The meniscus is the fibrous “shock-absorber” tissue in the knee joint. Its crescent shape rests on top of the tibia (the shin bone) and cups the femur (the thigh bone). The meniscus can be compared to a gasket in a hose: If it is cut, water leaks out.
If the meniscus is torn, it fails to diffuse the force that presses through the knee joint when you walk or run. A torn meniscus is often painful, requiring knee arthroscopic surgery — which is performed 1.4 million times each year in the United States. Most commonly, the surgeon removes the torn tissue, which relieves the immediate pain. Over time, though, the abnormal loads placed on the opposing smooth articular cartilage causes arthritis.
Repair of the torn meniscus has become easier with new surgical tools and better training of surgeons. Still, it is performed in less than 10 percent of all meniscus tears. The reasons given are varied.
Often, the surgeon does not believe that the torn meniscus tissue is healthy enough to heal after repair — or that the defect left behind is great enough to produce disability. We now know, however, that removing as little as 20 percent of the meniscus tissue leads to a 160 percent increase in force transferred to the tibia — and thus to arthritis due to overloading.
In 1986, to combat the disease of partial tissue loss, I designed a collagen meniscus implant (Menaflex or CMI). This was to be used as a regeneration template that, when sewn into the meniscus defect, promoted the regrowth of the missing tissue. This implant is still in use in the U.S. and around the world. When most of the meniscus is missing, it is often best to replace the meniscus entirely with a donor or cadaver meniscus called an allograft. This full replacement has more mechanical strength than my implant and is more appropriate for larger defects.
In all replacement and repair scenarios, there is a race between healing and a return to normal life. While the body is remodeling the implant into normal meniscus tissue, the patient risks tearing the implant by pivoting or twisting.
To accelerate this healing process, we can now add stem cells and growth factors to the implants. They provide a boost to the healing environment, speed the remodeling and diminish the risk of tearing. Tissues once thought to be too unhealthy to repair may now be able to heal thanks to these added cells and factors.
To investigate this question, we have designed a study where we repair the meniscus defect both with and without added growth factors. If the data shows that healing can indeed occur in these “difficult to repair” defects, many more meniscus tissues will be saved — and millions of people will be spared the pain of arthritis.
Dr. Kevin R. Stone is an orthopedic surgeon at The Stone Clinic and chairman of the Stone Research Foundation in San Francisco.