Cartilage structures and functions can relatively easily be harmed, often resulting in damage. Cartilage is a tough, flexible connective tissue that is found in many areas of the body. This fine, rubbery tissue mainly functions as a cushion for bones at joints. People with cartilage damage commonly experience joint pain, stiffness and inflammation (swelling). The English word “cartilage” comes from the Latin word cartilage, which means “cartilage” or “gristle.”
Fast facts on cartilage damage
- Cartilage is a fine, rubbery tissue that cushions joints
- It has several functions, including holding bones together and supporting other tissues
- There are three types of cartilage, the most spongy of which is yellow cartilage
- Two of the main symptoms of cartilage damage are swelling and stiffness
- There is a range of ways in which cartilage can be damaged, including overuse or underuse
- Telling the difference between cartilage damage, sprain or ligament damage can be challenging
- Diagnosis of cartilage damage will normally require magnetic resonance imaging (MRI) or arthroscopy
- There is a five point scale for grading cartilage damage
- Cartilage damage is often treated with non-steroidal anti-inflammatory drugs (NSAIDs)
- If cartilage damage is not treated, it can worsen until an individual can no longer walk.
What is cartilage?
Cartilage has several functions in the human body:
- Reduces friction and acts as a cushion between joints – cartilage reduces friction between bones by covering the surface of joints. If there were friction the joint would soon be damaged and destroyed. Cartilage also helps our weight-bearing functions when we run, bend, stretch or engage in any type of movement.
- Holds bones together – the bones on our ribcage are held together thanks to cartilage.
- Acts as a mold – some of our body parts are made either exclusively or almost exclusively from cartilage, for example, the external parts of our ears.
- The formation of bones – when we are young children the ends of our long bones are made of cartilage, which eventually turn into bones.
However, unlike other types of tissue, cartilage does not have a blood supply. Blood cells help repair tissue damage by diffusion. Consequently, damaged cartilage takes much longer to heal, compared to other tissues in our body which have a blood supply.
There are three types of cartilage:
- Elastic cartilage: also known as yellow cartilage is the most springy and supple type of cartilage. This type of cartilage makes up the outside of the ears, some of the nose, the larynx, and also the epiglottis.
- Fibrocartilage: the toughest type of cartilage, and it is able to withstand heavy weights. It is found between the discs and vertebrae of the spine and between the bones in the hips and pelvis. It is the only type of cartilage that contains type I collagen in addition to the normal type II.
- Hyaline cartilage: both springy and tough. It consists of a slimy mass of a firm consistency, however, it is also extremely elastic. It is found between the ribs, around the windpipe, and between the joints. The cartilage between the joints is known as articular cartilage. Hyaline cartilage has a pearly bluish color.
Elastic cartilage, fibrocartilage and hyaline cartilage can all suffer damage. For example, a slipped disk is an example of fibrocartilage damage, while a hard whack on the ear can cause elastic cartilage damage – hence the term cauliflower ear.
When cartilage in a joint, such as the knee joint is damaged, the consequences can be severe pain, inflammation and some degree of disability – this is known as articular cartilage damage (damage to the cartilage in a joint). According to the NIH (National Institutes of Health), USA, one third of US adults aged over 45 suffer from some kind of knee pain.
Symptoms of cartilage damage
Patients with damage to the cartilage in a joint (articular cartilage damage) will experience:
- Inflammation – this is the basic way our bodies react to irritation or injury (as well as infection). The area swells (becomes inflamed), becomes warmer than other parts of the body, and is tender, sore and/or painful.
- Range limitation – as the damage progresses, the range of movement in, for example the limb with the articular damage has a smaller range of movement.
In severe cases, a piece of cartilage can break off and the joint can become locked. This can lead to hemarthrosis (bleeding in the joint); the area may become blotchy and have a bruised appearance. Articular cartilage damage most commonly occurs in the knee, but the elbow, wrist, ankle, shoulder and hip joint can also be affected.
Causes of cartilage damage
- Direct blow – if a joint receives a devastating impact, as may happen if you have a bad fall, an automobile accident, or receive a powerful kick during karate training, the cartilage may be damaged. Sportsmen and sportswomen, especially those involved in high impact sports, such as martial arts, American football, rugby or wrestling have a higher risk of suffering from articular damage.
- Wear and tear – sustained stress on a joint over a prolonged period may eventually take its toll. An obese individual is more likely to damage his/her knee over a 20-year period than a person of normal weight, simply because the knee or hip joints are undergoing a much higher degree of wear and tear. Inflammation, breakdown and eventual loss of cartilage in the joints is known as osteoarthritis.
- Lack of movement – the joints need to move regularly in order to remain healthy. Prolonged periods of inactivity or immobility increase the risk of damage to the cartilage.
Diagnosing cartilage damage
Differentiating between cartilage damage in the knee and a sprain or ligament damage is not easy, because the symptoms overlap.
Although articular cartilage damage diagnosis may sometimes be extremely challenging, modern non-invasive tests make the job much easier than it used to be.
After carrying out a physical examination, the doctor may order the following diagnostic tests:
- Magnetic resonance imaging (MRI) – the device uses a magnetic field and radio waves to create detailed images of the body. It can often detect cartilage damage. However, in some cases, the damage cannot be seen on the MRI, even though it is present.
- Arthroscopy – a tube-like instrument (arthroscope) is inserted into a joint to inspect and diagnose it. Repairs can also be carried out. This procedure can help determine the extent of cartilage damage.
Grading of cartilage damage – the International Cartilage Repair Society set up an arthroscopic grading system which ranks the extent of cartilage defects:
- grade 0: (normal) healthy cartilage
- grade 1: the cartilage has a soft spot or blisters
- grade 2: minor tears visible in the cartilage
- grade 3: lesions have deep crevices (more than 50% of cartilage layer)
- grade 4: the cartilage tear exposes the underlying (subchronal) bone.
The size of each defect will also be measured. A defect less then 2cm2 is classed as small. Where the defect is located can also influence function, severity of pain, and treatment options. Pain is not a good pointer to articular cartilage damage severity. Some patients may have very mild pain and have more serious damage than others with severe pain.
Treatment for cartilage damage
Conservative treatment – some patients respond well to conservative treatment, which may include special exercises, the use of NSAIDs (non-steroidal anti-inflammatory drugs), and maybe a steroid injection.
Surgery – patients who do not respond to conservative treatment will need surgery. There are several surgical options, which one the surgeon will recommend will depend on several factors, including the age and activity level of the patient, how big the lesion is, and how long the injury has been present.
Surgical options include:
- Debridement – smoothing the lesion and removing loose edges to prevent irritation. The procedure is done using small arthroscopic instruments, such as a mechanical shaver.
- Marrow stimulation – under the damaged cartilage the surgeon drills tiny holes (micro fractures), exposing the blood vessels that lie inside the bone. This causes a blood clot to form inside the target area of the cartilage. The blood cells trigger the production of new cartilage. One drawback is that this procedure does not produce the desired type of cartilage – fibro cartilage instead of hyaline cartilage (which is much more supple). Fibro cartilage is will wear away more quickly and the patient may need further surgery later on.
- Mosaicplasty – cartilage from undamaged areas of the joint is moved to the damaged area. The cartilage that is moved has to be in a non-weight-bearing part of the joint. This procedure is not suitable when there is widespread damage, as in osteoarthritis. This treatment is only recommended for isolated areas of cartilage damage, generally limited to 10-20mm in size, most commonly found in patients under the age of 50 years who experienced a trauma in the affected area.
- Autologous chondrocyte implantation (ACI) – a small piece of cartilage is taken from, for example, the knee (biopsy) and sent to a laboratory which grows more cartilage cells from the sample. About 1 to 3 months later the new cartilage cells are implanted into the knee. A piece of outer layer of bone from the lower leg (periosteum) is taken and sewn into the area of cartilage damage. The cartilage cells that were cultivated in the lab are then injected into that area and the periosteum is sealed – the cartilage then grows back.
Complications of articulate cartilage damage
If left untreated, the joint, especially if it is a weight-bearing one, such as the knee, can eventually become so damaged that the person cannot walk. Apart from immobility, the patient may experienced progressively worsening pain.
All small articular cartilage defects can eventually progress to osteoarthritis if given enough time.
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