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The Complete Classification of Cartilage Lesions in the Knee

11th November 2021

Cartilage, or menisci, cover the surface of joints throughout the body and offer a smooth surface by which the bones can move across each other. There are two main purposes in acting as a shock absorber and as a mould.

Degenerative conditions such as osteoarthritis occur where there is degradation of cartilage within a joint leading to bone on bone contact (friction) which results in pain and compromises mobility, highlighting the important role cartilage plays in the bones and within the body.

Cartilage is a tough and flexible tissue, making it perfect for being shaped around the bones and being able to cope with everything the body has to throw at it. If you take the knee as an example it is responsible for keeping you mobile and active and coping with forces exerted from moving your entire body weight. It is also used where there is no bone structure i.e. the nose and ears, without which they would not be able to maintain their integrity.

The main drawback from cartilage is that it lacks its own complete bloody supply, meaning any damage incurred can take a lot longer to heal compared with your skin, muscles or ligaments. This also means that recovery from such injuries can take longer and require an extended period of rehabilitation.


There are three different types of cartilage in the body in that of elastic cartilage, fibrocartilage and articular (hyaline) cartilage.

Elastic cartilage forms the outside of the ears and some of the nose. It also forms the bit of tissue at the back of your throat which is responsible for stopping food going into your airways, also known as the epiglottis.

Fibrocartilage sits between the vertebrae of the spine to protect the individual discs as well as within the bones of the hips and pelvis.

Articular cartilage, also referred to as hyaline cartilage is found between joints as well as between the ribs and even around the trachea or windpipe. This is the toughest type of cartilage whilst also being spongy, making it perfect for absorbing shock from walking, running and jumping.

If you take the knee as an example about a third of the cartilage within the joint actually has some form of bloody supply (in the top section), though the remaining two thirds does not. It is articular (hyaline) cartilage present within the knee joint though once eroded it is only fibrocartilage which grows back, though this is not as strong.


There are a number of reasons why you may experience lesions of the cartilage, whether this is injury (trauma) based or through gradual degradation over time.

Traumatic events can affect cartilage within the joint, whether this is through a sports injury or following a trip or fall. The outcome and treatment required will vary depending on the severity of the injury.

Repeated minor trauma events can also affect the cartilage long term. If you continue to sprain your ankle then there is a greater chance of incurring a higher grading of injury due to there being instability in the joint. The same can be said for the cartilage in that it will be affecting the same region each time, gradually wearing away.

Long term immobilisation can have a negative effect on cartilage within the joint. Following a broken leg or ACL surgery the leg was often immobilised until the body was completely healed though this has been found to elongate mobility and compromise the healing process. It is now recommended that controlled application of force is actually beneficial for the healing process, with rigid walker boots used following foot and ankle injuries and ROM (range of motion) braces following surgery. These are designed to restrict over extension or flexion to minimise the risk of further damage being caused.

Osteochondritis dissecans is another common causes of lesions. This where the cartilage and bone break away and need to be pinned back in place.

Infection can also play a part in the degradation of cartilage though it is not as common as the aforementioned causes.


If untreated there is an increased risk of osteoarthritis long term. This is where the removal of cartilage results in bone on bone contact which is the source of pain and can compromise the mobility of the patient, making simple activities such as walking or even getting out of your chair difficult.

In Google there are 45,000 searches every month for osteoarthritis, of which knee is the most common, followed by hip and then thumb. In the UK 8.75 million are said to have sought treatment for a form of osteoarthritis, with 33% of people being over the age of 45 and 49% of women being older than 75 compared to just 42% of men of the same demographic.

Estimated figures suggest that knee OA accounts for 18% of all diagnoses, 11% for hip and 6% for thumb. In considering hip OA it is estimated that there are 2.12 million sufferers in the UK, which is the second highest in EMEA who have a total of 9.5 million sufferers. There are 100 to 200 total hip replacements per every 100,000 people each year, of which 33% are for men and 66% for women.

There is no cure for OA, only effective management. In the early stages this is managed via medication and physiotherapy but in serious cases will result in a joint replacement. In considering knee OA then bracing is now utilised as an additional treatment option which works to offset the affected side of the knee, thus reducing pain and increasing mobility.


There are 4 grades of cartilage lesions which will help to determine the treatment options and subsequent rehabilitation thereafter. This is determined via the Outerbridge classification system and references the subchondral bone, which is the bone residing beneath the white joint cartilage.

A grade 0 is classed as a normal knee.

A grade 1 occurs where there is a softening of the cartilage in combination with swelling, which can affect your mobility and begin to become painful.

A grade 2 is where there is Fibrillation where there is a partial-thickness defect. It is important to note that a grade 2 refers to those defects where the diameter does not exceed 1.5cm or where it fails to reach the subchondral bone.

A grade 3 is where the partial-thickness does exceed 1.5cm in diameter and/or reaches the subchondral bone.

A grade 4 is the most serious and occurs were the subchondral bone becomes fully exposed.

In considering the knee joint it is worth noting that once articular cartilage is eroded it is only fibrocartilage which will grow back, which is not as strong.


Statistics show that 10,000 people each year require cartilage surgery, though as many people incurring mild damage do not report this to their GP or visit a hospital. Accidental damage is seen as the most common cause, covering sports injuries and falls and relates to the under 35 years old demographic. Those who are 50 years and older will see cartilage damage in the form of osteoarthritis, with the condition affecting women more than men.

A study by Slauterbeck J R et al analysed 365 men and 175 women as to the distribution of the cartilage legions.

In men they found that the most common place for a legion was in the middle of the medial side of the knee, with 137 cases (38%) with 88 cases (24%) in the middle of the lateral side of the knee. The third most common occurs across both the anterior and middle parts of the medial side of the knee, totaling 53 cases (15%).

In women the results were very similar in terms of common locations of legions. Middle medial saw 65 cases (37%) middle lateral had 44 cases (25%) and anterior and middle lateral saw 23 cases (13%).

This study shows that despite gender legions tend to appear in the same places with roughly the same percentages.


As highlighted, there are 10,000 people every year in the UK who undergo surgery as a result of cartilage damage but there are no figures to show diagnosis for less serious grades. What is clear is that a failure to manage less serious grades of cartilage lesion can increase your chances of degenerative conditions in the future such as osteoarthritis, therefore prevention is better than cure…especially when there is no cure.

It is very difficult to self-diagnose cartilage damage, since this cannot be done visually. Typically a diagnosis can only take place via an MRI (magnetic resonance imaging) or via an arthroscopy, though the former can have a long waiting time. The latter normally takes place under a general anaesthetic but in some cases a local one can be used, but involves the insertion of a small camera to assess the joint in question.

Following an injury it is normally suggested that you rest for a few days to see if things remedy themselves prior to seeking medical advice, though obviously you will know when an injury is serious enough to warrant an immediate trip to A&E. In the case of cartilage damage you will not see a complete recovery from your injury, though at this stage the root cause of the complaint could be any number of things. Should you fail to see signs of recovery then you should speak with a medical professional so that a complete assessment and subsequent diagnosis can be obtained, from which a complete treatment programme can be compiled for you.

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