Articular Cartilage Injury

Articular cartilage is the smooth, white tissue that covers the ends of the bones in your knee. An articular cartilage injury is a crack, flap or worn patch in that surface, usually after a twist or a blow to the knee. This page explains the causes, the symptoms, how it is diagnosed and treated, and how it differs from osteoarthritis.

What is an articular cartilage injury?

Your knee is where your thigh bone (femur), shin bone (tibia) and kneecap (patella) meet. The ends of these bones are covered with articular cartilage, a smooth, firm layer that lets the joint glide with very little friction. It also spreads your body weight when you walk, run or climb stairs.

Cartilage has no blood supply, so it has very little ability to heal once it is damaged. An injury can be a soft or frayed patch, a crack, a flap that lifts away from the bone, or a full-thickness defect where the bone underneath is exposed. Sometimes a small piece breaks off and floats in the joint as a loose body.

Cartilage damage is common. In a study of more than 25,000 knee arthroscopies (keyhole operations), cartilage damage was found in 60% of patients. The back of the kneecap and the inner (medial) side of the thigh bone were the most common sites.^[3]

How is cartilage damage graded?

Surgeons and radiologists usually grade the damage from 1 to 4:

• Grade 1: the cartilage is softened or swollen, but the surface is intact.
• Grade 2: fraying or cracks that go less than halfway through the cartilage.
• Grade 3: cracks or a defect that go more than halfway through.
• Grade 4: the cartilage is lost down to the bone.

How is it different from osteoarthritis?

An articular cartilage injury is a localised patch of damage, often after an injury in a younger, active person. In knee osteoarthritis, the cartilage wears thin across a wider area of one or more parts of the knee, the bone underneath changes, and bony spurs form. A cartilage injury can be one of the things that leads to arthritis later, but this does not happen to everyone. If your knee shows wider wear, our page on knee osteoarthritis is the better guide.

What causes an articular cartilage injury?

Most injuries happen in one of these ways:

• A twisting or pivoting injury with the knee bent, often in sport
• A direct blow to the knee
• The kneecap dislocating, which can shear cartilage off the kneecap or the thigh bone (see patellofemoral instability)
• Another knee injury, such as an ACL injury or a meniscus tear
• Repeated load on a knee that is unstable, or on one side of a bow-legged or knock-kneed leg
• In children and young adults, a condition called osteochondritis dissecans, where a piece of cartilage and the bone beneath it loosens.

Cartilage damage often comes with other injuries. In the arthroscopy study above, the injuries most often found alongside it were a medial meniscus tear (37%) and an ACL tear (36%).^[3] Extra body weight adds to the load on a damaged area.

What are the symptoms of an articular cartilage injury?

Some cartilage injuries cause no symptoms at all. Cartilage itself has no nerves, so the pain comes from the tissues around it: the lining of the joint (synovium) when it becomes inflamed, and the bone underneath when it is overloaded.^[4] When there are symptoms, they include:

• Swelling, often after activity
• Pain when you put weight on the leg, squat, or go up and down stairs
• Catching, or the knee locking so that you cannot fully straighten it, when a loose piece gets caught in the joint
• The knee giving way
• Clicking or grinding.

Damage behind the kneecap tends to cause pain at the front of the knee when you sit for a long time, squat or kneel. This is often called chondromalacia patella.

When should you see a doctor?

See your GP or physiotherapist if your knee keeps swelling after activity, or the pain has not settled after a few weeks. Seek medical advice sooner if:

• Your knee locks and will not straighten
• It swells quickly after an injury
• You cannot put weight on your leg
• Your knee is hot, red and swollen, or you have a fever. Seek urgent care.

How is an articular cartilage injury diagnosed?

Diagnosis starts with your history and an examination of your knee, including its stability and the alignment of your legs. X-rays show the bones, any loose piece that contains bone, and whether there is wider arthritis.

An MRI scan shows cartilage more clearly than other scans, but it has two limits. First, small or shallow damage can be missed. In one study, MRI picked up less than half of the cartilage lesions later seen at arthroscopy, although every lesion it did report was confirmed.^[5] Second, cartilage changes are common in people without knee pain. In a review of 63 studies of adults with no knee pain or injury, cartilage defects were seen in 11% of those under 40 and 43% of those aged 40 or over.^[1] A cartilage finding on your report is therefore matched against your symptoms and examination before any decision about treatment.

How is an articular cartilage injury treated without surgery?

Many cartilage injuries are treated without surgery, and rehabilitation is the centre of that care.^[2] Treatment also looks at the rest of the knee, because an unstable knee, a torn meniscus or poor leg alignment can keep overloading the damaged area.

Physiotherapy and exercise

Swelling switches off the thigh muscles, and they waste quickly. A physiotherapist first helps settle the swelling, then builds strength in your quadriceps, hamstrings and buttock muscles so they absorb load and take pressure off the cartilage. Exercise that loads the knee does not appear to harm cartilage, although the trials so far are of low quality.^[6]

Changing your activities

While your symptoms settle, swap high-impact activities, such as long runs and jumping sports, for lower-impact ones such as cycling, swimming or a cross-trainer. Most people can then build back up step by step, guided by pain and swelling.

Weight loss

In people with knee osteoarthritis, each kilogram of weight lost took about 4 kilograms of load off the knee with every step.^[7] A damaged patch of cartilage carries the same load, so if you are overweight, losing weight is likely to help.

Off-loading brace

If the damage is on the side of the knee that takes most of your weight, an off-loading brace aims to shift some of the load to the healthier side.

Injections

A cortisone (steroid) injection can settle an inflamed, swollen joint for a while. Platelet-rich plasma (PRP) and lubricant (hyaluronic acid) injections are also used. For cartilage injuries, the evidence for all of these is limited and mostly short term, and none of them repairs cartilage.^[2]

When is surgery considered?

Surgery is considered when a loose piece makes the knee catch or lock, or when a full-thickness defect still causes pain and swelling after a good trial of rehabilitation. The options range from removing loose pieces and trimming unstable flaps, to microfracture, moving small plugs of your own cartilage and bone into the defect, and implanting cartilage cells. The right choice depends on the size and position of the damage, your age, and the rest of your knee, and an unstable ligament or poor alignment may need treatment too. You can read about each option on the cartilage repair surgery page.

What is the outlook for an articular cartilage injury?

The outlook depends on the size and depth of the damage, the health of the rest of your knee, and your weight. Untreated cartilage defects tend to get larger over time.^[8]

Over longer periods the evidence is mixed. In a small study of 37 people with a single deep defect that was left untreated, most still had good knee function 15 years later, and their arthritis was no worse than in their other knee.^[9] In a Norwegian study that followed 322 people for an average of 19 years, about half of the people had a poor long-term result, defined as a later knee replacement or realignment operation, or a low quality-of-life score. The risk was higher in people who were overweight, had more than one defect, or had a full-thickness defect.^[10] Strong thigh muscles and a healthy weight are the parts of the outlook you can influence.

References