This fine, rubbery tissue acts as a cushion between the bones of joints. People with cartilage damage commonly experience joint pain, stiffness, and inflammation (swelling).
In this article, we will describe the function of cartilage, how it can become damaged, and how that damage can be treated.
Here are some key points about cartilage damage. More detail and supporting information is in the main article.
What is cartilage?
Cartilage is tissue that cushions the bones.
Cartilage has several functions in the human body:
- Reduces friction and acts as a cushion between joints and helps support our weight when we run, bend, and stretch.
- Holds bones together, for instance, the bones of the ribcage.
- Some body parts are made almost entirely of cartilage, for example, the external parts of our ears.
- In children, the ends of the long bones are made of cartilage, which eventually turns into bone.
Unlike other types of tissue, cartilage does not have a blood supply. Because of this, damaged cartilage takes much longer to heal, compared with other tissues that are supplied by blood.
There are three types of cartilage:
- Elastic cartilage (yellow cartilage) - the most springy and supple type of cartilage. Elastic cartilage makes up the outside of the ears and some of the nose.
- Fibrocartilage - the toughest type of cartilage, able to withstand heavy weights. It is found between the discs and vertebrae of the spine and between the bones of the hip and pelvis.
- Hyaline cartilage - springy, tough, and elastic. It is found between the ribs, around the windpipe, and between the joints (articular cartilage).
Elastic cartilage, fibrocartilage, and hyaline cartilage can all be damaged. For example, a slipped disk is a type of fibrocartilage damage, while a hard impact on the ear can cause elastic cartilage damage.
When cartilage in a joint is damaged, it can cause severe pain, inflammation, and some degree of disability - this is known as articular cartilage. According to the NIH (National Institutes of Health), one-third of American adults aged over 45 suffers from some type of knee pain.
Patients with damage to the cartilage in a joint (articular cartilage damage) will experience:
- Inflammation - the area swells, becomes warmer than other parts of the body, and is tender, sore, and painful.
- Range limitation - as the damage progresses, the affected limb will not move so freely and easily.
Articular cartilage damage most commonly occurs in the knee, but the elbow, wrist, ankle, shoulder, and hip joint can also be affected.
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.
- Direct blow - if a joint receives a heavy impact, perhaps during a bad fall or an automobile accident, the cartilage may be damaged. Sportspeople have a higher risk of suffering from articular damage, especially those involved in high impact sports like American football, rugby, and wrestling.
- Wear and tear - a joint that experiences a long period of stress can become damaged. Obese individuals are more likely to damage their knee over a 20-year period than a person of normal weight, simply because the body is under a much higher degree of physical stress. Inflammation, breakdown, and eventual loss of cartilage in the joints is known as osteoarthritis.
- Lack of movement - the joints need to move regularly to remain healthy. Long periods of inactivity or immobility increase the risk of damage to the cartilage.
Telling the difference between cartilage damage in the knee and a sprain, or ligament damage, is not easy because the symptoms can be similar. However, 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. Although useful, an MRI cannot always detect cartilage damage.
- Arthroscopy - a tube-like instrument (arthroscope) is inserted into a joint to examine and repair it. This procedure can help determine the extent of cartilage damage.
Surgery for cartilage damage is generally a last resort.
Conservative treatment (non-surgical) - some patients respond well to conservative treatment, which can include special exercises, NSAIDs (non-steroidal anti-inflammatory drugs), and sometimes steroid injections.
Exercises may include physical therapy and/or a program the patient can do at home. If the damage is not extensive, this may be all the patient needs.
Surgery - patients who do not respond to conservative treatment will need surgery. There are several surgical options, depending on a number of factors, which include the age and activity level of the patient, how big the lesion is, and how long ago the injury happened.
Surgical options include:
- Debridement - smoothing the damaged cartilage and removing loose edges to prevent it from rubbing and irritating other parts of the body. 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 cartilage that triggers the production of new cartilage. Unfortunately, the new cartilage that grows is less supple than the original cartilage type. This means it wears away more quickly, and the patient may need further surgery later on.
- Mosaicplasty - healthy, undamaged cartilage is taken from one area and moved to the damaged site. This procedure is not suitable when there is widespread damage, as in osteoarthritis. Mosaicplasty is only used for isolated areas of cartilage damage, generally limited to 10-20 millimeters in size; this technique is most commonly used in patients under the age of 50 who picked up damage from an accident.
- Autologous chondrocyte implantation - a small piece of cartilage is removed and taken to a laboratory. Here it is grown to produce more cartilage cells. About 1 to 3 months later, the new cartilage cells are implanted into the knee where they grow into healthy tissue.
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 pain may slowly get worse.
All small articular cartilage defects can eventually progress to osteoarthritis if given enough time.
A physical therapist can suggest exercises that are suitable for an individual to strengthen the muscles around the joint. This will reduce pressure on the area with the damaged cartilage.
The Arthritis Foundation recommends:
- gentle stretching to maintain flexibility and range of motion
- aerobic and endurance training to achieve or maintain a healthy weight and improve mood and stamina
- strengthening exercises to build up the muscles around the joints
While exercise offers many benefits, it seems unlikely to result in a regeneration of cartilage.
As one review concludes:
"Contrary to general expectation, mechanical feedback does not play a relevant role in this process and, in contrast to bone, does not serve to regulate the complex biochemical metabolic machinery towards lasting optimality of cartilage form."
Increased use has not been found to result in thicher cartilage.