Multiple options are used to treat cartilage injuries to minimize its progression or to reduce associated health conditions:
– Repair techniques. One approach is arthroscopic debridement, a surgical intervention to remove damaged cartilage or bone. It is normally paired with bone marrow stimulation through perforations and microfractures to create tiny fractures in the underlying bone, through which blood and bone marrow begin to form. The aim is to facilitate access of blood and bone cells to the injury site in order to help the formation of ﬁbrocartilaginous tissue. The induced tiny fractures are effective in small injuries with an intact subchondral plate, which is a thin bone structure bordering articular cartilage. The subchondral plate has significant mechanical functions in transmitting loads from the cartilage into the underlying sponge bone that absorbs the load. These techniques are the methods of choice for surgeons as they are straightforward, fast and inexpensive. Nonetheless, the cartilage is usually repaired with ﬁbrous tissue, named collagen type I ﬁbrocartilage, because the number of available cartilage progenitor cells is too small to achieve a regeneration of the cartilage with the original properties. This approach delays degradation and repairs the injury but it will eventually be unable to stop subsequent degeneration of the tissue.
– Reconstruction techniques. These can be cartilage transplantation with tissue grafts from a donor – osteochondral allografts- or from the patient – osteochondral autologous grafts. The aim of this approach is to fill the defect with an original cartilage tissue that will provide a structure that integrates easily with the surrounding bone, with a more long-lasting articular cartilage. Autologous grafts, however, are a technically difﬁcult approach due to the limited availability of tissues for grafting. For most of the patients in need of a cartilage graft in one given site, their cartilage is overall in bad shape. Moreover, the donor cartilage site must be healthy and, normally, cells on the edge of the transplanted graft die, compromising its integration. Allografts are more adaptable than autologous grafts because there is usually more tissue area available. Thus, grafts can be designed for lesions of any shape or size, and they can be obtained from weight-bearing areas so that they are identical in form and curvature to the injured area. Cartilage for allografts can be harvested without endangering the donor site. But there are some disadvantages to this process. For instance, harvested cartilage tissue has to be used within a short period of time, since they must be kept fresh in serum, and this is only possible for a few weeks after extraction. Cryopreserved cartilage, preserved at very low temperatures, can last long but the matrix will have few viable cells, which will affect the recovery of the cartilage morphology – form, shape, and structure. Another problem with allografts is the risk of immune reactions and the transmission of diseases. A major reduction in cell viability has been observed when the implants are kept in culture, which severely limits the uses of this technique.
– Regenerative techniques use techniques of bioengineering to promote formation of hyaline cartilage tissue. This approach comprises the neoformation of cartilage tissue using different cells: Autologous Chondrocyte Implant (ACI); Mesenchymal Stem Cells or Chondrocytes in different scaffolds (MACI). The ﬁrst generation of these techniques, the ACIs, were associated with the increase of cartilage volume (hypertrophy) and with ossiﬁcations (bone tissue formation) of the grafted area. Subsequently, a second generation of regenerative techniques was developed, the MACI. This last technique introduces seeded scaffolds and membranes, made of biomaterials like type I collagen or hyaluronic acid and type I/III collagen, with 2 different types of cells. The combination of these biomaterial matrixes that mimic the natural matrix of cartilage diminishes the problems posed by the ACI approach. However, despite the achieved improvements with this second-generation of implants, there are still problems to overcome, mostly those associated with large areas of ﬁbrocartilage, possibly because of the low cellular density of the grafts and/or their poor proliferative capacity.