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Knee Injury – Meniscal Cartilage Tear

The meniscus are cartilage tissue which act like shock absorbers in the knee joint. A meniscus can be torn, commonly after a forceful twisting injury to the knee. Symptoms include knee pain, swelling, and locking of the knee. Some heal by themselves, but an operation to fix, trim or remove the torn meniscus may be advised.

The diagrams below illustrate the knee joint.

Cross-section diagram of a normal joint

The meniscus Each knee joint contains a medial and lateral meniscus (inner and outer meniscus). These are thick rubber-like pads of cartilage tissue. They are C-shaped and become thinner towards the middle of the joint. The menisci cartilages sit on top of, and are in addition to, the usual thin layer of cartilage which covers the top of the tibia. The menisci act like shock absorbers to absorb the impact of the upper leg on the lower leg and also help to improve smooth movement and stability of the knee. When people talk about a cartilage injury to a knee, they usually mean an injury to one of the menisci.

The rest of this leaflet is just about injury to the meniscus.

The knee is commonly injured in sports, especially rugby, football and skiing. You may tear a meniscus by a forceful knee movement whilst you are weight bearing on the same leg. The classical injury is for a footballer to rotate (twist) the knee whilst the foot is still on the ground – for example, whilst dribbling round a defender. Another example is a tennis player who twists to hit a ball hard, but with the foot remaining in the same position. The meniscus may tear fully or partially. How serious the injury is depends on how much is torn and the exact site of the tear.

Meniscal tears may also occur without a sudden severe injury. In some cases a tear develops due to repeated small injuries to the cartilage or to degeneration (wear and tear) of the meniscal cartilage in older people. In severe injuries, other parts of the knee may also be damaged in addition to a meniscal tear. For example, you may also sprain or tear a ligament.

Meniscal cartilage does not heal very well once it is torn. This is mainly because it does not have a good blood supply. The outer edge of each meniscus has some blood vessels, but the area in the centre has no direct blood supply. This means that although some small outer tears may heal in time, larger tears, or a tear in the middle, tend not to heal.

The symptoms of a meniscal injury depend on the type and position of the meniscal tear. Many people have meniscal tears without any knee symptoms, especially if they are due to wear and tear.

  • Knee Pain. The pain is often worse when you straighten the leg. If the pain is mild, you may be able to continue to walk. You may have severe pain if a torn fragment of meniscus catches between the tibia and femur. Sometimes, an injury that you had in the past causes pain months or years later, particularly if you injure the knee again.
  • Swelling. The knee often swells within a day or two of the injury. Many people notice that their knee is slightly swollen for several months if the tear is due to degeneration.
  • Knee function. You may be unable to straighten the knee fully. In severe cases you may not be able to walk without a lot of pain. The knee may lock from time to time if the torn fragment interferes with normal knee movement. Some people notice a clicking or catching feeling when they walk. (A locked knee means that it gets stuck when you bend it and you can’t straighten it without moving the leg with your hands.)

Note: a “clicking joint” (especially without pain) does not usually mean you have a meniscal tear.

For some people, the symptoms of meniscal injury go away on their own after a few weeks. However, for most people the symptoms persist long-term, or flare up from time to time, until the tear is treated.

  • The story and symptoms often suggest a meniscal tear. A doctor will examine the knee. Certain features of the examination may point towards a meniscal tear.
  • Your doctor may sometimes advise an X-ray of the knee. An X-ray will not show cartilage tissue, but it can check for any bone damage which might have also occurred with the injury.
  • The diagnosis can be confirmed by an MRI scan of the knee (see separate leaflet called ‘MRI Scan’ for more detail) or by arthroscopy (keyhole surgery – see below).

When you first injure your knee the initial treatment should follow the PRICE formula: protect, rest, ice, compression (with a bandage) and elevation. This, combined with painkillers, helps to settle the initial pain and swelling. Further treatment may then depend on the size of the tear, the severity of symptoms, how any persisting symptoms are affecting your life, your age, and your general health.

Non-operative treatment

Small tears may heal by themselves in time, usually over about six weeks. Some tears which do not heal do not cause long-term symptoms once the initial pain and swelling subside, or cause only intermittent or mild symptoms. In these cases, surgery may not be needed. You may be advised to have physiotherapy to strengthen the supporting structures of the knee, such as the quadriceps and hamstring muscles.

Surgery

If the tear causes persistent troublesome symptoms then an operation may be advised. Most operations are done by arthroscopy (see below). The types of operations which may be considered include the following:

  • The torn meniscus may be able to be repaired and stitched back into place. However, in many cases this is not possible.
  • In some cases where repair is not possible, a small portion of the meniscus may be trimmed or cut out to even up the surface.
  • Sometimes, the entire meniscus is removed.
  • Meniscal transplants have recently been introduced. The missing meniscal cartilage is replaced with donor tissue, which is screened and sterilised much in the same way as for other donor tissues such as for kidney transplants. These are more commonly performed in America than in the UK.
  • There is a new operation in which collagen meniscal implants are inserted. The implants are made from a natural substance and allow your cells to grow into it so that the missing meniscal tissue regrows. This is not yet available at all hospitals.

Arthroscopy is a procedure to look inside a joint by using an arthroscope. An arthroscope is like a thin telescope with a light source. It is used to light up and magnify the structures inside a joint. Two or three small (less than 1 cm) cuts are made at the front of the knee. The knee joint is filled up with fluid and the arthroscope is introduced into the knee. Probes and specially designed tiny tools and instruments can then be introduced into the knee through the other small cuts. These instruments are used to cut, trim, biopsy, grab, etc, inside the joint. Arthroscopy can be used to diagnose and also to treat meniscal tears. See the separate leaflet called ‘Arthroscopy and Arthroscopic Surgery’ for more details.

Following surgery, you will have physiotherapy to keep the knee joint active (which encourages healing) and to strengthen up the surrounding muscles to give support and strength to the knee.

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Meniscal Injury

The meniscus is important for transmitting loads across the knee. The menisci increase the surface area of contact and fill the gaps between differently shaped articulating surfaces: the round femoral condyles, the relatively flat tibial plateau on the medial side, and the convex tibial plateau on the lateral side.

Normal Medial Meniscus
Normal medial meniscus

Removing the menisci increases the contact pressure between the femur and the tibial articular surfaces and may predispose to early arthritis. On the medial side, load is shared equally between the medial meniscus and the articular surface. However, the lateral meniscus must bear most of the lateral side load transmission alone. It seems that degenerative changes are more likely after partial lateral meniscectomies than after partial medial meniscectomies.

The meniscus has been shown to play a vital role in load transmission across the knee joint. Biomechanical studies have demonstrated that at least 50% of the compressive load of the knee joint is transmitted through the meniscus in extension, and 85% of the load is transmitted in 90 degrees of flexion. In the meniscal deficient knee the contact area is reduced approximately 50%, which results in articular cartilage damage. Partial meniscectomy has also been shown to increase contact pressures significantly. Another proposed function of the meniscus is that of schock absorption, although it seems that the menisci do not play a significant role in shock absorption. The menisci are also believed to contribute to joint stability, especially in ACL deficient knees. Finally, the menisci may serve as proprioceptive structures providing a feedback mechanism for joint position sense.

Meniscal Injury

Turning or twisting of the knee may cause tearing of the meniscus. When the torn part is mobile, flexion and extension of the knee can displace the fragment out its normal position. Typical signs and symptoms are clicking, catching or snapping. A knee effusion may or may not be present, but most patients will have jointline tenderness.

Radial Medial Meniscal Tear
Flap Tear of the Medial Meniscus
Radial meniscal tear
Large meniscal flap tear

 

Giving way and locking are also frequent symptoms of a meniscal injury. Displaced bucket handle tears, which usually go with chronic ACL deficiency, will cause the knee to lock in flexion. Anteromedial pain with mechanical block to extension reflects a displaced bucket-handle tear or ACL tear.

Longitudinal tear
Bucket handle tear

 

Medial meniscal tears are more often symptomatic than lateral meniscal tears. Most tears occur in the posterior load-bearing area, causing medial and posteromedial jointline pain and effusion. Pain in the anterior third is not from a meniscal tear, because no weightbearing occurs there, and anterior medial meniscal tears are extremely rare. However, patients with a displaced bucket-handle medial meniscal tear may complain of anteromedial pain with a mechanical block to extension, which is often followed by an effusion.

Early clinical and MRI diagnosis, and appropriate treatment of meniscal tears, especially in people younger than 40, are very important for the longevity of the knee joint.

Meniscal Cysts

Meniscal cysts were first described by Ebner in 1904. They are often associated with a specific complex type of meniscal tear called a horizontal cleavage tear, usually of the lateral, rarely the medial meniscus. However, isolated cysts without meniscal pathology have also been reported. Clinically, meniscal cysts look like a small lump, usually at the level of the lateral joint line. The size of the lump often correlates to activity level and the chronicity and the complexity of the meniscal tear. They are encapsulated, hernia-like structures, and they contain viscous synovial, often gel-like, fluid which penetrates through the torn meniscus and accumulates under the skin.

Several theories have been proposed regarding cyst aetiology, including traumatic and degenerative origins. Histology shows a meniscal cyst formation which originates by influx of synovial fluid through microscopic and gross tears in the substance of the meniscus. A meniscal tear with a horizontal component, as well as a tract that provides an exchange of fluid between the joint and the cyst, is often seen. Meniscal cysts are multilocular and lined with synovial endothelial tissue.

Meniscal cysts can be drained with a needle (although this can be difficult because of the viscosity of the content of the cyst) but they will often come back, because a tear in the meniscus will allow further penetration of the synovial fluid into the cyst. The management of a meniscal cyst usually involves an MRI scan of the knee to determine the presence of a meniscal tear and the location of the cyst. In the presence of a meniscal tear, partial arthroscopic meniscectomy followed by arthroscopic cyst decompression is the treatment of choice. If a tear is not confirmed at the time of arthroscopy open decompression of the cyst, performed through a mini-arthrotomy, combined with “outside-in” meniscal repair is the best treatment option. Recurrent meniscal cysts are not uncommon and open cystectomy may be required. In any case, the peripheral meniscal body should be preserved and the meniscus should not be excised under any circumstances.

Medial Meniscal Cyst and Horizontal Tear
Medial meniscal cyst

Lateral Meniscal Cyst and Horizontal Tear
Lateral meniscal cyst

Clinically lateral meniscal cysts are far more common than the medial ones. However, MR imaging reveals a different pattern. A retrospective review of 2572 knee MRI reports, for the presence of meniscal tears and cysts, revealed that meniscal cysts occur almost twice as often in the medial compartment as in the lateral compartment! Medial and lateral tears occur with the same frequency. These findings, when viewed in the context of the historical literature on meniscal cysts, suggest that MR imaging detects a greater number of medial meniscal cysts than physical examination or arthroscopy, and that MR imaging can have an important impact on surgical treatment of patients.

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