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Cartilage Injury and Disease in Children
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Cartilage Injury and Disease in Children

The ability of body tissues and organs to regenerate after injury depends on their level of specialisation. For example, muscle, bone and skin have good regenerative powers, and can even function well after scarring. However, the cap of cartilage that covers the ends of your child’s bones is a highly sub-specialised tissue that performs a very specific function. The more specific a tissue’s function is, the less ability it has to regenerate. This means that, despite huge efforts at repair, regeneration and restoration, we can rarely achieve an exact duplicate of the original cartilage in either make-up or function, even in children.

However, there is an old adage in children’s, or ‘paediatric’, medicine that “children are not little adults”. In other words, the processes, treatment and outcomes of many medical conditions are different in children than they are in adults.

To a certain extent, this is true for injury and disease of the joints. Youth is typically an advantage – children have greater abilities to heal defective cartilage. This is partly due to younger patients having better healing potential particularly for inert tissues such as cartilage and thus they can heal these tissues better than adults.

The importance of the growth plate:

An important aspect regarding children and cartilage healing is associated with growth. The division between a child (or adolescent) and an adult depends on whether the growth plates at the end of long bones (epiphyses) are open or closed as these growth plates are not only the origin of bony growth to increase bone length, but are also the source of developing cartilage.

Plasticity of tissue and stem cells in children:

Cells in children are generally much more active than those in adults, and can grow faster and divide more readily. Younger cells also have greater plasticity, which means that they can turn into a variety of tissues, including cartilage, much more easily.

All the different tissues of the body, including hyaline cartilage, arise from stem cells. These cells are much more able to divide and differentiate in children, and are present in greater numbers than in adults. Defective or inflamed cartilage in the infant body can therefore be repaired much more easily than in adults.

Articular cartilage in children also has a certain degree of blood supply, whereas, in adults, the cartilage relies on the fluid in the joint cavity for its supply of nutrients. A good blood supply allows for greater regeneration, as not only do nutrients have better access to the cartilage but also defective cartilage can be more easily removed by the blood stream. In addition, new cells can more easily settle within the defective cartilage.

Finally, the attachment of the cartilage to the bone is very strong in children. The bone directly underneath the articular cartilage is, however, more prone to disease. These two factors means that cartilage defects are more likely to involve the underlying bone. Such defects are called ‘osteochondral lesions’ or osteochondritis dissecans. As the cartilage and bone form a unit, both types of tissue have to be addressed during repair.

This combination of factors allows for and often requires different approaches to the surgical treatment of children, particularly cartilage surgery. The good news is that these cartilage defects are rare and, if they happen, treatable.

This article focuses on the knee, as it is the most commonly affected joint. Nevertheless, the same concepts can be applied to other bones and joints in which cartilage disease and injury occurs, such as the ankle joint or the elbow.

Intended audience

This information is aimed at the relatives and caregivers of children who have been identified as having cartilage disorders. It is designed to offer an overview of what the procedures entail, as well as briefly discuss the advantages, disadvantages and expectations that children should have when undergoing such procedures.

Which cartilage diseases or injuries are common in children?

In general, cartilage defects are divided into ‘pure cartilage defects’, in which only the cartilage layer is affected, and ‘osteochondral defects’, in which both the cartilage and the underlying bone, are affected.

The bone plate supporting the articular cartilage is called “subchondral bone”. It acts as a mechanical support for the overlying cartilage. When it is defective, the articular cartilage suffers as part of the whole osteochondral unit. Although it is common for both the cartilage and the underlying bone to be damaged, it may be that only the cartilage or only the underlying bone is affected. In each scenario, the most appropriate treatment option can be selected.

Articular cartilage has only a limited number of possible diseases. The most common cartilage condition in children and adolescents is osteochondritis dissecans (OCD), which affects both the cartilage and underlying bone together.

At this point it is not clear why some children get OCD. It is thought that one possible cause of OCD is repetitive trauma to the cartilage (for example, during intense sports activity) combined with a reduction in blood supply to the bone.

Lesions can be different sizes and at different stages, although the most common location is the medial femur roll of the knee joint. OCD is usually classified into one of four stages, depending on the degree of the separation of the articular cartilage from the underlying bone unit. This classification is used to determine treatment with the more severe forms requiring surgical approaches, whereas the less severe forms may be treated non-operatively.

The second most common cartilage defect in children is due to trauma, such as following a fall or twisting of the knee during sport, for example. These injuries can result in pieces of articular cartilage being sheered off or directly impacted and crushed. This often occurs in conjunction with dislocations of the kneecap. OCD and cartilage injury can both result in loose bodies, or loose pieces of cartilage or cartilage plus bone, within the joint.

Sometimes these injuries can be “silent”. Which means it may have been a hit to the knee that was a little too much for the cartilage but the problems do not show up until later because cartilage injuries alone do not hurt.

Children rarely can also develop “wear and tear” related so called “degenerative cartilage lesions”. These are cartilage defects without an immediately obvious cause that either follow years after a trauma to a joint or can be the result of very early onset of osteoarthtitis or even rheumatoid arthritis in a child. This is more common in adults, but very infrequent in young patients. Should a child present with this kind of problem it is necessary to check for rheumatologic diseases.

What are the symptoms of cartilage disease or injury in children?

Unfortunately, defective cartilage can cause anything from no pain during rest or activity to pain even at rest. Furthermore, the pain within the (e.g. knee) joint is often non-specific. That means that the pain, as described by the child, cannot be directly translated into the correct diagnosis. This is where additional tests, such as X-rays, MRI, CT scans, sometimes bone scans and also a good physicians’ intuition comes into play.

Symptoms may include swelling of the joint, resulting in tightness and reduced activity, as well as pain. Although patients may report no pain at rest, they may experience pain and reduced activity after being active.

Furthermore, pain may follow trauma. This may be directly related to the trauma, or indicate a new cartilage injury, when the pain and/or swelling remains for some days. Loose bodies in the joint, which may occur in joints with defective cartilage or OCD lesions, can cause catching and locking of the joint.

However, these symptoms are not specific to cartilage disease or injury and may be caused by other knee conditions, or even by hip conditions. The young patient with knee pain should therefore be investigated without delay. In particular, if a child has persistent symptoms following a serious traumatic event or has long-standing, or ‘chronic’, joint pain, parents should consult their doctor.

How are cartilage problems in children diagnosed?

The diagnostic possibilities for the doctor are rather easy and usually staged in nature. Following complete patient history, including a family history (OCD lesions can be hereditary), the doctor will perform an examination of the child, with a special focus on the injured joint.

An array of typical joint tests will then be performed, some of which are specific for particular joint conditions. While there isn’t a particular examination that will indicate defective cartilage, the joint tests are required to rule out other conditions, such as ligament instability, meniscus defects or axis deformations.

Imaging studies are often required to substantiate a diagnosis. Initially standard X-rays will be performed to give an overview of the joint. The radiation associated with a knee joint X-ray is low.

If your child is suffering from a serious knee joint condition, magnetic resonance imaging (MRI) may be performed, as recommended by the ICRS. The difference between X-ray and MRI is that X-ray shows bone well but does not show cartilage or ligaments. On an MRI, all the soft tissues, ligaments and cartilage of the knee can be seen, as well as the bone. Importantly, MRI can reveal cartilage defects, including OCD lesions or loose joint bodies. Furthermore, MRI does not require radiation, and therefore does not endanger your child. The examination, however, does take around 30 – 45 minutes, during which your child has to stay still inside within the apparatus.

MRI is the ‘gold standard’ for assessing knee joint conditions and should be performed in any child suffering from serious, chronic or unsolved knee joint problems.

For very specific and rare knee joint conditions, or in cases of equivocal findings a CT scan or bone scan may be required. However, this is rather rare.

How are cartilage problems in children treated?

Injury to your child’s joint cartilage is a serious condition. However, there are a great variety of treatment options, which, combined with your child’s regenerative capacity, are excellent tools to repair the joint and often allow for return to full activity.

As articular cartilage is a tissue that grows very, very slow, the same applies after surgical cartilage repair. Therefore, the surgical procedure is only one part of the recovery process, with rehabilitation the other, and both stages are equally important.

Following cartilage repair, regular physical therapy sessions are required, some of which are highly customised for patients who have undergone cartilage surgery.

Recovery periods may often be long, and may require extended periods without placing weight on the joint. Temporary changes in sporting activities may be needed until the cartilage has healed.

When the rehabilitation programme is followed, the chances of healing are high. Children need help from their parents to understand the aims of the treatment, and to follow the rehabilitation programme. As a parent, you must be actively engaged in the treatment – it is not a passive activity, like waiting for a cast to come off after a bone fracture.

What is conservative therapy?

Today, there are usually two types of treatment. One is termed ‘conservative’, which means without an operation, while the other type is surgical, which means having an operation. Both treatment types apply to cartilage repair in children, while adult patients with general cartilage defects are more likely to undergo surgery.

The cartilage condition that is usually approached using conservative treatment is early-stage OCD. This is when the osteochondral unit is already affected and shows some changes but overall, it is still intact. This can only be diagnosed on MRI. Your child may already have symptoms at this stage, typically during and/or after activity, but not during rest.

As the osteochondral unit has a great potential for healing, conservative treatment approaches are the first choice. This allows the blood supply of the bony segment to be improved and the bony disease to heal, which takes the cartilage unit out of danger. However, this conservative therapy requires reduced or no sporting activity for at least 6–12 weeks (sometimes longer), physiotherapy and sometimes no weight bearing for several weeks. After that, the child has to gradually return to normal activity. This process can be monitored using MRI.

Another situation in which conservative treatment may be considered is (very) small cartilage and/or osteochondral defects. Very small in this case means around 1 cm2. If these defects are not associated with a free floating piece of cartilage then these could be treated non-operatively as they have the capacity to heal spontaneously. Clinical and MRI monitoring may be necessary to follow the progress of healing and sometimes these defects still require surgical intervention.

Conservative (non-operative) treatment may sometimes be time-consuming and difficult to understand, particularly for the young. However, there are no risks and conservative therapy can be very effective in children, which is rarely the case in adults.

What are the surgical options for a cartilage defect?

There are a variety of surgical therapies for repairing defective cartilage. Different surgical techniques are available for the treatment of articular cartilage defects and OCD lesions. While there may be preferences by surgeons to chose one technique over another, the scientific literature does not clearly define one technique to be clearly better than the other. For that reason your surgeon may present you with a particular technique that she or he is particularly comfortable with or feels for other reasons to fit your child best.

One therapy therefore cannot be pinpointed as the only one for a specific condition. Furthermore, the type of surgery depends strongly on the size of the defect, the location of the defect within the joint and the stage of the defect. Staging is particularly important for OCD lesions, as the chosen therapy depends greatly on the current disease stage. In children, a small lesion for surgical therapy would be 2 cm2, while a mid-sized lesion would be 2–4 cm2 and anything bigger, is a large lesion.

Lastly, the treatment is different for pure cartilage lesions, pure bony lesions with intact cartilage, and osteochondral lesions.

The surgical options for pure cartilage defects are microfracture, autologous osteochondral transplantation or mosaicplasty, and autologous chondrocyte implantation. Each of these techniques has advantages and disadvantages, and their use depends largely on the size and stage of the defect.

Microfracture procedures can be carried out using an arthroscope, meaning a minimally invasive or ‘key-hole’ procedure. The defective cartilage is removed using specialised instruments and the subchondral bone, which should be intact for this technique, is exposed. Small holes are then drilled into the subchondral bone, again using special instruments. Blood comes out of the small holes and settles in the prepared defect, forming a seal. The blood contains a number of stem cells, which differentiate over time into chondrocytes. This therapy can be very successful in children, as their ability to heal is so great. It should be used only for small lesions, and is not recommended for large lesions.

In larger pure cartilage lesions, autologous chondrocyte implantation (ACI) is a good treatment option. This technique requires one initial short arthroscopy of the knee joint for measuring and staging of the defective area. Small cartilage biopsies are taken from selected non-weight-bearing regions of the joint. This first operation is then finished and the patient can fully weight-bear after this surgery. The harvested biopsy is sent to a laboratory, where the chondrocytes are isolated and grown in a culture medium, After 3–6 weeks, the cells (chondrocytes) can be implanted into the defective cartilage region, usually via an open, rather than key-hole, procedure, where they grow to form new cartilage.

If the defective region is small but includes the underlying bone, osteochondral transplantation (OCT), ormosaicplasty, is an option. As explained above, the cartilage and bone form a unit and replacing only the defective cartilage means the overall defect may not heal properly. For OCT, cylinders of cartilage and bone together are harvested from a non-weight bearing area of the same joint. The harvested area will fill up with repair tissue over time, which is enough for a non weight-bearing region. The harvested cylinder will then be immediately placed into the defective region, which has been prepared by having a cylinder (of the same size) of cartilage and bone removed that includes the whole damaged region. Therefore both bone and cartilage are covered up immediately. The cylinder does not require further fixation, as it is ‘press-fit’. It is recommended that only one or two cylinders be transplanted, which is why it is used only for small defects.

An alternative to OCT in an osteochondral lesion would be to combine ACI with bone harvested from the patient’s femur or tibia (autologous bone) to replace the bony defect.

If a traumatic event has caused separation of a complete osteochondral fragment, and the event was recent, the ideal approach would be to re-fix the fragment using small pins or screws. If the trauma caused only a piece of cartilage to be separated, it can also be re-fixed, but with less likelihood of healing. However, if the piece is very small, it can often be simply removed and the defect left to spontaneously heal.

What are the surgical options for an OCD lesion?

If the child is suffering from an advanced-stage OCD lesion, conservative therapy is no longer indicated, and surgical therapy is preferred. If the cartilage is still intact and only the underlying bone is defective, the defective bone can be replaced by using bone graft from the adjacent bone (e.g tibia), and the patient’s own cartilage layer fixed on top of it using small pins or screws.

If a complete osteochondral fragment has been separated but is still intact, the underlying bony bed can be refreshed by removing dead bone to create a fresh bone surface and induce bleeding to maximise the healing. The complete OCD fragment is then placed back into the defective region, again using pins or screws.

If the cartilage layer is defective but the bone intact, which is rare within OCD lesions, then the cartilage repair therapies mentioned above can be used. This may also be necessary if the OCD fragment is broken into multiple pieces and cannot be fixed back into place.

What is rehabilitation?

An operation is 50% of the treatment, with rehabilitation the remaining 50%. This means that rehabilitation is equally as important as the operation. The reason for this is that, because hyaline cartilage is a very specialised structure, it requires a long time to recover.

As with surgery, rehabilitation is not identical for every patient. However, in general, your child will have to partially weight-bear (10–20kg) for 6 weeks after the operation. During this time, physiotherapy is required, as well as continuous passive motion (CPM). CPM is a machine that moves the joint (e.g., knee) passively so that movement and the flow of fluids occurs within the joint, which benefits the cartilage. This has to be performed 6–8 hours per day for the first 6 weeks after surgery.

If everything is fine, the child can move on to full weight bearing during weeks 7–12. After 12 weeks, normal walking is possible and strengthening exercises will be started, alongside stationary cycling, etc.

After approximately 6 months, light running, etc. will be possible. A full return to sport is usually not recommended before 1 year after surgery, and only then if the range of motion, strength and stamina are equal to that in the uninjured leg.

Those timetables usually apply for microfracture, ACI and complex OCD surgeries. For OCT and easier OCD procedures (e.g., only fixation), the recovery is much quicker, and return to sport is often allowed 3–6 months after the surgery.

Generally, the patient themselves is one of the most important parts of the rehabilitation process, as many of the exercises can be performed by the patient alone, especially later on after the surgery.

What are the expected outcomes?

In general, the outcome of surgery in children is much better that that seen in adult patients, as the regenerative capacity of children is higher.

This also applies to cartilage surgery. There is not a great deal of published data, and therefore conclusive statements on the best management approach for a particular lesion are not possible. Generally speaking, it is highly likely (above 90%) that the child will return to full activity without pain.

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