The meniscus – what is it?
Meniscus injuries are among the most common conditions in orthopaedics; they often take a long time to heal and can severely restrict patients’ quality of life. About 300,000 meniscus injuries are recorded every year.
In each knee joint, between the joint surfaces of the thigh bone and the shin bone, there are two C-shaped discs of tissue, the menisci. There is an inner (medial) and an outer (lateral) meniscus. The meniscus is an elastic, crescent-shaped disc that is firm but also slightly elastic. This allows it to adapt perfectly to the surfaces of the two joint partners and act as a shock absorber, stabiliser and load distributor in the joint. The most important function of the menisci is to relieve the joint and protect the cartilage.
The meniscus consists of dense fibrous tissue but has no nerve fibres and only a poor blood supply. A change in the meniscus tissue, e.g. a tear, therefore does not cause pain at first. Pain only occurs when the meniscus gets trapped in the joint and pulls harder on the joint capsule. The poor blood supply also means that a tear heals poorly. This must be taken into account in treatment.
If the meniscus is missing or large parts of it have been surgically removed, osteoarthritis of the knee is usually inevitable. In a healthy knee, the meniscus ensures that only half of the weight acts on the cartilage. If the meniscus is removed completely, the load on the cartilage increases two- to three-fold.
Types of injury
An injury to the meniscus is usually caused by wear and tear. Over many years, the meniscus tissue becomes brittle and loses elasticity. As a result, small tears develop in the tissue, which can widen into a large tear. With a deep tear, parts of the meniscus can become so mobile that they flip into the joint and cause pain. Flap tears (about 80% of all tears) in the rear part of the inner meniscus are particularly common.
In rare cases, a single overload or a sports accident can cause a meniscus tear. Especially with severe twisting of the knee that tears the anterior cruciate ligament, the meniscus can tear at the same time.
In simple terms, there are two types of meniscus injury. Flap tears are almost always caused by wear and start at the inner edge of the meniscus, in a section that has no blood supply. The other type are longitudinal tears, in which the meniscus splits along its fibres. These tears are more often caused by a single accident. The tissue can split so far that the inner part flips into the joint. This is called a bucket-handle tear. In this situation, the patient often can no longer straighten the knee, or the joint is locked in one position. If the split is close to the outer edge, there is a chance under favourable conditions that the defect will heal, i.e. a scar can form (though one that cannot bear much load).
Diagnosis
The symptoms of meniscus disease are pain, locking and swelling. Often the patient first notices slight pain on the inside of the knee during certain movements. Later, stabbing pain can occur, usually in connection with twisting movements of the knee. Typical movements are getting into or out of a car. Deep squatting is also often painful.
After a detailed interview about the location, duration, extent and nature of the pain, blood supply, motor function and sensation are examined, and a meniscus test is carried out. X-rays and MRI can also be used to diagnose meniscus damage. MRI in particular can provide information about the shape and extent of the meniscus tear, which is important for further treatment.
Non-surgical treatment
Meniscus tears caused by wear cannot heal, because the inner sections of the meniscus have no blood supply. However, if the person avoids extreme movements such as twisting the knee during sport, the knee pain can lessen or even disappear, which makes life more bearable again. This does not mean that the meniscus tear has healed.
Longitudinal tears near the outer edge of the meniscus, on the other hand, can heal under favourable circumstances, possibly with surgery, because small blood vessels from the joint capsule support healing. However, these tears account for less than 10% of all cases.
Usual conservative measures include oral anti-inflammatory painkillers with ointments and local injections or possibly joint injections of anaesthetics. Physical therapy can also include exercises for mobilisation, muscle strengthening and stretching, as well as electrotherapy and cold therapy.
Each case should be considered individually, taking into account the patient’s age and everyday physical strain at work and in sport.
Surgical treatment
The standard treatment of a meniscus injury is usually arthroscopic, i.e. keyhole surgery. Advantages of arthroscopic treatment are less surgical trauma and shorter rehabilitation. Patients can return to work and sport sooner. Standard procedures are sparing partial removal of the meniscus and meniscus suture. In partial removal, care must be taken to remove only the parts of the meniscus that are injured.
The principle is: as much as necessary, as little as possible. In children, every effort should be made to preserve the meniscus. The type of tear and any associated injuries are decisive. After arthroscopic partial meniscus removal, weight-bearing adapted to pain and guidance from a physiotherapist are recommended.
Careful and sparing removal of a meniscus tear is important for preserving the existing cartilage. Today, lost cartilage still cannot be replaced by anything. Great care must therefore be taken to keep consequential damage and premature osteoarthritis of the knee to a minimum.