The Menisci (plural of Meniscus) are pads between the bones at the joint. Menisci function in joint stability, shock absorption, load sharing and transmission of force, and in nutrition and lubrication of articular cartilage. The meniscus is often damaged at the time of a ligament injury. It's important to understand that after a ligament injury the meniscus is vulnerable to further damage because of the instability of the stifle. Maintaining proper restriction during recovery by avoiding all stressful actions like running & jumping will minimize the risk of further meniscal injury as well as providing the best conditions for the re-stabilization of the stifle and healing of any meniscal injuries that occurred at the time of the original ligament damage.
Is "Repair" of the Meniscus Being Advised Based on Noises From the Joint?
It is common for clicking & popping noises to develop in the joints after a joint injury. These noises have several different possible causes. The noises themselves are not necessarily an indication that there is meniscal injury, nor are these noises necessarily an indication that surgery is appropriate. But some surgeons will tell people that noises like this doubtlessly indicate a damaged meniscus and this means surgery is necessary. This is not true. Surgeons may say to clients that a surgical procedure is needed to "repair" the damaged meniscus. But in truth it is rare for any sort of repair to be attempted. The surgery that is contemplated is almost certainly a removal of all or part of the meniscus. Removal of all or part of the meniscus will inevitably result in greater arthritic changes in the joint in future. Therefore surgery to remove all or part of the meniscus should be done only reluctantly when symptoms like pain & locking up of the joint indicate meniscus damage which truly requires surgical excision. Noises from the joints of dogs who are otherwise functioning and recovering from ligament injury do not indicate surgery to remove meniscus tissue is appropriate.
Understanding the Meniscus
---- The menisci are 'fibrocartilaginous' structures which can be thought of as spongy elastic pads between the bones at the joint, composed predominately of collagen and open space filled with joint fluid.
---- The menisci contribute significantly to joint lubrication. The fluid of the joint moves through the porous structure of the menisci. Because 70+% of the total weight of menisci is fluid, normal movement causes compression of the menisci which squeezes fluid out from them into the joint space to allow smoother gliding of the joint surfaces. The menisci re-expand when the pressure is reduced, drawing in fluid. This pumping action also helps to distribute synovial fluid throughout the joint and aids in the nutrition of the articular cartilage.
---- By compressing under a load, the menisci also act as shock absorbers, absorbing energy and reducing the shock to the adjacent cartilage and subchondral bone.
---- The menisci protect the cartilage by acting as buffers between the surfaces of the femur and tibia where they meet and move against each other at the joint. The menisci transmit forces across the knee joint. The menisci provide added mechanical stability to the normal gliding of the femur on the tibia by deepening the surface of the tibial plateau to increase the congruity between the femoral condyles and the tibial plateau.
Diagnosing Meniscal Damage in Dogs With Ligament Injury:
The clinical diagnosis of meniscal tears becomes more difficult and unreliable in the presence of ligament injuries. Specificity also decreases because of the likely presence of tibial and femoral bone bruises that frequently accompany acute ligament tears. Pain from these bone injuries can cause joint-line tenderness, a finding that otherwise suggests the presence of a meniscal tear.
The Importance of Preserving the Meniscus
When there is a joint injury like a ligament rupture, it is important to preserve the menisci to the greatest extent possible. Loss of all or part of a stifle's meniscus has the potential to accelerate the breakdown of articular cartilage with resultant DJD (Degenerative Joint Disease). The more of the meniscus that is lost through injury or through surgical removal, the less competent the joint will be in future and the greater the potential for DJD. The risk of further damage to the menisci is minimized by greatly reducing activity after ligament injury while the dog's body re-establishes stability in the joint.
Whether or not your dog has surgery to temporarily stabilize the joint after ligament rupture, long term joint health is best assured by careful restriction during a slow return to normal activity over a period of at least several months, and by avoiding unnecessary surgical removal of all or part of the meniscus.
People are sometimes told that their dog's meniscus is damaged and that the meniscus cannot heal on its own therefore surgery is always required for meniscal injury. It is NOT true that surgery is always necessary. Whether or not surgery is best depends on the particular injury. Because there are many vets who are too quick to surgically remove a meniscus unnecessarily, you should be wary of accepting a vet's recommendation for surgery without careful consideration. Less severe meniscal injuries can heal without surgery.
---- Two methods are used by the body to repair meniscal damage:
1) Extrinsic --- Once a meniscal tear occurs, a fibrin clot forms within its margins, creating a scaffold into which angiogenesis develops from the perimeniscal capillary plexus. The fibrin clot contains factors, such as platelet-derived growth factor and fibronectin, that act as chemotactic and mitogenic agents for reparative cells to migrate and develop. Undifferentiated mesenchymal cells also migrate into the clot and a fibrovascular scar develops, gradually sealing the lesion. Further inflammatory response and angiogenesis result in healing of the lesion in about 10 weeks in the dog. It may take months or even years for the scar tissue to change into fibrocartilage, resembling that of the meniscus. Differences between the newly formed fibrocartilage and mature fibrocartilage are recognizable and include increased cellularity and, at times, increased vascularity in the repair tissue.
2) Intrinsic --- The chondrocytes within the meniscus have an inherent capability to generate a healing response, even in the avascular region. Chondrocytes are assisted by the fibrin clot, which not only acts as a scaffold, but also provides the chemotactic and mitogenic stimuli to promote healing.
Is Inappropriate Meniscal Surgery Often Recommended & Done?
In my opinion there are many vet surgeons out there who are much too quick to carve off parts of a damaged meniscus when the dog would be far better off with the joint left alone to recover using its own resources.
The history of surgical intervention is instructive. The menisci are now known to play an important role in the complex biomechanisms of the knee. But just a few decades ago doctors believed the menisci were functionless tissue that could be removed without consequence. Surgeons routinely removed the entire meniscus if there was any indication that it was even slightly damaged or for no reason simply as part of their standard procedure when doing any stifle surgery. In time this resulted in crippled dogs (and people) as Degenerative Joint Disease developed in the joints. Eventually the more observant doctors woke up to the fact that the menisci were important joint components, and in recent years the more enlightened surgeons have become less aggressive in removing all or part of the meniscus. But there are still many vet surgeons who cut far too much of a meniscus away. Some of these guys just can't stop themselves from getting in there and excising something. In the course of my research, when I talked with surgeons about their approach to dealing with an injured meniscus, I often heard "When In Doubt, Cut It Out" as a rule-of thumb they used. They won't usually tell clients that of course.
---- The history of surgery in general is filled with examples like this of too-aggressive surgical intervention. Never be too trusting of a surgeon. They became surgeons to cut; not to tell you no cutting is needed.
---- However, sometimes surgery to remove part of the meniscus is best. If your dog has on-going pain and is not improving, or the joint locks up, surgery may be required. I want to caution you that unneeded surgery may be recommended by some vets, but not leave you with the impression that the meniscus never requires surgical intervention.
Surgeons often do something they call "Meniscus Release" along with ligament injury surgery. 'Meniscus Release' (aka 'Meniscal Release') cuts the connection of part of the meniscus, removing it from what would be its functional position in a normal joint. This decreases the risk of injury to the meniscus at the cost of removing the meniscus from being a functioning part of the joint. 'Meniscus Release' has been found to be a factor in Degenerative Joint Disease. Should we be surprised when major alterations in complex structures bring with them unexpected problems?
"...recent studies done in Germany have suggested that meniscal release may be ineffective at reducing the incidence of late meniscal tears, and moreover, may, like a spontaneous meniscal injury, actually result in increased arthrosis in the knee. This remains a controversial area and some surgeons are now abandoning the practice..."
---TPLO advocate J.M. Fingeroth, DVM, DACVS
"...The purpose of the meniscal release is to allow the caudal horn of the medial meniscus to move away from the medial femoral condyle during cranial tibial translation, preventing meniscal impingement. Although meniscal release appears to be effective in reducing the rate of postliminary [after surgery] meniscal tears, it has the adverse affect of diminishing the load transmission and stability functions of the meniscus (Pozzi A, et al, 2006). Thus, the efficacy of meniscal release at diminishing the rate of postliminary meniscal tears must be weighed against its adverse effects on meniscal function when considering its use on clinical cases. ..." -- Michael P. Kowaleski DVM, DACVS
"...The meniscus both cushions the impact of the stifle on the tibia and to degree stabilises the stifle by limiting caudal movement of the femur on the tibia. Removing these functions by meniscal release must be a bad thing. Where the management of the cruciate deficient stifle is by some method of tibial plateau geometry altering technique, the stifle becomes stable only under load. The meniscus is therefore vulnerable to impingement between femur and tibia when under partial load or uncontrolled loading. It is presumed that damage, if not already present, will occur. [With meniscal release] The caudal horn is sectioned allowing it to move caudally, removing it from harm by the femur. The theory of meniscal release is based on the assumption that no meniscus being better than a damaged (painful) one...."
Beware of Short-Term Solutions
Since many surgeons tend to favor short-term solutions which do not consider long-term consequences, removing the meniscus or doing a meniscal release may look more like a good idea to these surgeons than it would to clients who expect their dogs to live at least several more years. A surgeon will cut away part or all of the meniscus, or do a meniscal release, and 6 months later the dog will have improved post-surgically and will not have had the risk of possible post-surgical injury to the meniscus. The surgeon calls avoiding that risk a good choice. But a year later arthritic changes will have started trouble in the joint which will worsen & worsen as time goes on. The meniscus is an important part of the joint. Removal of all or part of it, or 'release' of the meniscus sets the stage for inevitable future arthritic changes. Many surgeons are short-term thinkers. "The patient is better 6 months out" is success as far as they are concerned.
---- Of course there are exceptions to this surgeon sterotype I am presenting, but you should not assume that a surgeon is looking at your dog's treatment and future in the same way you are.
Meniscal injury may or may not need surgical intervention, but in making that decision it is wisest to be cautious and skeptical about recommendations you are given for meniscus removal. Don't just close your eyes and agree to whatever a surgeon recommends.
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