Articular Cartilage Restoration
Articular cartilage is the smooth, white tissue that covers the ends of bones where they come together to form joints. Healthy cartilage in our joints makes it easier to move. It allows the bones to glide over each other with very little friction.
Articular cartilage can be damaged by injury or normal wear and tear. Because cartilage does not heal itself well, doctors have developed surgical techniques to stimulate the growth of new cartilage. Restoring articular cartilage can relieve pain and allow better function. Most important, it can delay or prevent the onset of arthritis.
Surgical techniques to repair damaged cartilage are still evolving. It is hoped that as more is learned about cartilage and the healing response, surgeons will be better able to restore an injured joint.
The main component of the joint surface is a special tissue called hyaline cartilage. When it is damaged, the joint surface may no longer be smooth. Moving bones along a tough, damaged joint surface is difficult and causes pain. Damaged cartilage can also lead to arthritis in the joint.
The goal of cartilage restoration procedures is to stimulate new cartilage growth or implant new cartilage in the damaged area — either hyaline cartilage or fibrocartilage (a different and somewhat less durable form of cartilage).
Identifying Cartilage Damage
In many cases, patients who have joint injuries, such as meniscus tears or ligament tears, will also have cartilage damage. This damage may be hard to diagnose because hyaline cartilage does not contain calcium and cannot, therefore, be seen on an X-ray.
If other injuries exist with cartilage damage, doctors will address all problems during surgery.
Most candidates for articular cartilage restoration are young adults with a single injury, or lesion. Older patients, or those with many lesions in one joint, are less likely to benefit from the surgery.
The knee is the most common area for cartilage restoration. Ankle, shoulder, and elbow problems may also be treated.
Many procedures to restore articular cartilage are done arthroscopically. During arthroscopy, your surgeon makes two or three small, puncture incisions around your joint using an arthroscope.
Some procedures require the surgeon to have more direct access to the affected area. Longer, open incisions are required. Sometimes it is necessary to address other problems in the joint, such as meniscal or ligament tears, when cartilage surgery is done.
In general, recovery from an arthroscopic procedure is quicker and less painful than a traditional, open surgery. Your doctor will discuss the options with you to determine what kind of procedure is right for you.
The most common procedures for cartilage restoration are:
- Abrasion arthroplasty
- Matrix-induced autologous chondrocyte implantation
- Osteochondral autograft transplantation
- Osteochondral allograft transplantation
The goal of microfracture is to stimulate the growth of new articular cartilage by creating a new blood supply.
The procedure can be done with an arthroscope. A sharp tool called an awl is used to make multiple holes in the exposed bone surface, called subchondral bone. This action creates a healing response. New blood supply is able to reach the joint surface, bringing with it new cells that will form the new cartilage.
Microfracture generates fibrocartilage. While not as durable as the normal hyaline cartilage of the joint surface, fibrocartilage can be helpful for repairing smaller lesions (areas of damage).
The best candidates for microfracture are lower demand (less active) patients with single and smaller lesions and healthy subchondral bone. Larger lesions in very active patients may require other procedures that provide more durable hyaline cartilage.
Additionally, previous microfracture can worsen the results of a future cartilage restoration procedure; it should therefore be reserved for small lesions in lower demand patients.
Drilling, like microfracture, stimulates the production of healthy cartilage. Multiple holes are made through the injured area in the subchondral bone with a surgical drill or wire. The subchondral bone is penetrated to create a healing response.
Drilling can be done with an arthroscope. It is less precise than microfracture, and the heat of the drill may cause injury to some of the tissues.
Like microfracture, drilling does not yield hyaline cartilage and can potentially affect the outcomes of future cartilage restoration procedures in young active patients.
Abrasion arthroplasty is similar to drilling. It can be done with an arthroscope, but instead of drills or wires, high-speed burrs are used to remove the damaged cartilage and reach the subchondral bone.
Abrasion arthroplasty also produces fibrocartilage, not hyaline cartilage, so it, too, is most beneficial for treating smaller lesions in lower demand patients.
Matrix-induced Autologous Chondrocyte Implantation (MACI)
MACI is a two-step procedure in which new cartilage cells are grown and then implanted in the cartilage defect.
First, healthy cartilage tissue is removed from a non-weightbearing area of the bone. This step is done as an arthroscopic procedure. The tissue which contains healthy cartilage cells, or chondrocytes, is then sent to the laboratory. The cells are cultured on a collagen matrix (a biological scaffold) and increase in number over a period of 1 month.
An open surgical procedure, or arthrotomy, is then done to implant the newly grown cells onto another collagen matrix, which is secured within the defect using fibrin glue (a biological adhesive).
MACI is most useful for younger patients who have single defects larger than 2 cm in diameter. MACI has the advantages of providing more durable hyaline cartilage, and of using the patient's own cells so there is no danger of a patient rejecting the tissue. It does have the disadvantage of being a two-stage procedure that requires an open incision. It also takes several weeks to complete.
Osteochondral Autograft Transplantation
In osteochondral autograft transplantation, cartilage is transferred from one part of the joint to another. The procedure can be done with an arthroscope or using an open approach.
A cylinder-shaped plug (graft) of healthy cartilage tissue and subchondral bone is taken from an area of the bone that does not carry weight (non-weightbearing). The graft is then matched to the surface area of the defect and pushed into place. This leaves a smooth cartilage surface in the joint.
A single plug of cartilage may be transferred, or the surgeon may perform a procedure using multiple plugs, called mosaicplasty.
Osteochondral autograft is used for smaller cartilage defects. This is because the healthy graft tissue can be taken only from a limited area of the same joint.
This procedure is also helpful when an MRI reveals that the bone under the cartilage defect shows signs of stress or wear. This procedure provides more durable hyaline cartilage to the defect area.
Osteochondral Allograft Transplantation
If a cartilage defect is too large for an autograft, an allograft may be considered.
Like an autograft, an allograft is a graft composed of cartilage and bone. Allografts, however, are taken from a cadaver donor instead of the patient's own body. In the laboratory, the allograft tissue is sterilized, prepared, and tested for any possible diseases that might be transmitted to the recipient.
An allograft is typically larger than an autograft, but like autografts, allografts provide hyaline cartilage to the defect. The benefit of an allograft is that it can be shaped to fit the exact contour of the defect and then press fit into place.
Allografts are typically done through an open incision.
Stem Cells and Tissue Engineering
Current research is focused on new ways to make the body grow healthy cartilage tissue. This is called tissue engineering. Growth factors that stimulate new tissue may be isolated and used to stimulate new cartilage formation.
The use of mesenchymal stem cells is also being investigated. Mesenchymal stem cells are basic human cells obtained from living human tissue, such as bone marrow. When stem cells are placed in a specific environment, they can give rise to cells that are similar to the host tissue. In other words, if implanted in bone, they will stimulate the creation of bone cells.
The hope is that stem cells placed near a damaged joint surface will stimulate hyaline cartilage growth.
Tissue engineering procedures are still at an experimental stage. Most tissue engineering is performed at research centers as part of clinical trials.
After surgery, the joint surface must be protected while the cartilage heals. If the procedure was done on your knee or ankle, you may not be able to put weight on the affected leg. You will need to use crutches to move around for the first few weeks after surgery, or possibly longer depending on the type of procedure and location of the lesion.
Your doctor may prescribe physical therapy. This will help restore mobility to the affected joint. During the first weeks after surgery, you may begin continuous passive motion therapy. A continuous passive motion machine constantly moves the joint through a controlled range of motion.
As healing progresses, your therapy will focus on strengthening the joint and the muscles that support it. It may be several months before you can safely return to sports or other strenuous activities.
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AAOS does not endorse any treatments, procedures, products, or physicians referenced herein. This information is provided as an educational service and is not intended to serve as medical advice. Anyone seeking specific orthopaedic advice or assistance should consult his or her orthopaedic surgeon, or locate one in your area through the AAOS Find an Orthopaedist program on this website.