Joint, Ligament and Muscle Disorders

Articular Cartilage Restoration

Anatomy

The largest joint in the body, the knee is made up of the lower end of the thighbone (femur), the upper end of the shinbone (tibia), and the kneecap (patella). The ends of these bones, where they touch, are covered with articular cartilage, a smooth substance that protects the bones and enables them to move easily. Between the femur and tibia are C-shaped wedges, called menisci, that act as shock absorbers to cushion the joint. Large ligaments holding the femur and tibia together provide stability and long thigh muscles give the knee strength. All remaining surfaces of the knee are covered by a thin lining, or synovial membrane, that releases fluid to lubricate the cartilage, reducing friction to nearly zero in a healthy knee. Normally, these components work together in harmony, but when disrupted by disease or injury the result can be pain, muscle weakness and reduced function.

Description

Articular cartilage can be damaged by injury or normal wear and tear, resulting in a joint surface that is no longer smooth. In many cases, patients with joint injuries, such as meniscal or ligament tearsACL Injuries and ReconstructionCollateral Ligament InjuriesCombined Knee Ligament InjuriesPCL Injuries and Reconstruction, also have cartilage damage, but because hyaline cartilage contains no calcium and cannot be seen on X-rays, diagnosis can be difficult. However, the rough, damaged joint surface can make movement painful and difficult, and may lead to arthritis.

Damaged cartilage does not heal itself well, so doctors have developed surgical techniques to stimulate the growth of new cartilage. This procedure is used most commonly for the knee and most candidates are young adults with a single injury or lesion. Older patients, or those with many lesions in one joint, are less likely to benefit. Restoring articular cartilage can relieve pain, allow improved function, and delay or prevent the onset of arthritis.

Surgical Procedures

Articular cartilage restoration is often performed using knee arthroscopy, a minimally invasive surgical procedure used by orthopaedic surgeons to visualize, diagnose and treat problems inside the joint. In general, recovery from an arthroscopic procedure is quicker and less painful than recovery from traditional, open surgery, however it is not appropriate in all instances. Your doctor will discuss options with you to determine what procedure is best for you. Common procedures for cartilage restoration include:

• Microfracture—By creating a new blood supply, growth of healthy new cartilage is stimulated. Using a sharp tool, or awl, the surgeon makes multiple holes in the bone beneath the cartilage (subchondral bone). This causes a healing response. The new blood supply reaches the joint surface, bringing with it new cells that will form the new cartilage. Microfracture can be performed arthroscopically. Young patients with single lesions and healthy subchrondral bone are the best candidates for this procedure.
• Drilling—Like microfracture, drilling stimulates the growth of healthy new cartilage. Using a surgical drill or wire, multiple holes are made in the subchondral bone of the injured area to create a healing response. Drilling can be performed arthroscopically, but it is less precise than microfracture and the heat of the drill may cause injury to some surrounding tissues.
• Autologous chondrocyte implantation (ACI)—In this two-step procedure, new cartilage cells are grown and then implanted in the cartilage defect. First, healthy cartilage cells (chondrocytes) are arthroscopically removed from a nonweightbearing area of the bone and sent to a laboratory to be cultured, where they grow in number during the next 3 to 5 weeks. Next, during an open surgical procedure, or arthrotomy, the cartilage defect is prepared and a membrane covering sewn over the area and sealed with fibrin glue. The newly grown cells are then implanted by injecting them into the defect under this cover.

ACI is most beneficial for younger patients with single defects larger than 2cm in diameter. The patient's own cells are used, so there is no danger of tissue rejection. However, an open incision is required and the two-stage procedure takes several weeks to complete.

• Osteochondral autograft transplantation—A plug of healthy cartilage and subchondral bone (graft) is removed from a nonweightbearing area of bone. The graft is then matched to the surface area of the defect and impacted into place, leaving a smooth cartilage surface in the joint. When this procedure is performed using multiple plugs, it is referred to as a mosaicplasty. Osteochondral autograft is most beneficial for smaller cartilage defects because healthy graft tissue can only be taken from a limited area of the same joint. This can be done arthroscopically.
• Osteochondral allograft transplantation—When a cartilage defect is too large for an autograft, an allograft may be considered. Allograft, like autograft, is a plug or block of cartilage and subchondral bone, but this tissue is taken from a cadaver donor, then sterilized, tested for disease, and prepared in a laboratory before it is transplanted. Because an allograft is typically larger than an autograft, it can be shaped to fit the exact contour of the defect before being impacted into place. Allografts usually require an open incision procedure.

Preparation

Once the decision to have surgery is made, you may be asked you to see your primary care physician to be sure you do not have any medical problems that need to be addressed before surgery. Additional tests may be needed, such as blood and urine samples, electrocardiogram (EKG), or chest X-ray. If you have certain health risks, a more extensive evaluation may be required prior to surgery. Be sure to inform your othopaedic surgeon of any medications or supplements you take, as these may need to be stopped prior to surgery.

Surgery

Before the operation, you will be evaluated by a member of the anesthesia team. Based on your procedure, and with your input, the anesthesia team will determine the best option for you. Your surgeon will see you before the surgery and sign your knee to verify the surgical site.

Rehabilitation

After surgery, your knee must be protected while the cartilage heals, so it is important to follow your orthopaedic surgeon's instructions very carefully. You should expect to use crutches or other assistance until your surgeon tells you it is safe to put weight on your foot and leg. If you are staying alone, you should ask someone to check on you the first evening you are home.

Keep your leg elevated as much as possible for the first few days and apply ice as recommended to relieve swelling and pain. The incisions should be kept clean and dry, and the dressing should be changed as instructed. Your surgeon will tell you when you can shower or bathe. Pain medication can be prescribed to help relieve discomfort and other medications, such as aspirin, may also be recommended to lessen the risk of developing a blood clot.

A follow-up visit will be scheduled for several days after surgery to check your progress, review findings and begin your postoperative treatment program. Your surgeon may prescribe physical therapy to help you restore mobility to the joint. You may begin continuous passive motion therapy within the first few weeks after surgery, during which, a continuous passive motion machine will move your joint through a controlled range of motion. As healing progresses, your physical therapy will focus on strengthening the joint and the muscles that support it. Following your physical therapy program or a knee conditioning program will play an important role in how well you recover, however it will be many months before you can safely return to sports or other similar activities.

Complications

As with any surgery, there are risks associated with knee articular cartilage restoration. These occur infrequently and are typically minor and treatable. Potential postoperative problems include infection, blood clots and accumulation of blood in the knee.

• Warning signs—Certain symptoms, although uncommon, may indicate a more serious issue. Call your orthopaedic surgeon immediately if you experience any of the following: fever, chills, persistent warmth or redness around the knee, persistent or increased pain, significant swelling in your knee, increasing pain in your calf muscle.