The 60-second guide to… knee cartilage

Cartilage is one of the key components of our knee joints. And also one of the most commonly damaged.

But what is it actually made of, and how does it function within the knee? And if you injure it, what are the treatment options? Here are some simple ways to understand all things knee cartilage.

What exactly is cartilage?

Cartilage is found all over our bodies, from our nose and ear structures to the shiny surface of joints. It’s basically a mixture of proteins like proteoglycans, collagen (a key ingredient in most bodily tissue) and, sometimes, elastin (a particularly stretchy protein). Within this matrix of chemicals are cells, the main ones being chondroblasts and chondrocytes.

What does cartilage do?

Together, that matrix gives cartilage some unique properties. It’s at once tough and highly resilient, yet also soft, smooth and flexible. This makes it useful in several ways. It provides support for things like our airways (eg, the nose and trachea). It provides a protective covering on joint bones. It even provides the building blocks for our skeleton: in the embryo, hyaline cartilage ossifies to form bone.

So, there’s more than one type?

There are actually several distinct types of cartilage. The main ones are:

Hyaline – the most widespread kind, found in things like the ribs, nose and larynx

Elastic – the most flexible type, found in structures like the epiglottis and outer ear

Fibrocartilage – the strongest form, found in things like joint capsules and the spine

Which type is knee cartilage?

The cartilage in your knees is a combination of hyaline cartilage and fibrocartilage. And you’ll find them in two key places. First, the bone endings. These are covered in thin, shiny articular cartilage. That’s the hyaline. It acts like lubrication, allowing the bones to slide smoothly against each other. Second, the meniscus. This is a rubbery pad of tissue that sits between the femur (thighbone) and tibia (shinbone). It’s like a shock absorber, soaking up impact and spreading the load across your joint.

How do people hurt their knee cartilage?

There are really two main ways you can damage your cartilage. One is through trauma. That could be anything from a direct impact or twist to overuse (for example, kneeling on a hard floor repeatedly during DIY). A common injury to the meniscus is a meniscal tear, where the fibres stretch to breaking point. The other way is through long-term wear-and-tear. When this happens to the articular cartilage, we call it osteoarthritis. It basically means the smooth protective covering on the bones has worn away, leaving them to rub painfully against each other. Little bits of cartilage can break off and become trapped in the joint (“loose bodies”). Or a wider area of cartilage can wear away. The risk of osteoarthritis increases as we get older.

How do we treat cartilage damage?

The first step is to get a proper diagnosis: so a physical examination, potentially with some imaging to see what’s going on inside (see X-ray, CT, MRI, Ultrasound for knees – what’s the difference?). From there we can create a treatment plan based on the type and severity of your damage. This ranges from simple rest and pain management through to surgical interventions. One issue with cartilage is that it’s avascular, ie, doesn’t have a blood supply. This means healing can be very slow or – in the case of articular cartilage – impossible.