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TREATMENTS

The traditional management of a torn meniscus most often involves some measure of surgical treatment, such as partial or total meniscectomy, meniscal repair, or meniscal transplant. There are an estimated 650,000 arthroscopic meniscal procedures and a total number of 850,000 meniscal surgeries performed in the United States every year.^1-3

The most aggressive surgical treatment is meniscectomy, which involves either complete or partial removal of the meniscus depending on the horizontal extent of the tear. Guided by arthroscopy, the damaged portion of the meniscus is surgically debrided and removed. In either operation, a peripheral rim of the meniscus must be kept to preserve any form of normal function within the knee. The decision of whether to remove all or part of the meniscus is based on the severity of the tear, the restriction of activity caused by the tear, and the age of the tear. Total meniscectomy is generally performed on the most severe and avascular tears which cannot be otherwise repaired.^{62, 63}

Short-term follow-up of meniscectomy has generated some positive results. For example, a meniscectomy can provide temporary pain relief in early stages following the operation, especially when an acute tear had caused excessive pain or popping preoperatively. Another immediate result may be a greater feeling of stability, if the tear had previously been a source of instability. On long-term follow-up, however, these initial improvements have rarely been shown to last.^63-65 Complete pain relief from meniscectomy is nearly unheard of after more than 10 years and, at that point, more complex issues including limited range of motion, radiographic degeneration, crepitation, and severe functional impairment have usually begun to surface. In many cases, a simple meniscus tear, if operated on, can become a career-ending injury.^63-66 In long-term follow-up studies, four to 14 years after a meniscectomy, nearly 50% of patients had to decrease or stop their typical sporting activities.^{63, 64} This included the adolescents who underwent total meniscectomy. The X-ray progression of the degenerative change paralleled the reduction in activity. Some 17 years after follow-up after total meniscectomy, the incidence of degenerative arthritis as documented by X-ray was 300% more likely in the knee that had the meniscectomy versus the nonoperated knee.⁶⁴

Joint instability is a common result of meniscectomy, which is not surprising considering that the meniscus is a primary stabilizing component of the knee. One of the principle reasons for meniscal operation is to improve joint stability, yet meniscectomy often appears to have the opposite effect, eliciting even more instability, crepitation, and degeneration than the injury produced prior to operation. This is why reoperation rates after meniscectomy can be as high as 29% to improve the joint instability that the meniscectomy caused.^65-67 A knee joint becomes unstable when ligaments, cartilages, or bone structures are weakened and unable to carry out the level of function of a healthy knee. Such is the case when the meniscus is removed from the knee and unable to perform the usual weight-bearing and tracking functions, placing additional stress on the rest of the knee.^{68, 69} Common physical symptoms of instability after meniscectomy are crepitation, such as cracking or popping, and locking in the joint. On radiographic examination, this postoperative deterioration of the joint is evidenced by narrowing of joint space and flattening of the tibiofemoral surfaces. Because the knee is a joint designed for rotational motion, the shape of the bone structures is a vital part of mobility, and when those rotational mechanisms are altered, proper motion is not possible, causing the crepitation in the joint. For example, one study following over 1,000 meniscectomy patients found that 10 to 20 years after the surgery, 27% had more crepitus in the knees which underwent meniscectomy than they had in the untreated knees.⁶⁶ In this same group of patients, degenerative changes ranging from flattened tibial and femoral bone surfaces to significant joint space narrowing were found in 62.5% of the patients with X-ray evaluation of their knees. These researchers concluded that there was a direct correlation between the degeneration of these tibiofemoral surfaces and complaints on clinical examination.⁶⁵ A similar study found that 10 years after undergoing meniscectomy, 65% of patients had radiographic evidence of joint space narrowing greater that 50%.⁶⁹

The greatest risk of partial and total meniscectomy is in the development of long term degenerative osteoarthritis. Numerous studies have confirmed that a large percentage of the meniscectomy population experience joint osteoarthritis later in life.^70-76 One study found that 15 to 22 years after having a meniscectomy, the odds ratio of knee degenerative arthritis was 2.6 after medial meniscectomy and 5.3 after lateral meniscectomy, using the non-operated knee as the control.⁷¹ In one study, 20 to 29 years after meniscectomy, X-rays showed 53% had significant progression of degenerative arthritis compared to 13% of the nonoperated knees.⁷² Another group of researchers found that 21 years after meniscectomy, 71% of operated knees showed signs of at least mild degeneration and 48% showed signs of moderate or severe joint degeneration.⁷⁴ Another study found that 40% of meniscectomies resulted in degenerative osteoarthritis, and many were accompanied by other injuries, including a large number of ligament tears.⁷⁵ One study noted, that “although risk factors for post-traumatic osteoarthritis are multifactorial, the primary risk factor that stood out in this study was if a meniscectomy had been performed.” In this study the risk of developing osteoarthritis in the knee after meniscectomy was 100%.⁷⁶

Biomechanically, the development of osteoarthritis can be explained, in part, by the increased stress placed on the tibia and femur post meniscectomy. It is a known fact that reducing the size of contact area on a surface increases pressure in the remaining area. Therefore, by removing all or part of the meniscus from the knee, the area through which weight is transmitted in the joint is reduced, thus increasing the pressure on both the tibia and the femur, and their articular cartilage. The amount of contact stress on the tibiofemoral joint can increase by 65% with only a 10% reduction in contact area, and this percentage increases in proportion to the amount of meniscus removed. Complete removal of the meniscus can increase contact stress by as much as 700%.^74-77 (See Figure 10.) What this means for any knee without a meniscus is that it now bears the pressure proportional to carrying seven extra people on one knee.

An additional aspect contributing to the acceleration of the osteoarthritic process is through structural wear of the articular cartilage. (See Figure 11.) By depriving the joint of the ability to lubricate the articular cartilage, the motion of the femur against the tibia will begin to break down the cartilage. When these articular cartilage cells, which are metabolically active, degenerate faster than they can regenerate, the result is the accelerated breakdown (degeneration) within the joint.⁷⁶ One study which followed rabbits in three-month intervals after varying levels of injury, found that the amount of cartilage damage sustained was greatest in the meniscectomy subjects, proving this treatment to be even more damaging than non-treatment.⁷⁷ Although osteoarthritis (OA) may have a reputation as a slowly developing disease only prevalent in the elderly, this is clearly not the case. Cartilage loss can develop from adolescent injuries and appear as early as a few years after a meniscectomy.^78-81 Precursors to OA, such as evidence of biological cartilage alterations, can appear in as little as three months post meniscectomy.^{82, 83} Because OA develops steadily with time, this can have devastating effects by just five to 10 years after the procedure. The articular cartilage in a knee deteriorates at an average rate of 4.1% per year after meniscectomy.⁸⁴ This rate is about twice the rate of normal cartilage loss with aging.⁸⁵ After OA forms, the articular cartilage continues to deteriorate in the knee joint at a rate of about four to five percent per year.^{86, 87}

Figure 10. Increase in joint contact stress versus percent of meniscus removed. As the percentage of meniscus removed during surgery increases, joint contract stress increases exponentially. Thus arthroscopic meniscectomy dramatically increases the incidence of future degenerative knee arthritis. Source: 1. Baratz ME, et al. Meniscal tears: the effect of meniscectomy and of repair on intraarticular contact areas and stress in the human knee. A preliminary report. Am J Sports Med. 1986;14:270-275. 2. Lee SJ, et al. Tibiofemoral contact mechanics after serial medial meniscectomies in the human cadaveric knee. Am J Sports Med. 2006;34(8):1334-1344.

Figure 11. Healthy knee joint with intact meniscus and degenerated knee joint without meniscus. The removal of part or all of the meniscus during arthroscopic surgery accelerates the degeneration of the articular cartilage.