You have two different types of cartilage in your knee, leading to a lot of confusion when discussing cartilage injury:
- A surface covering (like in all of your moving joints) known as “articular” or “hyaline” cartilage which is tough and slippery, acting both as a shock absorber and allowing free movement of the joint.
- The cartilage pads (medial and lateral meniscus), which are thick, rubbery, C-shaped pieces made from fibrocartilage which also help to absorb impact, and also provide some stability to knee movement.
Articular cartilage and meniscus cartilage pad within the knee.
When articular (joint surface) cartilage wears away, or is damaged by trauma, this results in osteoarthritis (or “wear and tear” arthritis).
But a “torn cartilage” generally refers to damage to one of the cartilage pads – a meniscus tear. This can occur in isolation with an injury – usually an awkward twist whilst loading the joint, or standing from a crouch position when the meniscus is under most pressure. Alternatively, tears can occur without any injury as part as a process of wider knee joint degeneration (a “degenerative” tear).
Different types of meniscal tear.
Symptoms
An acute injury with a torn meniscus is painful. You may feel a pop or a tear as the knee twists, and it may be difficult to bear weight. The knee will swell gradually over 12-24 hours (NB much more rapid onset swelling would suggest a more severe injury – usually ACL rupture). Over a few days the acute pain and swelling will start to improve (rest, ice and anti-inflammatories will help), and with a physio-guided exercise programme many meniscal tears can settle over a period of weeks without ongoing problems.
But some patterns of tear cause more problems. If a section of torn meniscus cartilage displaces, it can either catch within the joint and cause locking (where the patient is briefly unable to move the knee) or giving way, or it can flip to the front of the knee like the handle of a bucket, in which case it becomes impossible to fully straighten the knee. These tears are more likely to require surgery, and if your knee won’t straighten, then this should be done urgently.
An experienced physio or knee surgeon will be able to determine a likely diagnosis of a torn meniscus by careful assessment (both of the story of the injury and subsequent symptoms, and a physical examination of the knee). As long as the knee is moving reasonably easily, and pain and swelling begin to settle, then scans are not generally needed at this stage as initial treatment will be with a physio-based exercise programme and gradual return to activities.
If symptoms do not settle in 2-3 months, or if a patient has locking or a block to full movement, then an MRI scan should be done which will show the tear and help a knee specialist to decide if surgery may be required.
MRI scan image which shows a displaced bucket-handle tear of one of the meniscus cartilage pads.
Surgery for a torn meniscus
The most common type of tear is a “degenerative” meniscal tear – typically in a patient aged over 50. Many of these will settle with appropriate non-operative management, but if pain persists, and if a scan shows that the rest of the knee is in a good state, then keyhole surgery can be considered to trim away the loose sections that may be causing persisting irritation. These type of tears are usually not repairable, and this operation is called an “arthroscopic partial meniscectomy” – normally done through two small (1cm) incisions, using a keyhole camera and specialist instruments to remove the torn cartilage edge. The first section of the video (link below) shows a degenerate tear being trimmed.
In younger patients, the meniscus has better potential to heal, so in teenagers and younger adults surgery may involve repairing rather than trimming the tear. This is usually possible with internal stitches inserted via one of the keyholes with a special device. The second section of this video shows me first assessing and then repairing a bucket handle meniscal tear in a teenager with a locked knee (the same patient as the MRI image above).
Meniscal tears that are sutured are slow to heal and need to be protected (usually in a brace) – it will be at least 3 months before this teenager is back to sports training.