optic camera about the size of a pencil) to either resect a tear in the white zone or repair a tear in the red zone. The best treatment option is to repair the torn cartilage. This will leave the athlete with his “normal” structures and decrease the likelihood of degenerative arthritic changes.
The next set of photos shows a tear of the meniscus in the red zone and the resulting repair. The “after” picture shows a meniscal dart holding the two edges of the tear together
Rehabilitation after a meniscus repair is usually different than a resection. Most physicians will have the athlete be non-weight bearing for one month to allow the meniscus to heal. The theory is that the movement of the femoral heads over the tear will disrupt the healing. Rehab should focus on early mobilization of the knee joint and quad and hamstring strength. This is done by performing quad sets straight leg raises, hamstring curls, knee extensions, and Theraband® calf pumps. Weight bearing exercises are added as directed by the physician.
Rehabilitation for resected meniscal tears is usually very aggressive, targeting early return to participation. These athletes are allowed to progress through rehabilitation as pain and swelling allow.
©2000 - 2009 David Edell
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Last Update for AthleticAdvisor.com: 10/24/2009 12:09:35 AM