This post is about tears in different parts of the meniscus within the knee. If you’ve been diagnosed with a torn meniscus, your physician may have told you that it was a medial meniscus tear or a lateral tear. First we’ll discuss what these two variations in meniscus injury are, and then we’ll discuss research findings addressing whether tear location matters to how you’ll do after surgery.
Lateral Meniscus = Outside
This diagram shows a cross-section of a right knee. (For further information and more images you can also take a look at the meniscus surgery background.) The diagram is seen from above, looking down onto the shinbone (tibia). At the top of the diagram is the front of the knee (anterior), and the bottom of the diagram is the back (posterior). You can see that there are two crescent-shaped wedges of tissue. They act as shock absorbers in the knee between the tibia and the thigh (femur). The wedge on the left is the medial meniscus, located on the inner side of the knee. The medial meniscus is located toward the midline of the body. It is located on the inside of each knee, whether it’s the left leg or right leg. Toward the outside of each knee (right on diagram) is the lateral meniscus. You’ll notice the lateral meniscus looks somewhat more circular, while the medical meniscus looks C-shaped.
Clinical research suggests it’s more likely that an acute tear (i.e., from an injury) will occur in the medial meniscus, perhaps 55-60% of the time. 1, 2 Because of where various ligaments attach in the knee, the posterior part of the medial meniscus (in diagram, large section on lower left) is not able to move or rotate very much. This may explain why more injuries occur on the medial side, especially after an injury such as when the foot is planted, the thigh is rotated in, and a blow occurs on the outside of the knee. By comparison, the more circular lateral meniscus moves more freely. Degenerative tears are also more common on the medial side. Over one-third of meniscus tears occur in combination with an injury to ACL.3 When a meniscus tear occurs with an ACL injury, it is more likely that the lateral meniscus will be torn. 4
Does Tear Location Matter?
Lateral Meniscectomy May Mean Less Desirable Outcome
In 2010 a study was published in the American Journal of Sports Medicine entitled “A Systematic Review of Clinical Outcomes in Patients Undergoing Meniscectomy.” It was authored by researchers from the Department of Orthopaedic Surgery at Rush University Medical Center in Chicago and Department of Orthopaedic Surgery at the University of Michigan in Ann Arbor. The authors reviewed a wide variety of previous research to examine what variables significantly influence the outcome of meniscectomy procedures.
The review found that four of seven prior studies evaluating meniscectomy and osteoarthritis showed a higher rate of the development of osteoarthritis in lateral meniscectomy than for medial meniscectomy. At least this was true if examining x-ray evidence (e.g., narrowing of the joint space), but it did not always show up clinically for patients. Three of seven prior studies reached a different conclusion about osteoarthritis evidence on x-ray. However, moving to broader clinical outcomes such as knee function, activity level, or future instability, lateral meniscectomy was associated with poorer postoperative outcomes than medial meniscectomy.
What Does This Mean for Me?
If you have a lateral tear and decide to have partial meniscectomy, you are not by definition destined to have a bad surgery outcome with down-the-road osteoarthritis or weaker knee function. Similarly, if you have partial meniscectomy for a medial tear, you are not assured of a good outcome free from arthritis or other issues. Lateral meniscectomy simply has a stronger association less good outcomes. Consider this when making your own choice about getting surgery or not.
2 “Epidemiology of meniscal injury associated with ACL tears in young athletes”; CPT Kelly G. Kilcoyne, MD et al.; The Cutting Edge, OrthoSuperSite; March 2012
3 “The landscape of meniscal injuries”; Poehling GG, Ruch DS, Chabon SJ; Clinical Sports Medicine; 1990; 9(3):539–549
4 “Meniscus tears: treatment in the stable and unstable knee”; Belzer J, Cannon WD Jr.; Journal of the American Academy of Orthopaedic Surgery 1993; 1:41-7