Articular cartilage is made up of collagen, proteoglycans and water. It lines the end of the bones that meet to form a joint. The primary function of the articular cartilage is to provide a smooth gliding surface for joint motion. Articular cartilage glides against other articular cartilage with approximately five times less friction than rubbing ice on ice.
The meniscus cartilage in the knee includes a medial (inside) meniscus and a lateral (outside) meniscus. Together they are referred to as menisci. The menisci are wedge shaped, and are thinner toward the center of the knee and thicker toward the outside of the knee joint. This shape is very important to its function.
The primary function of the menisci is to improve load transmission. A relatively round femur sitting on a relatively flat tibia forms the knee joint. Without the mensci, the area of contact force between these two bones would be consolidated, increasing the contact stress by 235-335 percent. The wedge shape menisci increase this contact area significantly. The mensci also provide some shock absorption, lubrication and joint stability.
There are two categories of meniscal tears, acute traumatic tears and degenerative tears.
Degenerative tears occur most commonly in middle-aged people and take place when repetitive stresses severely weaken the meniscal tissue.
Degenerative tears are not caused by acute (current) trauma or injury, but may be more symptomatic following them. This process of tissue degeneration makes it very unlikely that a surgical repair will heal or that the surrounding meniscus will be strong enough to hold the sutures used to repair it. One report showed that less than 10 percent of meniscal tears occurring in patients greater than forty years of age are repairable, this may be due to structural and cellular changes that occur with age. The patterns of these tears are also much more difficult to repair than acute tears.
Symptoms of a degenerative meniscus tear include:
- Pain along the joint line
- Catching and locking
Degenerative meniscal tears are often associated with arthritis (degenerative joint disease). If the degenerative meniscal tear is creating catching or locking in the knee it most likely treated with arthroscopic excision of the torn fragment. The torn fragment may also be removed if it is thought that the compression of that fragment is causing pain.
A torn meniscus is a likely precursor to arthritis, whether it is removed or not, because the normal load distributing and shock absorbing capabilities of the meniscus are compromised by the tear/injury. Recent evidence has shown that removing degenerative meniscal tears in the absence of these mechanical symptoms will likely not create long term pain relief or prevent arthritis. One study compared non-surgical rehabilitation and arthroscopic resection of the torn meniscus and found no significant difference in pain relief or function 2 years after the diagnosis.
Acute Traumatic Tears
Acute traumatic tears occur most frequently in the athletic population as a result of a twisting injury to the knee when the foot is planted.
Symptoms of an acute meniscus tear include:
- Pain along the joint line
- Locking and a specific injury
Often times these tears can be diagnosed by taking a thorough history and completing a physical examination. An MRI may be used to assist in making the diagnosis.
If an athlete suffers a meniscal tear, the three options for treatment include:
- Non-operative rehabilitation
- Surgery to trim out the area of torn meniscus
- Surgery to repair (stitch together) the torn meniscus
The treatment chosen will depend on the location of the tear, the size of the tear, the athlete's sport, ligamentous stability of the knee, patient's age and any associated injury.2
The location of tear is important because the outer portion of the meniscus has a good blood supply whereas the inner portion has a very poor blood supply.
This blood supply provides the cellular elements and biochemical mediators that are essential for the repair to heal. Without an adequate blood supply, the area of torn meniscus will not have a high likelihood of healing even if it is surgically repaired. If the tear is amendable to repair, the surgeon will use sutures or meniscal fixation devices to approximate the tear and facilitate healing.
Unfortunately, not all meniscal tears are reparable. In those situations where extensive damage precludes an attempt at repair, total or near-total meniscectomy may be performed to relieve the pain and mechanical symptoms of a displaced tear.
There is an abundance of evidence that suggests significant meniscal resection (complete or near-complete) can lead to progressive degenerative arthritis leading to premature pain and functional loss. For these people, meniscal allograft replacement or transplantation may be a viable treatment alternative.
Studies have shown that the success of mensical transplantation is dependent on the underlying arthritis present at the time of surgery. For this reason this surgery is most appropriate for young patients who have suffered a very significant acute meniscal tear that is not able to be repaired.
Another factor that may affect the success of a meniscal transplantation is knee alignment. If a patient has a varus ("bow legged") or valgus ("knock knee") knee alignment the likelihood of success is less.
At the current time this surgery is intended to return patients to daily function and low impact sports. It is not recommended that patients return to high impact or cutting and pivoting sports after a meniscal transplantation.
After mensical surgery, rehabilitation with a physical therapist or licensed athletic trainer will be needed to restore range of motion, strength and movement control to guide the athlete's return to sports. If the meniscus is repaired there may be a period of restricted knee flexion, especially during weight bearing, to protect the healing tear and the sutures used to repair it.
Rehabilitation for meniscal transplantation is a lengthy process, often taking more than 6 months for complete restoration of function. This process varies greatly depending on the patient's associated injuries/conditions and the surgical technique used.
Englund M, Guermazi A, Lohmander SL. The role of the meniscus in knee osteoarthritis: a cause or consequence? Radiol Clin North Am. 2009 Jul;47(4):703-12
Fowler PJ and Pompan D. Rehabilitation after mensical repair. Tech in Ortho, 8(2): 137-139, 1993.
Ryu RK, Dunbar V WH, Morse GG. Meniscal allograft replacement: a 1-year to 6-year experience. Arthroscopy. 2002 Nov-Dec;18(9):989-94.
Ulrich GS and Aronczyk SP. The basic science of meniscus repair. Tech in Ortho, 8(2): 56-62, 1993.
Zacharias J. Mensical Injuries: Anatomy, Diagnosis and Treatment. UW Sports Medicine conference. September 8, 1999.
"Meniscal Injuries." UWHealth.org. N.p., n.d. Web. 29 Aug. 2012. .