The meniscus is a crescent-shaped section of fibrocartilage in the knee (the word is in fact derived from the original Greek word for 'crescent' – 'meniskos'). There are two of them ('menisci') in each knee – the lateral meniscus and the medial meniscus – and their role is twofold;
- To be a form of shock absorber for the knee joint when walking, running or jumping to prevent potential damage to the bones.
- To help maintain 'rotational stability' in the knee (along with the Anterior Cruciate Ligament).
Tears to the meniscus are relatively common.
The two main causes of meniscus tears are:
- High velocity traumatic twist of a slightly flexed knee – this most frequently occurs in certain sports where participants are often stopping and turning suddenly or pivoting (e.g. basketball, racquet sports, football, soccer).
- Meniscal degeneration – most commonly due to arthritis / weight / age.
Generally speaking, a traumatic injury to the meniscus results in immediate symptoms, whereas degeneration of the meniscus happens over time and symptoms come on more slowly. Common symptoms include:
- Swelling / stiffness in the knee joint.
- Pain (generally in the very middle of the knee joint).
- Clicking / popping sound from knee (often with accompanying pain).
- Problems with walking / straightening the leg / squatting.
Tests / Diagnosis
The main test used to diagnose meniscus problems is a form of physical examination known as the McMurray circumduction test, where the knee is moved into different positions to see if this results in any pain or if there is a click or pop (which indicates a meniscus tear).
Other tests involved in diagnosis of meniscus tears may include:
Even though the meniscus is fibrocartilage and not bone (and so will not appear on an x-ray), an x-ray will help in assessing whether there are any other issues affecting the bones in the knee which may either be fully responsible for the symptoms or are contributing to them.
A knee arthroscopy will allow direct visualisation of the knee joint and the menisci.
An MRI scan, unlike an x-ray, will show up whether there is a tear in the meniscus.
The precise location of the tear and the type of tear will determine whether a meniscus tear will heal on its own or will require surgery. The meniscus is divided into two 'zones' – an outer 'red zone' and inner 'white zone' – the red zone has a blood supply and the white zone does not. A tear in the red zone may heal on its own, whereas a tear in the white zone never will.
Physiotherapy can help in both cases – however, surgery may be required in either case, normally performed via knee arthroscopy. It is important to receive treatment for a torn meniscus, as if it is left untreated it may cause instability in the knee and promote the development of osteoarthritis in the knee.