Knee Cartilage Repair, Regeneration, and Replacement

Injured cartilage typically does not heal on its own, so doctors have developed several surgical techniques that attempt to repair, regenerate, and replace cartilage.

These surgeries can be performed on almost any joint, but they are most commonly performed on knees. They are generally appropriate for people who have specific cartilage injuries rather than widespread cartilage damage, like that found in moderate to severe knee arthritis.

See How Knee Joint Problems Cause Pain

Knee Cartilage Repair

A surgeon can use special tools to remove frayed and tattered cartilage and smooth the remaining cartilage surface. This contouring of cartilage reduces joint friction, which in turn can:

• Reduce knee pain
• Restore knee function
• Potentially slow down future cartilage degeneration

The medical term for surgery to reshape knee cartilage is knee chondroplasty—“Chondro” refers to cartilage and “plasty” means to form or mold. Chondroplasty may be performed on a knee’s articular cartilage, meniscus, or both.

Knee debridement
Knee chondroplasty is often done in conjunction with debridement. During knee debridement the surgeon removes potential irritants to the joint, such as loose pieces of cartilage, and flushes the joint with a saline solution (lavage).

Knee Cartilage Regeneration

Cartilage tissue’s ability to repair itself is severely limited because it does not contain blood vessels, and bleeding is necessary for healing. A surgeon can encourage new cartilage growth by making small cuts or abrasions in the bone underneath the injured cartilage. The hope is that the blood from the damaged bone will facilitate new cartilage cell growth.

There are three common knee cartilage regeneration techniques that use bleeding to spur cartilage healing:

• Knee microfracture, which requires the damaged cartilage to be cleared away completely. The surgeon then uses a sharpened tool called an awl to pierce the bone.
• Knee drilling, which uses a drill or wire to make tiny holes the bone. There is some evidence that the heat from the drill can cause unnecessary injury to nearby tissue, which can eventually lead to bone cysts or other problems.¹Canale ST, Beaty JH. Campell’s Operative Orthopaedics, 12th ed. Philadelphia, PA: Mosby, Inc; 2013:p2185.
• Knee abrasion arthroplasty, which requires the damaged cartilage to be completely cleared away. The surgeon then uses a special tool to scrape and roughen the affected bone’s surface.

These regeneration techniques are used to treat damaged articular cartilage. They cannot be used to treat a damaged knee meniscus.

Knee Cartilage Replacement

Most knee cartilage replacement surgeries are called OATs surgeries—either osteochondral autograft transplantation or osteochondral allograft transplantation surgeries. A third option is called autologous chondrocyte implantation.

Osteochondral autograft transplantation uses cartilage from the patient.

• The surgeon removes a small (<1cm), round plug of healthy cartilage—and a tiny bit of underlying bone—from a non-weight-bearing area of the knee joint. The surgeon transfers the plug to the area being treated.
• This OATs procedure can be used to repair one or more relatively small cartilage defects in a knee. When more than one plug is used to treat a single cartilage defect, the procedure is called mosaicplasty.
• The surgery is usually done arthroscopically.

Osteochondral allograft transplantation uses cartilage from outside the patient, usually from a cadaver.

• The surgeon removes a circular plug of healthy cartilage from an outside donor.
• An allograft is usually used when cartilage defect being treated is too large for an autograft (≤2cm).
• This surgery usually requires an open incision.

Autologous chondrocyte implantation relies on newly grown cartilage cells. It requires two surgeries.

• First, the patient undergoes arthroscopic surgery to remove a small piece of healthy cartilage from a non-weight bearing area of the knee joint. That cartilage is cultured, allowing new cartilage cells grow.
• Three to five weeks after the first surgery, a second surgery is performed to implant the newly grown cartilage cells into the affected knee joint.
• This second surgery is not done arthroscopically; it requires an open incision.
• This procedure may be recommended when the cartilage injury is large (up to several centimeters) or there are multiple cartilage injuries to repair.

What cartilage replacement procedure is used will depend on the size of the cartilage injury being treated as well as the surgeon’s expertise and recommendation.

Stem Cell and PRP Therapy

A surgeon performing knee cartilage repair, regeneration, or replacement surgery may use stem cells or platelet-rich plasma (PRP) in hopes of encouraging new cartilage cell growth.

See Are PRP Injections Effective?

Both stem cells and platelets are involved in the body’s natural healing process and the restoration of damaged tissue. Stem cell and PRP therapies are generally considered safe. Research regarding whether or not they are effective is ongoing.

See All PRP Treatments Are Not the Same