Knees contain two types of cartilage: articular and meniscus. Articular cartilage helps the knee move freely. Meniscus cartilage serves as a cushion or shock absorber between the bones.
Sports injuries, accidents, and years of normal wear and tear can damage both types of cartilage in the knee, making it necessary to repair or replace the lost cartilage. The wearing down of cartilage is known as osteoarthritis.
Advances in orthopedic medicine provide many options for treating knee injuries. Some long-standing approaches include surgery to repair torn cartilage or knee joint replacement. In addition to these, there are now minimally invasive treatments using cartilage taken from elsewhere in the body or regenerated from a person’s own cells.
In this article, we review traditional and newly emerging approaches to knee cartilage replacement and repair.
If the loss of knee cartilage and symptoms are minor, you may be able to put off surgery or other interventions through physical therapy.
The main goal of physical therapy is to improve the strength and flexibility of the muscles around the knee joint to ease the burden on the joint itself. A 2018 study Trusted Source found that physical therapy helped reduce pain, not just in cases of mild knee osteoarthritis, but in people dealing with moderate pain, too.
The benefits of physical therapy for people with severe arthritis pain are not as significant, suggesting that pain intensity could be considered a major factor in deciding whether to pursue physical therapy as a treatment option.
A separate study in Seminars in Arthritis and Rheumatism Trusted Source also notes that weight loss achieved through exercise and diet can often help ease knee arthritis symptoms in people who have overweight or obesity.
In addition, a 2005 study Trusted Source found that 1 pound of weight loss removes 4 pounds of joint stress in people with knee osteoarthritis. So if a person loses 5 pounds, that’s the equivalent of removing 20 pounds of stress off the knee joint.
One way to stimulate the growth of new cartilage is through microfracture. In this procedure, tiny holes are drilled in one or more bones in the knee joint to stimulate greater blood flow and the release of cells that form new cartilage.
Microfracture is best suited for people who:
- are under the age of 40
- have experienced recent knee injuries
- have small areas of cartilage degradation, called lesions
Microfracture is not recommended for older adults with severe osteoarthritis or for repairing large lesions.
After the procedure, you’ll need to keep weight off your knee for about 6 weeks and use acontinuous passive motion (CPM) machine several hours a day to bend and straighten the knee. Resuming sports or other strenuous activities may take up to 9 months.
The cost of microfracture surgery is around $4,000, making it less expensive than some other knee repair procedures.
Another upside of microfracture surgery is a relatively low risk of infections or other complications. In some cases, however, the procedure isn’t successful in producing enough replacement cartilage, meaning that another form of treatment may be needed in the long term.
This procedure to grow new cartilage, also known as matrix-induced autologous chondrocyte implantation (MACI), is a two-step process. It starts with an arthroscopic cartilage biopsy of the knee. The biopsy tissue is then sent to a lab, where the cartilage cells are manipulated to start growing. When the new cartilage is ready to be implanted, the surgeon shapes it to fit the portion of natural cartilage that needs to be replaced.
The most suitable candidates for MACI are those who:
- are young and have good regenerative ability
- have symptomatic cartilage injuries
- have small isolated lesions less than the size of a dime
A 2015 study Trusted Source found that MACI is a safe and effective approach to cartilage replacement for most people.
MACI is usually an outpatient procedure, though you can expect to wear a knee brace for about 6 weeks while your knee regains strength and stability. MACI can cost about $40,000. However, insurance providers often cover most of those costs.
Aside from the high cost and the need for two separate operations, the other main downside to MACI is that there’s a risk of cartilage overgrowth, which can require a third surgery to treat.
The primary arguments for MACI are that it’s an effective treatment for small areas of cartilage repair and that it uses a person’s own cells, reducing the risk of rejection by the body.
Also called a mosaicplasty, this surgery uses healthy cartilage from elsewhere in the knee to replace cartilage that has significantly worn away. A similar procedure, called osteochondral allograft, is done using donor tissue.
During the procedure, a surgeon removes the damaged cartilage and a portion of underlying bone. Picture the coring of an apple. Then a replacement core, made of bone and cartilage from another part of the body or a donor knee, is used to fill in the hole. Usually, no screws or mechanical devices are needed to secure the replacement tissue.
Like other knee procedures, an osteochondral autograft or allograft requires about 4 to 6 weeks of recovery before the knee can start to bear weight. With the help of rehabilitation, a complete return to sports or other activities should be possible within 6 to 9 months.
An allograft can cost as much as $10,000 or more. Other downsides include a limited availability of donor tissue and the risk that the body might reject the implant.
The rehabilitation period is usually longer with an allograft than with an autograft, and an autograft is usually less expensive and carries a smaller risk of complications. Research suggests that autografts provide satisfactory outcomes for at least 10 years among 72 percent Trusted Source of people who undergo the procedure.
The ideal candidates for this procedure should be young in order to have regenerative cells available for the graft. In addition, an allograft is typically used to repair areas of worn cartilage that are no larger than a dime.
However, because an autograft involves the removal of healthy material from elsewhere in the body, it is a more invasive surgical procedure. Some people are also hesitant to run the risk even a low one of problems resulting from the harvest of healthy cartilage and bone.
When other less invasive approaches haven’t improved knee pain and movement, severe knee arthritis may require a knee replacement.
The procedure begins with an incision from above the knee down past the knee joint. All or part of the damaged knee joint is then removed and replaced with a prosthetic knee joint that duplicates the movement and function of a natural knee.
The worn out surfaces of the knee, which used to be covered in cartilage, are also resurfaced with metal, plastic, and ceramic materials to provide new gliding surfaces.
The cost of knee replacement surgery can vary from $19,000 to $50,000 or more, depending on the type of surgery, the hospital, and other factors. That’s why it’s especially important to discuss your costs with your insurance provider and understand exactly how much of the procedure will be covered.
By participating in physical therapy following the operation, most people can resume normal, everyday activities within 6 weeks, though a full recovery can take several months. On the plus side, knee replacement can eventually restore full function to the knee joint and relieve you of the pain that can make walking or even standing difficult.
Special centers, such as Yale University, are using robotic surgery to improve component positioning, biomechanics, and quality of movement for knee replacement surgeries.
As with any surgery, knee replacement carries the potential risk of infection or other complications. Because the knee is a complicated joint, there’s a chance that the prosthetic knee may not completely meet your expectations. As a result, you may need to consider a second operation or adjust to life with the new knee as it is.
Knee cartilage can cause daily pain and reduced mobility when it has been severely injured or worn down to the point where it no longer provides smooth bone movement within the joint or cushioning between the bones. It is not a condition that will improve on its own.
Repairing or replacing damaged knee cartilage can:
- provide pain relief
- improve knee function
- delay or prevent osteoarthritis or other complications
If you’re experiencing knee pain, have a discussion with your primary care physician. They can refer you to a physical therapist or an orthopedist who specializes in knee health. The solution isn’t always surgery, though for severe cartilage damage, some invasive intervention is likely.
Your age and activity level are two key factors in determining what approach is best for you. The nature and severity of the problem in your knee is another factor.
Be sure to talk with your doctor about what’s involved in various procedures and recovery periods. It’s also important to find out the costs of a procedure and how much of that expense will be covered by your insurance.
Regardless of which knee cartilage treatment you have, you should be prepared for a lengthy recovery and rehabilitation phase. A study in the World Journal of Orthopedics Trusted Source notes that rehabilitation after any cartilage resurfacing procedure is necessary for success.
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