Classification according to severity

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 are visible. Large fraying or tears are not visible. The exact degree of cartilage damage is determined athroscopically.

In the case of first-degree damage, the cartilage appears 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. 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 very important to distinguish between a simple and deep tear and a coarse 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.Cartilage abrasion, on the other hand, is unfortunately often characterized by progressive damage, which leads to an increase in the symptoms. In this case, the cartilage cannot recover from the damage on its own, and so the cartilage damage usually develops quickly into grade 3 cartilage damage.

Third grade damage to the knee joint cartilage is characterized by a lesion that affects more than half of the thickness of the layer. This can be a deep tear, either caused by permanent overuse of the knee joint or often by a traumatic event. If the deep cartilage damage is more of a broad chafing, this already points to an early exposure of the bone that 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 be further subdivided into three subclasses according to IRCS.

In the first grade, the defect does not reach 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 degree of cartilage damage is always an indication for surgical treatment. There are various surgical techniques available to repair the defect and make it painless for the patient.

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