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How do I know if I have a Cartilage Problem? (Imaging of Cartilage Injuries)
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How do I know if I have a Cartilage Problem? (Imaging of Cartilage Injuries)

The first thing to explain, especially for patients, is why imaging of the knee is required. When patients arrive with a cartilage problem, often in the knee joint (although sometimes in the ankle or hip), the first step is clinical evaluation. However, imaging is also required, particularly in patients with a possible cartilage problem.

If an X-ray is taken, it only reveals whether or not there is osteoarthritis or, after trauma, whether or not there is a fracture. Younger patients in particular can have problems in their knee that are not shown on X-ray, and magnetic resonance imaging (MRI) is therefore required.

Intended audience

This information is aimed at patients who have been identified as needing imaging for cartilage disorders. It is designed to offer an overview of what the procedures entail, as well as briefly discuss the advantages, disadvantages and expectations you should have when undergoing such procedures.

What is MRI?

MRI machines use magnetic fields and radio waves to form images of a wide range of structures in the body. An MRI is required to see possible cartilage problems in the joint and, more importantly, the MRI has to be a good one. For that, either a 1.5 Tesla or, even better, a 3 Tesla MRI is needed.

Tesla’ is a measure of the strength of the MRI’s magnet field. Modern MR systems usually have field strength of 1.5 or 3.0 Tesla. Basically, the higher the field strength of the magnet, the better the quality of the MRI. Additionally, for a high-quality MRI, a dedicated joint coil is needed. The coil is a small cage around the joint that improves the quality of the MRI. In the knee joint, for example, there are special coils called ‘dedicated multi-channel knee coils’, which have 8 or 16 channels. These channels further improve the quality of the MRI, as more signals can be gained and, therefore, the cartilage layer can be imaged in greater detail.

The better the coil, and the better the scanner, the better the quality of the MRI images. If you have images with high resolution and good quality, good contrast and a good signal-to-noise ratio, it will be possible to see if there are any lesions in this relatively tiny cartilage layer.

Furthermore, the physicians performing the MRI should be aware that you might have a cartilage problem, so that they can use a high resolution and a good MRI protocol to properly visualise the cartilage. Otherwise, the images may show a problem, but it will not be possible to determine the size of the cartilage lesion, the number of lesions, and the status of the meniscus, the cruciate ligaments, and the underlying bone.

It is very important to have an idea of the condition of the bones, as the patient may have isolated cartilage injuries or cartilage defects, or may have bone and cartilage (‘osteochondral’) defects, which include the underlying bone. This is very important for choosing the right kind of therapy.

In addition, the size of the cartilage defect is crucial. For very small defects, microfracture therapy can be used.

However, if there is a bigger defect, and the surrounding cartilage is not good quality, cartilage transplantation, such as ACI, MACI, or osteochondral transplantation, may be required. It is helpful to know that beforehand, as the patient can sign a special preoperative document that gives the surgeon permission to perform a cartilage biopsy, which is necessary for these procedures. Cartilage biopsy for a second surgery cannot be performed without prior patient permission, as it is considered a form of therapy.

MRI therefore not only allows the surgeon to choose the most appropriate procedure but also select the correct preoperative documents for the patient to sign. It is also important because the postoperative care of the patient could be completely different, with a different or longer rehabilitation programme.

This is why it is important that patients have an MRI before their procedure, particularly one that is cartilage-sensitive, so that the doctor can see what is happening with the cartilage, the size of the defect and the number of defects.

Can other imaging techniques give the same information as MRI?

An X-ray, as discussed above, shows the status of the joint, and whether there is osteoarthritis or a fracture. In other words, X-ray simply visualises bony structures and abnormalities. Therefore, cartilage defects cannot really be visualised.

Ultrasound visualises muscle or tendon injuries. Cartilage can be partially visualised if it is within the depth of the penetrating ultrasound waves. This ability is limited, however, as high resolution ultrasound has the disadvantage of low tissue penetration.

Computed tomography (CT) is also not sensitive for cartilage. In addition, the radiation associated with CT presents a problem. CT combined with intra-articular contrast agent, known as arthroCT, can be performed. However, this still has the problem of the radiation, coupled with the infectious risk associated with an intra-articular (within the joint) injection of contrast agent. This technique is only be used if the patient cannot go into an MRI machine due to severe claustrophobia or the presence of a pacemaker or similar implanted device.

The majority of cartilage injury patients, however, are younger and can usually go into an MRI machine.

Are there any disadvantages to MRI?

There are no real disadvantages to MRI, especially if a contrast agent is not needed. The only risks are the classical contraindications for MRI, such as cardiac pacemakers, open heart surgery or open cranial surgery, and active electronic devices such as infusion pumps, etc. Patients with large metal implants, particularly if ferromagnetic (i.e., attracted to magnets), are also not allowed to have an MRI.

There is some noise in the MRI machine, but patients are given ear defenders. The machine can also be unpleasant if patient is very claustrophobic.

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