The knee contains a medial and a lateral meniscus. The function of the menisci are to even out joint forces and distribute them throughout the knee by acting as shock absorbers. The medial mensicus also takes on the role as a restraint to anterior tibial translation (tibia moving forward in relation to the femur) in a knee that does not have a functional anterior cruciate ligament. The medial meniscus can be torn acutely or chronically.
Types of Tears
There are six different types of tears. The vertical longitudinal tear is common and usually associated with anterior cruciate ligament, or ACL, tears. The bucket-handle tear will often flip over itself and fill up the central cavity of the articulating joint space. A radial tear refers to an injury that starts centrally and extends peripherally. Flap tears begin as a radial tear, but extend circumferentially. These cause locking symptoms. A horizontal cleavage injury is frequently associated with older individuals and has a strong association with meniscal cysts. A complex tear contains more than one type of tear.
Symptoms
Patients with symptomatic tears will often complain of joint line tenderness over the torn meniscus. The other common site of tenderness is in the posterior knee. An acute tear is often accompanied by an effusion that develops over a few hours rather than immediately. Chronic tears can have intermittent effusions and tenderness. Patients' knees can exhibit the sensations of "giving out" or "locking up." Another common complaint is decreased range of motion.
Overall meniscal tears are not common in very young children. Adolescent and young adult meniscal injuries are typically due to a trauma, while older adults can have either traumatic or chronic degeneration leading to meniscal tears.
Identification
A physician will typically perform a full knee exam. The basics of any knee exam include visually inspecting the knee and looking for deformities or fluid. The physician will then palpate important structures. Specific to the medial meniscus will be the medial joint line. The next step is to test the range of motion and strength in all movement planes.
Imaging Studies
A plain X-ray of the knee will not show the clinician a meniscal tear, however an X-ray is necessary to evaluate for bony anatomy. Weight bearing views of the knee can help evaluate for osteoarthritis. Osteoarthritis is often closely associated with meniscal injuries.
An MRI is the best imaging study to show the meniscal injury. Radiologists can determine if there is a meniscal tear based on changes in the MRI signal within the mensicus that reach an articulating surface. According to University of Wisconsin researcher Arthur A. De Smet and his collaborators in a study published in the Feb. 1, 2008, edition of the "American Journal of Roentgenology," the longitudinal type of tear has the most common incidence of false-positive diagnosis of the medial meniscal tears on MRI.
Treatment
Treatment is either nonsurgical or surgical. Asymptomatic tears found incidentally on MRI do not need to be repaired. Small tears, partial tears, and degenerative tears can be treated non-operatively. Nonsurgical treatments include rest, non-steroidal anti-inflammatories (NSAIDs), such as acetaminophen or ibuprofen, and physical therapy.
Surgical treatment can be done either open or arthroscopically. Some meniscal tears can be repaired, while others are debrided--cleaned up. Debridement of a meniscus is referred to as a partial meniscectomy. Some patients will require a meniscal transplant if they fail a partial or total meniscectomy.
References
- "AAOS Comprehensive Orthopaedic Review"; Jay Lieberman; 2009.
- "Current diagnosis and treatment in orthopaedics"; Harry Skinner; 2006.
- American Academy of Orthopaedic Surgeons: Meniscal Tears
- "American Journal of Roentgenology": Clinical and MRI findings of meniscal tears
