Cartilage damage in the knee: Symptoms and Treatment

Cartilage damage in the knee is quite common. Mostly the damage here is caused by wear and tear. On the one hand, this wear and tear occurs as part of a completely natural aging process. The result of this process is called arthrosis (chronic degenerative joint disease).

The knee joint has to carry almost our entire body weight and is subjected to many more loads and movements every day. It is therefore not surprising that risk factors for cartilage damage in the knee are mainly overweight and incorrect or excessive stress on the knee joint, such as certain sports, and of course, advanced age. From the age of 70 onwards, almost everyone can be found to have more or less pronounced osteoarthritis of the knee joint.

In addition, defective positions in the knee, such as knock-knees or bow legs, can also cause increased wear and tear of the cartilage. More rarely, injuries such as torn inner ligaments or cruciate ligaments are at the beginning of a process that ultimately leads to damage to the cartilage in the knee.

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The diagnosis of osteoarthritis offers the physician quite classic changes, which are particularly well visible in the X-ray image. The joint space is narrowed because the cartilage is worn out. As a reaction to this, the surrounding bone is hardened, and in some cases, new bone parts form to increase the contact surface, thus attempting to absorb the increased pressure caused by the missing cartilage.

In order to better classify cartilage damage to the knee joint or cartilage damage behind the patella, we use the classification according to Outerbridge, which differentiates between grades 0 to 4. (see below)

  • Grade 0: no existing cartilage damage;
  • Grade 1: the cartilage is completely preserved, but softens under pressure
  • Grade 2: the cartilage is slightly separated on the surface;
  • Grade 3: the cartilage is torn up to the bone;
  • Grade 4: the cartilage is wholly lost down to the bone, the bone is exposed.

However, the extent of the patient’s symptoms does not always have to be directly related to the extent of the changes in the joint, which is why it is always important not to rely solely on imaging but to carry out an extensive anamnesis with the patient.

Cartilage damage to the knee can only be inadequately assessed by X-ray. The best method of examining cartilage damage is the MRI of the knee. The MRI of the knee is an examination method that, in addition to cartilage damage, can also show damage to the meniscus (inner and outer meniscus), as well as damage to the posterior and anterior cruciate ligament over time.

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Severity classification

Cartilage damage in the knee grade 1

Grade 1 cartilage damage according to the Outerbridge classification corresponds to slight damage to the knee joint.

In general, this cartilage damage is also known as chondropathy. To classify a cartilage damage as first-degree, a lesion does not necessarily have to be recognizable.

The surface of the cartilage is still intact, and only slight softening and discoloration of the cartilage tissue or small superficial tears and fissures can be seen. Large fraying or tears are not visible.

The exact degree of cartilage damage is determined arthroscopically. In the case of first-degree damage, the cartilage is softened and more easily injured. Grade 1 cartilage damage is caused by overloading the knee joint and often causes only mild symptoms and rarely pain so that surgical therapy is usually not sought.

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Cartilage damage in knee grade 2

The cartilage of the knee joint consists of different layers that differ slightly in their composition and ensure the stability and resilience of the cartilage.

With a cartilage damage of grade 2, according to Outerbridge, there are significantly deeper tears and fraying compared to grade 1.

In some areas of the cartilage, a tear can reach so deep into the cartilage that half of the tissue is affected. However, the bone of the thigh and the tibia below the cartilage is not affected by the damage and is still covered by cartilage.

Therapeutically it is essential to distinguish between a simple and profound tear and a harsh rubbing of the cartilage. The damage mentioned first is usually not changed even in imaging follow-up examinations of the cartilage damage and therefore does not necessarily require surgical therapy.

Unfortunately, cartilage abrasion, on the other hand, is often characterized by further progressive damage, which leads to an increase in the symptoms.

In this case, the cartilage cannot recover from the damage on its own, and thus the cartilage damage usually develops quickly into grade 3 cartilage damage.

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Cartilage damage in the knee grade 3

Damage to the knee joint cartilage of the third degree characterizes a lesion that affects more than half of the thickness of the layer.

This can be a deep tear, either caused by permanent overstraining of the knee joint or often by a traumatic event.

If the severe cartilage damage is more of a broad chafing, this already points to an early exposure of the bone, which is located below the cartilage and is involved in the formation of the knee joint. Depending on the affected cartilage layer, the third-degree damage can again be divided into three subclasses, according to IRCS.

In the first class, the defect does not extend to the calcifying layer of cartilage in the second grade, this layer is also affected by the lesion, and in the third grade, the defect even extends into the subchondral layer, which is the border between cartilage and bone.

The third-grade cartilage damage is, in any case, an indication for surgical treatment. There are various surgical techniques available to repair the defect and make it painless for the patient.

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Cartilage damage in knee grade 4

Grade 4 cartilage damage corresponds to the most severe damage to the knee joint cartilage after Outerbridge.

The lesion not only affects the completely damaged cartilage itself but has spread to the adjacent structure, in this case, to the bone involved in the formation of the knee joint.

In this context, one also speaks of damage in the form of ulcers, since these are defects that affect all layers of tissue and spread from the top layer to the depths.

There is maximum wear and tear of the joint, and the bone itself may also be deformed and bear traces of wear and tear.

These can be, for example, grinding furrows due to the constant mechanical stress in the form of friction in the knee joint. The consequences of the fourth-degree cartilage damage are severe pain on the part of the affected patient and a significantly limited ability to bear weight.

This severe cartilage damage should be treated urgently to prevent further damage to the bone.

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Affected persons usually complain mainly about pain. Initially, this is usually only experienced under stress, but in the course of time, it also increases under rest conditions. In an advanced state, the knee joint may also lose its function, sometimes accompanied by an effusion (in its chronic form, also called a Baker’s cyst) or deformations of the joint.

Swelling in the knee

A swelling of the knee joint manifests itself by an increase in the size of the joint and can easily be detected by comparing it with the good side.

This swelling can be the storage of fluids such as water, pus, or blood. In the case of water retention, the water present in the knee also has many possible causes and is very unpleasant for the patient.

Water retention is caused by mechanical or inflammatory damage to the structures involved in the knee joint and does not occur in a healthy knee joint.

In addition to the cartilage and bone damage, it can, therefore, also originate from the muscles, ligaments, and vision or from the bursa of the knee joint.

In order to make a diagnosis, it is essential to distinguish whether the swelling was preceded by trauma and how long it took to develop.

In order to find the cause of the swelling and for the purpose of initial symptomatic treatment, a puncture of the knee joint is suitable in the event of water accumulation in the knee joint.

This can reduce the pressure in the joint space, blood or pus can be detected, and the spot can then be used to search for various pathogens and bacteria.

As a further therapy, the cause of the knee swelling should be treated. In addition to surgical measures, drug-based pain therapy, exercise therapy as part of a physiotherapeutic treatment, and strengthening of the leg muscles, which is particularly recommended in cases of slight cartilage damage, can be considered or prescribed as an accompanying measure.

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The problem with cartilage damage is that the human body is only able to regenerate cartilage tissue to a minimal extent. This is due to the fact that this type of tissue is not supplied by nerve cells and blood vessels, which are, however, very important for the healing process. It is assumed that only about 4% of cartilage cells can be renewed, although this depends on age.

In most cases, the damage tends to increase over time rather than improve. For this reason, the aim of treatment is to prevent further damage from occurring. First of all, all risk factors must be eliminated or reduced as much as possible. Overweight should be reduced, strenuous sports and other overexertion should be avoided, and underlying diseases or malpositions should be eliminated. 

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Besides, depending on the X-ray findings and the patient’s level of suffering, a decision is made as to which therapy is most appropriate.

Of great importance is physiotherapy, i.e., a conservative (non-operative) therapy. If the changes are less pronounced, this can be sufficient to enable a patient to live a life free of complaints. Arthroscopy (joint endoscopy) is particularly popular. During this procedure, bone or cartilage parts can be removed, the cartilage can be smoothed, and the joint can be cleaned and rinsed (lavage or debridement). Painkillers and/or shoe insoles can be used to accompany the procedure.

If these measures do not suffice to improve the symptoms significantly, there are several newer methods to combat cartilage damage in the knee: Especially in younger patients, it is advisable to transplant healthy cartilage tissue into the knee. In addition, there are entirely new drugs on the market that very specifically inhibit specific inflammatory triggers that are responsible for the damage to the knee joint cartilage. Although these drugs are currently still being tested and are very expensive, they promise great success.

Finally, it should be mentioned that cartilage cultivation is currently being researched. It is now possible to cultivate cartilage cells from hematopoietic stem cells in the laboratory, and such cartilage cultivation and subsequent transplantation are already being carried out successfully in some areas of the US.

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Healing of the cartilage damage in the knee joint

Depending on the size, localization, and depth of the cartilage damage and the complaints of the patient concerned, various surgical therapies are carried out. These therapies aim to use the body’s self-healing tendency to achieve the best possible stabilization of the cartilage tissue and allow the patient to be free of complaints.

However, healing and regeneration of the original cartilage tissue is not possible. Instead, replacement substances for the lost cartilage can be used in various ways.

The self-healing rate is highest in young people who have suffered a cartilage injury due to a traumatic event.

In this case, no surgery is required in addition to drug-based pain therapy and exercise training. With the procedure known as micro fracturing, a hole can be drilled into the bone below the cartilage in the case of small cartilage defects.

This leads to bleeding into the cartilage and to the accumulation of stem cells and graft factors. Although these cells cannot restore the cartilage and thus do not achieve complete healing, they do stimulate the formation of fibrous cartilage and scar tissue at the defective site, which in the best case leads to an alleviation of the patient’s symptoms.

In addition to this surgical technique, autologous cartilage (OATS) or only cartilage cells can be transplanted into the knee joint (ACT) to replace the defective cartilage.

It is also possible to scrape and smooth the surface of minor lesions, but this reduces the thickness of the entire cartilage.

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