The knee is one of the most stressed joints in our body due to our bipedal or upright stance and thus gait. It is a joint articulated by two of the longest lever arms in our body: the femur and tibia. For you physics minds out there, that equates to a high torque and pressure across this articulation. So what helps cushion this joint with all the compressive loading and torque that occurs in our daily life?
Part of the anatomical answer is our medial (inner) and lateral (outer) meniscal tissue. The main job of the meniscus is to help absorb shock and cushion our knee joints. The meniscal tissue is robust and thick early in life, but depending upon what you choose to do with your body, whether it be running, competitive sports, or vocation that requires repetitive squatting, bending or kneeling, you may hasten adverse changes in this all-important shock absorber. It is not surprising that the competitive athlete is more at risk of early arthritic changes of the knee some of which are related to meniscal tears. 
Meniscal tears can occur from pivoting/cutting over a fixed foot during an athletic event such as soccer or rugby or from trauma such as landing on a flexed or bent knee. "In the United States, arthroscopic partial menisectomy (removing part of the torn meniscal tissue) after a meniscal tear is the most frequent orthopedic surgical procedure." [2, 3] The problem with fixing the underlying tear surgically when the meniscus is resected or cut out is that it has been shown to increase the long-term risk of knee osteoarthritis (OA) four-fold. [3, 4, 5] Recent research in a multicenter, randomized, controlled study of 351 patients suggests physical therapy is comparable in results to surgery for meniscal tears.  Of these 351 patients, 70 percent that were assigned to the physical therapy group had a similar outcome to that in the group assigned to surgery at six months.  Based on these findings it seems prudent that individuals with similar findings should initially be managed with physical therapy. We are given one dose of cartilage to last a lifetime; we need to know how to better protect it and understand certain activities place us more at risk.
A recent study published this past June in the Journal of Orthopaedic and Sports Physical Therapy identified risk factors for meniscal tears in a systematic review of the literature.  In their study, they found strong evidence with the following factors placed individuals at greater risk of degenerative meniscal tears:
1) age greater than 60 years
2) males 3 times more at risk
3) work-related kneeling and squatting for greater than one hour a day
4) climbing 30 flights of stairs daily
5) waiting longer than a year to between an anterior cruciate ligament injury and reconstructive surgery -- found to be strong risk factor for medial meniscal tear, but not lateral meniscal tear
6) Body Mass Index (BMI) greater than 25 kg/m2
7) playing soccer or rugby (more for acute meniscal tears)
This study is an important guide to help us identify which risk factors we may be susceptible to given our lives. We can then try to modify how we are working, living, and exercising to help develop preventative strategies to offset the occurrence rate of meniscal tears.
1) Vad V, Hong H, Zazzali M et al. Exercise recommendations in athletes with early osteoarthritis of the knee. J Sports Med. 2002;32:729-739
2) Englund M, Guermazi A, Gale D et al. Incidental meniscal findings on knee MRI in middle-aged and elderly persons. N Engl J Med. 2008;359:1108-1115.
3) Snoeker B, Bakker E, Kegel C, Lucas C. Risk factors for meniscal tears: A systematic review including meta-analysis. J Orthop & Sports Phys Ther. 2013; 43:352-367.
4) Bakker P, Coggon D, Reading I, Barrett D, McLaren M, Cooper C. Sports injury, occupational physical activity, joint laxity, and meniscal damage. J Rheumatol. 2002;29:557-563.
5) Roos H, Laur'en M, Aldalberth T, Roos EM, Jonsson K, Lohmander LS. Knee osteoarthritis after meniscectomy: prevelance of radiographic changes after twenty-one years, compared with matched controls. Arthritis Rheum. 1998;41:687-693.
6) Katz J, BrophyR, Chaisson C et al. Surgery versus physical therapy for a meniscal tear and osteoarthritis. N Engl J Med. 2013; 368:1675-1684.
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