Meniscus tear

Synonyms in the broadest sense

Meniscus lesion, meniscus rupture, meniscus fissure, meniscus laceration, meniscus injury, meniscus tear

German: Meniskusriss

Definition

A meniscus tear /l esion / rupture represents an injury of one of both cartilage discs (meniscus), which are located in the knee joint between the thighbone and the shinbone. A meniscus tear / rupture can occur suddenly through an accident or it can develop gradually within the course of general abrasion of the knee. Meniscus rupture causes pain in the knee joint.

Anatomy of the meniscus

The meniscus

The meniscus consists of two fibrous cartilage discs that have a half-moon form, the interior and exterior meniscus, which are situated between the thigh and shinbone.

Structure

Position in the knee joint

Both meniscuses are situated as C or half-moon structures between the thigh head (femur condyles) and the shinbone head (tibia condyles). They are fixed by the joint capsule in a framework of fusions and partially provided with nutrition via their vessels. It is evident that the interior meniscus is linked to the joint capsule over nearly its entire length. This finding explains the fact that an interior meniscus is significantly less flexible than the more strongly bent and less firmly fixed exterior meniscus. In addition to fusions of the outer wall, the interior and the exterior meniscus are also fixed at their ends, which are formed to points. These end points of a meniscus are called anterior horn or posterior horn, according to their locations. Both “horns” indicate many sensitive / sensatory nerve endings for transmitting pain and for controlling the spatial positioning of the knee joint. Furthermore, fibrous connections also exist between the interior meniscus and the inner ligament of the knee joint (medial collateral ligament).

Nutrition

One differentiates morphologically (= related to the cellular structure) the meniscus base, which is in immediate contact with the joint capsule (red zone) from the intermediate meniscus region (light red zone) and the white fringes. Vessels penetrate through the red zone until the central third of the meniscus (designated as light red). By contrast, the white fringe indicates no vessels. It is nourished via the joint fluid (= joint lubrication). This knowledge has significant effects on the successful treatment of different meniscus injuries. While good chances of successful treatment exist for injuries in the red and light red regions through the vascularization and thus healing nourishment, a meniscus rupture in the white fringe region is significantly more difficult to treat. A real healing in the strict sense of the word is not possible in this zone (restitution of the intact meniscus; coalescence of the rupture).

Danger of injury =

It has been demonstrated by studies that meniscus injuries occur more often in the region of the interior meniscus, independent of their causes. The reason for this is certainly the relative rigid fixation of the interior meniscus in contrast to that of the exterior meniscus. In addition, the region of the posterior horn is especially vulnerable for injuries (approximately 75% of all injuries of the interior meniscus affect the region of the posterior horn), because the meniscus in this region if especially stressed.

Function of the meniscus

If one observes the superficial character of the knee that joins the thigh to the shinbone with their cartilage covering, then one determines that they are situated asymmetrically to one another (round femur and straight tibia) and that their joint surfaces (contact surfaces of the knee joint cartilage) do not coincide with one another. This asymmetry, which exerts a negative effect on age-dependent cartilage attrition, is compensated by the meniscuses. Thus when walking, the body load is transmitted evenly to the cartilage of the tibia.

In addition to compensating the asymmetry, they serve as a type of protective „buffer“ for the cartilaginous surfaces of the knee joint, because they can be deformed to a certain degree under stress. Furthermore, the meniscus is significant for stabilizing the knee joint and it helps the joint lubrication (knee joint fluid =synovial fluid) to be evenly distributed in the knee joint. On one hand, the synovial fluid is responsible for the smooth functioning of the cartilage surfaces; on the other hand, it serves the nutrition of the knee joint cartilage.

Since the knee joint cartilage represents one of the most important components of the knee joint, which can be damaged especially by a ruptured / lacerated meniscus, a short discourse will be made at this point about the function of the cartilage of the knee joint:

The cartilage of the knee joint represents a supporting connective protective tissue, which consists of cartilage cells (= chondrocytes) that have an abundant amount of water and so-called intercellular substances (basis substances, fibers, that lie between the cells). According to the consistency of the intercellular substance, one differentiates between:

• Hyaline cartilage (skeletal cartilage)
• Elastic cartilage
• Fibrous or connective tissue cartilage

While cartilage can be found in many regions of the body, in the area of the knee the hyaline and also the fibrous or connective tissue cartilage (= a mixture of collagen and hyaline cartilage) is especially important. If the cartilage has been worn out by strong exertion or through injuries, the body can neither repair this cartilage tissue nor synthesize it again. Then a doctor refers to a clinical picture of arthrosis (for more information, refer to explanations of the concepts Arthritis, Gonarthrosis).

In the region of the knee joint, the meniscus protects the cartilage in a special manner. The meniscus cushions impacts, but it also stabilizes the knee, in connection with the cruciate ligaments of the knee. In MRI video sequences, it could be demonstrated that ligament connections of the meniscus were especially required for the shock-absorbing function. Thus, loosened / ruptured ligament connections among other things could also be made responsible for meniscus ruptures, which can develop under certain conditions from superficial meniscus lesions. The yellow arrow indicates a healthy meniscus.

Torn or ruptured meniscuses (meniscus tear) destroy the cartilage tissue of the knee joint, by preventing the cushioning function to occur at all or to its full extent. In addition, stimulating substances are released, which can cause an inflammation of the knee joint and which can thereby damage cartilage enzymatically. Subsequently, arthritis of the knee can occur prematurely.

Summary: structure of the meniscus

• Enlargement and asymmetric compensation of contact surfaces for knee cartilage
• Buffering or cushioning function
• Stabilization of the knee joint
• Mixing of the knee synovial fluid

Enlargement of contact surfaces

The knee joint connects the thighbone (= femur) with the shinbone (= tibia). Since both femur and tibia have different structures and they thus demonstrate different joint surfaces, they would also create a minimal contact surface, if one were to set them together without a knee joint and meniscus. In order to avoid this instability and lack of function, the meniscus was created during the course of human development, which could also be designated as a flexible „washer disc“, in the terminology of a craftsman.

Stabilization

Stabilizing functions are attributed especially to the posterior horn of the meniscus. It works like a brake block between thigh and shinbone and prevents the shinbone head from sliding forward.

Buffer function

On the basis of the great elasticity, which results from fibrous cartilage tissue that run through the structure of the meniscus, impacts which come from femur or tibia will be buffered. Here a comparison is suitable to the shock absorbers of an automobile.

Causes for meniscus tear

A meniscus lesion / tear can be caused by an accident (= traumatic) or by disproportionate stress (=degenerative). The frequency of distribution can approximately be described as follows in the range of meniscus lesions:

• 50% of meniscus lesions are degenerative in nature. They arise in the course of life by increased stress, whereby diverse occupational groups are affected, such as for example professional football players, floor-tilers, miners, gardeners, etc. Thus, people are affected by professional activity that disproportionately stresses the knee. .
• 40% of meniscus lesions occur as the result of an indirect violent action (= secondary traumatic lesion occurrence). The following examples pertain to indirect violent action: sudden over-extension or bending of the knee joint, which unintentionally constricts the posterior horns of the meniscus. Then if force is exerted on the constricted meniscus, for example, by stretching the shinbone, the meniscus can be ruptured or torn. The injury mechanism is frequently encountered with dynamic sport types (football, skiing).
• 8% of the meniscus lesions occur by direct violent action (= primary traumatic meniscus rupture), for example through accidents (car accident, falling) with simultaneous fractured bones.
• 2% of the meniscus lesions occur for genetic reasons. Some people have meniscus deformities that are genetically caused. An example of this is the so-called disc meniscus. The creation of cysts and increased deposition of calcium in the region of the meniscus (= chondocalcinosis) can lead to a meniscus rupture in the framework of a clinical picture.

Lesion forms / rupture types

According to the location of the injury in the meniscus tissue, the following lesion forms can be differentiated in the range of the interior as well as the exterior meniscus:

• Bucket-handle tear (= longitudinally running meniscus tear with displacement of torn meniscus components into the knee joint)
• Transverse tear (originating from the meniscus fringe, this rupture type leads to the meniscus basis)
• Longitudinal tear (rupture type that runs along the meniscus body, similar to the bucket-handle tear; however without rupturing the meniscus fringe)
• Lobe tear in the posterior horn or anterior horn (= a combination of longitudinal and transverse tear)
• Horizontal tear (lesion in the longitudinal course, whereby an upper- and under lip is created)
• Rupture of the meniscus base

Which lesion form of the meniscus is present cannot be determined with certainty by a physical examination. However, magnetic resonance imaging of the knee joint'Bold text' can depict the lesion form.

Complaints with a meniscus rupture (clinical symptoms)

Patients with a meniscus lesion have pain in the region of the knee joint cleft and they frequently can only move the knee to a limited extent. Especially, with frequently occurring injuries to the posterior horn, a maximal bending of the knee joint is no longer possible, With torn meniscus components (often with bucket-handle tear), the knee joint can also block movement, if an articular constriction of the meniscus rupture occurs between the joint surfaces.

Different causes of a meniscus lesion result in different pain symptoms: traumatic meniscus lesions are usually experienced as very painful, while lesions that are caused by degenerative modifications are often very difficult to determine in the course of an examination. A differentiation from arthrosis of the knee joint without damage to the meniscus can be difficult to determine.

Diverse examination methods of the orthopedist help to establish a diagnosis, but also to exclude other illnesses by a differential diagnosis (refer to diagnosis)

Diagnosis

Within the scope of the physical examination, the doctor verifies the so-called „special meniscus symptoms“. Thereto he applies reliable standard tests, e.g. according to Steinmann, Apley – Grinding, Böhler, McMurray and Payr. Hereby in various forms, e.g. in stretching, bending and twisting positions of the shinbone, it will be attempted to squeeze femur and tibia surfaces together. By provoking specific pain, one can then differentiate injury to the exterior meniscus from damage to the interior meniscus, within the scope of the diagnostic methods.

Each diagnosis of meniscus injury begins with the physical examination by the physician that is described above.

In order to confirm the suspected diagnosis of the meniscus injury, additional diagnostic methods will be applied.

Nuclear magnetic resonance / magnetic resonance imaging (MRI)

By clicking onto the heading, you will receive detailed information related to MRI that is usually general. At this point, it is merely indicated in a subject-related manner that over 90% of meniscus ruptures can be diagnosed by means of magnetic resonance imaging. It is the diagnostic imaging method of choice for unclear symptoms.

Roentgen (X-ray) examination

While an X-ray examination is inconspicuous for recent meniscus injuries, and thus yields hardly any information within the framework of traumatic injuries, it is very affirmative for chronic injuries (e.g. persistent, occupational-related meniscus stress). To some extent, calcium deposits in the meniscus and cartilage in the knee joint can be recognized. An estimation of the general attrition of the knee joint (gonarthrosis) is possible. In order to be able to exclude eventual accompanying, skeletal injuries after an accident, an X-ray examination is made usually in two different levels (a.p.=frontal and lateral).

Sonography (ultrasonic examination)

Although the x-ray diagnosis is not made routinely, since other forms of examination are more definitive, the sonography can indicate accompanying ligament injuries or a cyst in the hollow of the knee joint (Baker’s cyst). Thus for example injuries in the range of lateral and / or cruciate ligaments, can be made visible, and also in the region of the vessels.

Arthroscopy

In order to delineate an unclear knee joint pain or to confirm the suspected diagnosis of a meniscus lesion, an arthroscopy, i.e. an „endoscopy“, of the knee joint can be performed (video-controlled, minimally invasive operation). Hereby, while the physician can directly view the interior space of the joint, the greatest advantage of the arthroscopy is that the condition can be surgically treated, if needed.

With the „key-hole operation“ (arthroscopy) the knee is only opened by a small incision of the skin. A rod-shaped camera will be inserted into the knee joint through this tiny incision and it provides images to a monitor in the OP room. An additional, small incision at another site enables the introduction of surgical instruments. By means of a sampling hook, the composition of cartilage, cruciate ligaments and meniscus can be investigated. Subsequently, via this second step a treatment of the meniscus injury can also immediately occur, e.g. the partial removal of torn meniscus (meniscus tear) parts.

Indication for a surgical operation

Not every form of meniscus affliction must be treated surgically. For this reason, the diagnosis plays an important role within the scope of meniscus afflictions, including diverse diagnostic tests.

The location of the meniscus lesion is also of great importance with respect to the therapy. For example, if the lesion lies in an area of the exterior zone that is provided with good blood circulation, it can be treated conservatively, e.g. by resting the joint in a splint and applying medicines that reduce swelling, if needed, in combination with needle puncture and injections of the knee joint. A meniscus suture also has a good prospect of success in this instance.

However, if the doctor determines that an irreparable rupture exists, for example on the basis of the lesion type or the localization of the meniscus rupture, then normally the surgical removal of the torn portion of the meniscus is necessary. Otherwise, the torn portion of the meniscus functions within the joint as foreign material, which also damages the cartilage in a special manner and enhances the clinical picture of arthrosis of the knee joint.

In the meantime, nearly all operations are being performed via endoscope in the region of the meniscus. An endoscopic meniscus operation is substantially gentler than open operations, which were performed previously with a larger skin incision. Thereby, they help to avoid subsequent damage and to retain as much meniscus tissue as possible while exhausting a maximum of all surgical possibilities. With regard to the stability and buffer function of the knee joint, it is especially important to retain the meniscus basis.

However, the valid guideline is: “A symptomatic meniscus rupture should be repaired as early as possible, in order to avoid subsequent damage.”