Updated June 25, 2015.
A discoid lateral meniscus is an abnormally shaped meniscus within the knee joint. The meniscus is a C-shaped wedge of cartilage that helps support and cushion the knee joint. In each knee there are two menisci, one on the inside (medial) and one on the outside (lateral) of the knee joint. In some people the lateral meniscus is shaped more like a solid disc rather than the normal C-shape.
Most people with a discoid meniscus never know they have an abnormality.
 It is estimated that between 3-5% of people have a discoid lateral meniscus. Most people live normal, active lives with a discoid meniscus--even high performance athletes. Therefore, if your doctor finds that you have a discoid meniscus, but it is not causing any problem, it should be left alone. For example, sometimes during a knee arthroscopy a discoid meniscus is seen when a different problem is being treated--these should be simply left alone, not treated surgically.
The two most common reasons people find they have a discoid meniscus are that they have an MRI that shows the abnormality, or they are having an arthroscopic knee surgery and are found at that time to have the discoid meniscus. Again, in both of these scenarios, the discoid lateral meniscus is best left alone.
Symptoms of A Problematic Discoid Menicus
In some people, the discoid meniscus can cause problems, usually a popping sensation with pain over the outside part of the knee joint. This is why some people use the phrase 'popping knee syndrome' when talking about a discoid meniscus.
 Signs of a discoid meniscus can include:
- Popping of the knee
- Knee swelling
- Pain along the outer side of the knee
- Pain with squatting/kneeling
Diagnosis of the discoid meniscus is typically made when looking at an MRI of the knee. The normal meniscus contours are absent, and more meniscus tissue than normal is seen on the MRI. If there is a tear in the discoid meniscus, that is typically seen on the MRI as well.Â
Treatment of a Discoid Meniscus
If patients are found to have a discoid meniscus, but it is not causing symptoms, no treatment should be performed.
In patients with a painful discoid meniscus, simple treatments consisting of knee exercises and stretching can be performed. Anti-inflammatory medications or a cortisone shot may be considered.
If these simple treatments do not relieve the symptoms, patients may choose arthroscopic surgery for the discoid meniscus. If the discoid meniscus is torn, the torn portion can be removed. In addition, the discoid meniscus can be surgically shaped into a normal appearing meniscus.
Recovery from surgical treatment of a discoid meniscus is about 6 weeks to regain full strength and mobility of the joint. Most patients require no immobilization, and limited restrictions of weight-bearing. It is common for individuals who have surgery to perform physical therapy, and avoid impact exercise activities while recovering from the surgical procedure.Â
While there is no evidence to show that patients with a discoid meniscus have any higher chance of developing knee arthritis later in life, there is evidence that patients who tear their meniscus can have longer term problems. Any patient who sustains a meniscus tear should take steps to help prevent any progression of arthritis in their knee joints.
Sources:
Jordan MR. "Lateral Meniscal Variants: Evaluation and Treatment" J Am Acad Orthop Surg July 1996 ; 4:191-200.