UW Health's Sports Medicine doctors treat a wide range of common athletic injuries, including meniscular knee injuries.
From Our Physicians
There are two types of knee cartilage: articular cartilage and meniscus cartilage.
Articular cartilage lines the end of the bones that meet to form a joint and is made up of collagen, proteoglycans and water. 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, which are referred together 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 (upper leg/thigh bone) sitting on a relatively flat tibia (shin bone) forms the knee joint. Without the mensci, the area of contact force between these two bones would increase the contact stress by 235 to 335 percent. The wedge shaped menisci decrease this contact area significantly while also providing shock absorption, lubrication and joint stability.
There are two categories of meniscal tears: degenerative tears and acute traumatic tears.
Degenerative tears occur most commonly in middle-aged to older adults and take place when repetitive stresses severely weaken the meniscal tissue.
Degenerative tears are not caused by acute trauma or injury, but may be more symptomatic following one. This process of tissue degeneration makes it very unlikely that a meniscus repair will heal. One report showed that less than 10 percent of meniscal tears occurring in patients greater than 40 years of age are repairable, which may be due to tear patterns as well as structural and cellular changes that occur with age.
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 causes catching or locking in the knee, often times a torn fragment of the meniscus must be removed surgically. The torn fragment also may be removed surgically if the fragment is being compressed and causing pain.
A torn meniscus often leads to arthritis, whether the torn meniscus is removed or not, because the meniscus becomes less effective with distributing loads and functioning as a shock absorber. Recent evidence shows that removing degenerative meniscal tears in the absence of catching, locking or excessive compression is unlikely to create long term pain relief or prevent arthritis. One study compared individuals receiving rehabilitation without surgery and another with individuals undergoing surgical removal of the degenerative tear (without catching, locking or compression) and found no significant difference in pain relief or function two years after the diagnosis.
Acute Traumatic Tears
Acute traumatic tears occur most frequently in athletes as a result of a twisting injury to the knee when the foot is planted (in contact with the ground during a cut or pivot). Symptoms of an acute meniscus tear include:
- Pain along the joint line
- Catching and/or locking
- A specific injury causing immediate pain (and any of the above symptoms)
Often times these tears can be diagnosed by taking a detailed history and completing a physical examination. An MRI may be used to assist in making the diagnosis since the MRI allows the meniscus (and other soft tissue structures) to be seen.
If an athlete suffers a meniscal tear, the three options for treatment include:
- Rehabilitation without surgery
- Surgery to remove 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, knee stability, the athlete’s age and any associated injury.
The location of the tear is important because the outer portion of the meniscus has a good blood supply whereas the inner portion has poor blood supply. Areas with good blood supply are much more likely to heal than areas with poor blood supply.
Figure 1 shows the blood vessels (perimeniscular capillary plexus) entering the outer portion of the meniscus. This blood supply provides the cellular elements and biochemical mediators that are essential for the repair to heal. Without 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 repaired, the surgeon will use sutures or meniscal fixation devices to fix the tear.
Unfortunately, not all meniscal tears are repairable. In those situations where extensive damage does not allow for a repair, the entire meniscus (or almost all of the meniscus) may be removed to relieve pain, catching and/or locking.
Evidence suggests that a complete (or nearly complete) removal of the meniscus can lead to degenerative arthritis that gets worse over time, leading to premature pain and a loss of function with everyday activities. For these individuals, meniscal allograft replacement or transplantation may be a viable treatment alternative. This is when a cadaver meniscus is used to replace a meniscus that is significantly damaged in a patient.
Studies have shown that the success of mensical transplantation is more likely if less arthritis is present at the time of surgery, making it most appropriate for young patients who have suffered a very significant acute meniscal tear that is unable 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, the likelihood of success is less. If left untreated, an osteotomy to correct alignment may be indicated.
At the current time, this surgery is intended to return patients to daily function and low impact sports. The surgery is not recommended to return to high impact or cutting and pivoting sports (i.e. football, soccer, basketball, etc.) after a meniscal transplantation.
After meniscal surgery, rehabilitation with a physical therapist or licensed athletic trainer is 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 (knee bending), especially during weight bearing, to protect the healing tear and the sutures used to repair it. Return to sport often takes around four months.
Rehabilitation for meniscal transplantation is a lengthy process, often taking six to 12 months for complete restoration of function. This process varies greatly depending on the patient’s associated injuries/conditions and the surgical technique used.