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The meniscii (singular meniscus) are semicircular fibrocartilaginous structures around the circumference of the tibial condyles. They help in distributing the stresses on the joint, act as secondary stabilizing structures and help in nutrition of the articular cartilage. The meniscus covers a large portion of the articular surface – 30 percent on the medial side and 50 percent or more on the lateral side. The meniscus is under tension (like a stretched rubber band) when the leg is bearing weight. Any disruption in the continuity of its circumference results in loss of the tension (hoop stress) and makes the meniscus non-functional, i.e., it can no longer act as a shock-absorber. Only the outer third of the meniscus has blood supply (red zone). The inner two-thirds of the meniscus (white zone) derives its nutrition by diffusion. A tear in the outer third has potential to heal. Meniscal tears in the inner two-thirds have poor ability to heal.
Damage to the meniscii can occur from twisting injuries, especially when the weight of the body is on that leg. About one-third of the meniscal tears are associated with injury to the ligaments (most commonly ACL).
The meniscus can also get worn out with age. This is more likely when there is mal-alignment in the knee: bowleg (varus) or knock-knee (valgus) deformity.
Meniscal damage and degeneration results in increased load on the joint surface (hyaline cartilage) and accelerates its wear. Eventually, this leads to osteo-arthritis of the knee.
Meniscal tears in older patients often occur as a part of osteoarthritis. This is associated with degeneration of the hyaline cartilage and bowleg deformity. In these cases, arthritis is the primary problem and meniscal damage is secondary. Treatment must be directed towards meniscus as well as the underlying arthritis.
- Meniscal tears can be vertical (with or without bucket-handle displacement), horizontal, complex or radial, depending on the plane of the tear.
- Meniscus root tear is a special type of tear which occurs at or near the attachment of the meniscus. This particular type of tear (and also, a radial tear) makes the meniscus non-functional because it is displaced from its anatomic position. This type of tear can occur in young patients as a result of injury. It can also occur in older patients who have knee arthritis with bowleg deformity.
- Pain: This is usually a sharp stabbing or a catch that occurs in a certain position of the knee. It can be reproduced by the surgeon during physical examination (McMurray’s test).
- Locking: Inability to fully straighten the knee is called locking. This happens when a portion of the meniscus gets caught between the articular surfaces of the joint. Attempting to straighten causes severe exacerbation of the pain.
- Swelling: This occurs due to fluid accumulation after any episode of locking.
- Instability: Rarely, a large meniscal tear can cause loss of confidence or giving way (buckling) of the knee.
- Para-meniscal cyst: These are fluid-filled swellings that occur as a result of a horizontal meniscal tear.
TREATMENT OF MENISCAL TEARS
- Associated ligament injury: It is very important to address associated ligament instabilities; otherwise meniscal injury can recur.
- Any deformity in the knee denotes that the meniscal tear is most likely secondary to arthritis (which is the primary problem). In this case, treating the meniscus alone will give only temporary relief.
- Horizontal and complex tears: These tears are difficult to repair. They are trimmed to remove any unstable portions of the torn meniscus (meniscal balancing). Horizontal tears associated with parameniscal cysts need adequate removal in order to decompress the cyst.
- Vertical tears: Tears in the outer third have ability to heal and hence are amenable to repair. Small tears without unstable segments can be left alone. Larger tears need repair. The torn portion should be healthy, easily reducible and free from distortion. Any associated ligament instability should be treated at the same time. Tears in the inner two-thirds (white-on-white) and those with fraying and softening or distortion of the meniscus are excised
- Root tears: When there is no underlying arthritis or deformity, repair of root tears gives excellent results.
A variety of techniques are used to repair torn menisci. A large number of repair devices are available for performing meniscal repair.
This is done in carefully selected young patients with total or near total loss of meniscus – as this can lead to rapid degeneration of the articular cartilage. In this procedure, meniscus from a cadaveric source (allograft) is implanted in the place of the original meniscus. Any ligament instability and mal-alignment of the knee must also be addressed for a successful result.
In this procedure an implant made of collagen or other matrix is used instead of cadaveric meniscus. The criteria for case selection and the technical considerations are the same as for cadaveric graft. Early results are satisfactory; long term results are awaited
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