Cartilage damage in the knee

What is the cartilage in the knee used for?

An approx. 5 mm thick layer of cartilage covers the bone in the knee joint. The smooth surface of the cartilage allows the joint to move smoothly. In addition, the cartilage evenly distributes the pressure and impact load on the underlying bone. This protects the bone and reduces overloading. The cartilage has no nerves and stops growing after puberty. The cartilage layer that forms accompanies us throughout our lives.

How does cartilage damage occur?

Over the years, cartilage becomes increasingly worn and loses its ability to store water. As a result, the cartilage surface becomes brittle and cracks. This brittle surface is more susceptible to impacts and shearing forces. As the cartilage has no pain fibres, we do not feel this change at first. We may notice a rubbing noise (crepitation) when we put more strain on it. In contrast to cartilage, bone has pain fibres. If the bone is exposed, we feel the affected joint with the corresponding pain.
However, joint cartilage can also be damaged by chronic incorrect loading or an accident (trauma).

How is cartilage damage recognised?

Minor cartilage damage in the knee joint can lead to massive restrictions and causes pain, noise and joint swelling depending on the load. The cartilage continues to wear away, which ultimately leads to osteoarthritis.

The extent of the symptoms depends on the size and depth of the cartilage defect and its localisation.
In the case of chronic cartilage damage, patients report initial pain, pain on exertion and inflammation. The knee is swollen and the mobility of the knee joint is restricted. Patients also have an unsteady gait, the knee joint feels unstable and sometimes buckles.

Stages of cartilage damage

Damage to the articular cartilage can occur on the surface with small tears, but can also affect the entire cartilage in the knee. This causes the rough, painful surface of the bone to appear.
Cartilage damage is divided into four stages:

• Stage/Grade I: Soft cartilage
• Stage/Grade II: Rough surface with cracks
• Stage/Grade III: Deep cracks in the cartilage that extend to the bone
• Stage/grade IV: Complete consumption of the cartilage with exposed bone; this is also referred to as a bony bald spot

Diagnosis

If cartilage damage is present, a detailed clinical examination and radiological clarification (X-ray) as well as an MRI of the knee joint are required. Further investigations may be necessary, such as an image of the entire leg to determine the position of the leg axis. A rotational CT scan can be performed to determine the rotation of the knee joint. All these findings must be analysed in detail, as cartilage therapy can only be successful if existing abnormalities, such as lateral movement of the kneecap, are eliminated.

Symptomatic cartilage damage in young patients should be treated surgically in order to prevent or slow down the development of osteoarthritis in the knee joint and to enable pain-free sporting activities again. However, it is important to realise that the recovery phase (rehabilitation) can take a long time (up to a year).

Treatments

Cartilage damage looks different depending on the cause, whether accident-related (acute) or wear-related (chronic), and is treated differently accordingly. Acute cartilage damage, for example, is characterised by a clearly defined defect (punch defect) compared to healthy cartilage with sharp edges. This is not the case with chronic cartilage defects. If the cartilage defect is not treated, further cartilage wear of the knee joint occurs and, in the further course, knee joint arthrosis develops.

Conservative treatment methods

Conservative therapy for cartilage damage is very limited. After puberty, the cartilage loses its self-healing potential, i.e. from this point onwards, we have to make do with the cartilage for the rest of our lives. For these reasons, the natural course of cartilage damage leads to deterioration. The cartilage damage becomes larger and deeper over time, which leads to clinical deterioration with corresponding pain and restrictions in everyday life and sporting activity. Conservative therapy cannot cure cartilage damage, but can only alleviate it by slowing down the wear and tear of the cartilage. The following conservative therapies are possible:

• Physiotherapy
• osteopathy
• Painkillers
• Cartilage-supporting agents
• Lubricating injections: Hyaluronic acid injections temporarily improve the lubrication of the defective joint. This reduces inflammation in the joint and the patient experiences less pain. Another option is injections with the patient's own blood.
• Other options: Watch your own weight or reduce it, eat a healthy balanced diet, exercise regularly with guided movements such as swimming or cycling.

Surgical treatment methods

The surgical treatment of cartilage damage depends on the size (extent) and depth of the defect and must be customised. Factors such as the integrity of the exposed bone, the quality of the cartilage on the opposite side of the defect and the age of the cartilage defect also play a decisive role. Furthermore, the younger the patient, the greater the chances of success of the methods described below for acute cartilage damage. These include

• Fixation of the bone/cartilage splinter with a screw that can usually be dissolved.
• Arthroscopic sealing of superficial cartilage tears.
• Microfracturing: Firstly, the cartilage defect is prepared so that a clean, stable cartilage edge is present. Small holes are then made in the exposed bone using a drill or special awls. Blood containing stem cells comes out of these holes. Among other things, these stem cells can transform into cartilage and thus protect the exposed bone again. This method is usually performed arthroscopically (joint endoscopy) and is suitable for smaller cartilage defects (< 2.5 cm2).
• Transplantation of cartilage-bone cylinders: This technique is also known as mosaicplasty or OATS (osteochondral autologous transplantation system). This method is also only used for smaller cartilage defects (< 2.5 cm2). Special hollow punches are used to take autologous cartilage-bone cylinders from a non-weight-bearing part of the knee joint and insert them directly into the cartilage defect. This method is used if the underlying bone is damaged in addition to the cartilage defect.
• AMIC: The AMIC technique is used for larger cartilage defects. AMIC stands for autogenous matrix-induced chondrogenesis, i.e. matrix-induced cartilage production. The cartilage defect is exposed and cleaned to restore stable cartilage edges. This is followed by microfacturing as described above.
• Cartilage transplantation: Another option would be to have your own cartilage cells cultivated in a laboratory from biopsies obtained from the first operation. This method is also known as ACT (autologous chondrocyte transplantation). After approximately four weeks of cultivation in a laboratory, the cartilage cells can be introduced into the corresponding defect in a second operation.
• Bone defects: If there are bone defects that are deeper than 4 mm, these must be filled using the patient's own bone (e.g. femur) or donor bone (cancellous bone grafting).

The above-mentioned surgical techniques are mainly used for acute cartilage defects. In addition to age, the opposite side of the cartilage defect also plays a role. This should not show any major damage, otherwise the rough surface can have a negative effect on the surgical result. Another option for covering more chronic cartilage defects is the artificial replacement of the injured cartilage.

If the cartilage wear is so advanced that bone ultimately rubs against bone (final stage of osteoarthritis), a partial prosthesis (e.g. a sled prosthesis, a sliding patella replacement) or a complete surface replacement is necessary. A correction of O-/X-legs (so-called corrective osteotomy) is also sometimes necessary.

Novel cartilage therapy

This new type of cartilage therapy, which can be performed in a minimally invasive manner througharthroscopy , uses the body's own cartilage tissue. All steps are carried out in the same operation. Healthy cartilage is removed from the edges of the cartilage defect and, if necessary, also from areas of the knee joint that are subject to less stress. These healthy pieces of cartilage (chips) are collected and then mixed with the tissue adhesive (thrombin), which is obtained from the patient's own blood. The resulting cartilage paste is used to fill the cartilage defect. The filled cartilage defect is then moistened with particles of the patient's own blood, which contain many growth factors. This activates the cartilage cells in the inserted cartilage pieces, which then form new cartilage over a period of months.

Aftercare

The follow-up treatment must be customised to the previous operation. If cartilage therapy has been performed, the knee joint must be immobilised for six weeks with the aid of walking sticks. The knee joint is immobilised in a special splint for the first two days. This splint should then only be worn at night for six weeks. During the first two weeks, flexion of the knee joint by 30° is permitted during the day (use of an orthosis with joint). In the second to fourth week, flexion up to 60° is possible and in the fourth to sixth week, flexion up to 90° is possible. During these six weeks, walking is only permitted with poles with a maximum load of 15kg. The return to sport begins gradually six months after the operation. Full contact sports should not be resumed until 12 months after the operation.

Patients with a surface replacement can immediately put weight on the knee joint and move it. However, walking sticks are recommended for about four weeks to protect the soft tissue.
It is also important to undergo several weeks of physiotherapy to relieve swelling and to strengthen and stretch the thigh muscles.

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