Cartilage damage in the knee is injury to the articular cartilage that covers the ends of the bones, caused by trauma, by a condition called osteochondritis or by wear [1][4]. Cartilage does not heal by itself; methods such as physiotherapy may relieve symptoms but do not repair the damage [4]. Candidates for operations such as microfracture and cartilage grafting are mostly young adults with a single area of damage; widespread wear (osteoarthritis) is a separate condition [1][5].
What is cartilage, and what does cartilage damage mean?
Articular cartilage is the smooth, white tissue that covers the ends of the bones where they meet in a joint; it lets the bones glide with very little friction [1]. When it is damaged the joint surface may become rough, movement becomes painful and arthritis can develop [1].
The meniscus is a separate structure; meniscus tears are covered in a separate article in this guide.
What causes cartilage damage?
Articular cartilage can be damaged by an injury or by normal wear and tear [1]. Three situations are distinguished:
- Localised (focal) cartilage damage: usually appears after an injury sustained during sport [4][5]
- Osteochondritis dissecans: occurs in children and adolescents. A small segment of bone begins to separate from the bone around it because its blood supply is disrupted; the segment and the cartilage covering it can crack and loosen. It is thought to be related to repetitive stresses; it is most often found in the knee, at the lower end of the thigh bone [2]
- Widespread wear (worn knee cartilage, osteoarthritis): develops as the cartilage wears over time [1]; an untreated cartilage injury can also lead to it [4]. It causes pain and stiffness in both knees and is more common in older people [7]
What are the symptoms of cartilage damage?
The symptoms of knee cartilage damage are pain, swelling, locking and a feeling that the knee is unstable (giving way) [5]. After an injury the knee may not straighten fully, and a popping sound may have been heard at the time of the injury; the same symptoms occur with ligament and meniscus tears [7].
In osteochondritis dissecans the first symptoms are usually pain and swelling brought on by sport; in advanced cases the joint may catch or lock [2].
How is cartilage damage diagnosed?
Assessment begins with the history and an examination [2]. Articular cartilage contains no calcium and so cannot be seen on an X-ray [1]. An X-ray shows bone and is essential for the initial diagnosis of osteochondritis dissecans; MRI gives better images of soft tissues such as cartilage [2].
In arthroscopy a small camera is inserted into the knee joint; the method is used both to diagnose and to treat knee problems [3].
Does cartilage damage heal, and does cartilage grow back?
Cartilage does not heal itself well [1]. According to a Cochrane review, untreated cartilage injuries do not mend by themselves and can lead to osteoarthritis; the available treatments, too, are often aimed at relieving symptoms such as pain rather than providing a cure [4].
Osteochondritis dissecans in children follows a different course: in many children, especially while they are still growing, the affected bone and cartilage heal on their own; most children start to feel better over 2 to 4 months of rest and non-surgical treatment [2]. In young people who have finished growing and in young adults the segment is more likely to separate [2].
What helps cartilage damage? "Cartilage-rebuilding" medicines
According to NICE in the UK, supportive care is used first for cartilage damage; this includes exercise, weight loss, physiotherapy, painkillers, taking load off the knee, applying heat or cold, and a cortisone injection into the joint [5]. Non-surgical methods such as physiotherapy may relieve symptoms but cannot heal the damage [4].
At home, it is advised to put as little weight as possible on the knee and to apply an ice pack wrapped in a towel for up to 20 minutes every 2 to 3 hours [7]. Ask your pharmacist or doctor which painkiller is suitable.
Glucosamine and chondroitin, known as "cartilage-rebuilding" or "cartilage-strengthening" products, did not, alone or together, reduce joint pain to a clinically meaningful degree compared with a dummy medicine (placebo) in an analysis combining 10 large trials (3803 patients) in people with knee and hip osteoarthritis, nor did they affect the narrowing of the joint space on X-ray [6].
The evidence on hyaluronic acid, PRP and stem cell injections is set out in the knee injections article in this guide.
Surgery for cartilage damage: for whom, and by which method?
According to NICE, surgery is considered for people whose symptoms persist despite supportive care [5]. Most candidates are young adults with a single area of damage; older people, and those with many areas of damage in the same joint, are less likely to benefit [1].
Widespread wear (osteoarthritis) is a separate condition: NICE states that cartilage cell implantation should not be used in severe osteoarthritis; if the damage leads to advanced osteoarthritis, knee replacement becomes an option [5]. These are covered in the knee osteoarthritis and knee replacement articles in this guide.
In osteochondritis dissecans, surgery is considered when non-surgical treatment has not been enough, when the segment is loose or detached, when it is more than 1 centimetre in diameter, or in teenagers who are close to the end of growth. The segment may be drilled, fixed with pins and screws, or replaced with a piece of bone and cartilage (a graft) [2].
Many of the procedures are done by arthroscopy (keyhole surgery) [1]. The main methods are:
- Clean-up (debridement): by arthroscopy the damaged cartilage is trimmed and loose fragments of bone or cartilage inside the joint are removed [3]
- Microfracture: small holes are made in the bone beneath the cartilage so that blood can reach the area and new cartilage can form. The tissue that forms is fibrocartilage, which is not as durable as the joint's normal (hyaline) cartilage; the method is better suited to less active people with a single, smaller area of damage [1]
- Cartilage grafting (osteochondral graft, mosaicplasty): pieces of bone and cartilage taken from a non-weightbearing part of the joint are transferred to the damaged area; it is used for smaller defects. For larger defects a piece taken from a donor (cadaver) may be considered [1]
- Cartilage cell implantation (autologous chondrocyte implantation): in a first operation cartilage cells are taken from an undamaged part of the knee and multiplied in a laboratory, and in a second operation they are placed in the damaged area. NICE recommends this method only for people who have not had previous cartilage repair surgery, whose defect is larger than 2 square centimetres and who have minimal osteoarthritic damage in the knee, and on condition that it is done at a tertiary referral centre [5]
Recovery after surgery and results
After surgery the joint surface must be protected: for the first few weeks, or longer depending on the type of procedure, you may not be able to put weight on the leg and crutches are used; it may be several months before a return to sport and strenuous activities [1]. After surgery for osteochondritis dissecans, crutches are needed for about 6 weeks, followed by 2 to 4 months of physiotherapy; a gradual return to sport may be possible after about 4 to 5 months [2].
According to the American Academy of Orthopaedic Surgeons, restoring cartilage can relieve pain, allow better function and delay or prevent arthritis [1]. The Cochrane review comparing microfracture with mosaicplasty, however, found three small trials (133 patients), judged the quality of the evidence to be very low and could not conclude which is better; with both methods there were patients whose symptoms came back [4].
When not to wait
See a doctor if knee pain does not improve within a few weeks; in the following situations seek care without waiting [7]:
- The knee is very painful, cannot be moved or cannot take any weight
- The knee is badly swollen or has changed shape
- The knee locks, gives way or painfully clicks
- There is a very high temperature together with redness or heat around the knee
Frequently asked questions
- Does knee cartilage grow back by itself?
- Untreated cartilage injuries do not mend by themselves; non-surgical methods such as physiotherapy may relieve symptoms but do not repair the damage [4]. In growing children, however, osteochondritis dissecans heals on its own in many cases [2].
- How long does a knee cartilage injury take to heal?
- It depends on the type of damage and on the treatment. Most children with osteochondritis dissecans start to feel better over 2 to 4 months of rest and non-surgical treatment [2]. After cartilage repair operations crutches are needed for the first few weeks, and a return to sport may take several months [1].
- Do cartilage-rebuilding or cartilage-strengthening medicines work?
- In an analysis combining data from 3803 patients with knee and hip osteoarthritis, glucosamine, chondroitin and the two together did not reduce pain to a clinically meaningful degree compared with placebo, nor did they affect the narrowing of the joint space [6].
- What is a knee cartilage graft, and who is it for?
- It is the transfer of pieces of bone and cartilage taken from a non-weightbearing part of the joint to the damaged area; it is used for smaller defects [1]. Cartilage cell implantation, in turn, is recommended by NICE only for people whose defect is larger than 2 square centimetres, who have minimal osteoarthritic damage in the knee and who have not had previous cartilage repair surgery [5].
- Can worn knee cartilage be repaired by surgery?
- Widespread wear, that is osteoarthritis, is a separate condition. NICE states that cartilage cell implantation should not be used in severe osteoarthritis; if the damage leads to advanced osteoarthritis, knee replacement becomes an option [5]. People with many areas of damage in the same joint are also less likely to benefit from cartilage repair operations [1].
This article is a general summary; diagnosis and treatment decisions are made by the doctor who examines you.
Sources
- Articular Cartilage Restoration. American Academy of Orthopaedic Surgeons (OrthoInfo), n.d.. orthoinfo.org
- Osteochondritis Dissecans. American Academy of Orthopaedic Surgeons (OrthoInfo), n.d.. orthoinfo.org
- Knee Arthroscopy. American Academy of Orthopaedic Surgeons (OrthoInfo), n.d.. orthoinfo.org
- Surgical interventions (microfracture, drilling, mosaicplasty, and allograft transplantation) for treating isolated cartilage defects of the knee in adults. Cochrane Database of Systematic Reviews (Gracitelli GC, et al.), 2016. pubmed.ncbi.nlm.nih.gov
- Autologous chondrocyte implantation for treating symptomatic articular cartilage defects of the knee (TA477). National Institute for Health and Care Excellence (NICE), 2017. nice.org.uk
- Effects of glucosamine, chondroitin, or placebo in patients with osteoarthritis of hip or knee: network meta-analysis. BMJ (Wandel S, et al.), 2010. pubmed.ncbi.nlm.nih.gov
- Knee pain. NHS (nhs.uk), 2023. nhs.uk
This article is general information and does not replace an examination or imaging. If you have symptoms, see a doctor.
More in this area
- Anterior cruciate ligament tear: is surgery always needed?
- Baker's cyst: what causes a swelling behind the knee and how does it settle?
- Knee injections: what do cortisone, hyaluronic acid, PRP and stem cells do?
- Knee osteoarthritis: exercise, weight, injections and replacement, what and when?
- Knee pain: what causes it, what helps and who should you see?
- Knee replacement surgery: who is it for and what is recovery like?
- Meniscus tear: exercise or arthroscopy?
- Kneecap pain and chondromalacia patella: what causes it and how does it settle?