The menisci 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 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.
The menisci 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.
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.
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.
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.
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:
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.