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Knee News

Here's Something New on Medial Meniscus Tears

Every orthopedic condition has a cause, effect, and then usually, symptoms that help point to the underlying problem. Meniscal tears in the knee are no different. Trauma or the degenerative effects of aging (cause) can lead to flattening and pushing of the meniscus out of the joint space (effect). Movement of the meniscus out of the knee joint is called extrusion.

The menisci (plural for meniscus) sit between the femur (thigh bone) and the tibia (lower leg bone). The menisci are sometimes referred to as the cartilage of the knee, but they really aren't the same as the articular cartilage that covers the surface of the joint.

The two menisci of the knee work like a gasket to spread the force from the weight of the body over a larger area help the ligaments with stability of the knee. Without the menisci, any weight on the femur will be concentrated to one point on the tibia. But with the menisci, weight is spread out across the tibial surface.

Weight distribution by the menisci is important because it protects the articular cartilage on the ends of the bones from excessive forces. Without the menisci, the concentration of force into a small area on the articular cartilage can damage the surface, leading to degeneration over time.

In addition to protecting the articular cartilage, the menisci help the ligaments with stability of the knee. The menisci make the knee joint more stable by acting like a wedge set against the bottom of a car tire. The menisci are thicker around the outside, and this thickness helps keep the round femur from rolling off the edge of the flat tibia.

Without an intact, solidly attached meniscus, the knee joint space narrows down (result). Pressure from the two sides of the joint rubbing together cause bone spurs to form around the joint (result). Loss of the joint cartilage is another end-result of meniscal damage.

Eventually the person starts to notice pain, swelling, and problems with the knee (symptoms). Some even report a bone-on-bone sensation with walking or during other weight-bearing activities. That's when they seek the help of an orthopedic surgeon.

In this article, Dr. J. M. Marzo from the Department of Orthopaedics at the State University of New York (Buffalo, NY) reviews the importance of the meniscus to normal knee biomechanics. A particular focus of the article is a tear of the meniscus at the posterior horn. A complete tear or rupture of the posterior horn is called an avulsion.

The front portion of the meniscus is referred to as the anterior horn, the back portion is the posterior horn, and the middle section is the body. The posterior horn is an important anatomical feature. Without it, stress on the meniscus is enough to cause significant load on the joint. That's when the degenerative processes speed up.

How often does it happen that someone ends up with a posterior horn avulsion of the medial meniscus? It was once thought that this was a relatively uncommon injury. But with the availability of MRIs, doctors have documented a much higher incidence than previously thought. Up to 28 per cent of all medial meniscal tears involve the posterior horn. A large number of those (more than three-fourths) develop meniscal extrusion.

What can be done about this problem? Treatment often depends on the patient's age, intensity of symptoms (mild versus severe), and activity level. The goal is to protect the knee joint and prevent degenerative changes that end up as painful knee arthritis. For the older, less active adult, it may be possible to get by with some activity modifications, antiinflammatory drugs (or just pain relievers), and weight loss for those who are overweight.

When it looks like surgery might be needed, the patient has several options to choose from. If at all possible, the surgeon tries to save the meniscus. Repair is preferred over removal. The meniscus is no longer routinely removed but rather reattached whenever possible. Rehab after surgery is important so if a patient isn't willing (or able) to follow the surgeon's guidelines, then surgery may not be successful.

If it's not possible to repair the meniscus, then partial removal is considered. With complete removal of menisci that cannot be repaired, transplantation may be possible in a small, limited number of cases. Meniscal transplantation is referred to as a salvage procedure. The author did not say much more than that about transplantation.

But he did offer arthroscopic and MRI views of knees with degenerative medial meniscal detachment at the posterior horn. Diagrams and illustrations helped show how the surgeon can measure how much the meniscus has extruded (as seen on MRI scans). Dr. Marzo also provided his thoughts on the best way to perform surgery on patients with meniscal detachment. The goal is to restore the menisci's ability to absorb stress and still support normal knee biomechanics.


John M. Marzo, MD. Medical Meniscus Posterior Horn Avulsion. In Journal of the American Academy of Orthopaedic Surgeons. May 2009. Vol. 17. No. 5. Pp. 276-283.

05/28/2009

*Disclaimer:* The information contained herein is compiled from a variety of sources. It may not be complete or timely. It does not cover all diseases, physical conditions, ailments or treatments. The information should NOT be used in place of visit with your healthcare provider, nor should you disregard the advice of your health care provider because of any information you read in this topic.
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