Introduction
The meniscus is very important to the long-term health of the knee. In the past, surgeons would simply take out part or all of an injured meniscus. But today’s surgeons know that removing the meniscus can lead to early knee arthritis. Whenever possible, they try to repair the tear. If the damaged area must be removed, care is taken during surgery to protect the surrounding healthy tissue.
Anatomy
What Parts of the Knee are Involved?
There is one meniscus on each side of the knee joint. The C-shaped medial meniscus is on the inside part of the knee, closest to your other knee. (Medial means closer to the middle of the body.) The U-shaped lateral meniscus is on the outer half of the knee joint. (Lateral means further out from the center of the body.)
The menisci (plural for meniscus) protect the articular cartilage on the surfaces of the thighbone (femur) and the shinbone (tibia). Articular cartilage is the smooth, slippery material that covers the ends of the bones that make up the knee joint. The articular cartilage allows the joint surfaces to slide against one another without damage to either surface.
Most of the meniscus is avascular, meaning no blood vessels go to it. Only its outer rim gets a small supply of blood. Doctors call this area the red zone. The ends of a few vessels in the red zone may actually travel inward to the middle section, the red-white zone. The inner portion of the meniscus, closest to the center of the knee, is called the white zone. It has no blood vessels at all. Although a tear in the outer rim has a good chance of healing, damage further in toward the center of the meniscus will not heal on its own.
Related Document: A Patient’s Guide to Knee Anatomy
Rationale
What does my Surgeon Hope to Accomplish?
The meniscus is a pad of cartilage that acts like a shock absorber to protect the knee. The meniscus is also vital for knee stability. When the meniscus is damaged or is surgically removed, the knee joint can become loose, or unstable. Without the protection and stability of a healthy meniscus, the surfaces of the knee can suffer wear and tear, leading to a condition called osteoarthritis.
Related Document: A Patient’s Guide to Knee Osteoarthritis
Most tears of the meniscus do not heal on their own. A small tear in the outer rim (the red zone) has a good chance of healing. However, tears in the inner part of the meniscus often require surgery. When tears in this area are causing symptoms, they tend to get bigger. This puts the articular cartilage on the surfaces of the knee joint at risk of injury.
Surgeons aim to save the meniscus. If an injured part must be removed, only the smallest amount of the meniscus is taken out. Preserving the nearby areas of the meniscus is vital for keeping the knee healthy. If a tear can possibly be repaired, surgeons will recommend a meniscal repair.
A torn meniscus may cause symptoms of pain and swelling and sometimes catching and locking. The goal of surgery is to take these symptoms away. When the knee locks and you have to tug on it to get it moving, a small flap from a meniscal tear may have developed. The flap may be getting caught in the knee joint as you bend it. Or a small piece of the meniscus could actually be floating around inside the joint. This fragment, called a loose body, can get lodged between the moving parts of the knee, causing the knee to lock. In these cases, surgery may be needed, sometimes right away, to fix the flap or to remove the loose body.
Only when the majority of the meniscus is damaged beyond repair is the entire meniscus removed. Surgeons are experimenting with solutions to replace the meniscus.
Preparations
What do I need to know before surgery?
You and your surgeon should make the decision to proceed with surgery together. You need to understand as much about the procedure as possible. If you have concerns or questions, be sure and talk to your surgeon.
Once you decide on surgery, you need to take several steps. Your surgeon may suggest a complete physical examination by your regular doctor. This exam helps ensure that you are in the best possible condition to undergo the operation.
On the day of your surgery, you will probably be admitted for surgery early in the morning. You shouldn’t eat or drink anything after midnight the night before.
Surgical Procedure
What happens during meniscal surgery?
Meniscal surgery is done using an arthroscope, a small fiber-optic TV camera that is used to see and operate inside the joint. Only small incisions are needed during arthroscopy. The surgeon does not need to open the knee joint.
Before surgery you will be placed under either general anesthesia or a type of spinal anesthesia. The surgeon begins the operation by making two or three small openings into the knee, called portals. These portals are where the arthroscope and surgical instruments are placed inside the knee. Care is taken to protect the nearby nerves and blood vessels.
Partial Meniscectomy
The procedure to carefully remove a damaged portion of the meniscus is called partial meniscectomy. The surgeon starts by inserting the arthroscope into one of the portals. A probe is placed into another portal. The surgeon watches on a screen while probing the meniscus. All parts of the inside of the knee joint are examined. When a meniscal tear is found, the surgeon determines the type and location of the tear. Surgical instruments are placed into another portal and are used to remove the torn portion of meniscus.
When the problem part of the meniscus has been removed, the surgeon checks the knee again with the probe to be sure no other tears are present. A small motorized cutter is used to trim and shape the cut edge of the meniscus. The joint is flushed with sterile saline to wash away debris from the injury or from the surgery. The portals are closed with sutures.
Meniscal Repair
Suture Repair
Using the arthroscope and a probe, the surgeon locates the tear. The probe is used to push the torn edges of the meniscus together. A small rasp or shaver is used to roughen the edges of the tear. Then a hollow tube called a cannula is inserted through one of the portals. The surgeon threads a suture through the cannula and into the knee joint. The suture is sewn into the two edges of the tear. The surgeon tugs on the thread to bring the torn edges close together. The suture is secured by tying two to three knots. Additional sutures are placed side by side until the entire tear is fixed.
An alternate method is to pierce the knee joint with one or two curved needles. The needle goes from the outer edge of the meniscus completely through the tear. The surgeon may feed a suture from another portal into the end of the needle. Or the suture can be threaded into the needle from the outside of the knee. Both ways get the suture through the tear and allow the surgeon to sew the torn edges of the meniscus together.
View animation of sewing the edges of a torn meniscus
Suture Anchor Repair
Special fasteners, called fiber stitch, are sometimes used to anchor the torn edges of the meniscus together. These implants are biodegradable, meaning they eventually break down and are absorbed by the body. Suture anchors have barbed shafts and are pointed like an arrow. They work like a staple or straight pin to hold the healing tissues together.
Repairs using suture anchors work best for younger patients who have a single tear near the outer rim (red zone) of the meniscus. (As described earlier, this part of the meniscus has the richest blood supply.) A probe is often used to line up the torn edges of the meniscus. Then the surgeon uses a small surgical tool to punch an arrow through the damaged part of the meniscus. Usually only two or three arrows are needed. Larger tears may require up to six arrows. The arrows anchor the two torn edges together while the tear heals. It takes about six months before the arrows begin to be absorbed by the body.
View animation of anchoring the edges of a torn meniscus
Rehabilitation
After Surgery
Rehabilitation proceeds cautiously after surgery on the meniscus, and treatments will vary depending on whether you had part of the meniscus taken out or your surgeon repaired or replaced the meniscus.
Patients are strongly advised to follow the recommendations about how much weight can be borne while standing or walking. After a partial meniscectomy, your surgeon may instruct you to place a comfortable amount of weight on your operated leg using a walking aid. After a meniscal repair, however, patients may be instructed to keep their knee straight in a locked knee brace and to put only minimal or no weight on their foot when standing or walking for up to six weeks.
Patients usually need only a few therapy visits after meniscectomy. Additional treatments may be scheduled if there are problems with swelling, pain, or weakness. Rehabilitation is slower after a meniscal repair or allograft procedure. At first, expect to see the physical therapist two to three times a week. If your surgery and rehabilitation go as planned, you may only need to do a home program and see your therapist every few weeks over a six-to eight-week period.