Cartilage preservation encompasses a group of surgical procedures intended to recreate normal cartilage for treatment of well-defined injuries to the cartilage of a joint. These types of procedures are typically employed in younger patients who have smaller, isolated lesions in only one area of the joint cartilage. It is not used for older patients with multiple, larger lesions in various areas of the joint. As mentioned, the damaged area is typically small and has well-defined borders with good quality cartilage surrounding the lesion. Despite out best efforts, the cartilage that heals in place of the injury is not identical to the natural cartilage one is born with. The healing cartilage is called “fibrocartilage” and it resembles a type of scar cartilage. This fibrocartilage lacks the highly specialized organization and structure of the fibers and cells that exists in normal healthy cartilage, and as a result it does not last as long as normal cartilage. Despite great advances in medicine, no technology yet exists that perfectly recreates normal cartilage, but if the proper procedure is performed on the right patients, outcomes of cartilage preservation surgery are generally very good.
Microfracture is a procedure that was created to address small (about the size of a nickel or smaller) lesions. The procedure is performed arthroscopically and involves debridement of any scar tissue within the joint and around the lesion. The edges of the damaged area are tested for stability to ensure that no additional cartilage breaks off. The edges are then sharply contoured to create stable, well-defined borders. Then using specialized tools called awls, small holes are made in the bone approximately 3-4mm apart from each other. Puncturing the subchondral bone (bone just beneath the cartilage) creates a pathway for bone marrow cells to flow from the marrow inside the bone into the cartilage defect. The blood will fill in the cartilage defect, akin to filling a pot hole in the road. This blood is filled with stem cells that eventually become cartilage-producing cells. Over a period of weeks new cartilage fills the prior defect. After surgery, patients must not put any weight on the operative leg in order to allow the cartilage to develop. Moving the knee is necessary, though, to facilitate cartilage development.
OATs (Cartilage Bone-Plug Transplant)
An OATs (Osteochondral Allo/Autograft Transplant) procedure is another way to treat cartilage defects in the knee. This procedure is best suited for mid-size defects that are larger than lesions best treated with microfracture. In a similar manner, the defect is filled in much like a pot hole on the street, yet with this procedure a plug of bone with the attached normal cartilage (an osteochondral graft) is transplanted from a donor site to the recipient site. The donor plug can either be taken from the patient’s own body (autograft), typically from a part of the knee that doesn’t bear much, if any, load during activity, or it is taken from a cadaver graft (allograft). The size of the lesion is measured and a special coring device (much like an apple coring tool) is used to remove bone from the defect site. This allows for insertion of the donor bone plug. The bone plug is gently tapped into place, snuggly fitting in the recipient hole. This procedure allows bone-to-bone healing of the graft and surrounding bone and more importantly, the cartilage is normal cartilage unlike the fibrocartilage produced with microfracture.
Cartilage Cell Transplant
Autologous Chondrocyte Implantation (ACI) is one of the final types of cartilage preservation procedures used in the knee. It is typically reserved for revision cases that have failed prior procedures such as microfracture or OATs or for larger lesions. This procedure is much more time-intensive and technically demanding. It requires two separate surgeries. The first surgery is a diagnostic surgery performed arthroscopically to evaluate the severity and size of the lesion. If it is determined that the lesion is amenable to ACI, then a biopsy of cartilage is taken from the knee at this time. This sterile biopsy is sent to a specialized lab which cultures the cartilage producing cells (chondrocytes), creating a higher concentration of cells. Once enough cells have grown, the second surgery proceeds. This surgery is partly arthroscopic and partly open. The cultured cells are inserted into the defect and a patch is sewn over the cells covering the defect. The edges are then covered with a biologic glue to seal the cells under the patch. This procedure allows the patient’s own cartilage cells to regenerate cartilage, filling the defect. While some of the cartilage that forms is new cartilage, it is not identical to the surrounding normal cartilage based on its structure and organization. Despite this, properly performed ACI can have good results.