1 April, 2022
Osteochondral graft or transplant, a substitute technique for cartilage injuries
Articular cartilage is a unique tissue. Its matrix allows movement between the joint surfaces with the least possible friction and supports countless cycles throughout the person’s life. An injury to this structure, which does not affect the integrity of the subchondral bone, will not repair itself spontaneously and, as it is asymptomatic, can lead to progressive degeneration of the joint up to severe osteoarthritis, whose only possibility of treatment would be a replacement by a mechanical prosthesis. There are three treatment techniques for hilar cartilage injuries: palliative, reparative and substitutive, also known as osteochondral graft or transplant, which we will talk about today. Let’s see…
To prevent the advancement of this process, different treatments have been developed with the purpose of forming a repair tissue with structure, histological composition and functional behaviour equal to that of natural articular cartilage. There are three types of techniques for the treatment of these injuries:
- Palliative, which generally consists of debridement and joint lavage, commonly known as a joint “washout”.
- Reparative, which consist of treatments based on the regenerative capacity of the subchondral bone, which we have already discussed extensively in other blog posts.
- Substitutes: represented by osteochondral or cartilage and bone grafts.
HOW TO OBTAIN HYALINE COLLAGEN
After an injury to articular cartilage, chondrocytes – specialised cells of cartilage tissue – attempt to repair the injury. To do this, they increase the synthesis of proteoglycans, proteins responsible for forming and maintaining the structure of cells. The repair thus obtained stimulates type I collagen, which generates fibrocartilage, and not type II, which promotes the production of hyaline cartilage.
This is important to mention because fibrocartilage does not have the same biomechanical characteristics as hyaline cartilage and therefore increases friction and induces greater wear. This has always been the workhorse of reparative techniques, where it has not been possible to obtain type II collagen, the main characteristic of the hyaline cartilage of the joints. To overcome this barrier is the osteochondral transplant.
ADVANTAGES OF OSTEOCHONDRAL TRANSPLANTATION
Fresh osteochondral transplantation has several advantages. One of them is the feasibility to carry it out with any size and measure to be obtained from a tissue bank. In addition, they can be used for large lesions, without donor site morbidity. Remaining viable chondrocytes are also observed after years of transplantation, with fresh grafts offering the highest chondrocyte viability.
As I demonstrated in my doctoral thesis in 2006, frozen chondrocytes and even those cryopreserved at -196ºC do not keep the chondrocytes alive, so, once the transplant is done, most of these cells die and therefore the tissue ceases to be viable. Fresh cartilage transplantation represents, a priori, a great advance in the treatment of degenerative cartilage lesions, in selected cases.
Cartilage is considered an immunologically privileged tissue, since the host’s immune response is lower with cartilaginous tissues due to its avascular properties, due to the lack of vascular structures inside. Therefore, in these cases of fresh cartilage transplantation, there are no rejection reactions, such as those produced in heart, kidney, liver transplants…
INDICATIONS FOR OSTEOCHONDRAL TRANSPLANTS
Osteochondral allografts should be used in young, healthy patients with moderate physical demand, who present isolated chondral defects and without associated ligamentous injuries. It is mainly indicated in osteochondritis dissecans and post-traumatic osteochondral injury. Regarding chondral lesions, bipolar lesions or also known as mirror lesions, full-thickness lesions and those with an area greater than 2 cm2 are included. The ideal use of this technique is in lesions of 1 to 4 cm2, although it can be used in lesions of up to 8 cm2.
One of the drawbacks in this surgery is that not much time can pass between the donation and the tissue being transplanted. Ideally, it should be less than 3 weeks, so the logistics of the process are complex.