Articular cartilage fulfills important functional tasks in the joints. It serves as a buffer between the joint bones and thus ensures that the bones cannot rub against each other. Cartilage injuries can be caused by an accident or a sports injury, for example.
Without adequate treatment, osteoarthritis(joint wear and tear) can develop in the affected joint. This causes the cartilage in the joint to gradually break down, which can lead to severe pain. Heavily worn cartilage can no longer be restored: The damage caused is irreversible. In severe cases, only an artificial joint can help.
The knee joint, like the hip, is very often affected by osteoarthritis.
The following video shows how bones rub directly against each other in severe osteoarthritis:
Early osteoarthritis can be prevented or postponed with timely cartilage regeneration procedures in line with guidelines. In recent years, a large number of successful therapeutic procedures have been established for the treatment of local traumatic cartilage defects.
This is why early and correct treatment is so important. If treatment is too late, cartilage regeneration is no longer possible.
The selection of the appropriate therapy procedure for the individual patient depends, among other things
- the type and size of the cartilage damage (e.g. defect depth, accident-related, more wear-related, defect localization....),
- the patient's requirements and
- any additional joint injuries such as ligament instability, meniscus tears and deviations in the mechanical leg axis (malalignments such as knock knees and bow legs)
depending on the patient.
Any accompanying injuries must also be corrected as part of multimodal regenerative joint therapy. Such joint injuries promote knee osteoarthritis. It is therefore necessary to treat them in order to achieve a good long-term result in cartilage regeneration.
The German Society for Orthopaedics and Trauma Surgery (DGOU) collects information and publishes it in the German Cartilage Register. According to this register, well over 50 percent of treated cartilage damage to the knee is associated with concomitant damage or malalignment.
Illustration of different stages of osteoarthritis © bilderzwerg / Fotolia
Conservative therapies are all approaches that do not involve surgery. In the case of cartilage damage to the knee, the main options are
- Physiotherapy,
- orthopaedic aids (e.g. insoles and joint orthoses),
- physical therapy (application of cold, heat, lymphatic drainage, ultrasound)
can be considered. They help to relieve the corresponding joint area or to promote accompanying inflammatory changes.
Non-steroidal anti-inflammatory drugs, e.g. diclofenac, are used for medicinal treatment. They reduce joint pain and inflammation. These medications are a good therapeutic supplement, especially in acute cases following injury and surgery.
A variety of cartilage preparations and nutritional supplements are also available. In particular
- Vitamin D,
- chondroitin and
- glucosamine and
- other vitamins and substances
play a role here. These also appear to have a positive influence on tissue regeneration after surgical cartilage therapy. They can temporarily alleviate symptoms and are therefore suitable supplements. However, they cannot cause the impaired cartilage in the knee to regenerate.
Furthermore
- Joint injections with PRP (platelet-rich plasma), which is produced from the patient's own blood by centrifugation, and
- hyaluronic acid, also in combination with PRP
have a positive influence on cartilage regeneration after surgical cartilage therapy.
The DGOU Clinical Tissue Regeneration Working Group is currently the largest scientific committee on cartilage regeneration in Europe. Cartilage specialists from German-speaking European countries participate in it.
It regularly issues updated recommendations on cartilage therapy based on the latest available literature. These recommendations are published internationally and are therefore recognized. Many cartilage centers worldwide follow the recommendations.
Articular cartilage refixation
Injuries such as kneecap dislocation often result in the shearing off of cartilage-bone fragments. In acute cases, these fragments can be fitted into the defect if they are well preserved. The surgeon fixes them with self-dissolving pins or screws. Successful healing depends on a solid connection between the cartilage-bone part and the bony base of the defect.
Cartilage refixation, as well as many other cartilage treatment therapies, can be performed arthroscopically. The video shows how minimally invasive arthroscopy works:
BMS (Bone Marrow Stimulation) microfracturing, nanofracturing, microdrilling
According to the recommendations of the DGOU 2021 Clinical Tissue Regeneration Working Group, these procedures are possible for defects up to 2 cm² in size.
These techniques were developed back in the 1980s. They are used duringarthroscopy (arthroscopy). The surgeon removes the diseased cartilage tissue from the healthy cartilage down to the bone lamella.
He then breaks through the bone lamella under the defective cartilage with drills or chisels, like scarifying a lawn. This is called microfracturing, nanofracturing or Pridie drilling (where only thin drill wires of approx. 1.2 mm are used). Nanofracturing stands out among the techniques because a defined and standardized depth and thickness can be achieved for the holes.
Fracturing leads to blood leakage. The aim is to introduce regeneration cells (stem cells) from the bone marrow into the defect area.
However, the number of stem cells from the holes in the defect area is often very low. There is also a very high risk of complications: injury to the sensitive bone lamella in the cartilage defect using the techniques described above leads to bone outgrowths in the defect in 30 to 60 percent of cases. These bone outgrowths can then cause problems again after a short time.
In addition, the long-term treatment results are not sustainable. After just two to three years, the cartilage deteriorates again.
This is why specialists are performing this therapy less and less frequently.
Matrix-supported bone marrow stimulation mBMS, AMIC ®, BMAC microfracturing, nanofracturing
According to the recommendations of the DGOU 2021 Clinical Tissue Regeneration Working Group, these procedures are suitable for defect sizes of 1.0 - 4.5 cm².
The use of additional matrices has improved BMS techniques. These are membranes made of collagen, hyaluronic acid meshes and other materials. They are intended to provide a three-dimensional structure for the cells that have the potential to form cartilage. This refers to chondrogenic cells, e.g. stem cells. This allows these cells to adhere better and thus fill the defect more effectively.
The use of these membranes leads to better and longer-lasting cartilage regeneration results than BMS alone.
This technique can often also be performed arthroscopically, depending on the size and location of the damage to be treated. To date, very good medium-term study results and initial longer-term results of this technique are available.
Whether this procedure will prove successful in the long term (> 12-15 years) cannot yet be conclusively assessed with the studies to date. The publication of ten-year results of this technique is expected in 2023.
Osteochondral transplantation (OCT)
According to the recommendations of the DGOU 2021 Clinical Tissue Regeneration Working Group, these procedures are suitable for defect sizes of 1.0 - 1.5 cm².
OCT is also known as cartilage-bone transplantation. The surgeon removes cartilage-bone cylinders from an area of the joint that is subject to little stress. These are then transplanted into the suitably drilled defect area.
The cylinder requires a sufficiently large bony portion in order to heal solidly into the surrounding bone. The cartilage portion of the cylinder immediately fills the defect area with high-quality hyaline cartilage. The gaps remaining between the cylinders are covered with a low-grade scar tissue.
The results are good for small cartilage (bone) defects. However, the destruction of healthy cartilage surfaces is problematic. This can lead to very similar symptoms at the cylinder removal site as at the original defect site. In order to keep this removal discomfort to a minimum, OCT is only recommended for cartilage defects up to approximately 1.5 square centimetres.
The procedure has advantages if there are smaller defects in the cartilage AND the bone. This is the case, for example, with osteochondrosis dissecans (articular mouse). Both tissues can be treated quickly and effectively with this procedure.
However, it is a demanding procedure: The cartilage thickness of the removed cylinder should ideally correspond to that in the defect area. Otherwise, unfavorable pressure and shear forces arise.
Illustration of a cartilage-bone transplant © giana | AdobeStock
Potential method minced cartilage, cartilage chips, Autocart®
According to the recommendations of the DGOU 2021 Clinical Tissue Regeneration Working Group, these procedures are suitable for defect sizes of 1 - 3.5 cm².
Cartilage cells are normally statically embedded in the cartilage tissue. Under certain circumstances, however, they are able to migrate a few millimeters out of the embedded cartilage and then divide again. As a result, they form new cartilage tissue.
In the method described, the surgeon harvests pieces of cartilage from the defect area or from areas of the knee that are subject to little strain. These pieces are crushed and then inserted into the defect to fill it. Cartilage cells can then migrate from the small pieces of cartilage and form new cartilage tissue through division.
By adding
- Platelets made from the body's own rich fibrin (PRF) and plasma (PRP),
- membranes/matrices or
- fibrin glue
are intended to better stimulate the cells to form new tissue.
Some techniques also work with microfracturing, microdrilling/nanofracturing under the defect. Some animal studies have achieved better cartilage regeneration rates with this technique than with microfracturing (BMS) alone.
However, it is currently not clear which combination of which sub-steps of the method will form cartilage tissue successfully and sustainably. There is therefore no generally recognized standardized procedure that has been proven to guarantee good cartilage regeneration in the medium term. Initial studies currently indicate that a large proportion of the cartilage cells may be destroyed when the cartilage is minced.
This procedure has become increasingly widespread in recent years. However, it is not currently one of the scientifically proven and recommended procedures of the DGOU's Clinical Tissue Regeneration Working Group. Instead, it is a "potential method"! This means that the procedure has great potential under certain circumstances.
However, theprerequisite is that studies demonstrate a clear perspective after an observation period of at least five years. They must show that a certain type of minced cartilage procedure is better than other methods.
This method can currently only be recommended if it is part of a controlled scientific study. All other described cartilage regeneration methods and even BMS/microfracturing currently show scientifically safer results than minced cartilage.
Minced Cartilage, Autocart ®, cartilage chips is NOT a single-stage cartilage cell transplantation. According to the current state of scientific knowledge (as of 2023), patients who receive this technique are still taking a high risk. If you nevertheless decide to undergo this therapy, you should be aware of this!
Autologous chondrocyte transplantation(ACT) is the transplantation of the patient's own cartilage cells. It was further developed into matrix-induced autologous chondrocyte transplantation(mACT).
Due to its excellent long-term results, only mACT is used in Europe today.
According to the recommendations of the DGOU 2021 Clinical Tissue Regeneration Working Group, these procedures are suitable for defect sizes from 2 cm².
The transplantation of autologous cartilage cells (autologous chondrocyte transplantation) has been used successfully since the early 1990s. It is mainly used to reconstruct cartilage in the case of traumatic defects or osteochondrosis dissecans (OD; osteochondrosis). It is a scientifically proven procedure.
It is now the best scientifically investigated procedure for cartilage regeneration in the knee worldwide. The procedure offers excellent long-term results for over 15 years!
In ACT, the cultivated cartilage cells are injected under a watertight periosteal flap sewn onto the cartilage defect. This procedure was further developed into mACT: Here, the cells are introduced into or onto matrices.
The technique can now even be carried out arthroscopically using arthroscopy.
This procedure is already superior to the cartilage regeneration procedures described above in the long term for defects over 2 square centimeters.
Prerequisites for ACT
Patients with localized cartilage damage who have not yet developed osteoarthritis are suitable for ACT. ACT is not possible in the case of extensive wear and tear of the articular cartilage, i.e. osteoarthritis.
The basic requirements for the treatment of cartilage damage described above apply to mACT in particular.
The mACT treatment is particularly suitable for patients after the end of growth (puberty) and up to the age of 55.
Carrying out the cartilage transplant
This cartilage therapy on the knee is carried out in several stages.
The surgeon first removes a small amount of cartilage from a non-weight-bearing part of the knee joint using arthroscopy.
In the clean room of a certified laboratory, the cartilage cells are extracted from the cartilage substance and multiplied. Once the required number of cells has been reached, the cartilage cells are
- are seeded into a special three-dimensional collagen sponge structure,
- mixed into a three-dimensional gel or
- formed into three-dimensional spheroids, which largely correspond to the original biological cell environment in the cartilage.
There, the cells already begin to produce new cartilage matrix.
In the laboratory, the
- vitality,
- sterility and
- the ability of the cartilage cells to form hyaline cartilage.
Only when these values are optimal is the transplant delivered to the hospital or the attending physician.
The second procedure takes placethree to six weeks after the arthroscopic harvest. It can be partially performed arthroscopically. The surgeon transplants the cultivated, multiplied cartilage cells into the patient in the manufacturer-specific form.
First, the surgeon removes damaged cartilage from the defect area. To do this, he either makes a skin incision about 5 cm long or uses an arthroscope. He then fits the transplant into the defect. The transplant lies
- as a cell-colonized membrane,
- as a cell gel or
- in the form of self-adhesive small cartilage cell spheres (spheroids)
are present. While spheroids and gel are self-adhesive, the matrix is glued or sutured in place with fibrin glue.
Illustration of the transplantation of cartilage cells © dissoid | AdobeStock
After the second operation, the mACT, a hospital stay of only 2-3 days is usually required. In favorable cases, the procedure can also be performed on a day surgery or outpatient basis.
As with all cartilage regeneration procedures, aftercare is crucial to the success of the treatment.
Costs of mACT
The procedure has the disadvantage that two surgical interventions are required. It is also strictly regulated. This results in high prices of up to €13,000 for cell cultivation alone (as of 2023).
However, international studies show that the therapy can still be worthwhile: With timely therapy, this results in lower long-term costs for a healthcare system than the use of less effective methods. A study published in 2021 shows that mACT can avoid around 21% of knee prosthesis implantations.
This is why health insurance companies in Germany finance the procedure for outpatient use in certain cases where the defect is 2 cm² or larger.
Unfortunately, this does not yet fully apply in Austria and Switzerland. However, a large number of artificial joints are implanted here, sometimes in young patients. Therefore, in the opinion of the specialist societies, there is a need for action in Austria and Switzerland in the short term.
Which cartilage regeneration therapy can patients expect to achieve the best results for their individual cartilage damage? The recommendations of the DGOU Tissue Regeneration Working Group on cartilage therapy for different defect sizes are based on current scientific knowledge as of 2021. They provide good guidance.
Cartilage defects up to 3 cm²
There are several treatment options for defect sizes between 1 cm² and 3 cm². However, if the longest possible effectiveness of the cartilage regenerate is desired, there is little alternative to mACT. The following diagrams are intended to provide orientation:
It can be seen how often good to very good results can be expected even more than 12 years after cartilage therapy on the knee. For mBMS, publications with good to very good study results are expected in over 70% > 10 years in 2023.
No long-term results > 12 years are yet available for the other procedures described.
Cartilage damage with simultaneous bone defects
If bone damage is present in addition to cartilage damage, this is referred to as an osteochondral lesion.
The aim must be to also rebuild the foundation during suitable cartilage therapy on the knee. The foundation is the underlying bone, for which the body's own bone from the iliac crest or lower leg is usually used in the form of bone fragments or bone cylinders.
The aim is to restore the boundary layer of cartilage to bone (subchondral lamella) as accurately as possible. Once this has been achieved, one of the cartilage regeneration procedures described can be used, with the exception of BMS.
The advantage of OCT for such defects is that cartilage and bone defects up to 1.5 cm² can be treated elegantly.
The use of so-called osteochondral allografts is indicated as a potential method. They are widely used in the USA. These are parts from knee joints of deceased young patients who have made themselves available for organ donation. These are then measured, milled to a suitable size and transplanted into the defect area.
This procedure is still rarely used in Europe due to the current low availability of donors.
The following diagram summarizes the recommendations of the DGOU tissue regeneration working group (as of 2021) for different defect sizes. It can be seen that neither BMS nor minced cartilage have been included in the recommendations for cartilage-bone defects.
The Society for Cartilage Regeneration and Joint Preservation (QKG) provides recommendations for follow-up treatment.
Patients should only bear partial weight on their affected leg for around ten weeks after all knee cartilage therapies. However, the exact duration depends on the size of the defect and the localization.
Restriction of mobility is sometimes necessary, especially for cartilage regeneration procedures
- behind the kneecap or
- in the patellar gliding bearing.
The use of "continuous passive motion" (CPM) for guided passive or partially active movement of the operated joint on a motorized splint has proven particularly effective in the first six weeks after surgery. Daily motorized splint treatment lasting several hours is recommended for the first six weeks. This stimulates the cartilage cells to form the stable shock-absorbing cartilage substance.
During this follow-up treatment, the regeneration cells fill the defective area with regenerated tissue over the next few months. The quality of the regenerated tissue depends crucially on the
- procedure and the cells used,
- the size of the defect,
- the age of the patient,
- accompanying damage or malpositions,
- previous operations and
- other factors
and other factors. It can take up to two years for the corresponding cartilage tissue to mature.
There are now also designated physiotherapeutic "cartilage specialists" for follow-up treatment. They offer sophisticated phase-oriented post-treatment concepts.
Recently, after cartilage therapy
- nutritional supplements,
- vitamins and injections such as PRP (platelet-rich plasma) and
- hyaluronic acid
are recommended. They can improve the quality of the cartilage regenerate and thus the treatment result.
Successful cartilage therapy can only be expected if additional injuries(cruciate ligament rupture, meniscus damage) are treated at the same time. If there are unstable ligament conditions in a joint, the corresponding shear stresses usually lead to the loss of the cartilage regenerate. This means that the regenerative cartilage procedure fails.
Cartilage damage due to ligament injury of the knee joint © bilderzwerg / Fotolia
Pathological stress peaks must also be eliminated in order for cartilage regeneration to be successful. They are caused by a misalignment of the leg axis(knock-knee, bow-leg) or the course of the kneecap.
Therefore, in the case of cartilage damage and axial deviation, the corresponding cartilage therapy procedure is combined with a realignment osteotomy. This is a correction of the axial deviation. In the case of cartilage damage in the patellofemoral joint, a ligament or bony correction may also have to be carried out here.
Correction of a leg axis malalignment
The causes of a leg axis malalignment can be varied. In addition to congenital deformities, there are also deformities of the upper or lower leg bone acquired over the course of a person's life.
It is problematic, for example, if the fracture of the upper or lower leg bone does not heal exactly in the original position. The newly created bend in the bone can lead to misalignment of the entire leg axis. This can lead to a unilateral bow leg or knock-knee.
Misalignment of the leg axis can promote osteoarthritis © Double Brain / Fotolia
The focus is on reducing pain and improving the patient's quality of life. The progression of unilateral joint damage should be prevented. At best, the treatment should prevent the need for an artificial knee joint altogether. In most cases, however, it is possible to postpone the implantation of a knee endoprosthesis further into the future.
In very young patients with minor cartilage damage on one side of the knee joint, the leg axis is straightened. Cartilage repair procedures can be used to support the damaged side. If one side of the joint is severely damaged, the axis is slightly overcorrected. This eliminates a higher load on the previously healthy side.
For many years, a corresponding bone wedge was removed from the thigh or lower leg bone for the correction (closing surgical technique, corrective osteotomy). In recent years, new open techniques have been developed. The resulting osteotomy gap is held open with appropriate plates. The gap is either left open or filled with autologous, exogenous or synthetic bone material.
Navigation devices (e.g. OrthoPilot®, Aesculap) have proven particularly useful for the precise correction of the leg axis. This allows the appropriate correction to be set and checked intraoperatively.
Correction of ligament instabilities
If the ligaments in the knee joint are not stable, this can also lead to increased wear and tear. As a result, cartilage and bone on the loose side of the knee joint can be damaged.
The cruciate ligaments play a particularly important stabilizing role here. If there are instabilities here, they must be surgically stabilized before or during cartilage therapy. Otherwise, the meniscus and the cartilage layer will be subjected to greater pressure and shear forces.
The meniscus has an important joint-protecting and pressure-reducing function in the knee joint. It should therefore be preserved or sutured during cartilage regenerative surgery wherever possible. Defects of more than 1/3 of the meniscus significantly worsen the outcome of cartilage regeneration. Increased cartilage abrasion can lead to premature osteoarthritis. Pain, inflammation and swelling of the knee joint are the result.
