Until recently, a torn meniscus had three surgical options—remove part or all of the meniscus, sew the torn edges together, or replace the entire meniscus with a cadaver meniscus (transplant). Repairing (suturing) the torn edges can only be performed on the thickest part (outer rim) of the meniscus—and most tears occur in the thinner inner rim. Plus, this type of repair has about a 20-40% failure rate. While meniscal transplants have a good success rate, only a small percentage of patients qualify for this procedure. Arthroscopically trimming the mensicus (menisectomy) is the most common procedure and minimizes the problems associated with removing the entire meniscus. Some of the potential problems associated with removing all or part of the meniscus are:
- shock absorption is lost forever
- since the spacer on the one side of the joint is missing, more forces are transmitted through that side of the joint
- the joint surfaces of the femur (thighbone) and tibia (shinbone) are going to become stressed, softened, and eventually break down (‘arthritis’) and there will be arthritic pain
- the leg may demonstrate ‘bow legged ness’ or ‘knock-knees’, due to the collapse of the joint on the one side (one ‘compartment’)
- the bone may attempt to try to heal the problem – causing totally unhelpful bony outgrowths called ‘osteophytes’ (‘bone mushrooms’). These may form at the joint line or in the notch where the cruciate ligaments reside.
- eventually the cruciate ligaments may become incompetent and rupture
Recently, a synthetic meniscus has been developed and is being used primarily in Europe. This implant is made from a slowly degrading polyurethane foam and is designed to treat irreparable meniscal tears. It provides a structrue for the in-growth of tissue in the meniscus, after the removal of the damaged meniscal tissue by the surgeon. The body of this implant is highly porous—some 80% of the implant is air—and allows blood vessels to grow into the material and tissue to be generated around them.
The implant degrades over four to six years and is removed/replaced by the body’s own tissue. Patients are usually non-weigtbearing for an extended period of time (comparable to a meniscal repair or transplant) and are restricted to 90 degrees of loaded knee flexion for up to 6 months. Impact activities such as running or jumping can be introduced at 9-12 months. Full return to sports activities is the expected outcome.
Maintaining healthy tissue is important for normal pain free knee function. A synthetic meniscus now allows surgeons to replace damaged tissue with (eventually) near-normal tissue, preventing or at least greatly reducing the risks associated with menisectomy.