Why Do Meniscus Tears Cause Pain?
Steve A. Mora, MD
Why do meniscus tears cause pain and can some be treated without surgery?
It is not always easy predicting which tears will cause pain and which ones will not. I have seen very small tears be problematic enough that the patient elected to undergo a surgical procedure. I personally had a meniscus tear that remained painful for about 4 months before it stopped hurting. In my case I believe the pain was due to swelling and pain producing biological substances and not from a loose fragment irritating the joint. I was a lucky one that did not go on to have surgery. Here are a few reasons why we believe that some meniscus tears cause pain.
This information may help you make a decision on whether or not you should try waiting instead of having surgery.
Interestingly not all meniscus tears cause pain. Tears that recently occurred seem to be painful As time goes on they may hurt less. The tears that have unstable torn flaps usually cause pain. This is usually because the torn loose piece moves around the knee and irritates the surrounding structures. The torn fragments can move around the tight joint space leading to clicking, locking, swelling, catching and irritation. It is for this reason why arthroscopic trimming of the loose fragments may help. I liken this to a hang nail on a finger. The bigger the hang nail the more likely it catches and gets pulled. This is a similar occurrence with a meniscus. If your MRI shows a large flap or a piece of meniscus that has flipped on itself, it is probably going to keep hurting.
Meniscus tears also release inflammatory proteins or mediators which can lead to pain and some swelling. These pain producing proteins have been well studied. This is probably why even a small acute tear can hurt. Its probably also why anti inflammatory medications can help. I always remind my patients that the pain may be curtailed with medication but the tear might still remain. I follow this by saying as long as there is no catching or locking it is probably safe to wait and hope that the pain improves with time.
In some cases a meniscus tear causes a lot of swelling. This may be due to bleeding at the time of the initial tear or it may be from exuberant swelling. In this cases the pressure from the swelling pushes on the posterior neurological and soft tissue structures causing pain. Once again anti inflammatory medication and/or a steroid injections may help. In these cases swelling control is very important. I usually recommend resting, wrapping, stretching and waiting for the swelling to diminish. Once again if the MRI shows no obvious loose flaps and there is no catching or locking it might be safe to observe and wait for improvement.
Another possible reason for pain has to do with the joint surface experiencing a greater amount of force across the surface due to the meniscus not being able to cushion forces across the joint. Meniscus tears affect the pivotal function of the meniscus leading to altered force dissipation. The increased joint force leads to more pressure on the cartilage and subchondral bone leading to subchondral bone swelling and pain. This is usually seen when meniscus tears are concurrently present with osteoarthritis. This new understanding has led to the developement of a new procedure called sub chondroplasty. The subchondroplasty procedure is done by injection calcium in gel form into the swollen bone. In time the calcium solidifies and helps to support the bone under the meniscus tear and arthritis. This about this like adding rebar to concrete foundations. The rebar allows the concrete to accept a greater amount of force before cracking. because of this new approach to treating meniscus tears with arthritis I usually order an MRI even in cases where the X-Ray shows significant arthritis. If the MRI shows a lot of edema and if the meniscus tear was acute I may offer the patient arthroscopy for the meniscus tear, chondroplasty for the worn out cartilage and subchondroplasty for the bone edema. After surgery it is important that the knee be unloaded by using crutches for 6 weeks. These are very difficult cases to manage because the existance of arthritis makes the results less predictable.
When the meniscus tear is treated with arthroscopic partial meniscectomy, aka trimming, the loose torn fragments are removed. The normal meniscus tissue which is not torn is left alone. The torn meniscus does not regenerate; therefore, the torn area that gets trimmed will remain without meniscus tissue forever. There has been one recent study looking at the effects of adult stem cell treatment after arthroscopic meniscectomy (Vangsness et al). The researchers found that stem cells did not regenerate the torn meniscus but it did help with post operative recovery and pain. If a tear is repairable, sutures will be used to mend the tear. In rare cases the tear is so large that the removing the torn pieces with surgery does not relieve all the pain; or perhaps it relieves pain only for a short period. In these cases, the late development of pain is usually due to the increased pressure on the joint surface and future development of degeneration, a.k.a. arthritis. It is thought that the larger the meniscus tear, the greater the risk of developing post meniscus tear arthritis. It will however take a few years to develop arthritis following a large meniscus tear. Therefore it is important to know the details of the surgery so that you can take measures to slow the progress of the degeneration. This can be done by maintaining an optimal weight, focusing on flexibility of the joint (stretching), injection of Hyaluronate, unloading knee braces and avoiding high contact activities.
Fortunately the majority of meniscus tears respond successfully to arthroscopy partial meniscectory or repair. The take home message is that the smaller your tear the greater chance of not requiring surgery. In addition, if the tear is relatively small and there is no arthritis your chance of a good result is high.
About Steve A. Mora MD:
Dr. Mora is a native of Orange County. He graduated from Anaheim High School in Orange County CA. He completed his training at the UC Irvine where he finished in the top of his class earning the coveted AOA Medical Society honors. He completed his Orthopedic Surgery training USC where he was elected chief resident of his class. He completed an extra year of training with a Sports Medicine, Cartilage, Shoulder, Hip arthroscopy and Knee Fellowship at Santa Monica Orthopaedic and Sports Medical Group. He is currently practicing Orthopedic Surgery in Orange County at Restore Orthopedics and Spine Center.
Dr. Mora’s practice focus on Sports Trauma, Knee Arthroscopy, Shoulder Arthroscopy, Hip Arthroscopy, Elbow Arthroscopy, and Cartilage Restoration of the knee. He sees athletes of all levels including professional soccer players and UFC/MMA combat athletes.
He is team doctor for the Anaheim Bolts pro indoor soccer team and Foothill High School.
Dr. Mora’s family heritage is Peruvian. He speaks fluent Spanish.
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Restore Orthopedics and Spine Center
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