In each knee, there is a medial and lateral meniscus attached to the proximal tibia that accepts the femoral condyles. The shape and composition of the menisci serve to increase the surface area of contact at the tibiofemoral joint. On the medial side, the meniscus is oval-shaped and attaches to the capsule and medial collateral ligament. On the lateral side, the meniscus is more circular and attaches to the lateral capsule. The cusp-like form of the meniscus conforms to the convex shape of the appropriate femoral condyle. Due to the structural makeup of the meniscus, compression during weight-bearing activities is absorbed via circumferential tension (hoop stress) and allows the meniscus to deform peripherally. By increasing the surface area, there is a resultant decrease in stress on both the tibia and femur. Each meniscus is anchored to the intercondylar area at the anterior and posterior horns. The peripheral aspects of each meniscus adheres to the tibial plateau and capsule via coronary ligaments, and an anterior transverse ligament connects to two menisci. With the loose attachments of the meniscus to the knee, significant movement is permitted by each meniscus. According to Neumann, the quadriceps and semimembranosus muscles attach to both menisci, while the popliteus muscle attaches to the lateral meniscus only. These muscular attachments can aid in stabilizing the relatively loose menisci during knee motion, but also can put too much stress on the meniscus during recovery from surgery. The menisci are also important for guiding arthrokinematic motion, proprioception, lubricating the articular cartilage, and stabilizing the knee.
The mechanism of injury can often be useful in diagnosing the pathology. In traumatic cases, the meniscus is often torn by twisting of the femur on a flexed knee and fixed tibia. Due to the proximity of the menisci to other structures of the knee (MCL, ACL, etc.), common mechanisms of injury, such as a valgus collapse, can injure the meniscus as well (remember the medial meniscus attaches to the MCL). Patients often complain of having "twisted" their knee, hearing a "pop," joint line pain that is increased during weight-bearing, and possibly having the joint lock in place. It is widely accepted that the medial meniscus is torn more frequently than the lateral, however, one of the studies we looked at stated that the opposite might be true. Meniscal tears are commonly associated with ACL injuries. During an ACL rupture as a result of a valgus collapse, it is the lateral meniscus that has been found to be torn more frequently due to the compression forces between the tibia and femur. The medial meniscus is found to be torn more frequently in the chronic ACL-deficient knees as a result of repetitive translation of the tibiofemoral joint. In the acute cases, we may or may not see joint effusion and a flexed-knee gait pattern. Patients may be unable to achieve full extension, due to a block caused by a meniscal tear. When the mechanism of injury is not clear, or in non-traumatic cases, we as clinicians have many options to assess the integrity of the menisci. The McMurray Test is used commonly when assessing the menisci, but due to its low diagnostic accuracy, should only be used when clustered with other tests (pain with flexion overpressure, pain with extension overpressure, joint line tenderness, and a hx of locking - check out the knee homepage for the criteria!). Another special test, the Thessaly Test, has very good diagnostic accuracy. As far as imaging goes, MRIs are commonly used with a contrast to identify meniscal tears, but do not always visualize well enough to be certain. Arthrograms are a cheaper option, but are not as sensitive and specific as an MRI. An arthroscopy can increase certainty with direct visualization.
There are many factors that should come into consideration when addressing a meniscal injury in an individual. One of the most important ones is age. The standard meniscus has good blood supply to the peripheral 1/3, decent blood supply to the middle 1/3, and poor blood supply to the central 1/3. Obviously, the blood supply can translate into ability to regenerate. When we are younger (especially the skeletally immature), there is increased vascularity throughout the entire meniscus, which translates into an even higher potential for regeneration. With this knowledge, it is widely accepted that adolescents will have a surgical procedure for a meniscal repair. In a study on young athletes, meniscal repairs had good results for peripheral and central tears. The study used the "inside-out" technique that has shown significant success. Another factor that comes into play is whether or not an ACL reconstruction occurred at the same time. Many studies have shown that individuals who simultaneously had their ACL reconstructed and a meniscal repair had better results. The theory is that the hemarthrosis created by the ACL reconstruction aided in healing factors for the meniscus. Studies have also shown that the risk for retearing the meniscus is higher when located centrally, where there is poorer blood supply. Stability of the knee can play a role in the likelihood of retearing the meniscus as well. In an unstable knee, additional arthrokinematic motion can occur; thus, additional stress can be placed on the meniscus. A large contributing factor to potential for repair is the type of tear i.e. bucket-handle, longitudinal, radial, etc. The issue is that this cannot be identified without direct visualization. Tears like a bucket-handle often are partially removed instead of repaired, due to the destruction of the collagen tension lines. Another important note is that these factors can play a role in the pace of the rehab program. With characteristics that are shown to have increased healing rates, a more aggressive rehab protocol can be utilized.
In the adult population, since repairs are less likely to be successful, a partial meniscectomy is often preferred over a total meniscectomy. In the past, total meniscectomies were performed frequently without concern; however, over time a link has been shown between those who had their entire meniscus removed and the development of osteoarthritis. As the understanding of the importance of the menisci increased, we learned how the menisci were responsible for decreasing the stress placed on the articular cartilage and bone. As a result of this finding, surgical procedures were adjusted to try and preserve the meniscus as much as possible, which led to thedevelopment of the partial meniscectomy. In those who choose to still pursue a complete meniscectomy, it has been shown that adherence to an exercise program can delay or reduce the risk of developing OA. One of the major correlations for developing OA is reduced thigh muscle strength. It is known that an exercise program can reduce this risk factor. In a partial meniscectomy, the tear is often removed and the remaining meniscus is smoothed out, so that any fraying cannot lead to another tear. In elderly individuals, where degeneration injuries are more common, studies have shown an initial bout of conservative therapy (physical therapy) can often delay or sometimes eliminate the need for a partial meniscectomy, however, this is a debatable topic where further research is needed. One study in particular found that in an exercise group vs. an arthroscopic partial meniscectomy + exercise group, no difference was found in results. It should be noted that the participants only had non-traumatic meniscal injuries.
In the athletic population, some athletes have the option of returning to sport to finish the season, while having the meniscal tear remain. This could delay surgery until the season is finished. However, if the athlete was unable to withstand the symptoms, surgery could be utilized. The article did not discuss if conservative therapy was used during the season to try and alleviate symptoms. An important consideration is the time period between injury occurrence and surgical procedure. An article found that better results were achieved if the repair occurred within 8 weeks of injury for traumatic meniscal injuries. The longer the tear was present, the more likely OA developed.
As far as rehabilitation of individuals following meniscal repairs goes, PTs are often found following the protocol of the surgeon in a step-by-step process. As expected, there is a wide variety of both conservative and accelerated programs that can vary from 10 weeks to 7 months for return to sports. Research is underway that will hopefully aid in determinig the appropriate speed of a rehab program. A study on animal meniscal repairs found that 80% of the tensile strength was achieved after 12 weeks. Variable factors include whether or not an immobilization period is used (and how long that phase is), weight-bearing restrictions, ROM limitations based on time from surgery, concomitant surgeries such as ACL reconstruction can influence the rehab protocol, and of course activities that stress the meniscal repair more forcefully. One study showed that prolonged immobilization is linked to decreased collagen content. It is interesting to note that it is not necessarily the weight-bearing element that stresses the meniscus, but the combination of weight-bearing with gliding of the tibio-femoral joint and of course rotation of the knee.
As physical therapists we work on treating the patients' impairments, such as flexibility, strength deficits (especially the quads), and tasks that involve a high level of balance and neuromuscular coordination. Sport-specific training is included, when appropriate. An additional method of treatment that should be considered is the use of aquatic therapy. Aquatic therapy has been used in accelerated ACL rehab programs with success and could find benefit with meniscal repairs as well. The pool environment addresses the concern of weight-bearing and stress put on the repair. More advanced exercises can potentially be implemented earlier in the pool due to that decrease in stress. Something to consider, however, is the resistance put on hamstrings, due to their attachment to the menisci. Be sure to know any limitations the surgeon has on hamstring activity before using the pool.
Some more experimental methods are out there to try and facilitate meniscal repair. The fibrin clot is a procedure where a fibrin clot matrix is injected into the meniscal tear to promote normal healing processes. While the meniscus was repaired, it was unable to resist the stresses that a normal, healthy meniscus can withstand, so the additional healing factors can potentially improve the process. Another procedure being explored is vascular access channels. As the name might explain, tunnels are created to connect the vascular areas of the meniscus to the avascular areas that are damaged in order to try and redirect the healing nutrients to the injured site. This method has had positive results in the initial studies and could potentially be useful for particular cases! Synovial abrasion is a process that involves surgical irritation of the synovial lining of the knee. The purpose is to have the healing cells from the synovium aid in healing the damaged meniscus. This technique is used frequently during surgeries.
Many researchers are also trying to develop working meniscal transplants. Right now there are various methods of transplants for a meniscus: fresh allografts, deep-frozen allografts, cryopreserved allografts, and freeze-dried allografts. Of the four listed there, the fresh allografts and cryopreserved allografts provided the best potential results, but the long-term outcomes are still unknown. On a related topic, researchers are also looking at constructing collagen scaffolds that can provide the characteristics necessary for fibrochondrocyte ingrowth that could lead to meniscal regeneration. Something to look out for in the future!
A recent study utilized a treatment known as AposTherapy for individuals with degenerative meniscal injuries and potential development of OA. The researchers analyzed the gait of the participants. Each individual was then given shoes that had an element placed on the hindfoot and an element placed on the forefoot (customized following the results of the gait analysis) that were designed to alter the gait of the individual. Participants gradually built up tolerance wearing the devices each day. After 12 months, significant changes were noted in the participants' gait patterns, especially increased gait speed, SLS, and step length. When further research is done, this could be an interesting treatment option to delay the need for surgical intervention and could be useful for treating those at risk for developing OA as well.
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