The knee joint menisci are crescent-shaped discs of fibrocartilage, wedge-shaped in cross-section, which fill the space between the otherwise incongruent upper and lower leg bones in the knee joint. In the past, no significant importance was attached to them - today it is known that they are essential for the even distribution of pressure in the knee. If they are destroyed or removed (e.g. due to damage to the meniscus tissue), pressure peaks can occur in the knee joint cartilage with secondary damage to the same and the development of osteoarthritis. For this reason, attempts are made today to preserve the menisci as far as possible.

Causes

Meniscus damage is, on the whole, a very common condition of the knee joint. In principle, two main causes of damage can be distinguished: acute tears or avulsions, as observed in severe injuries of the knee joint (e.g. in cruciate ligament ruptures, fractures of the tibial plateau), or more chronic damage, which can be understood as a summation of smaller injuries of the meniscal tissue. The latter are the more common variant and are not infrequently associated with instabilities following ligament injuries or arise in the wake of osteoarthritis, which is common in old age.
In adults, only the outer 20-30% of the tissue is supplied with blood. Accordingly, the healing tendency is poor in the inner part, which is supplied only by diffusion of nutrients from the synovial fluid.

Meniscus damage does not necessarily cause discomfort. If they do lead to problems, this often manifests itself in pain in the area of the back of the knee or at the sides, especially when the knee joint is bent. Sometimes torn off parts of the menisci can get jammed in the joint space and lead to the fact that one cannot fully extend or bend the knee - there is then a so-called blockage, which is quite indicative of a meniscus injury.
The aforementioned back-localized complaints are ultimately very non-specific and are also found in other diseases of the knee.

Examination Methods

During the physical examination, various tests are performed that are indicative of meniscus damage. At present, it is almost never possible to conclude with certainty from such tests whether the menisci are actually the cause of the complaints, since the pattern of complaints can also be found in other diseases, e.g. arthrosis. MRI examinations are often ordered, in which cross-sectional images of the knee are obtained, on which the menisci can be easily visualized. Simple X-rays are not suitable for diagnosing meniscus damage, but they can be used to rule out arthrosis.
Ultimately, all examinations are subject to a certain degree of uncertainty, so that it is not uncommon for an arthroscopy, i.e. a reflection of the joint, to provide certainty.

Treatment

As a rule, only meniscal damage that also causes symptoms needs to be treated. Tears detected by MRI without corresponding clinical signs do not require therapy. Fresh meniscus injuries can heal without surgical intervention, especially if they are located in the zone with a good blood supply. Effective medicinal treatments are hardly available at present. Persistent complaints or acute entrapments are therefore mostly treated surgically.
If the tissue as such is well preserved and only torn, a suture is often performed to support healing. In the case of chronic damage, so-called degenerative changes, a suture has only very limited chances of success. In most cases, the diseased tissue must be removed.

Today, this is done sparingly while preserving the undamaged part. The meniscus surgery is minimally invasive and has become a clear domain of arthroscopy.

The majority of meniscus diseases and their treatment fall into the groups described above. A particular problem is posed by the rare cases in which large parts of the meniscus are destroyed or removed in young people. In these cases, a wear and tear disease of the knee joint can develop early in life with corresponding consequences for the function of the knee. So far, there are no well established procedures for the replacement of the menisci. Sometimes attempts are made to replace parts of the meniscus with suitable pieces of animal collagen.
Transplantation of menisci (derived from multi-organ donors) is also sometimes performed. However, such procedures have not yet been able to show that they can change the course of the disease in the long term and are therefore of a rather experimental nature.

Since the healing capacity of meniscal tissue is very limited, there are efforts to improve it by using growth factors or stem cells. Corresponding investigations have also been carried out at the Orthopedic University Clinic in Magdeburg in cooperation with other centers, but have not yet found their way into clinical practice. It remains to be seen here whether the healing ability of the menisci can be improved by such procedures in the future.
Performance of the procedure as already noted, arthroscopies can be classified as minimally invasive procedures. In most cases, only two small accesses of less than 1 cm are needed to the joint, which are located at the front of the knee. Additional incisions may be necessary. An optical system with a camera is inserted into the joint through one access, allowing the surgeon to view the interior of the joint with the menisci. Instruments specially developed for arthroscopy allow appropriate manipulations to be performed on the meniscus via the second access.

The majority of such procedures can be performed on an outpatient basis, i.e. the patient leaves the clinic on the same day. In the case of removal of the worn tissue, the knee can usually be loaded again immediately. However, this does not mean that the patient can immediately engage in normal sports or professional activities. The extent of the procedure appears smaller on the outside than it is in arthroscopic surgery. It usually takes a few weeks to fully restore knee joint function. If suturing of the meniscus has been performed, weight bearing on the knee must be limited for a period of time. Healing requires 6 weeks or longer. Weight bearing on the extended leg and normal walking is usually possible, sports that put a strain on the knee such as soccer or skiing must be avoided for at least 3 months.

Late Complications

It is sometimes the case that sutured meniscus tears do not heal. This is often due to the poor healing tendency of the tissue described above. A follow-up operation to remove the unhealed tissue may then be necessary.