The meniscus is a type of cartilage cushion in the knee that protects the true joint cartilage from injury as the thigh bone moves over the top of the leg bone. There are actually two menisci in your knee, one is on the inner (medial) side of the knee and the other is on the outer (lateral) side of the knee. The meniscus is C-shaped and has a wedged profile that allows it to conform to the shape of the thigh bone. The lateral meniscus is known to have a congenital variant known as a discoid meniscus — it is shaped like a hockey puck, rather than being the normal C-shape.
Many people have a discoid meniscus and do not even know it. These abnormally shaped menisci can be prone to tearing. The most common mechanism of a tear is when the knee joint is bent and then twisted.
Symptoms of a torn discoid lateral meniscus include:
- Pain along the lateral joint line of the knee.
- Swelling that starts a few hours after the injury.
- Mechanical symptoms include joint locking or the inability to completely straighten the knee.
- Popping or clicking within the knee.
A physical exam of the knee will often diagnosis a meniscus tear. An X-ray should be done to make sure that there is no bone fracture. An MRI should then be done to confirm the physical exam findings and make sure that there are no associated injuries.
Treatment of a discoid meniscus tear requires surgery. First, the central portion of the discoid meniscus is removed (saucerized) to create a C-shaped meniscus. This process will often remove the torn portion of the meniscus; but if not, then the remaining meniscus can be treated like a regular meniscus tear. If the tear can be repaired, then it should be fixed. If the tear is not fixable, then the torn portion may be removed back to stable edges to prevent propagation of the tear and any further injury to the overlying cartilage. If a repair is performed, then physical therapy will be necessary for three months before returning to sports.