The knee is the most complex joint in the body and is formed by the articulation between the thigh bone
Cartilage replacement is a surgical procedure performed to replace the worn-out cartilage with the new cartilage. It is usually performed to treat patients with small areas of cartilage damage usually caused by sports or traumatic injuries. It is not indicated for those patients who have advanced arthritis of knee. Articular or hyaline cartilage is the tissue that covers bone surface of the knee which helps in smooth interaction between the two bones in knee joint. It has less capacity to repair by itself because there is no direct blood supply to cartilage.
Cartilage replacement helps relieve pain, restore normal function, and can delay or prevent the onset of arthritis. The goal of cartilage replacement procedures is to stimulate growth of new hyaline cartilage. Various arthroscopic procedures involved in cartilage replacement include:
- Microfracture: Microfracture involves creating numerous tiny holes in injured joint surface using a special tool, called "awl". The holes are made in the bone under the cartilage, called as subchondral bone. This creates a new blood supply to the cartilage which stimulates the growth of new cartilage.
- Drilling: This procedure is like microfracture where multiple holes are created in the injured joint area using a surgical drill or wires.
- Abrasion Arthroplasty: This procedure is like drilling but involves use of high speed burs to remove the damaged cartilage.
- Autologous chondrocyte implantation (ACI) - Ii is a two-step procedure, where healthy cartilage cells are removed from the non-weight bearing joint, grown in the laboratory and then implanted in the cartilage defect during the second procedure. During this procedure, a patch is harvested from the periosteum, a layer of thick tissue that covers the bone and is sewn over the defected area using fibrin glue. The new cartilage cells are then injected under the periosteum into the cartilage defect to allow the growth of new cartilage cells.
- Osteochondral Autograft Transplantation: In this procedure, plugs of cartilage is taken from the non-weight bearing areas of knee, from the same individual and transferred to the damaged areas of the joint. This method is used to treat smaller cartilage defects since the graft which is taken from the same individual will be limited.
Following cartilage replacement your doctor may recommend physical therapy to help restore mobility to the affected joint.
Osteochondral Allograft Transplantation: In this procedure, healthy cartilage tissue or a graft is taken from a donor from the bone bank and transplanted to the area of cartilage defect.
Cartilage Repair and Transplantation
Articular Cartilage is the white tissue lining the end of bones where these bones connect to form joints. Cartilage acts as cushioning material and helps in smooth gliding of bones during movement. An injury to the joint may damage this cartilage which cannot repair on its own. Cartilage can be damaged with increasing age, normal wear and tear, or trauma. Damaged cartilage cannot cushion the joints during movement and the joints may rub over each other causing severe pain and inflammation.
Cartilage restoration is a surgical procedure where orthopedic surgeons stimulate the growth of new cartilage that restores the normal function. Arthritis condition can be delayed or prevented through this procedure.
Several techniques are employed for cartilage restoration including dietary supplements, microfracture, drilling, abrasion arthroplasty, osteochondral autograft, and allograft transplantation.
Dietary supplements: Dietary supplements such as glucosamine and chondroitin are the non-surgical treatment options for cartilage restoration. Chrondroitin sulphate and glucosamine are naturally occurring substances in the body that prevent degradation of cartilage and promote formation of new cartilage. Chrondroitin sulphate and glucosamine obtained from animal sources are available as over the counter products and are recommended for cartilage restoration. Apart from these various other nutritional supplements are also recommended such as calcium with magnesium and vitamin D as a combination, S-Adenosyl-Methionine and Methylsulfonylmethane.
Microfracture: In this method, numerous holes are created in the injured joint surface using a sharp tool. This procedure stimulates healing response by creating new blood supply. Blood supply results in growth of new cartilage.
Drilling: In this method, a drilling instrument is used to create holes in the injured joint surface. Drilling holes creates blood supply and stimulate growth of new cartilage. Although the method is like microfracture, it is less precise and the heat produced during drilling may damage other tissues.
Abrasion Arthroplasty: High speed metal-like object is used to remove the damaged cartilage. This procedure is performed using an arthroscope.
Osteochondral Autograft Transplantation: Healthy cartilage tissue (graft) is taken from the bone that bears less weight and is transferred to the injured joint place. This method is used for smaller cartilage defects.
Osteochondral Allograft Transplantation: A cartilage tissue (graft) is taken from a donor and transplanted to the site of the injury. Allograft technique is recommended if larger part of cartilage is damaged.
Autologous Chondrocyte implantation: In this method, a piece of healthy cartilage from other site is removed using arthroscopic technique and is cultured in laboratory. Cultured cells form a larger patch which is then implanted in the damaged part by open surgery.
Osteoarticular transfer system (OATS): Osteoarticular transfer system (OATS) is a surgical procedure to treat isolated cartilage defects which usually 10 to 20mm in size. The procedure involves transfer of cartilage plugs taken from the non-weight bearing areas of the joint and transferring into the damaged areas of the joint.
This procedure is not indicated for wide spread damage of cartilage as seen in osteoarthritis.
The procedure is usually performed using arthroscopy. During the procedure, the plugs taken are usually larger and therefore only one or two plugs are needed to fill the area of cartilage damage. The area of damaged cartilage is prepared using a coring tool which makes a perfectly round hole in the bone in damage. The hole is drilled to a size that fits the plug. Next the plug of normal cartilage is harvested from a non-weight bearing area of the knee, is then implanted into the hole that was created in the damaged area. The size of the plug used should be slightly larger than the hole so that it fits into the position. This procedure allows the newly implanted bone and cartilage to grow in the defected area.
Possible complications of OATS include donor site morbidity causing pain, avascular necrosis, and fracture. Other complications such as hemarthrosis, effusion and pain may also occur. Following OATS rehabilitation is recommended by use of crutches and limiting the range of motion.
OATS is "osteochondral autograft transfer system". It is one of the two types of cartilage transfer procedures and the other procedure is "Mosaicplasty". Cartilage transfer procedures involve moving healthy cartilage from a non-weight bearing area of the knee to a damaged area of the cartilage in the knee. In mosaicplasty, plugs of cartilage and bone are taken from a healthy cartilage area and moved to replace the damaged cartilage of the knee. Multiple tiny plugs are used and once embedded, resembles a mosaic pattern, hence the name. With the OATS procedure, the plugs are larger. Therefore, the surgeon only needs to move one or two plugs of healthy cartilage and bone to the damaged area of the knee.
OATS is not recommended in everyone. OATS is typically used for patients aged<50 and with minimal cartilage damage, usually because of trauma, and available healthy cartilage for transfer.
In the OATS procedure, the surgery usually begins with an arthroscopic examination. Arthroscopy is performed in a hospital operating room under general anesthesia. Your surgeon makes a tiny incision over the knee and inserts an arthroscope. The arthroscope is a small fiber-optic viewing instrument made up of a tiny lens, light source and video camera to enable the surgeon to visually examine the knee.
If the surgeon decides the procedure can be performed, the scope is removed and an incision is made over the knee. The surgeon prepares the damaged area of cartilage. Using a special coring tool, surgeon makes a hole in the cartilage sized to fit the plug exactly. Your surgeon then harvests the plug of healthy cartilage and bone from the non-weight bearing part of the knee. This plug is transferred to the cored hole and implanted into the prepared hole of the damaged area of the knee. Over the time, a successful OATS surgery will enable the bone and cartilage to grow into the damaged area of the knee successfully resolving the patient's knee pain.
- You will wake up in the recovery room and then be transferred back to the ward.
- A bandage will be around the operated knee. You will usually be able to remove this the next day but leave the steri-strips in place. These will fall off.
- Once you are recovered your IV will be removed and you will be shown several exercises to do.
- Your surgeon will see you prior to discharge and explain the findings of the operation and what was done during surgery.
- Pain medication will be provided and should be taken as directed
- It is normal for the knee to swell after the surgery. You will be sent home with a cryocuff cold therapy unit. Elevating the leg when you are seated and placing Ice-Packs or the cryocuff on the knee will help to reduce swelling. (20 min 3-4 times a day until swelling has reduced)
- You will be sent home with a CPM machine (continuous passive motion) and given instructions on proper usage.
- You may shower once the bandage is removed. Leave the steri strips intact.
- Please make an appointment 10-14 days after surgery to monitor your progress and remove your sutures.
- It is important to be compliant with your rehabilitation exercises to ensure a good outcome.
Risks and Complications
General anesthesia risks are extremely rare. Occasionally patients have some discomfort in the throat because of the tube that supplies oxygen and other gasses. Please discuss with the anesthetist if you have any specific concerns.
Risks specifically related to the OATS surgery
- Post-operative bleeding
- Deep Vein Thrombosis (DVT)
- Numbness to part of the skin near the incisions
- Injury to vessels, nerves and a chronic pain syndrome